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Arch Iranian Med 2008; 11 (1): 65 – 89

Review Article

Neurotoxic Disorders of Organophosphorus Compounds and Their Managements

Mahdi Balali-Mood MD PhD•*, Kia Balali-Mood PhD**

Organophosphorus compounds have been used as and as chemical warfare nerve agents. The mechanism of of organophosphorus compounds is the inhibition of , which results in accumulation of and the continued stimulation of acetylcholine receptors. Therefore, they are also called anticholinesterase agents. Organophosphrus pesticides have largely been used worldwide, and poisoning by these agents, particularly in developing countries, is a serious health problem. Organophosphorus nerve agents were used by Iraqi army against Iranian combatants and even civilian population in 1983 – 1988. They were also used for chemical terrorism in Japan in 1994 – 1995. Their use is still a constant threat to the population. Therefore, medical and health professionals should be aware and learn more about the toxicology and proper management of organophosphorus poisoning. Determination of acetylcholinesterase and activity in blood remains a mainstay for the fast initial screening of organophosphorus compounds but lacks sensitivity and specificity. Quantitative analysis of organophosphorus compounds and their degradation products in plasma and urine by mass spectrometric methods may prove exposure but is expensive and is limited to specialized laboratories. However, history of exposure to organophosphorous compounds and clinical manifestations of a syndrome are sufficient for management of the affected patients. The standard management of poisoning with organophosphorous compounds consists of decontamination, and injection of sulfate with an oxime. Recent advances on treatment of organophosphorus pesticides poisoning revealed that blood alkalinization with and also magnesium sulfate as adjunctive therapies are promising. Patients who receive prompt proper treatment usually recover from acute toxicity but may suffer from neurologic complications.

Archives of Iranian Medicine, Volume 11, Number 1, 2008: 65 – 89.

Keywords: Neurotoxic disorders • anticholinesterase agents • chemical warfare agents • pesticides • poisoning

Introduction the continued stimulation of acetylcholine rganophosphorus (OP) compounds have receptors. Therefore, they are also called been used as pesticides and also as anticholinesterase agents. are also O chemical warfareArchive nerve agents.1 The ofanticholinesterase SID agents, but they are less toxic mechanism of toxicity of OP compounds is the than OP pesticides, thus are mainly used as home inhibition of acetylcholinesterase (AChE), and herbicides.2 resulting in an accumulation of acetylcholine and OP compounds are not ideal pesticides because of the lack of target vector selectivity, and severe Authors’ affiliations: *Medical Toxicology Center, Imam Reza Hospital, Mashhad University of Medical Sciences, Iran, toxicity and even death in humans and domestic **Structural Bioinformatics and Computational Biochemistry Unit, animals. Their have been recognized Department of Biochemistry, South Parks Road, The University of since the 1930s, when they were also developed Oxford, Oxford OX1 3QU, UK. 3 •Corresponding author and reprints: Mahdi Balali-Mood MD for use as chemical warfare agents. A few OP PhD, Medical Toxicology Center, Imam Reza Hospital, Mashhad compounds (glyphosate, merphos) are used as 91735-348, Iran. herbicides, but they are structurally different from Tel.: +98-511-859-8973, Fax: +98-511-859-1057, E-mail: [email protected]. the OP pesticides and their AChE-inhibiting power Accepted for publication: 6 June 2007 is very weak.4 OP nerve agents are more toxic than

Archives of Iranian Medicine, Volume 11, Number 1, January 2008 65 www.SID.ir Neurotoxic effects of organophosphorus compounds and their managements

OP pesticides and because of their high toxicity, developed and stockpiled as chemical warfare they are also called lethal agents.5 nerve agents during the last century.19 But its An important step in the synthesis of OP human exposure until the Iraq-Iran war was compounds was made by von Hofman, who restricted to one prospective study with VX and synthesized methylphosphor chloride in 1873. at low levels and to case reports of accidental Michaelis in 1903 introduced a compound with P- exposure to sarin and .6 CN bond, which led to the synthesis of a number The first use of nerve agents in the war of insecticides and the . Lang and occurred in February 1984 in Majnoon Island by von Kreuger synthesized compounds with P-F the Iraqi army against the Iranian troops. Among linkage in 1932. Schrader developed sarin and the chemical warfare agents applied by the Iraqi tabun in 1937 and in 1944 Germans developed army, the nerve agent tabun was found in the soman. Britons developed VX in 1952.6, 7 environmental samples and in the postmortem Over the past five decades, numerous examination of the patients who died soon after the structurally different OP compounds have been exposure. More than 300 patients died within 30 synthesized.2, 8 Presently, more than 100 different min of exposure in the field and several thousands OP compounds are used worldwide as were poisoned by tabun.18 Toxicological analyses insecticides.9 The advantage of a lower of the blood, urine, skin, and gastric juice of the environmental stability, compared with chemical war gas victims revealed tabun and sulfur organochlorine compounds and a high mustard.18 Later in 1987 and 1988, particularly effectiveness against different insect species is during the Halabjah massacre, another nerve agent accompanied by the disadvantage of high (sarin) was also identified.1, 20 mammalian toxicity.10 The widespread use and A confirmed terrorism attack with sarin easy accessibility of these compounds result in a occurred in a residential area of the city of huge number of intoxications. It was estimated that Matsumoto, Japan, on June 27, 1994. About 600 between 750,000 and 3,000,000 human OP residents and rescue staff were poisoned; 58 were intoxications occurred worldwide,9, 11 resulting in admitted to hospital and 7 died.21 On March 20, several thousands of fatalities annually.12 1995, terrorists released sarin at several points in Occupational and accidental OP exposure are the the Tokyo subway, which killed 11 and poisoned main causes for mild poisonings,13 – 15 whereas more than 5,500 people.22, 23 severe cases are mostly due to suicidal attempts Based on the above information, OP and self-poisoning. 16, 17 compounds have induced tragedies with lots of In some parts of the developing world, human morbidities and mortalities. OP pesticides poisoning causes more deaths than infectious are still used in most parts of the world and diseases.11 Use of pesticides is poorly regulated and unfortunately are easily available in some often dangerous; their easy availability also makes developing countries. Thus occupational and them a popular method of self-poisoning. In 1985, accidental exposure and even intentional ingestion the UN Food and Agriculture Organization (FAO) are common and can induce health problems. In produced a voluntary code of conduct for the spite of the establishment of organization for pesticide industry in an attempt to limit the harmful prohibition of chemical weapons (OPCW) and its effects of pesticides.16 Unfortunately, the lack of active role in chemical warfare agents (CWA) adequate governmental resources in the developing control, OP nerve agents are still a big threat to the Archive16 of SID world makes this code ineffective. The World population worldwide as a chemical war or Health Organization (WHO) has recommended terrorism agents. Therefore, medical and health that access to highly toxic pesticides be restricted, professionals should be aware and learn more but it has not been applied in some developing about the toxicology and proper management of countries such as the Islamic Republic of Iran. OP OP poisoning. pesticides are still easily available in this country, thus their exposure either as occupational or Definition, classification, and chemical intentional oral ingestion are common and induce structures health problems as well as environmental OP compounds including are 1, 18 chemically derived from phosphoric, phosphonic, hazards. 4 Several highly toxic OP compounds were phosphinic, and thiophosphoric acids.

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Figure 1. General chemical structure of an organophosphate. R1 and R2 are alkyl-, alkoxy-, alkylthio-, or amido-groups. X is the acyl residue (labile fluorine-, cyano-, substituted- or branched- aliphatic, aromatic, or heterocyclic groups).

Organophosphates are usually esters, amides, or thiol derivatives of phosphoric, phosphonic, or phosphinic acids, which have the general structural Figure 2. Chemical structure of nerve agents. formula as shown in Figure 1.24 OP compounds are divided into two main ing organophosphate compounds. The principal G groups; pesticides and chemical warfare nerve agents; GA, GB, and GD have common names of agents. Very few OP compounds such as tabun, sarin, and soman, respectively. The other G glyphosate and merphos have been used as agents and V agents do not have common names. herbicides. OP herbicides are structurally different The oldest and main V agent is called VX.18 from the OP pesticides and their AChE-inhibiting power is very week. Mechanism of action OP pesticides vary in chemical structures. The mechanism of action of OP compounds Variations in the chemical structure of main groups that has well been known for more than 70 years, of OP pesticides are summarized in Table 1. is the inhibition of . Two types of As a group, OP compounds exhibit marked cholinesterase are involved: variability of action depending on the specific 1. Acetylcholinesterase (AChE), which is a substituents occurring as R1, R2, and X. For specific for the diagnosis of OP example, extreme toxicity is associated with those poisoning and is called true cholinesterase. It is compounds in which X is a strongly usually estimated in red blood cells (RBC) and electronegative group such as a halide, cyanide, or is thus also called RBC ChE or erythrocyte thiocyanate. The structures of these four agents acetylcholinesterase (EAChE). (tabun, sarin, soman, and VX) are presented in 2. Butyrylcholinesterase (BChE), which is less Figure 2.25 specific but more sensitive than AChE and is Nerve agents are divided into two groups of G so called pseudocholinesterase. It is usually and V agents. The G agents are fluorine estimated in plasma and is thus also called compounds of organophosphate except for tabun plasma ChE. (GA), which is a cyanide compound of The reaction between OP compounds and organophosphate. The V agents are sulfur contain- AChE occurs in three step reactions as shown in

Table 1. Chemical structures of main groups of OP pesticides and examples in each group. Type of group Archive Outline of structure of SID Examples Phosphate O , || , crotoxyphos, ,

(R-O)2-P-O-X heptenphos, Phosphorothioate S Bromophos-ethyl, bromophos-methyl chlorpyriphos- || methyl, , dichlofenthion, fenchlorphos,

(R-O)2-P-S-X O-alkyl phosphorothioate S -S-methyl, || vamidothion,

(R-O)2-P-O-X Phosphorodithioate S Azinophos-ethyl, azinophos-methyl, || , mecarbam, menazon,

(R-O)2-P-S-X morphothion,

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Figure 3. accommodated in the active center, as suggested Step 1 is the formation of a reversible enzyme- by molecular modeling via kinetic studies of inhibitor complex. phosphorylation and aging with a series of Step 2 is the phosphorylation and inactivation HuAChE mutants (E202Q, F338A, F295A, of the enzyme molecule. F297A, and F295L/F297V).25 A variety of Step 3 is the aging reaction involving formation proteolytic (e.g., chymotrypsin and of a monophosphoric acid residue bound to the trypsin) may also be inhibited by OP compounds. enzyme.18 Soman and sarin are detoxified in part via a two- The toxic manifestations and lethality after step pathway involving bioactivation of the parent nerve agent exposure appear to follow the compound by the system, then irreversible phosphorylation of the serine- hydrolysis of the resulting oxygenating metabolite containing active site of AChE. The time between () by serum and liver paraoxygeanse (PON1). OP exposure and the irreversible phosphorylation Serum PON1 has been shown to be polymorphic in is called aging. The kinetics of aging and human populations.26 spontaneous reactivation of nerve agent-inhibited Even though all OP compounds have a common human cholinesterase is dependent on the agent. mechanism of action, their effectiveness as The aging varies from a few minutes (soman) to 22 inhibitors of AChE, vary widely. OP compounds hours ().24 can be classified as direct or indirect inhibitors of Different aging mechanisms are involved. Both AChE. Direct inhibitors are effective without any tabun and butyl-tabun appear to be similarly further metabolic modification after absorption

Step1:

O O . X AChE OH.R O x AChE OH + R 1O P 1 P

R2 R2

Step2: O O

X AChE P AChE OH.R 1O P O OR 1+.HX

R 2 R2 Archive of SID

Step3:

O O

P OR AChE O AChE O 1 P OH+R1.O

R 2 R2 Figure 3. Different steps of AChE reaction with OP. (Separate new JPG file with high resolution is attached).

