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CHAPTER 2-10: ANTICHOLINERGICS

Beth H. Manning

INTRODUCTION

Anticholinergic intoxication can occur with a wide variety of prescription and over-the-counter medications and with numerous plants and mushrooms. Common drugs that have anticholinergic activity include antihistamines, antipsychotics, antispasmodics, skeletal muscle relaxants, and tricyclic antidepressants. Common combination products containing anticholinergic drugs include Atrohist, Donnagel, Donnatal, Hyland's Teething Tablets, Lomotil, Motofen, Ru-Tuss, Urised, and Urispas. Common anticholinergic medications are described in Table II–5. Plants and mushrooms containing anticholinergic alkaloids include jimsonweed (Datura stramonium), deadly nightshade (Atropa belladonna), and fly agaric (Amanita muscaria).

TABLE II–5.ANTICHOLINERGIC DRUGSa
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TABLE II–5. ANTICHOLINERGIC DRUGSa
Tertiary Amines Usual Adult Single Dose (mg) Quaternary Amines Usual Adult Single Dose (mg)
Atropine 0.4–1 Anisotropine 50
Benztropine 1–6 Clidinium 2.5–5
Biperiden 2–5 Glycopyrrolate 1
Darifenacin 7.5–15 Hexocyclium 25
Dicyclomine 10–20 Ipratropium bromide N/Ab
Flavoxate 100–200 Isopropamide 5
Fesoterodine 4–8 Mepenzolate 25
L-Hyoscyamine 0.15–0.3 Methantheline 50–100
Oxybutynin 5 Methscopolamine 2.5
Oxyphencyclimine 10 Propantheline 7.5–15
Procyclidine 5 Tiotropium N/Ac
Scopolamine 0.4–1 Tridihexethyl 25–50
Solifenacin succinate 5–10 Trospium chloride 20
Tolterodine 2–4    
Trihexyphenidyl 6–10    

aThese drugs act mainly at muscarinic cholinergic receptors and sometimes are more correctly referred to as antimuscarinic drugs.

bNot used orally; available as metered-dose inhaler and 0.02% inhalation solution and 0.03% nasal spray.

cSupplied as 18-mcg capsules for inhalation.

MECHANISM OF TOXICITY

  1. Anticholinergic agents competitively antagonize the effects of acetylcholine at peripheral muscarinic and central receptors. Exocrine glands, such as those responsible for sweating and salivation, and smooth muscle are mostly affected. The inhibition of muscarinic activity in the heart leads to a rapid heartbeat.

  2. Tertiary amines such as atropine are well absorbed centrally, whereas quaternary amines such as glycopyrrolate have a less central effect.

  3. Pharmacokinetics. Absorption may be delayed because of the pharmacologic effects of these drugs on GI motility. The duration of toxic effects can be quite prolonged (eg, benztropine intoxication may persist for 2–3 days; see also Table II–66).

TOXIC DOSE

The range of toxicity is highly variable and unpredictable. The potentially lethal dose of atropine has been estimated to be greater than 10 mg in adults. Ingestion of 30–50 jimsonweed seeds has been reported to cause significant toxicity. Doses up to 360 mg of trospium chloride produced increased heart rate and dry mouth but no other significant toxicity in healthy adults.

CLINICAL PRESENTATION

The anticholinergic syndrome is characterized by warm, dry, flushed skin; dry mouth; mydriasis; delirium; tachycardia; ileus; and urinary retention. Jerky myoclonic movements and choreoathetosis are common and may lead to rhabdomyolysis. Hyperthermia, coma, and respiratory arrest may occur. Seizures are rare with pure antimuscarinic agents, although they may result from other pharmacologic properties of the drug (eg, tricyclic antidepressants and antihistamines).

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