Bulgarian Journal of Veterinary Medicine, 2016 ONLINE FIRST ISSN 1311-1477; DOI: 10.15547/bjvm.983 Review TOXICITY STUDIES OF DRUGS AND CHEMICALS IN ANIMALS: AN OVERVIEW S. A. SAGANUWAN Department of Veterinary Physiology, Pharmacology and Biochemistry, College of Veterinary Medicine, University of Agriculture, Makurdi, Benue State, Nigeria Summary Saganuwan, S. A., 2016. Toxicity studies of drugs and chemicals in animals: An overview. Bulg. J. Vet. Med. (online first). Toxicity study is the investigation of either short or long-term toxic effects of a drug or chemical on animals. The toxicity is dose-dependent as asserted by Paracelsus over 500 years ago. However, short-term toxic effect is determined using median lethal dose (LD50) first introduced by Trevan in 1927 and revised many times. Presently there is a growing preponderance of rejection of scientific papers on acute toxicity study, simply because of the belief that in the current hazard and safety as- sessment of drugs and chemicals, LD50 values are no longer used. In view of this, literature search was carried out with a view to investigating the relevance of LD50 in development and assessment of drugs and chemicals. The findings revealed that in the past, many animals had been used for LD50 determination. OECD has reduced the number of test animals to 5–15 and presently it is further re- duced to 2–6. Acute toxicity study is being carried out in medicinal plants research and in the study of patent medicine. Although the application of LD50 has been drastically reduced, it is still applied and accepted in some parts of the world. Moreover, animals on which LD50 tests are conducted, should be allowed to die to see the end effect of the test drug or chemical because euthanisia of test animals may mask some toxicity signs of the test agents. Therefore, toxicity study of drugs and chemicals is a sci- entific process necessary for discovery and development of drugs as well as identification of potential toxicants. Key words: median lethal dose, Paracelsus, therapeutic agent, toxicant, toxicity INTRODUCTION Attempts have been made to see whether polycyclic hydrocarbons or the number of the chemical structure of the molecule chlorine atoms in chlorinated hydrocar- itself may serve as a predictor of toxic or bons. Such classification had some suc- carcinogenic effects (Golberg, 1983; cess but is far from perfect (Goddard et Rosenkranz et al., 1999). Such predictions al., 1996). Nevertheless, Paracelsus as- are often based on particular active sites, serted that toxicity effects of toxicants and such as the number of aromatic rings in therapeutic agents are dose-dependent Toxicity studies of drugs and chemicals in animals: An overview (Castleman, 2002). In that regard, Trevan Turnbull, 2000). The random stopping introduced the concept of the median le- rule in UDP improves the overall ability thal dose (LD50) in 1927. Median lethal of the test to respond to varying underly- dose is the amount of test agent that can ing conditions, but also causes the re- causes death in 50% of test animals. There ported level of confidence and the actual are different methods used to estimate level of confidence to differ somewhat median lethal dose (Karber, 1931; Reed & (Botham, 2003). Of all the principles of Muench, 1938; Miller & Tainter, 1944; the three alternatives (fixed dose; acute Litchfield & Wilcoxon, 1949; Lorke, toxic class and up-and-down), up-and- 1983; ASTM, 1987; Dixon, 1991; Sa- down is the most suitable, because it gives ganuwan, 2011; Saganuwan et al., 2011; end-point-evidence toxicity and obeys Saganuwan & Onyeyili, 2016). Earlier stopping criteria to limit number of ani- methods adopted for the estimation of mals used, using only 2–6 animals with median lethal dose used many animals possible 1–3 deaths (Shiryaev & (40–100), but for up-and-down procedure, Spokoing, 2000). 4–15 animals can be used (OECD, 1987; 2000a,b; 2001a,b,c; Stitzel, 2000; HISTORICAL BASIS OF TOXICITY UNECE, 2003). Saganuwan (2014) re- STUDIES vised the up-and-down procedure (UDP) to the use of 2–6 animals that may likely Roman herbalists were as likely to be kil- give 1–3 reversals. If there is no death lers as healers. As a result, throughout the above 15,000 mg/kg body weight, the test Roman Empire herbalists became ob- agent is practically safe and that serves as sessed with the identification of herbal the limit boundary. The revised method poisons and the development of antidotes saves time, reserves large numbers of known as theriaca (in Greek meaning animals that may be wasted and ignores remedies for venomous bites). The ancient complex mathematical manipulation in- world’s most poison-paranoid ruler was volved (Saganuwan, 2014). The method is Mithridates Eupalor (120–60 B.C.), king faster and its findings are relatively com- of Pontus, on the Black Sea. He took in- parable to the findings with other methods creasing doses of poisons to develop a (Saganuwan, 2012). For all the methods, tolerance and make himself immune. In 66 the study outcome is likely to