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into the body. Indirect inhibitors need to be hazards, especially at warmer temperatures or transformed in the body to be effective. All thiono when droplets are created by explosion or spray. OP pesticides, that are those containing a P=S Based on information achieved from animal bond (mainly the phosphorothioates and studies, the lethal inhaled dose of G agents in phosphorodithioates), are not active inhibitors of humans may be about 1 mg.25 The G agents also AChE, but require activation by oxidation of the represent a skin contact hazard, particularly when P=S to the P=O group. The practical importance of evaporation is minimized and contact is prolonged this classification is that direct inhibitors cause by contamination of clothing. However, the symptoms and signs quickly during or after percutaneous absorption of G agents is much less exposure, whereas in the case of indirect inhibitors rapid and complete than the inhalation form.33 symptoms and signs appear later and the effects VX does not pose a major inhalation hazard last longer after cessation of exposure. The under usual circumstances, but it is well absorbed dichlorvos is an example of a direct through the skin.33 The relative lethality as inhibitor while malathion and parathion are determined in animal studies is indirect inhibitors.4 VX>soman>sarin>tabun.34 Acute toxic values of People with BChE genetic variations may be at nerve agents in humans are summarized in Table 2. risk. The clinically most important variant is The acute toxicity of nerve agents is due atypical (D70G) BChE, because people with this primarily to irreversible inactivation of AChE variation have two hours apnea after receiving a leading to an accumulation of toxic levels of dose of succinylcholine that is intended to paralyze acetylcholine.35 Like other OP compounds, these muscles for three to five minutes in anesthesia.27 agents act by binding to a serine residue at the In addition, OP compounds covalently bind to active site of a cholinesterase molecule, thus other serine esterases, namely carboxylesterase forming a phosphorylating protein that is inactive (CaE), neuropathy target esterase (NTE), trypsin, and incapable of breaking down acetylcholine. The and chymotrypsin. 28, 29 Furthermore, binding to a resulting accumulation of toxic levels of tyrosine residue of human serum albumin has also acetylcholine at the synapse, initially stimulates been observed.30 and then paralyses cholinergic synaptic The persistence of unbound OP in the body is transmission. Cholinergic synapses are found in dependent on the physico-chemical properties and the central nervous system (CNS), at the the activity of endogenous OP hydrolyzing termination of somatic nerves, in the ganglionic enzymes, primarily paraoxonases.31 Lipophilic OP synapses of autonomic nerves, and at the compounds, e.g., the pesticide parathion and its parasynaptic nerve endings such as those in the active form , may distribute into deep sweat glands.36 compartments resulting in long-term The rate of aging varies greatly among the toxicologically relevant plasma concentrations.32 nerve agents. The half-time of aging is within minutes after soman exposure, about five hours Toxicity after sarin exposure, and >40 hr after exposure to The most toxic OP compounds are nerve agents tabun and VX.34 and the least toxic are carbamates. Inactivation of neurotoxic esterase by some OP The vapor pressure of the three G agents (GA, pesticides can lead to organophosphate-induced GB, and GD) makes Archivethem significant inhalational ofdelayed neuropathySID (OPIDN). The nerve agents Table 2. Summary of available acute toxic values of nerve agents in humans. Term Unit Route Tabun Sarin Soman VX

LD50 mg/kg PC — 28 — — 3 LD50 mg/m Inhalation — 70 — — LCLo µg/kg PC — — — 86 LDLo mg/kg PC 23 — 18 — LDLo mg/m3 Inhalation 150 — 70 — TDLo µg/kg IV 14 2 — 1.5 TDLo µg/kg Oral — — — 30 TDLo µg/kg SC — — — 3.2

LD50=; LCLo=lethal concentration at the lowest dose; LDLo=lethal dose at the lowest concentration; TDLo=toxic dose at the lowest concentration; Based on Grob (1956)6,35.

Archives of Iranian Medicine, Volume 11, Number 1, January 2008 69 www.SID.ir Neurotoxic effects of organophosphorus compounds and their managements inhibit neurotoxic esterase at many time the LD50, because the OP pesticides are difficult to remove, delayed neuropathy with VX is much less than dermal absorption is frequently prolonged. Uptake that of G agents.37 Possible involvement of of active ingredients through the skin from neurotrophic factor (growth-related enzyme powdered and granulated formulations may be ornithine decarboxylase) during early stages of relatively inefficient; the presence of aqueous OPIDN particularly after diisopropyl dispersing agents or organic in a spray fluorophosphates (DFP) has been reported.38 Nerve concentrate or formulation may greatly enhance agents also bind quickly to cardiac muscarinic (M2) uptake. On the basis of radioautographic studies in receptors at higher than physiologic human and animals, it appears that skin absorption concentrations, but whether this contributes to of parathion is transepidermal. The rate of dermal cardiac toxicity is unknown.39 They also interact absorption of parathion in the rabbit is 0.059 with the nicotinic acetylcholine receptor-ion mg/min/cm2. 41 channel complexes, but only at tissue When 14C-malathion was applied to the ventral concentrations of 10 to 100 times greater than that forearm of 12 volunteers, radioactivity equivalent fully inhibiting AChE. Sarin, soman, and tabun are to a “corrected” average of 8.2% of the total dose partial agonists of those channel complexes, was recovered from urine produced during the first whereas VX acts as an antagonist.18 five days. This percentage is an essentially There is also evidence that nerve agents affect accurate indication of the absorption during the noncholinergic mechanisms in the CNS at a dose period because almost all (90.2%) of the 18 approaching LD50. Antagonistic effects of δ- radioactivity was recovered in the urine after amino butyric acid (GABA)-ergic systems may intravenous (IV) injection of malathion.18, 42 explain convulsive activity after organophosphate poisoning. Effects of soman and tabun on the Inhalation exposure uptake and release of GABA and glutamate in the Exposure by respiratory and dermal routes were synaptosomes of cerebral cortex of guinea pigs did compared in workers spraying parathion, who not support the previous beliefs that nerve agents either breathed a pure air supply but did not wear caused convulsions by affecting the uptake or protective clothing, or who wore total protective release of GABA or glutamine.40 However, clothing but did not have any respiratory indirect evidence was obtained that soman and protection. Total urinary output of 4-nitrophenyl as tabun inhibit catabolism of GABA and derived from the respiratory source, compared with glutamine.40 that derived from the dermal source, was 1.2% in Acute exposure to tabun, sarin, and/or soman one test and 12% in another.25 The total exposures alters brain levels of cyclic AMP and cyclic GMP by the dermal and respiratory routes were in the as a result of effects of adenylcyclase and proportion of 1000:1 and the efficiency of dermal phosphodiesterase systems.21 VX at 10 µM absorption was 1 to 2%. Therefore, the dermal produced significant reduction in cell absorption by the respiratory route was within two minutes as measured by changes in the significant.18 acidification rate of medium after four hours of exposure. Two alkali degradation products of VX Oral exposure produced no cytotoxicity.18 When 32P- was given orally to Archive ofvolunteers, SID it was absorbed and excreted rapidly: Toxicokinetics 76 to 100% of the radioactive substance appeared More data on the toxicokinetics of OP in the urine in 24 hr.18 pesticides than nerve agents are available. Distribution Absorption The intrinsically reactive chemical nature of OP Absorption varies by route of exposure. OP pesticides means that any dose entering the body is compounds are absorbed by the skin as well as by immediately liable to a number of the respiratory and gastrointestinal tracts. biotransformations and reactions with tissue constituents, so that the tracing of radiolabeled Dermal exposure material alone does not give any clue to the Absorption by the skin tends to be slow, but unchanged parent compound. In view of the

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inherent instability of the OP pesticides, storage in metabolites and thereby to estimate an approximate human tissue is not expected to be prolonged. half-life of an OP pesticide in the body. The half- Experimental animal studies indicate rapid life of most OP pesticides and their inhibitory excretion of these compounds.28 However, some metabolites in vivo is comparatively short. For OP pesticides are very lipophilic and may be taken example, the serum half-life of malathion was 2.89 into, and then released from fat depots over a hr in a 24-year-old white male who, in a suicide period of many days.18 attempt, injected approximately 3 mL of 50% The lipophilic diethyl phosphoryl pesticides malathion IV into his right forearm.3 are: azinphos-ethyl, bromophos-ethyl, , coumaphos, , parathion, , and Excretion . They may remain in the body for many There is no evidence of prolonged storage of days or weeks in severe cases, and may promote a OP pesticide compounds in the body, but the recurrence of clinical effects after an initial period process of elimination can be subdivided roughly of apparent recovery.43 For example, a case of according to the speed of the reactions involved. poisoning promptly treated by Most OP pesticides are degraded quickly by the conventional treatment caused a recurrence of metabolic reactions described. The elimination of symptoms attributed to mobilization of the the products, mostly in the urine and in a lesser organophosphate stored in adipose tissue.42 In amounts in the feces and expired air, is not contrast, dichlorvos (a dimethyl phosphate) and delayed, so that rates of excretion usually reach a omethoate (a dimethyl phosphorothioate) are peak within two days and decline quite rapidly.18 rapidly hydrolyzed by plasma and tissue esterases Experimental animal studies have shown that to inactive products and are unlikely to cause late most of a radiolabeled dose of OP pesticides is clinical effects.3, 41 rapidly excreted in expired air, urine, and feces. Thus, it was reported that from 67 to 100% of the Metabolism administered radioactivity was recovered within Metabolism occurs principally by oxidation and one week in the combined urine and feces of cows, hydrolysis by esterases and by reaction with rats, and a goat that were given various doses of glutathione. Demethylation and glucuronidation 32P-dichlorvos.43 may also occur. Oxidation of OP pesticides may Very little data are available on the result in more or less toxic products. In general, toxicokinetics of the nerve agents. A two- phosphorothioates are not directly toxic but require compartment model, with a biological half-life of oxidative metabolism to the proximal . The one to one and a half minutes, has been glutathione transferase reactions produce products described.43 Toxicokinetics of the four stereo that are, in most cases, of low toxicity.42 isomers of soman in atropinized rats were Hydrolytic and transferase reactions affect both reported.43 The extremely toxic C (±)P(-) isomers the thioates and their oxons. Numerous could be followed in rat bloods for more than four conjugation reactions follow the primary metabolic and two hours at doses of six and three LD50 (82 processes, and elimination of the phosphorus- µg/kg), respectively.43 The toxicokinetics of P(-) containing residue may be via the urine or feces.28 isomers were described with three-compartment Parathion, for example, must be activated by an model, with terminal half-lives of 40 – 64 and 16 – oxidative conversion via liver cytochrome P450 22 min at doses of six and three LD50, Archive of SID42 microsomal enzymes to paraoxon, a potent respectively. . Both compounds are Toxicokinetic studies with nerve agents in rapidly hydrolyzed by plasma and tissue esterases, different animal species indicate that the to diethyl thiophosphoric acid, diethyl- phosphoric elimination half-life of so-called G agents (e.g., acid, and p-nitrophenol. These products are soman and sarin) will be rather short (less than one excreted mostly in the urine and represent most of hour),43 whereas VX was found to persist for a parathion dose. Phosphorothioates containing a several hours after IV exposure and even longer P=S bond need to be converted into the analogous after percutaneous challenge.43 Accidental or oxone before they acquire substantial homicidal exposure to nerve agents will occur anticholinesterase activity.4 most likely by the inhalational or percutaneous It is possible to determine the rate of disposal of route. Due to the high toxicity of these compounds,

