CHAPTER 150 Anticholinergics Larissa I. Velez and Sing-Yi Feng PERSPECTIVE antimuscarinic side effects provide valuable diagnostic clues (Box 150­2; see also Box 150­1). Anticholinergic agents are divided into three main groups: anti- Accidental and intentional poisoning by anticholinergic drugs muscarinics, affecting the muscarinic acetylcholine (ACh) recep­ occurs commonly with over­the­counter antihistamines such as tors; neuromuscular blockers, blocking nicotinic ACh receptors; diphenhydramine and cyclizine. Poisoning from drugs with only and ganglionic blockers, affecting ACh sympathetic and para­ anticholinergic effects rarely results in death when adequate sup­ sympathetic nicotinic ganglia (Fig. 150­1). This chapter refers portive care is provided. However, the impaired sweating with an only to antimuscarinic agents, and the terms anticholinergic anticholinergic overdose may result in fatal hyperthermia in the and anti muscarinic are used interchangeably. The prototypical agitated or seizing patient.4,5 Patients taking therapeutic doses of anti cholinergic agents are the naturally occurring belladonna anticholinergics are at increased risk of death from heatstroke alkaloids—atropine (racemic mixture of d­ and l­hyoscyamine), when they are exercising or exposed to heat. Finally, deaths from scopolamine (l­hyoscine), and hyoscyamine—found in many trauma or drowning caused by perceptual distortion are also plant members of the Solanaceae family. Atropine is the major attributed to anticholinergics.6 alkaloid of Atropa belladonna, an important pharmaceutical Poisonings with belladonna alkaloids are common. Deliberate source of that drug. Datura stramonium, or Jimson weed, contains ingestions of seeds or teas brewed from the leaves of the ubiqui­ scopolamine, grows in almost all climates, and is often involved tous Jimson weed for their hallucinogenic effects occur in many in plant­related belladonna poisoning.1,2 Other plants that have cultures,1 and it remains popular as a recreational stimulant antimuscarinic agents include henbane (Hyoscyamus niger) and among teenagers.7 Commercially available herbal teas contami­ mandrake (Mandragora officinarum). nated with atropine and smoking of herbal cigarettes cause inad­ Physicians (and Renaissance­era Italian women) have used vertent poisoning.8,9 A cluster of poisonings occurred in Oslo belladonna alkaloids for hundreds of years as mydriatics (Box when the difficult­to­detect drug scopolamine was disguised as 150­1).3 The belladonna alkaloids and their synthetic congeners Rohypnol tablets and given to known illicit drug users.10 The taint­ are used today as pupillary dilators (atropine, homatropine, tropi­ ing of heroin with anticholinergics leading to a complex toxi­ camide, cyclopentolate), as antispasmodics (dicyclomine), to drome has also been reported in drug users in several eastern states decrease gastric secretions (propantheline), to prevent motion of the United States.4,5 Although the reason for this tainting was sickness (scopolamine), and to treat asthma (ipratropium, tiotro­ never explained, it may have been an attempt to reproduce an old pium) and bradycardia (atropine). Atropine and glycopyrrolate combination of scopolamine and morphine used in obstetric are used to dry airway secretions and to block vagal responses to anesthesia called the twilight sleep.11 laryngoscopy and endotracheal intubation. The significant central nervous system (CNS) effects of scopolamine also facilitate the PRINCIPLES OF DISEASE induction of perioperative amnesia. The anticholinergic antiparkinsonian agents are synthetic ter­ Atropine and atropine­like drugs inhibit muscarinic ACh recep­ tiary amine congeners of atropine and include benztropine and tors both centrally and peripherally at the end­organ sites of the trihexyphenidyl. They are used as second­line antiparkinsonian parasympathetic nervous system (see Fig. 150­1). Although the agents and to counteract the extrapyramidal side effects of neuro­ term anticholinergic is commonly used, the most precise term to leptics. These agents readily cross the blood­brain barrier and thus describe the pharmacologic action of these drugs is antimusca- exhibit central antimuscarinic effects. rinic. These drugs do not block the effects of ACh on nicotinic Tolterodine and oxybutynin are anticholinergic agents used for receptors in the ganglia or at the neuromuscular junction, with the management of urinary incontinence and bladder spasms. the exception of the synthetic quaternary amines. Muscarinic They have special selectivity for the muscarinic receptors of the receptors affect smooth muscle function in the eye, intestinal tract, urinary bladder. These agents do not penetrate the blood­brain and bladder and also regulate