be influ- B.C., Romans attacked him, he attempted enced by the choice of starting dose to poison himself but he has become tol- level(s) relative to the true LD50 value, erant and finally ordered a slave to stab especially in the case of shallow slopes him to death to escape embarrassment (Gribaldo et al., 2005). Therefore, infor- from enemies (Castleman, 2002). The mation on toxic effects seen only at dose bubonic plague caused by Yersinia pestis levels close to a lethal dose will not be and spread by rat flea, Xenopsylla cheopis obtained (Van der Heuvel et al., 1990). probably began in Asia in the year 1330, However, the dangerous dose for humans spreading to Norht Africa, Europe and the may be 1–100% more or less of the de- Middle East. This epidemic caused 25 to termined LD50 (Dreisbach & Robertson, 33% drop in population of Europe bet- 1987). Because small numbers of animals ween 1330 and 1350. Programmes were were used, the actual level of confidence launched against the Jews of Europe, who is generally not exact (Jennison & were thought responsible for the epi- 2 BJVM, ××, No × S. A. Saganuwan demic, even though the pope pointed out Paracelsus to introduce many potentially the ludicrousness of this belief (Stolley, toxic minerals into medicine in very small 1995). The bubonic plague caused by doses. He used arsenic, sulphur, lead, an- Yersinia pestis toxin ravaged Europe for timony and particularly mercury, not just many centuries although at the Interna- for syphilis but also for many other dis- tional Medical Congress in Berlin, 1890, eases. In time, physicians came to view Robert Koch reminded his contemporaries mercury as a panacea and Paracelsus era that so-called vibroids seen in anthrax and marked the beginning of toxicology (Cas- relapsing fever are the cause of these dis- tleman, 2002). That notwithstanding, eases (Moxon, 1990). The most vocal about 40,000 people died of ergotism in champion of the Doctrine of signative was 1992 in France and Spain. Some people of Phillippus Aureolus Theophrastus Bom- India, Africa and Asia living in jungles bastus Von Hohenheim (1493–1541 have good knowledge of poisonous plants A.D.), the founder of toxicology, the son and animals and so they use them to catch of a Swiss alchemist/physician. A brilliant fish, poisoning arrow heads for hunting as arrogant student of medicine, he lived up warfare and assassination of their foes to his name, Bombastus, but later changed (Garg, 2004). Even in the Europe, cap- it to Paracelsus (i.e. greater than Celsius), tives of war have poisoned their masters convinced that he was more brilliant than using poisonous plants (Castleman, 2002). the Roman Physician Celsius (53 B.C.–7 By 1500 B.C., written recordings indi- A.D.). He was born in the village of Ein- cated that hemlock, opium, arrow poisons siedeln near Zurich, Switzerland on 14 and certain metals were used to poison November, 1493. In 1502, following the enemies or for states executions. Notable death of his mother, the family moved to poisoned victims include Socrates, Cleo- Villach in Carinthia, Southern Austria, patra and Claudius (Radenkova-Saeva, where he further became municipal physi- 2008). cian and also taught chemistry. Paracelsus With roots extending to antiquity, received his baccalaureate in medicine in toxicology is a profession which recog- 1510 and addoclorate in 1516 from the nises that the past is often a prologue to University of Ferrara. He travelled the present (Stirling, 2006). Watson et al. throughout Europe, British Isles, Egypt (2000) provide a concise and informative and the holy land to broaden his know- review of toxicology from its Greek roots ledge (Borzelleca, 1999). He returned to to the ubiquitous use of risk assessment. It Villach in 1524 and remained there until has grown to be a science with change, 1527. Because of his fame, his lectures evolution and even controversy based on were well attended and he burnt medical toxicological method, concept or theory textbooks of Avicenna and Galen. He dividing the science of toxicology to ana- challenged them which led to his leaving lytical toxicology, aquatic toxicology, ar- the university. Paracelsus taught at the chaeological toxicocology, biochemical University of Basel, Switzerland in the toxicology, clinical toxicology, environ- 1520s and discovered the dose-response mental toxicology, experimental toxicolo- relationship of a poison. This insight came gy, forensic toxicology, genetic toxicolo- too late to save thousands of alleged gy, immunotoxicology, industrial toxico- witches executed in part of Europe for logy, inhalation toxicology, medical toxi- possession of poisons but it allowed cology, neurotoxicology, ocular toxico- BJVM, ××, No × 3 Toxicity studies of drugs and chemicals in animals: An overview logy, ophthalmic toxicology, pathological sis was laid by regulatory agencies on toxicology, pesticide toxicology, photo- determining toxicity profiles of all phar- toxicology, radiation toxicology and vete- maceutical substances available for animal rinary toxicology.