Archives of Iranian Medicine, Volume 11, Number 1, January 2008 71 www.SID.ir Neurotoxic effects of organophosphorus compounds and their managements plasma concentrations in a nano molar range are shortly after exposure to OP pesticides. expected, which represents a considerable Exposure to low-vapor concentrations may challenge for the quantitative analysis of nerve affect only the eyes, nose, and airways. , agents in biologic samples. visual disturbances, rhinorrhea, and/or some degree of dyspnea develop within seconds to Toxicodynamy several minutes. The severity of dyspnea is dose Toxicodynamy of OP compounds were mostly dependent. Usually, these effects do not progress explained under the mechanism of action. The significantly once the patient is removed from common nerve agents are chiral compounds with contamination. After inhalation of high-vapor two (e.g., sarin) or four enantiomers (soman), concentrations, victims lose consciousness within having different inhibitory potency with AChE and one or two minutes and then have seizures, flaccid toxicities in vivo.44 Unfortunately, the more toxic paralysis, and apnea. Other early effects of high- enantiomers persist substantially longer than the vapor concentrations include miosis and copious less toxic ones. Chemical or enzymatic secretions. Involuntary micturation/defecation may decomposition of nerve agents results in the also occur. Unless medical assistance is immediate, formation of inactive phosphonic acids, which are the patients may die within 30 min.18,21 renally excreted.45 Skin Clinical effects In dermal absorption, symptoms and signs Clinical effects after OP exposure are divided usually manifest in about two to three hours. into acute poisoning and chronic poisoning. However, it is possible to observe effects within half to one hour, depending on the circumstances Acute poisoning of the intoxication. A few OP compounds may be Initial clinical manifestations following acute retained in the fat tissue of the body, which may exposure vary according to the route of exposure. result in delayed symptoms for up to 24 hr.4 Percutaneous absorption of OP compounds Clinical manifestations according to the route of varies according to the body site exposed and the exposure ambient temperature. VX was absorbed nearly The acute effects of OP exposure occur after eight times more rapidly from facial skin than it inhalation, contact with skin and eye, and by was from the volar forearm and absorption ingestion. Most often, exposure to OP nerve agents increased markedly as surrounding temperature is to vapor (inhalation) or liquid (percutaneous). rose from 18 to 46°C.46 Initial local effects of After small to moderate doses, initial effects and liquid, which are seldom noticed, include muscular their time of onset are determined by the route of fasiculations and sweating at the contamination exposure. In contrast, large doses cause similar site. A large droplet may also cause gastrointestinal effects by all exposure routes, although the time of effects and complaints of malaise and weakness. onset varies.36 Droplets containing near-lethal or lethal doses can For most OP pesticides, dermal exposure and cause loss of consciousness, seizures, flaccid subsequent absorption through intact skin paralysis, and apnea. The onset of these effects is represents the most important route of entry in case sudden, usually after an asymptomatic interval of of occupational exposure. 10 to 30 min.18 Archive of SID Gastrointestinal absorption occurs following accidental or intentional use of an OP pesticide and Eyes may rarely occur through contaminated food Miosis rapidly occurs after splash exposure or ingestion. Parenteral exposure is very rare and only eye contact with vapor. It will appear later in case a few cases were reported.4,18 of systemic poisoning. Unilateral miosis can occur, if only one has been exposed. Miosis may be Inhalation accompanied by deep, aching eye pain, Inhalation of OP pesticides depends on conjunctival irritation, and visual disturbances. volatility of the compound, on the type of Dim vision may be because of constricted pupils or formulation, and on the technique of application. inhalation of cholinergic fibers of the retina or However, acute effects appear immediately or central nervous system. The miotic pupil may

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improve vision (the pinhole effect), although a restlessness and anxiety, mental confusion, complaint of blurred vision is common.35 Direct convulsions, and coma. As a result, depression of installation of diluted nerve agent into the eye does the respiratory and vasomotor centers in brain may not produce tissue damage.36 occur and complicate the clinical picture.6,18,48

Gastrointestinal Cardiovascular effects The oral route of entry is important in Cardiovascular cholinesterase inhibition accidental and intentional OP . increases the vagal nerve influence on heart rate, Occupational accidental ingestion may occur in and the expected result is bradycardia. In a person children and as a result of poor work practices and who is accidentally poisoned, however, other lack of personal hygiene. Following oral ingestion, factors, such as fear, hypoxia, and ganglionic nausea and vomiting may occur. Abdominal pain stimulation, may contribute to acceleration of heart and diarrhea together with a cholinergic syndrome, rate. In experimental studies in animals, nerve CNS, and cardiovascular effects can produce in agents and other OP compounds have been shown moderate to severe OP poisoning. Clinical features to slow cardiac conduction, leading to a decrease of cholinergic syndromes, CNS, and in cardiac output.6 In 36 of 200 mildly exposed cardiovascular effects are described in the patients only 13 (6.5%) had heart rates of less than following relevant sections.18 65, and 70 (35%) had heart rates exceeding 90.6,18 ECG abnormalities other than bradycardia have Parenteral been described in animals exposed to nerve agents Intradermal injection of paraoxon or surface and in human beings exposed to organophosphate application of maloxon or dichlorvos to human insecticides.49 Reported abnormalities include skin produced a long-lasting, local sweating atrial fibrillation, idioventricular dysrhythmias, response in a few minutes.47 Intramuscular multiform ventricular extrasystoles, torsades de administration of DFP to people with pointes, ventricular fibrillation, and complete heart schizophrenia, manic-depressive psychosis, and to block.48 Sudden death occurring after the patient normal controls at a rate of 2 mg/min per day had appeared to recover from the respiratory and (about 0.028 mg/kg/day) for seven days caused neurologic effects of acute organophosphate anorexia, vomiting, and diarrhea, somewhat more insecticide exposure has been reported.49 However, severe in normal than in psychotic people.47 this has not been described after nerve agent Suicidal attempts or self-poisoning by exposure.18 parenteral OP pesticides are very rare, but were observed by the first author of this article.18 Life-threatening complications The most life-threatening complication is Cholinergic syndromes respiratory failure, which is mainly due to central Parasympathic stimulations or cholinergic effect of the nerve agents.6,50 Although in one syndromes are due to the acetylcholine animal experiment with sarin, the authors accumulation at the nerve endings, stimulating concluded that respiratory paralysis could be both muscarinic and nicotinic receptors. purely central, purely peripheral, or both central Muscarinic effects include increased bronchial and peripheral, depending on the doses of sarin and secretion, excessive Archivesweating, salivation and ofatropine employed.SID50 Hypoxia is also a major lacrimation, pinpoint pupils, bronchoconstriction, problem in the nerve agent poisoning, which may abdominal cramps (vomiting and diarrhea), urinary cause cerebral edema and convulsions and may frequency, bradycardia, hypotension, and in severe also induces histopathologic brain damage. intoxicated patients pulmonary edema may occur. Cardiovascular complications are sometimes Nicotinic effects comprise of tachycardia, severe and life threatening.51 hypertension, mydriasis, twitching and In guinea pigs, the nerve agents like tabun, fasciculation of muscles, and in more severe cases, sarin, soman, or VX at five to ten times the LD50 paralysis of diaphragm and respiratory muscles.18,48 induced circulatory arrest a few minutes after apnea in nontreated animals.52 treatment Central nervous system effects by atropine (10 mg/kg) and HI6 or HLo7 (30 CNS effects include headache, dizziness, mg/kg) two minutes later, rapidly restored the heart

Archives of Iranian Medicine, Volume 11, Number 1, January 2008 73 www.SID.ir Neurotoxic effects of organophosphorus compounds and their managements rate and arterial pressure and respiratory function thus can be anticipated that the intermediate to various extent. The nerve agent injection caused syndrome occurs in some cases of nerve agent marked sinus bradycardia and a subsequent poisoning. complete atrioventricular block within one to two minutes. In guinea pigs with depressed respiratory Severity grading of intoxication function (<50%), intermittent ST-T wave Severity grading of OP poisoning can be made alterations and second-degree atrioventricular heart based on clinical manifestations, cholinesterase block were observed.33 Other reported ECG activity, and initial atropine dose required for abnormalities in animal experiments and in atropinization. humans being exposed to nerve agents include torsades de pointes, atrial fibrillation, Clinical idioventricular dysrhythmias, complete heart The patients with OP poisoning can be divided block, and ventricular fibrillation.21,36,52 into four groups of mild, moderate, severe, and Histopathologic changes compatible with toxic fatal as shown in Table 3. myocarditis were observed following sarin and 51 Inhibition of cholinesterase soman exposure in animal experiments, but it has The patients with nerve agent poisoning may be not been reported in humans. divided into three groups according to their Similar life-threatening complications may cholinesterase activities (Table 4). occur in severely OP pesticides-intoxicated BChE activity has less quantitative value than patients. AChE activity.

Intermediate syndrome Atropine dose The intermediate syndrome consists of marked The patients with OP nerve agent poisoning can weakness of the proximal skeletal musculature also be divided into three groups according to the (including the muscles of respiration) and cranial initial dose required for atropinization: nerve palsies, which may occur on one to four days • Mild <2mg after acute OP pesticide poisoning. This syndrome • Moderate <2 – 10 mg that was observed after certain organophosphate • Severe >10 mg 53,54 poisoning, has not yet been reported after nerve Based on the first author’s experience, patients agent poisoning. Intermediate syndrome is with OP pesticide poisoning require much more probably a consequence of cholinergic overactivity atropine doses and thus the above atropine dosing at the neuromuscular junction and a connection has for the severity grading of OP pesticides should be been made between the intermediate syndrome five to ten times higher.18 and OP-induced myopathy. Myopathy has been observed histologically in experimental animals Chronic poisoning with the nerve agents tabun, soman, and sarin.55 It Chronic and/or subacute OP poisoning is usua-

Table 3. Severity grading of OP poisoning based on clinical features. Grade Symptoms Signs Mild Dizziness, anxiety, headache, nausea, weakness, Failure of accommodation, Archivetightness of breath of SIDrhinorrhea, sweating, salivation, coughing, lacrimation Moderate (Worsening of the above features plus the followings) Pallor, miosis, lack of concentration, Restlessness, confusion, dyspnea, disorientation, tachycardia, hypertension, muscle abdominal pain, diarrhea twitching, fasciculation, respiratory depression, bronchorrhea, loss of consciousness, bronchospasm Severe (Worsening of the above features plus the followings) Convulsions, respiratory failure, pulmonary edema, flaccid paralysis involuntary micturition/defecation Cyanosis, deep coma Fatal Coma, convulsions, miosis, — hypersecretions and apnea within a few minute after exposure

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Table 4. Severity grading of OP poisoning based on Temporary psychological effects such as cholinesterase inhibition. depression, fatigue, insomnia, irritability, Grade Butyrylcholinesterase Acetylcholinesterase nervousness, and impairment of memory have activity (%) activity (%) been described after exposure to nerve agents.6,18 Mild 40 – 50 50 – 90 Moderate 10 – 40 10 – 50 An electroencephalogram (EEG) in a person Severe <10 <10 who was severely intoxicated with sarin showed marked slowing with bursts of high-voltage waves lly occupational and may occur in workers who at a rate of five per second.60 Epileptic type have daily exposure during production and storing. changes in EEG were observed following sarin It is of course more common in agricultural poisoning up to 11 months after exposure.21 workers who are involved in spraying of OP pesticides or in sheep divers. However, chronic OP Diagnosis poisoning is much less common than acute Initial diagnosis of OP poisoning can be made poisoning and often may not be diagnosed, if the based on the history of exposure (intentionally or physician does not pay attention to the occupation accidentally oral OP pesticide taken, occupational, of the patient. terrorism, and chemical warfare attack), and Most of the OP compounds are rapidly clinical manifestations. In low-level exposure, the metabolized and excreted, so subacute or chronic route of absorption may affect the clinical features, poisoning does not occur. However, since several but in high-level exposure, severe intoxication OP compounds cause slowly reversible inhibition occurs, although the occurrence time is faster of cholinesterase, accumulation of this effect can through inhalation than by skin absorption.18 occur. Thus, signs and symptoms resembling those Onset and intensity of symptoms and signs also occurring after a single high dose may be produced vary depending on the compound (direct/indirect by repeated small doses absorbed on prolonged inhibitors), and on the level of exposure. The first exposure. symptoms are usually nausea, headache, tiredness, Some OP pesticides are able to induce delayed giddiness, papillary constriction, and blurred neuropathy in experimental animals and the vision, which is often described as ‘though a veil structure-activity relationship for this effect has has fallen over the eyes’. Depending on the been in part identified. severity of poisoning these symptoms become Cases of delayed neuropathy have been worse with the onset of vomiting, abdominal pain, reported only as a sequel to acute human poisoning diarrhea, sweating, and salivation.61 with few OP compounds, most of which are no Progressive worsening is characterized by longer in use. Cases of delayed neuropathy muscular twitching, which usually commence in occurring after long-term, low-level exposure are the tongue and the eyelids, progressing to tremor, not yet presented.4 convulsions, and finally paralysis. There is also bronchoconstriction and bronchial hypersecretion Delayed neuropathy and in the final stages, paralysis, convulsions, Organophosphate-induced delayed neuropathy respiratory depression, and coma are observed. In (OPIDN) is a symmetrical sensorimotor fatal OP poisoning the immediate cause of death is axonopathy, tending to be most severe in long generally asphyxia resulting from respiratory axons and occurring seven to 14 days after depression.4 exposure. In severe Archivecases, it is an extremely ofEstimation SID of AChE in erythrocytes is required disabling condition.56 Inhibition of NTE appears to to confirm the anticholinesterase exposure and to be necessary for OPIDN to develop. However, estimate the severity of intoxication. BChE other mechanisms such as a trophic factor estimation may also help, although it is not specific (ornithine decarboxylase, a growth-related and may be low because of genetic variations.27 enzyme) decrease in spinal cord following the A reasonable correlation exists between red cell neuropathic agent DFP may be involved.57 and plasma cholinesterase inhibition and the Although OPIDN has not observed after nerve clinical signs of acute intoxication. The correlation agent poisoning in experimental studies,58 and in tends to increase as the rate of inhibition is faster. accidental nerve agent poisoning, a case of sensory When inhibition occurs slowly and repeatedly, as polyneuropathy seven months after sarin poisoning happens on chronic or repeated exposure, the has been reported.59 correlation with illness may be low or totally non-