sweat, salivary, and mucosal gland barrier and thus do not cause significant CNS effects. activity. Cardiac cholinergic receptors associated with vagal nerve Many other drugs with anticholinergic activity cause side effects fibers affect heart rate and conduction through the atrioventricu­ in addition to their main pharmacologic action. Some examples lar node. Muscarinic receptors in the CNS appear to be involved are the tricyclic antidepressants, drugs that are structurally related in new information storage, general perceptive and cognitive func­ to the tricyclics (such as carbamazepine and cyclobenzaprine), tions, and motor coordination.12­14 the phenothiazines, and the antihistamines (H1 blockers). In Generalized inhibition of muscarinic receptors by atropine patients with significant toxicity from any of these drugs, these results in tachycardia, pupillary dilation, loss of accommodation, 1970 Chapter 150 / Anticholinergics 1971 Autonomic Somatic Adrenal medulla Sympathetic Parasympathetic Preganglionic neuron ACh N receptor ACh N receptors ACh N receptors Ganglia No ganglia Adrenal medulla Postganglionic neurons Epinephrine (via blood) Effector NT NE Ach Ach Ach α β Adrenergic receptor Adrenergic Muscarinic Muscarinic Nicotinic receptor receptor receptor receptor Cardiac and Sweat glands2 Cardiac and Skeletal muscle4 smooth muscle, Target organ smooth muscle, gland cells, gland cells, nerve terminals1 nerve terminals3 Figure 150-1. The sites of nicotinic and muscarinic acetylcholine receptors. Ach, acetylcholine; N, nicotinic; NE, norepinephrine; NT, neurotransmitter. 1Causing tachycardia, hypertension, diaphoresis, mydriasis. 2Causing diaphoresis. 3Causing bradycardia, diarrhea, diaphoresis, urination, miosis, bronchospasm, bronchorrhea, lacrimation, salivation. 4Causing fasciculations. Drugs Exhibiting Primarily Drugs Exhibiting Anticholinergic Effects as Part BOX 150-1 Anticholinergic Toxicity BOX 150-2 of Toxic Manifestations Belladonna Alkaloids and Representative Tricyclic Antidepressants or Related Drugs Synthetic Congeners Cyclobenzaprine (Flexeril) Atropine Carbamazepine (Tegretol) Scopolamine Amitriptyline Homatropine Imipramine Cyclopentolate Doxepin Tropicamide Amoxapine Propantheline (Pro-Banthine) Desipramine Ipratropium (Atrovent) Nortriptyline Glutethimide (Doriden) Antiparkinsonians Benztropine (Cogentin) Phenothiazines Trihexyphenidyl (Artane) Chlorpromazine (Thorazine) Procyclidine (Kemadrin) Prochlorperazine (Compazine) Biperiden (Akineton) Mesoridazine (Serentil) Ethopropazine (Parsidol) Thioridazine (Mellaril) Prototypical H1 Receptor Blockers Diphenhydramine (Benadryl) Chlorpheniramine (Chlor-Trimeton) Brompheniramine (Dimetane) depression follows the initial CNS stimulation. In adults, CNS Cyclizine (Marezine) depression can predominate without an initial CNS stimulation. Meclizine (Antivert) Antimuscarinic effects occur in a predictable order with salivation, Hydroxyzine (Atarax, Vistaril) bronchial secretions, and sweating suppressed first, followed by Dimenhydrinate (Dramamine) mydriasis and tachycardia. The organs least sensitive to antimus­ Phenothiazine carinic drugs are the bladder and the gastrointestinal tract. Patients Promethazine (Phenergan) with anticholinergic toxicity often do not exhibit all the signs and symptoms described in the toxidrome. Instead, many patients present with just a few symptoms; tachycardia (68% of patients) and decreased secretions (75% of patients) are the most common.18 inability to sweat, drying of mucosal surfaces, gastrointestinal Poisoning by anticholinergics has been reported after ingestion, paralysis, and urinary retention. In the CNS, muscarinic inhibi­ smoking, and topical absorption.19 Systemic absorption is common tion causes stimulation, seizures, coma, choreoathetosis, memory after use of eye drops.19,20 Anticholinergics are generally rapidly impairment, and perceptual and cognitive dysfunction.12­17 The absorbed and widely distributed throughout the body. However, mnemonic “hot as a hare, red as a beet, blind as a bat, dry as with plant and seed ingestions or after an overdose, the onset a bone, mad as a hatter” describes the more florid manifestations of symptoms can be delayed. Prolonged anticholinergic toxicity of the antimuscarinic syndrome. With increasing doses, CNS is also reported, which may indicate slowed gastrointestinal 1972 PART IV ◆ Environment and Toxicology / Section Two • Toxicology absorption of the ingested drug or residual drug in the gastroin­ a cardiotoxic agent, such as a tricyclic antidepressant, carbamaze­ testinal tract.21,22 pine, or a phenothiazine, for which the antimuscarinic side effects are of less importance. Rarely, diphenhydramine ingestions have CLINICAL PRESENTATION been associated with sodium channel