Archives of Iranian Medicine, Volume 11, Number 1, January 2008 75 www.SID.ir Neurotoxic effects of organophosphorus compounds and their managements existent. For instance, after continuous exposure, Ellman assay,69 allow the sensitive and specific clinical signs of intoxication may appear only at determination of AChE activity in whole blood and AChE inhibition of 85 – 90% level, whereas after of BChE activity in plasma.32, 70 It may be used single exposure, they appear at 60 – 70% AChE under field conditions.71 However, serious inhibition. limitations for the diagnosis of low-level exposure Diagnosis of a certain nerve agent requires to these compounds have to be considered. toxicological analyses of the environmental and/or Standard determination of AChE and BChE blood samples for the nerve agents. A biosensor activity may indicate inhibition of the enzyme, that is a potentiometer enzyme electrode for direct which may be due to OP or other cholinesterase determination of organophosphate nerve agent has inhibitors such as carbamates. Thus, reduced been developed.62 activity of AChE/BChE points to exposure by a A fiberoptic enzyme biosensor for the direct cholinesterase inhibitor without specifying the measurement of OP nerve agents is also developed. agent. Low-level exposure to nerve agents with no Concentrations as low as 2 µM can be measured in clinical signs and symptoms of OP poisoning, may less than two minutes using the kinetic response. not reveal enzyme inhibition. This is because of When stored in buffer at 4°C, the biosensor shows marked inter-individual variations of AChE and long-term stability.63 BChE activities and to intra-individual variations 10 A new method for retrospective detection of of BChE activities. Knowing pre-exposure exposure to organophosphate nerve agents was control enzyme activities would improve applied to estimate serum sarin concentrations of substantially the diagnosis of low-level exposure to the Matsumoto incident. The concentrations ranged nerve agents. However, determination of from 0.2 – 4.1 ng/mL of serum.64 Definitive cholinesterase activities is a valuable tool for evidence for the acute sarin poisoning of the Tokyo confirming the clinical diagnosis of OP poisoning. subway was made by detecting sarin-hydrolyzed Clinical symptoms are expected at inhibition of products from erythrocytes of four victims in more than 50% of brain AChE and 70% of postmortem examinations.65 diaphragm AChE, respectively.32 Inhibition levels Although diagnosis of an anticholinesterase greater than 90% are associated with severe may be sufficient for the management and toxicity. administration of atropine, oxime therapy requires Functional similarities of synaptic and 72 the recognition of the agent.66 Cholinesterase erythrocyte AChE, indicate that changes in activity in postmortem blood as a screening test for erythrocyte AChE activity reflect the situation at OP nerve agent exposure was performed in 53 non- target tissues in the peripheral compartment (e.g., preserved postmortem whole blood specimens. neuromuscular junction). In the central There was a negligible loss of cholinesterase compartment, the degree of AChE inhibition may activity by the seventh day of the study. It could be different because of the lipophilicity of the OP therefore be applied as the screening test for and its distribution to the CNS, respectively. This anticholinesterase nerve agents.67 assumption is supported by clinical data achieved Diagnosis of the delayed neurotoxic effects can from the patients who were poisoned by OP 32,17 be made by estimation of NTE, although it is pesticide. unlikely to occur following the nerve agents Erythrocyte AChE showed to be a far more poisoning. Marked reductionArchive of the neurotrophic ofreliable parameterSID than BChE for the assessment of factor (ornithine decarboxylase) during the early antidotal efficacy, which is due to different kinetic stages of the neurotoxicity may also be helpful properties of BChE inhibited by pesticides and where it will be possible to perform.68 nerve agents.70, 73 The analysis of the cholinesterase status of patients who were poisoned by OP may Toxicological analyses provide a valuable tool for making the decision on 1. Cholinesterase determination the duration of antidotal oxime therapy in case of Determination of AChE and BChE activity in rapidly aging (soman) or long persisting (VX) whole blood and plasma, respectively, is a rapid, agents. convenient, and cheap screening method to establish exposure to OP pesticides and nerve 2. Detection of OP compounds and their agents. Modifications of the original colorimetric metabolites

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The identification and quantitative analysis of collected soon after the end of the work are trace concentrations of OP compounds in plasma suitable for metabolite determination when 24-hr after human exposure require sophisticated gas urine collection is impractical. When using spot chromatography-mass spectrometry (GC-MS) or specimens, creatinine or specific gravity can be liquid chromatography-mass spectrometry (LC- determined in order to select and discard those MS) equipment and well-trained operators. The samples that are too diluted or too concentrated.4 analysis of unbound nerve agent in biological samples is the most specific method for diagnosis Biochemical and hematological changes and verification of exposure (limit of detection at Acid-base and electrolyte disturbances are 1 nmol/L). However, the rather short life-time of common during the severe OP poisoning. Arterial nerve agents in the body will limit their detection blood gas analysis and estimation of serum to a maximum of several hours after exposure.74 electrolytes, liver and kidney function tests, OP nerve agents are hydrolyzed in vivo into the amylase, CPK, and LDH may be required for the substance-specific alkylmethylphosphonic acid, management of patients. Hypokalemia and which is further degraded to methyl phosphonic hyperglycemia are common and should be acid. Hydrolysis products of nerve agents may be considered and corrected. Elevation of serum analyzed in plasma and urine by GC-MS20 or amylase and lipase may reveal acute pancreatitis. directly by LC-MS.74, 75 The applicability of these Transient elevation of liver enzymes, hematuria, procedures was demonstrated with samples leukocyturia, and proteinuria may be observed collected from victims poisoned by sarin and VX during nerve agent poisoning. Blood cell count and in Japan.45, 76 other hematological tests may be performed as For most OP pesticides, the blood or urine clinically indicated. However, transient concentration of the substance itself or its leukocytosis particularly in polymorphonuclear metabolites represent an indicator of exposure. The cells may be observed.18 measurement of nitrophenol in urine to assess the internal dose of parathion has been among the Other investigations oldest tests developed. Exposure to fenitrothion Chest radiography, electrocardiography (ECG), may also be surveyed by measuring p-nitrocresol EEG, electromyography, nerve conduction in urine. velocity, spirometry, computed tomography, The alternative is measuring alkylphosphates in magnetic resonance imaging, and further urine. The rationale for the use of this method investigations should be performed in OP resides in the fact that metabolism of most OP poisoning as clinically indicated. yields alkylphosphates or alkyl(di) as terminal products. Since these metabolites can Course and prognosis be produced by several different OP, this method is The first four to six hours are the most critical not compound specific and is only usable to assess in acute OP poisoning. If there is improvement in exposure to all parent compounds, which may symptoms after initial treatment then the patient generate these derivatives. will be very likely to survive if adequate treatment The measurement of alkylphosphates in urine is continued. Delayed toxicity represents an onset requires rather sophisticated analytical methods of effects on the central and peripheral nervous such as gas liquid chromatography.Archive So far, the ofsystems appearingSID days to weeks after exposure. measurement of alkylphosphates has been This may occur independently of the effects performed in few studies, mostly for research observed in acute poisoning due to cholinesterase purposes. Biological assessment of exposure inhibition. Death in cases of heavy exposure is through urinary metabolite determination may be a usually related to respiratory collapse, reflecting very sensitive method, which is capable of depression of the respiratory center, weakness of revealing exposure in a range of doses that are too the muscles of respiration, bronchoconstriction, low to be detected with AChE monitoring. and excessive pulmonary secretions. Death may OP metabolites are usually excreted in the urine also result from cardiac arrest, because of cardiac within a short time and the peak of emission occurs dysrhythmias, and various degrees of heart a few hours after the beginning of exposure. block.6,18,77 Therefore, in occupational exposure, samples Patients with high exposure to nerve agents

Archives of Iranian Medicine, Volume 11, Number 1, January 2008 77 www.SID.ir Neurotoxic effects of organophosphorus compounds and their managements may die within a few minutes in the field. Those filter and not a surgical or similar mask) and heavy with physical and chemical protection rubber gloves (surgical gloves offer negligible () who remain in a heavily protection) and avoid skin contact with victims contaminated area, may become intoxicated after until decontamination has been carried out. 36,68 30 min. Patients with moderate to severe As soon as possible victims should be removed intoxication who receive first aid and emergency from the contaminated place, and decontamination medical treatment may survive within a few days must be initiated. should be given at the to a few weeks, according to the severity of onset of effects as appropriate (e.g., autoinjector intoxication and type of treatment. However, containing atropine, , and ). hypoxia, coma, convulsions, and respiratory failure For unconscious or severely intoxicated patients, are the signs of poor prognosis.18 priorities must follow the ABCs of resuscitation. The patients who remain severely hypoxic, Oxygen administration and assisted ventilation cyanotic, and receive atropine, may develop should be undertaken as soon as possible in those cardiac arrhythmias and die very soon. Those who with respiratory distress. Because atropine will develop apnea and are not instantly receiving reverse bronchoconstriction within minutes, one assisted ventilation may develop brain damage and might hesitate to intubate a dyspneic, conscious either die or become vegetative. It is unlikely that patient who probably will improve quickly. nerve agents possess the potential to give rise to However, in a severely poisoned, unconscious, OPIDN.6,18 apneic patient, endotracheal intubation with Soldiers who are caught unaware and who are assisted ventilation should be undertaken as exposed to large amounts of nerve agents before quickly as possible. put on respirators and other protective clothing, Airway resistance may be very high initially, rapidly develop severe symptoms and signs and are causing some mechanical ventilators to unlikely to survive. Those who slip rapidly into malfunction, but it will return toward normal after respiratory failure and who become incapable of atropine administration. Frequent airway self-administrating their own autoinjector suctioning may be required for copious bronchial systems/devices will also have a poor prognosis, secretions. Supplemental oxygen through an unless emergency medical treatment is rapidly endotracheal tube with positive end-expiratory provided.18 pressure is indicated for severely hypoxic patients. It is important to improve tissue oxygenation Management before atropine administration to minimize the risk of ventricular fibrillation. Advanced life support, First aid advice for lay persons including IV line placement, should be provided to The primary principle of first aid is to take care all victims with evidence of respiratory of life-threatening events. In this context the air- compromise or other signs of severe OP way should be kept clear to maintain respiration, exposure.36 particularly when the patient is unconscious or has vomited. The mouth and pharynx should be cleared Decontamination and dentures removed. The jaw should be Decontamination must be carried out at the supported and the patient placed in a face down earliest opportunity to limit skin absorption of the position with the head down and turned to one agent and prevent contamination of the rescuers. Archive ofThorough SIDdecontamination is essential before side, with the tongue drawn. casualties enter an emergency department or other First aid advice for medical and paramedical site of medical care to avoid contamination of staff personnel and other patients. The first rule for managing chemical casualties If the eyes have been exposed, they should be is that the emergency responders must protect irrigated as soon as possible with running water or themselves from contamination resulting from saline. Skin decontamination should be done by contact with casualties and the environment. This pouring on large amounts of a chlorine-liberated can be done by approximate personal protective solution such as 5.0% hypochlorite solution equipment and by thoroughly decontaminating the (household bleach) followed by copious water patient. At minimum, rescuers should wear a rinsing. If bleach is not available, the skin should protective mask (or mask containing a charcoal be blotted gently (without rubbing) with generous

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amounts of alkaline soap and water followed by a exposure or soman poisoning with atropine and water rinse. Copious amounts of water alone can chloride and permits survival at higher be used if nothing else is available; water will agent challenges. This protection apparently is due dilute and physically wash away the agent, but it to the fact that the more lethal nerve agents cannot will not hydrolyze it. Contaminated clothing and attack AChE molecules bound by carbamates. jewelry should be removed, and the underlying Carbamylation of 20 to 40% of the EAChE is skin should be thoroughly decontaminated. Care associated with antidotal enhancement. should be taken to clear under the nails, pretreatment will not reduce the effects of the intertriginous areas, axilla, groin, and hair.36 agents, and by themselves carbamates provide no Fetal bovine serum acetylcholinesterase (FBS- benefit. Pretreatment is not effective against sarin AChE) protected mice from multiple LD50 doses and VX challenge and should not be considered a of OP nerve agents.47 BChE purified from human panacea for all nerve agents. It is of value for plasma (HuBChE) was also effective both in vitro soman intoxication when agent challenge is and in vivo in mice and rats as a single followed by atropine and an oxime. Pretreatment is prophylactic antidote against the lethal effects of ineffective unless standard treatment is nerve agents.48 Addition of the oxime HI6 to FBS- administered after the exposure.18 AChE as a pretreatment drug, amplified the Because is toxic at the amounts efficacy of enzyme as a scavenger of nerve required, pyridostigmine is the drug of choice for agents.77 pretreatment. The standard dosage is 30 mg orally Recombinant DNA-derived AChEs revealed a every eight hours for impending nerve agent great improvement over wild-type AChE as system attack. Because pyridostigmine does not bioscavengers; they can be used to develop cross the blood-brain barrier, it causes no central effective methods for the safe disposal and stored nervous toxicity. Carbamates must never be used OP nerve agents and potential candidates for pre-or after nerve agent exposure; in that setting, postexposure treatment for OP toxicity.78 By the carbamate administration will worsen, rather than utilization of cell immobilization technology, protect from toxicity.83 Excessive doses cause immobilized Escherichia coli with surface- many of the same toxic effects as do the nerve expressed OP hydrolase was made to detoxify agents, and the recommended amounts caused nerve agents.79 By protein engineering techniques annoying side effects in more than half of the one BChE mutant G117H was made to hydrolyze population in a war zone.6,83 Administration of V and Gagents but reacts much too slowly.80 eptastigmine IV protected mice better than Organophosphate acid hydrolyses (OPAH) physostigmine against soman exposure.83 from two species of Ateronomas were cloned and Pretreatment with a drug mixture sequenced to detoxify G agents, which was (pyridostigmine, benactyzine, and effective.81 that were covalently trihexyphenidyl), and antidotal treatment linked to a polyurethane matrix can effectively be (HI6+benactyzine) was investigated in rats. This used to remove and decontaminate nerve agents cholinergic- pretreatment was from the skin or wounds. This could protect effective in restoring respiratory and circulatory medical personnel from secondary contamination changes induced by soman.84 while attending chemical casualties, and civilians exposed to highly toxicArchive nerve agents.65 ofAntidotes SID A reactive skin decontamination (RSD) lotion Available antidotes (atropine, oximes) do not active against classical nerve agents and mustard necessarily prevent respiratory failure or was developed. Inactivation process was time and incapacitation.85 However, early aggressive agent dependent and also related to ratio of OP to medical treatment with antidotes and intensive care RSD lotion.82 management are the keys to prevention of morbidity and mortality associated with OP Pretreatment in OP nerve agents poisoning poisoning. Recent experience and studies by In animal studies, pretreatment with reversible clinical toxicologists revealed that blood carbamate AChE inhibitors, such as alkalinization by sodium bicarbonate, and also pyridostigmine and physostigmine, enhances the magnesium sulfate should be added to the efficacy of postexposure treatment of soman treatment regime of OP poisoning.86

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Atropine which are divided into mono and bispyridium Atropine sulfate should be titrated with the goal oximes. Names and suppliers of the common of the treatment being drying the secretions and oximes are summarized in Table 5. resolution of bronchoconstriction and Although oximes have been designed to bradycardia.87 Thus there is no actual dose for reactivate the inhibited AChE, clinical experience atropine. The dose (2 mg) of atropine available in has indicated that they are not always effective as autoinjector is not adequate for the moderate to reactivators and none of them can be regarded as a severe exposure to nerve agents. In fact, atropine broad-spectrum antidote.89 The choice of oximes is should be given IV in doses to produce mild to based on the data presently available and may also moderate atropinization (dryness of tongue, be dependent on factors other than protection oropharyngeal, and bronchial tree, tachycardia, against lethality, such as cost and availability of mydriasis, and flushing) as soon as possible. At the oxime and its side effects. Obidoxime least the same amount as the initial atropinization (Toxogonin) is likely to cause more toxic effects dose should be infused in 500 mL dextrose 5% (particularly with high doses) than pralidoxime and constantly to sustain the atropinization and repeat HI6.90 HI6 is the least toxic, but is less unstable in it as needed until the patient becomes solution and is not commercially available in many asymptomatic. Continuous infusion of atropine parts of the world. effectively antagonizes the muscarinic effects and Pralidoxime (PAM-2Cl), HI6, and HGG-12 some of the CNS effects of OP poisoning, but has were used in dogs with soman and tabun no effect on skeletal muscle weakness, seizures, poisoning. PAM-2Cl (in conjunction with atropine unconsciousness, or respiratory failure.36 and diazepam) revealed the best protection in Large doses of atropine require higher soman-poisoned dogs, with the respective concentration of atropine preparation (e.g., protective indices of 9, 6.3, and 3.5. None of them 100mg/10 mL made in Germany) or at least a vast were effective against tabun poisoning.91 Efficacy amount of atropine (10 – 100 mg) in dextrose 5% of two other oximes, HLo-7 and pyrimidoxime in solution, ready made for IV infusion in severely 3x LD50 dose of sarin, soman, and GF and 2x LD50 OP-intoxicated patients. However, based on of tabun were tested in mice. HLo-7 produced clinical experience of the first author, much lower significant (P<0.05) reactivation of phosphorylated atropine doses are required for nerve agents than AChE, resulting in 47, 38, 27, and 10% for the severe OP-pesticides poisoning. reactivation of sarin, GF, soman, and tabun in Atropine should not be given IV to a hypoxic inhibited mouse diaphragm AChE, respectively.92 patient. If the patient is hypotensive, atropine can In this comprehensive study, the order of be given through an endotracheal tube or effectiveness against soman was HI6, HLo7, and intratracheally for more rapid absorption through pyrimidoxime. HLo7 was very effective against the peribronchial vessels.36 Aerosolized atropine tabun poisoning, while HI6 and pyrimidoxime has also been used and can be administered quickly were of moderate value. HI6 and HLo7 were by inhalation. Studies suggest that in addition to extremely effective against GF, while obidoxime the local effects in the lungs, it is also absorbed was moderately effective and PAM-2Cl and systemically.88,89 pyrimidoxime were the least effective.93 In soman-intoxicated guinea pigs, HI6 was Oximes therapeutically slightly more effective than HLo7. Oximes are mainlyArchive pyridinium compounds, of SID Table 5. Common oximes used in the treatment of OP nerve agent poisoning. Type of oxime Generic name Trade name Supplier/Country Monopyridinium Pralidoxime chloride(2-PAM) Protopam Ayerst/USA/Canada Pralidoxime Contrathion SERB/France Methylsulfate Pralidoxime (P2S) UK government Methanesulfonate Bispyridinium Trimedoxime (TMB-4) Obidoxime Toxogonin Merck/Germany HI-6 HLo-7 HGG-12

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HLo7 was more effective against tabun continued until the full recovery or until atropine is intoxication than HI6.94 required. Obidoxime was hepatotoxic at high Pharmacokinetics and effects of HI6 in blood recommended doses of 8 mg/kg initially, and 3 and brain of soman-intoxicated rats have been mg/kg/hr.5 It may be given at a dose not more than studied.95 High doses of HI6 can reach the brain in 500 mg initially and 750 mg/day. Liver function sufficient amount to reactivate inhibited brain tests should be checked regularly during AChE. Signs of soman poisoning correlated obidoxime therapy to avoid severe hepatotoxicity.1 positively to acetylcholinesterase inhibition and negatively to the concentration of inbound HI6 in Diazepam the brain and that soman intoxication significantly Behavioral efficacy of diazepam against nerve decreased uptake of HI6 into the brain.95 agents in rhesus monkeys was studied. The results Reactivating potency of obidoxime, pralidoxime, revealed that diazepam would be an excellent HI6, and HLo7 in human AChE inhibited by adjunct to the traditional nerve agent therapy to soman, sarin, cyclosarin, and VX were studied in facilitate behavioral recovery from nerve agent vitro.95 intoxication that might be encountered by the After soman, sarin, cyclosarin, and VX, the medical military personnel on the battlefield.98 reactivating potency decreased in the order of Despite the introduction of diazepam as a HLo7>HI6>obidoxime>pralidoxime.96 Dose symptomatic , a number of studies response effects of atropine and HI6 treatment in have been performed that indicate the effects of soman and tabun poisonings were studied in diazepam may be more specific. These studies guinea pigs. Atropine had a large effect on the have mainly investigated the effects on cholinergic efficacy of HI6 against the nerve agents. They and GABAergic systems.18,46 were also more effective against soman than against tabun. Adjunctive treatment with diazepam Gacyclidine enhanced the efficacy of HI6 and atropine against Gacyclidine is an antiglutamatergic compound soman.97 that was studied as a complement to the available The effects of common oximes in different emergency treatment in organophosphate nerve agent poisoning are summarized in Table 6. poisoning. It was used in conjunction with ProPAM, the tertiary amine analog of atropine, pralidoxime, and diazepam in nerve agent pralidoxime penetrates the CNS more readily than poisoning in primates.18 Gacyclidine prevents the pralidoxime. Consequently, proPAM would be mortality observed after early administration of the expected to have greater beneficial effect in nerve above classical emergency medication. EEG agent poisoning than pralidoxime. This expectation recordings and clinical observations also revealed has not in general been realized in experimental that gacyclidine prevented soman-induced seizures studies.18 and motor convulsions. It also markedly accelerated clinical recovery of soman-challenged Dosage regimen of oximes primates. Gacyclidine prevented the In spite of many oximes tested in animal neuropathology observed three weeks after soman experiments, the human experience either in exposure in animals.18,99 In case of severe nerve pesticides or war/terrorism limited to pralidoxime agent poisoning, gacyclidine represented a and obidoxime. ArchivePralidoxime should be ofpromising SIDadjuvant therapy to the currently administered IV at a dose of 30 mg/kg initially available polymedication to insure optimal over 30 min followed by constant infusion of 8 management of OP nerve agent poisoning in man. mg/kg/hr in dextrose 5% solution. It could be This drug is currently being evaluated in human

Table 6. Relative effects of oximes in OP nerve agents poisoning. Oximes GA sarin GB soman GD tabun GF VX Pralidoxime +++ ++ + + +++ Pyrimidoxime ++ ++ ++ + ++ Obidoxime ++ +++ ++ ++ +++ HI6 +++ ++++ ++ ++++ +++ HLo7 ++++ +++ ++++ ++++ ++ HGG12 NA +++ + NA NA NA=no data available; +=least effective; ++=partially effective; +++=moderately effective; ++++=most effective; OP= organophosphorus.

Archives of Iranian Medicine, Volume 11, Number 1, January 2008 81 www.SID.ir Neurotoxic effects of organophosphorus compounds and their managements clinical trial for different neuroprotective High-risk groups indications.18,100 1. Pregnant women and mother’s milk Organophosphate nerve agents may cross the placenta and induce fetal intoxication. The fetus is Blood alkalinization by sodium bicarbonate more sensitive to OP compounds than the mother Effects of sodium bicarbonate in OP pesticide and also more sensitive to atropine than the poisoning were investigated in patients with mother. 18 Based on clinical experience with moderate to severe intoxication. It was aimed to pregnant women exposed to sarin during the Iran- make an alkalinization to reach and sustain the Iraq war in Sardasht and Halabjah, and also with arterial blood pH between 7.45 and 7.55. Sodium pregnant women poisoned with OP pesticides, bicarbonate was administered IV, firstly to correct mortality was higher in fetus than the mother. the metabolic acidosis and then 3 – 5 mg/kg/24hr Some pregnant women survived from sarin as constant infusion until recovery or until atropine poisoning but the fetus died within a few hours to a was required. Arterial blood gas analysis was few days. Atropine and oximes should be performed in certain intervals to adjust the dosing. 101 administered with caution and at lower doses to The preliminary results were promising, and the 86, 102 pregnant women. Obstetric consultation is final results were satisfactory. required. If fetal death occurs, the dead fetus Since alkalinization products of nerve agents should be removed as soon as the clinical condition particularly soman are less toxic, it seems that of the mother is improved. administration of IV infusion of sodium OP compounds may be excreted in the mother’s bicarbonate to produce moderate alkalinization, milk. It would therefore be advisable to stop breast may also be effective in nerve agent poisoning and 18 103 feeding at least for a few days after exposure. should be added to the treatment regimen. 104 Roberts and coworkers, were concerned about 2. Children the safety of alkalinization regime but the other Children are more susceptible to OP nerve investigators provided data about the safety of 103 agents as were seen during the Hallabjah massacre. alkalinization. Mortality was higher in children than in adults.

They are also more sensitive to atropine and Drug interactions oximes. Atropine should be administered with The reported drugs that are contraindicated in caution, by monitoring vital signs, particularly the severe OP nerve agent poisoning are: morphine pulse rate. If the pulse rate exceeds more than 160 and its derivatives, aminophylline, theophylline, beats/min atropine infusion should be stopped and and . Drugs that are known to be restarted when the pulse rate drops to below 140 hydrolyzed by the enzyme cholinesterase, such as beats/min. suxamethonium (succinyl ) and procaine, Based on clinical experience with children should also be avoided.18 poisoned by OP pesticide, pralidoxime should be administered at 25 mg/kg as an initial loading Hemoperfusion dose, which should be infused over 15 – 30 min Effects of hemoperfusion (HP) through coated followed by 10 – 20 mg/kg/hr to provide a plasma resin adsorbent synachrome E-5 was studied in concentration of >4 mg/L. 106 five anesthetized dogs following intoxication by two to six LD50, VX andArchive in another four dogs with of SID 3. Elderly two to three LD50 sarin. HP therapy prevented the Elderly people are also more susceptible to OP development of serious signs of intoxication nerve agent intoxication. Experience with the sarin provided that the dose of both nerve agents was poisoning during Iran-Iraq was in Sardasht and only 2x LD50. It was then concluded that HP in Halabjah revealed that morbidity and mortality nerve agents of sarin and VX is only partially were higher among elderly people. Multiple organ 105 successfull. failure and complications were more common Clinical experience of the first author of this among the elderly than the other adult age groups. study with the management of OP nerve agents and Administration of atropine, oxime, and diazepam, pesticides in humans revealed that HP may be and any other medications should be performed 18 effective in severely intoxicated OP patients. with caution. Depending on the age and clinical

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condition of the patient, critical care therapy together with mydriasis and dryness of the tongue should be initiated more rapidly. In fact, the elderly were more recorded following atropinisation. patients with OP poisoning should be treated as the Morbidity and mortality were higher in patients priority group as the children. 18 with severe respiratory distress and cyanosis who received large doses of atropine. It was very vital 4. Rescue staff and hospital personnel to correct the severe hypoxemia and cyanosis Rescue staff and hospital personnel who are in before atropinization (see management). Thus, contact with patients of OP nerve agent poisoning suctions of naso/oropharyngeal and bronchial may become intoxicated because of the secondary secretion (clear airway) and performing adequate exposure. Among 59 rescuers and duty doctors, ventilation is the first priority. Intermediate eight had mild symptoms of sarin poisoning during syndrome that was described following OP the Matsumoto incident. All the rescue activities pesticide poisoning,5 has not been observed with had taken place without gas masks or the nerve agent poisoning. decontamination procedures.107 Secondary It should be noted that sulfur mustard was the contamination was observed in house staff who most common chemical warfare agent that was treated victims during the Tokyo subway incident. used by the Iraqi army. Thus, mixed poisoning by Over 20% of the house staff had symptoms tabun and sulfur mustard was also common. No including ocular pain, headache, sore throat, exact statistical records of the nerve agents were dyspnea, nausea, dizziness, and nasal pain, but available. It has been estimated that >2000 patients none were seriously affected.108 However, the with nerve agent poisoning (later on diagnosed as rescue staff and medical personnel either in the tabun) were treated in March 1984. Another field, during transportation, or in the hospital massive nerve agent poisoning occurred during the should be protected by proper, gas masks, clothing, Halabjah massacre. It was also diagnosed as sarin and thick gloves (not surgical gloves). mixed with sulfur mustard.62,63 Based on the first author’s experience, the Iranian experience in management of OP management of OP nerve agents poisoning is poisoning summarized in a flow chart (Figure 3). Iranian experience in management of acute OP pesticide poisoning, revealed that in addition to the Preventive measures standard treatment, blood alkalinization with It is essential that persons intending to use OP sodium bicarbonate and also magnesium sulfate pesticides are provided with adequate health may be effective in moderate to severe precautions and other safety instructions before intoxication. 18 usage. This information should be provided by the Observations during the nerve gas attack of the manufacturer in the form of either an information Iraqi army against the Iranian troops in Majnoon leaflet or a label attached to the pesticide container. Island revealed that the heavily exposed people Protective clothing is important. OP pesticides can died within 30 min following coma, convulsions, be absorbed through the skin, resulting in hypersecretion and respiratory failure, and apnea. poisoning. The risk is greater in hot weather when Although the medical facilities were not adequate the user is sweating. Protective measures may in Majnoon Island, first aid treatment and include a long-sleeved shirt, long trousers or decontamination wereArchive performed. The patients ofoveralls, andSID a hat of some sort. The more toxic OP with moderate to severe intoxication were pesticides will require gloves, waterproof transferred from the filed hospital to medical outerwear (preferably made of heavy PVC), and centers in big cities for further management. rubber boots. The label should list these details. Recorded clinical manifestations included: Clothing worn during spraying should be miosis, hypersecretions, hypotension, nausea, washed daily after use. Contaminated clothing vomiting, abdominal cramps, diarrhea, loss of should be washed separately from the general wash consciousness, respiratory depression, cyanosis, to avoid cross-contamination. When working with pulmonary edema, muscle twitching, and liquid concentrates, there is often a danger that convulsions. Bradycardia and hypotension were they will splash the eyes. This not only can damage more observed before treatment with atropine the eyes, but also can allow a significant amount of whereas tachycardia and normal hypertension the chemical to be absorbed into the bloodstream.

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Management of nerve agent (NA) poisoning:

Heavy exposure N.A. exposure Low exposure Asymptomatic

Rapid Death Moderate exposure Symptomatic Discharge

(Application of auto injector containing atropine, oximes & diazepam)

Eye damage Eye Skin Inhalation Ingestion

D E C O N T A M I N A T I O N Removal G.A.L. in 1 hr from contamination

Opthalmologic Consultation T R I A G E

Symptoms only Signs of general intoxication Asymptomatic

Psychiatric evaluation Hospitalization Discharge & Discharge Cholinesterase ABC’s Atropininsation Estimation, Clinical evaluation, oximes, diazepam Clinical recovery Paraclinical Investigations Alkalinisation

Complications Psychiatric (Organ failure) Severe Respiratory Distress assessment Archive of SID

I.C.U. Discharge Monitoring, antidotes, supportive therapy Relevant Para clinical investigations Consultation Death

Sequelae Recovery Psychiatric assessment Discharge

Figure 3. Flow chart on the management of OP poisoning

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Simple goggles or a face shield will protect and leave for at least eight hours. Absorb into against this danger. Eye protection is the most sawdust, sand, or earth and then rinse. important if contact lenses are worn, because the Contaminated sawdust, sand, earth, and chemical may seep in behind the lenses. The lenses containers should be burnt in a proper incinerator. must be removed before the eyes are washed, and When no incinerator is available, bury in an in the time it takes to remove them, serious damage approved dump or in an area where there is no risk can occur. With some pesticides, a respirator may of contamination of surface water. Before burying, be required. The label should specify when this is mix liberally in sodium carbonate (washing soda) necessary. The correct canister or cartridge must crystals to hydrolyze the product. be used. For workers who are exposed on a regular basis Greater precautions are necessary when mixing to OP pesticides, it is advisable for them to have a the concentrated material than when spraying. pre-employment examination to determine their Measurements should be accurate and spillages baseline cholinesterase levels. These tests should should be cleaned up promptly. Mix the chemicals be undertaken on a regular basis to determine carefully, using a stick or paddle. Ensure that there whether exposure is occurring with subclinical is minimal skin exposure by wearing gloves. If any findings. When the RBC or plasma cholinesterase concentrate is spilled on the skin, wash it off as falls below 25% of baseline levels, workers should soon as possible. The hazards of spraying increase be taken off the job and should not return to work dramatically on windy days because there is an until their cholinesterase levels return to normal.4 increased risk of inhaling spray drift or contaminating the skin. Also, the risk of drift on to Conclusions and recommendations other properties or crops is increased. Always wash OP compounds either as pesticides or nerve hands before eating, drinking, or smoking. After agents, have induced a lot of human morbidities spraying, take a shower, and change clothing. and mortalities. OP pesticides are still used in most By preference, all chemicals should be stored in parts of the world and unfortunately are easily a locked shed, out of the reach of children and available in some developing countries and thus animals. Chemicals should also be kept away from occupational and accidental exposure and even work areas and separate from other stored intentional ingestion are common and induced materials such as animal foods. Always leave health problems. chemicals in their original containers. If they must WHO has recommended that access to highly be transferred to another container, ensure that it is toxic pesticides be restricted and wherever this has one not normally used for food or drink. This been done, suicide rates have fallen. Proper secondary container should be labeled properly and legislations and pesticides control, particularly OP be of a variety that is not likely to leak. compounds, which are the most commonly used Following spillage, empty any of the product pesticides are recommended. Biological pest remaining in damaged/leaking container(s) into a control that has recently been applied in some clean empty container(s), which should then be countries should be extended and advanced to tightly closed and suitably labeled. replace OP pesticides. If it is a liquid product, prevent it from In spite of the establishment of OPCW and its spreading or contaminatingArchive other products, ofactive role SID in CWA control, chemical nerve agents vegetation, or waterways by building a barrier of attack either as a war or terrorism remains a big the most suitable available material, e.g., earth or threat to the population in any part of the world. sand. Sweep up the spillage with sawdust, sand, or Therefore, medical and health professionals should earth (moisten the powders), and place it in a be aware and update their knowledge on the suitable container for disposal. Decontamination toxicology and proper management of OP and clean-up procedures utilize the instability of poisoning. OP pesticide products with alkali. The following procedure has been developed for decontaminating Acknowledgment spills of OP pesticides: Financial support of the Iran Chapter of the Apply a 10% sodium carbonate (washing soda Academy of Sciences for Developing World solution) to the contaminated area, brush well in, (TWAS) at ISMO, Ministry of Sciences, Research,

Archives of Iranian Medicine, Volume 11, Number 1, January 2008 85 www.SID.ir Neurotoxic effects of organophosphorus compounds and their managements and Technology of I.R. of Iran is acknowledged. organophosphorous chemical warfare agents. In: Hartley FR, ed. The Chemistry of Organophosphorus Compounds. Chichester: John Wiley and Sons; 1996: References 781 – 840. 1 Balali-Mood M, Shariat M. Treatment of 20 Black RM, Clarke RJ, Read RW, Reid MTJ. Application organophosphate poisoning. Experience of nerve agents of gas chromatography-mass spectrometry and gas and acute pesticide poisoning on the effects of oximes. J chromatography-tandem mass spectrometry to the Physiol Paris. 1998; 92: 375 – 378. analysis of chemical warfare samples, found to contain 2 Ballantyne B, Marrs T. Overview of the biological and residues of the nerve agent sarin, sulfur mustard and their clinical aspects of organophosphates and carbamates. In: degradation products. J Chromatogr A. 1994; 662: Ballantyne B, Marrs TC, eds. Clinical and Experimental 301 – 321. Toxicology of Organophosphates and Carbamates. 21 Tokuda Y, Kikuchi M, Takahashi O, Stein G. Prehospital Oxford: Butterworth & Heinemann; 1992: 3 – 14. management of sarin nerve gas terrorism in urban 3 Minton NA, Murray VS. A review of organophosphate settings: 10 years of progress after the Tokyo subway poisoning. Med Toxicol Adverse Drug Exp. 1988; 3: sarin attack. Resuscitation. 2006; 68: 193 – 202. 350 – 375. 22 Nozaki H, Aikawa N, Fujishima S, Suzuki M, Shinozawa 4 Jeyaratnam J, Maroni M. Organophosphorous Y, Hori S, et al. A case of VX poisoning and the compounds. Toxicology. 1994; 91: 15 – 27. difference from sarin. Lancet. 1995; 346: 698 – 699. 5 Lockridge O, Masson P. Pesticides and susceptible 23 Nagao M, Takatori T, Matsuda Y, Nakajima M, Iwase H, populations: people with butyrylcholinestrase genetic Iwadate K. Definitive evidence for the acute sarin variants may be at risk. Neurotoxicology. 2000; 21: poisoning diagnosis in the Tokyo subway. 113 –126. Toxicol Appl Pharmacol. 1997; 144: 198 – 203. 6 Sidell FR. Soman and sarin: clinical manifestations and 24 Worek F, Koller M, Thiermann H, Szinicz L. Diagnostic treatment of accidental poisoning by organophosphates. aspects of organophosphate poisoning. Toxicology. 2005; Clin Toxicol (Phila). 1974; 7: 1 – 17. 214: 182 – 189. 7 Holmsted B. The third symposium on the prophylaxis 25 Sidell FR, Borak J. Chemical warfare agents: II. Nerve and treatment of chemical poisons. Fund Appl Toxicol. agents. Ann Emerg Med. 1992; 21: 865 – 871. 1985; 5: S1 – S9. 26 Josse D, Lockridge O, Xie W, Bartels CF, Schopfer LM, 8 Eto M. Organophosphorous Pesticides: Organic and Masson P. The active site of human paraoxonase Biological Chemistry. Cleveland: CRC Press; 1974. (PON1). J Appl Toxicol. 2001; 21 (suppl 1): S7-S11. 9 Kwong K. Organophosphate pesticides: biochemistry and 27 Dunn M, Sidell F. Progress in medical defense against clinical toxicology. Ther Drug Monit. 2002; 24: nerve agents. JAMA. 1998; 262: 649 – 652. 144 – 149. 28 Ooms AJJ, van Dijk C. The reaction of 10 Lotti M. Low-level exposures to organophosphorous organophosphorous compounds with hydrolytic esters and peripheral nerve function. Muscle Nerve. 2002; enzymes--III: the inhibition of chymotrypsin and trypsin. 25: 492 – 504. Biochem Pharmacol. 1966; 15: 1361 – 1377. 11 Forget G. Pesticides and the third world. J Toxicol 29 Boter HL, Ooms AJJ. Stereospecificity of hydrolytic Environ Health. 1991; 32: 11 – 31. enzymes in their reaction with optically active 12 Eddleston M, Gunnell D, Karunaratne A, de Silva D, organophosphorus compounds--II: the inhibition of Sheriff MH, Buckley NA. Epidemiology of intentional aliesterase, acetylesterase, chymotrypsin, and trypsin by self-poisoning in rural Sri Lanka. Br J Psychiatry. 2005; S-alkyl p-nitrophenyl methylphosphonothiolates. 187: 583 – 584. Biochem Pharmacol. 1967; 16: 1563 – 1569. 13 Amr MM. Pesticide monitoring and its health problems 30 Black R, Harrison J, Read R. The interaction of sarin and in Egypt, a Third World country. Toxicol Lett. 1999; 107: soman with plasma proteins: the identification of a novel 1 –13. phosphonylation site. Arch Toxicol. 1999; 73: 123 – 126. 14 Cocker J, Mason HJ, Garfitt SJ, Jones K. Biological 31 Sogorb MA, Vilanova E. Enzymes involved in the monitoring of exposure to organophosphate pesticides. of organophosphorous, carbamate, and Toxicol Lett. 2002; 134: 97 – 103. insecticides through hydrolysis. Toxicol Lett. 15 Brown MA, Brix KA. Review of health consequences 2002; 128: 215 – 228. from high-, intermediate-, and low-level exposure to 32 Eyer P, Worek F, Kiderlen D, Sinko G, Stuglin A, Archive ofSimeon-Rudolf SID V, et al. Molar absorption coefficients for organophosphorus nerve agents. J Appl Toxicol. 1998; 18: 393 – 408. the reduced Ellman reagent: reassessment. Anal Biochem. 16 Eddleston M, Karalliedde L, Buckley N, Fernando R, 2003; 312: 224 – 227. Hutchinson G, Isbister G, et al. Pesticide poisoning in the 33 Morita H, Yanagisawa N, Nakajima T, Shimizu M, developing world--a minimum pesticides list. Lancet. Hirabayashi H, Okudera H, et al. Sarin poisoning in 2002; 360: 1163 – 1167. Matsumoto, Japan. Lancet. 1995; 346: 290 – 293. 17 Thiermann H, Szinicz L, Eyer F, Worek F, Eyer P, 34 Lee M, Clement J. Effect of soman poisoning in Felgenhauer N, et al. Modern strategies in therapy of haematology and coagulation parameters and serum organophosphate poisoning. Toxicol Lett. 1999; 107: biochemistry in rabbits. Milit Med. 1990; 155: 244 – 249. 233 – 239. 35 Grob D. The manifestations and treatment of poisoning 18 Balali-Mood M, Balali-Mood K. Nerve agents. In: Brent due to nerve gas and other organic phosphate J, ed. Critical Care Toxicology. Philadelphia, USA: anticholinesterase compounds. Arch Intern Med. 1956; Elsevier Mosby. 2005: 1379 – 1393. 98: 221 – 239. 19 Black R, Harrison J. The chemistry of 36 Ohbu S, Yamashina A, Takasu N. Sarin poisoning on

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Tokyo subway. Southern Med J. 1997; 90: 587 – 593. 52 Stewart W. The effects of sarin and atropine on the 37 Young G, Koplovitz I. Acute toxicity of respiratory center and neuromuscular junctions of the rat. cyclohexylmethylphosphonofluoridate (CMPF) in rhesus Can J Biochem Physiol. 1959; 37: 651 – 660. monkeys: serum biochemical and hematologic changes. 53 Rickett D, Glenn J, Beers E. Central respiratory effects Arch Toxicol. 1995; 69: 379 – 383. versus neuromuscular actions of nerve agents. 38 Rickell D, Glenn J, Houston W. Medical defense against Neurotoxicology. 1953; 8: 466 – 475. nerve agents: new direction. Milit Med. 1987; 152: 54 Singer A, Jaax NK, Graham J. Cardiomyopathy in soman 35 – 41. and sarin intoxicated rat. Toxicol Lett. 1987; 36: 39 Gordon J, Inns R, Johnson M. The delayed neuropathic 243 – 249. effects of nerve agents and other organophosphate 55 Furlong CE, Li WF, Richter RJ, Shih DM, Lusis AJ, compounds. Arch Toxicol. 1983; 52: 82 – 86. Alleva E, et al. Genetic and temporal determinants of 40 Albuquerque EX, Deshpande SS, Kawabuchi M, et al. pesticide sensitivity: role of paraoxonase (PON1). Multiple actions of anticholinesterase agents on Neurotoxicology. 2000; 21: 91 – 100. chemosensitive synapses: molecular basis for prophylaxis 56 Worek F, Kleine A, Falke K, Szinicz L. Arrhythmias in and treatment of organophosphate poisoning. Fundam organophosphate poisoning: effect of atropine and Appl Toxicol. 1985; 5: S182 - S203. bispyridinium oximes. Arch Int Pharmacodyn Ther. 41 Ecobichon DJ, Comeau AM. Pseudocholinesterases of 1995; 329: 418 – 435. mammalian plasma: physicochemical properties and 57 De Bleecker J, van den Neucker K, Willems J. The organophosphate inhibition in eleven species. Toxicol intermediate syndrome in organophosphate poisoning: Appl Pharmacol. 1973; 24: 92 – 100. presentation of a case and review of the literature. 42 Liu D, Watanabe H, Ho I. Acute effects of soman, sarin, J Toxicol Clin Toxicol. 1992; 30: 321 – 331. and tabun on cyclic nucleotide metabolism in rat 58 Klette KL, Levine B, Dreka C, Smith ML, Goldberger stratium. J Toxicol Environ Health. 1986; 19: 23 – 32. BA. Cholinesterase activity in postmortem blood as a 43 van der Schans MJ, Lander BJ, Wiel Hvd, Langenberg screening test for organophosphate/chemical weapon JP, Benschop HP. Toxicokinetics of the nerve agent (±)- exposure. J Forensic Sci. 1993; 38: 950 – 955. VX in anesthetized and atropinized hairless guinea pigs 59 McLeod C, Singer A, Harrington D. Acute and marmosets after intravenous and percutaneous neuropathology in soman poisoned rats. Neurotoxicology. administration. Toxicol Appl Pharmacol. 2003; 191: 1984; 5: 53 – 58. 48 – 62. 60 Cao CJ, Mioduszewski RJ, Menking DE, Valdes JJ, Katz 44 van der Schans MJ, Polhuijs M, van Dijk C, Degenhardt EJ, Eldefrawi ME, et al. Cytotoxicity of organophosphate CE, Pleijsier K, Langenberg JP, et al. Retrospective anticholinesterases. In Vitro Cell Dev Biol Anim. 1999; detection of exposure to nerve agents: analysis of 35: 493 – 500. phosphofluoridates originating from fluoride-induced 61 Worek F, Koller M, Thiermann H, Szinicz L. Diagnostic reactivation of phosphylated BuChE. Arch Toxicol. 2004; aspects of organophosphate poisoning. Toxicology. 2005; 78: 508 – 524. 214: 182 – 189. 45 Minami M, Hui D, Katsumata M, Inagaki H, Boulet C. 62 Schier J, Ravikumar P, Nelson L, Heller M, Howland M, Method for the analysis of the methylphosphonic acid Hoffman R. Preparing for chemical terrorism: stability of metabolites of sarin and its -substituted analogue injectable atropine sulfate. Acad Emerg Med. 2004; 11: in urine as applied to the victims of the Tokyo sarin 329 – 334. disaster. J Chromatogr B Biomed Sci Appl. 1997; 695: 63 Anzueo A, Berdine G, Moore G. Pathophysiology of 237 – 244. soman intoxication in primates. Toxicol Appl Pharmacol. 46 Sivam S, Hoskins B, Ho I. An assessment of comparative 1986; 86: 56 – 68. acute toxicity of diisopropyl-fluorophosphate, Tabun, 64 Sekijima Y, Morita H, Yanagisawa N. Follow-up of sarin Sarin, and soman in relation to cholinergic and poisoning in Matsumoto. Ann Intern Med. 1997; 127: GABAergic enzyme activities in rats. Fundam Appl 1042 – 1046. Toxicol. 1984; 19: 23 – 32. 65 Mulchandani A, Kaneva I, Chen W. Detoxification of 47 Rowntree DW, Nevin S, Wilson A. The effects of organophosphate nerve agents by immobilized diisopropylfluorophosphonate in schizophrenia and Escherichia coli with surface-expressed manic depressive psychosis. J Neurol Neurosurg organophosphorus hydrolase. Biotechnol Bioeng. 1999; Psychiatry. 1950; 13: 47 – 62. 63: 216 – 223. 48 Senanayake N, KaralliedeArchive L. Neurotoxic effects of of66 Mulchandani SID A, Pan S, Chen W. Fiber-optic enzyme organophosphorous insecticides. An intermediate biosensor for direct determination of organophosphate syndrome. N Engl J Med. 1987; 316: 761 – 763. nerve agents. Biotechnol Prog. 1999; 15: 130 – 134. 49 Ludomirsky A, Klein HO, Sarelli P, Becker B, Hoffman 67 Polhuijs M, Langenberg JP, Benschop HP. New method S, Taitelman U, et al. Q-T prolongation and for retrospective detection of exposure to polymorphous ("torsade de pointes") ventricular organophosphorus anticholinesterases: application to arrhythmias associated with organophosphorus alleged sarin victims of Japanese terrorists. Toxicol Appl insecticide poisoning. Am J Cardiol. 1982; 49: Pharmacol. 1997; 146: 156 – 161. 1654 – 1658. 68 Nagao M, Takatori T, Matsuda Y. Definitive evidence for 50 Rengstorff RH. Accidental exposure to sarin: vision the acute sarin poisoning diagnosis in the Tokyo subway. effects. Arch Toxicol. 1985; 56: 201 – 203. Toxicol Appl pharmacol. 1997; 144: 198 – 203. 51 Decandole C, Duglas W, Evans C. The failure of 69 Ellman G, Courtney K, Anders V, Featherstone R. A new respiration in death by anticholinesterase poisoning. Br J and rapid colorimetric determination of Pharmacol. 1953; 8: 466 – 475. acetylcholinesterase activity. Biochem Pharmacol. 1961;

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7: 88 – 95. decontamination using immobilized enzymes. Chem Biol 70 Worek F, Mast U, Kiderlen D, Diepold C, Eyer P. Interact. 1999; 119-120: 463 – 470. Improved determination of acetylcholinesterase activity 85 Sawyer TW, Weiss MT, Boulet CA, Hansen AS. in human whole blood. Clinica Chimica Acta. 1999; 288: Toxicity of organophosphate nerve agents and related 73 – 90. phosphonylated oximes compared to their 71 Taylor P, Kovarik Z, Reiner E, Radic Z. anticholinesterase activity in neuron cultures. Fundam Acetylcholinesterase: converting a vulnerable target to a Appl Toxicol. 1991; 17: 208 – 214. template for antidotes and detection of inhibitor 86 Balali-Mood M, Ayati MH, Ali-Akbarian H. Effect of exposure. Toxicology. 2007; 233: 70 – 78. high doses of sodium bicarbonate in acute 72 Mortensen SR, Brimijoin S, Hooper MJ, Padilla S. organophosphorous pesticide poisoning. Clin Toxicol Comparison of the in vitro sensitivity of rat (Phila). 2005; 43: 571 – 574. acetylcholinesterase to chlorpyrifos-oxon: what do tissue 87 Tuovinen K, Hanninen O. Protection of mice against IC50 values represent? Toxicol Appl Pharmacol. 1998; soman by pretreatment with eptastigmine and 148: 46 – 49. physostigmine. Toxicology. 1999; 139: 233 – 241. 73 Worek F, Widmann R, Knopff O, Szinicz L. Reactivating 88 Kassa J, Fusek J. The positive influence of a cholinergic- potency of obidoxime, pralidoxime, HI 6 and HLo 7 in anticholinergic pretreatment and antidotal treatment on human erythrocyte acetylcholinesterase inhibited by rats poisoned with supralethal doses of soman. highly toxic organophosphorus compounds. Arch Toxicology. 1998; 128: 1 – 7. Toxicol. 1998; 72: 237 – 243. 89 Munro NB, Watson AP, Ambrose KR, Griffin GD. 74 Noort D, Benschop HP, Black RM. Biomonitoring of Treating exposure to chemical warfare agents: exposure to chemical warfare agents: a review. Toxicol implications for health care providers and community Appl Pharmacol. 2002; 184: 116 – 126. emergency planning. Environ Health Perspect. 1990; 89: 75 Black RM, Read RW. Application of liquid 205 – 215. chromatography-atmospheric pressure chemical 90 Holstege CP, Kirk M, Sidell FR. Chemical warfare. ionisation mass spectrometry, and tandem mass Nerve agent poisoning. Crit Care Clin. 1997; 13: 923 – spectrometry, to the analysis and identification of 942. degradation products of chemical warfare agents. 91 Orma P, Middleton R. Aerosolized atropine as an J Chromatogr A. 1997; 759: 79 – 92. antidote to nerve gas. Ann Pharmacother. 1992; 26: 937 76 Katagi M, Nishikawa M, Tatsuno M, Tsuchihashi H. – 938. Determination of the main hydrolysis product of O-ethyl 92 van Helden HP, Busker RW, Melchers BP, Bruijnzeel S-2-diisopropylaminoethyl methylphosphonothiolate, PL. Pharmacological effects of oximes: how relevant are ethyl methylphosphonic acid, in human serum. they? Arch Toxicol. 1996; 70: 779 – 786. J Chromatogr B Biomed Sci Appl. 1997; 689: 327 – 333. 93 Nelson-Corvino T, Nahata M, Angelos M, Tschampel M, 77 Munro N. Toxicity of the organophosphate chemical Morosco R. Availability, stability, and sterility of warfare agents GA, GB, and VX: implications for public pralidoxime for mass casualty use. J Ann Emerg Med. protection. Environ Health Perspect. 1994; 102: 18 – 37. 2006; 47: 272 – 277. 78 Wolfe AD, Rush RS, Doctor BP, Koplovitz I, Jones D. 94 Dawson R. Review of oximes available for treatment of Acetylcholinesterase prophylaxis against nerve agent poisoning. J Appl Toxicol. 1994; 14: 317 – organophosphate toxicity. Fundam Appl Toxicol. 1987; 331. 9: 266 – 270. 95 Boskovic B, Kovacevic V, Jovanovic D. PAM-2 Cl, HI- 79 Raveh L, Grunwald J, Marcus D, Papier Y, Cohen E, 6, and HGG-12 in soman and tabun poisoning. Fundam Ashani Y. Human butyrylcholinesterase as a general Appl Toxicol. 1984; 4: S106 –S115. prophylactic antidote for nerve agent toxicity. In vitro 96 Clement JG, Hansen AS, Boulet CA. Efficacy of HLo-7 and in vivo quantitative characterization. Biochem and pyrimidoxime as antidotes of nerve agent poisoning Pharmacol. 1993; 45: 2465 – 2474. in mice. Arch Toxicol. 1992; 66: 216 – 219. 80 Caranto GR, Waibel KH, Asher JM, Larrison RW, 97 Lundy PM, Hansen AS, Hand BT, Boulet CA. Brecht KM, Schutz MB, et al. Amplification of the Comparison of several oximes against poisoning by effectiveness of acetylcholinesterase for detoxification of soman, tabun, and GF. Toxicology. 1992; 72: 99 – 105. organophosphorus compounds by bis-quaternary oximes. 98 Melchers BP, Philippens IH, Wolthuis OL. Efficacy of Biochem Pharmacol. 1994; 47: 347 – 357. HI-6 and HLo-7 in preventing incapacitation following 81 Saxena A, Maxwell DM,Archive Quinn DM, Radic Z, Taylor P, ofnerve agentSID poisoning. Pharmacol Biochem Behav. 1994; Doctor BP. Mutant as potential 49: 781 – 788. detoxification agents for organophosphate poisoning. 99 Cassel G, Karlsson L, Waara L, Ang KW, Goransson- Biochem Pharmacol. 1997; 54: 269 – 274. Nyberg A. Pharmacokinetics and effects of HI 6 in blood 82 Broomfield CA, Lockridge O, Millard CB. Protein and brain of soman-intoxicated rats: a microdialysis engineering of a human enzyme that hydrolyzes V and G study. Eur J Pharmacol. 1997; 332: 43 – 52. nerve agents: design, construction and characterization. 100 Koplovitz I, Menton R, Matthews C, Shutz M, Nalls C, Chem Biol Interact. 1999; 119-120: 413 – 418. Kelly S. Dose-response effects of atropine and HI-6 83 Cheng TC, DeFrank JJ, Rastogi VK. Alteromonas treatment of organophosphorus poisoning in guinea pigs. prolidase for organophosphorus G-agent Drug Chem Toxicol. 1995; 18: 119 – 136. decontamination. Chem Biol Interact. 1999; 119-120: 101 Marrs T. The role of diazepam in the treatment of nerve 455 – 462. agent poisoning in a civilian population. Toxicol Rev. 84 Gordon RK, Feaster SR, Russell AJ, LeJeune KE, 2004; 23: 145 - 157. Maxwell DM, Lenz DE, et al. Organophosphate skin 102 Balali-Mood M, Salimifar H, Shariate M. Effects of

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sodium bicarbonate in human organophosphate 105 Castro CA, Larsen T, Finger AV, Solana RP, McMaster poisoning. “Proceedings of the Third International SB. Behavioral efficacy of diazepam against nerve agent Chemical and Biological Medical Treatment Symposium. exposure in rhesus monkeys. Pharmacol Biochem Behav. Spiez, Switzerland; May 7 – 12, 2000: 18 – 27. 1992; 41: 159 – 164. 103 Balali-Mood M, Afshari R, Kahrom M, Ayati MH, Ali- 106 Balali-Mood M, Balali-Mood K, Hosseini-Shirazi F. Akbarian H, Zare G. Use of high doses of sodium Recent advances in treatment of acute bicarbonate in acute organophosphorous pesticide organophosphorous nerve agents poisoning. Iran J poisoning is advancing. Clin Toxicol (Phila). 2007; 45: Pharm Res. 2006; 2: 82 – 88. 92 – 93. 107 Volans A. Sarin: guidelines on the management of 104 Roberts DM, Dawson AH, Hittarage A, Jeganathan K, victims of a nerve gas attack. J Accid Emerg Med. 1996; Sheriff MH, Buckley NA. Plasma alkalinization for acute 13: 202 – 206. organophosphorus poisoning--is it a reality in the 108 Newmark J. Therapy for nerve agent poisoning. Arch developing world? Clin Toxicol (Phila). 2007; 45: Neurol. 2004; 61: 649 – 652. 90 – 91.

Archive of SID

Narenjestan-e Ghavam, a beautiful house and garden (now a museum)—19th century, Qajar period, Shiraz, Iran.

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