Toxic Fungi of Western North America

by Thomas J. Duffy, MD

Treatment of muscarine poisoning

The treatment for this symptom complex is atropine titrated to reduce symptoms, induce slight dryness of mouth and restore normal or nearly normal pupil size. The initial adult dose of atropine is 0.5 to 1.0 mg given very slowly intravenously. Repeat doses of 0.5-1.0 mg can be given at 10-20 minute intervals to either of two endpoints: A. 1 mg doses until bronchial hypersecretion, pulmonary edema and significant cardiac arrhythmias have cleared or B. 0.5 mg of atropine until the pupils are normal or nearly so. The second end-point may take longer to achieve; its use requires increased diligence and slower administration of atropine to avoid overdosage. Usually no more than 2.5 mg of atropine is required.

For severe poisoning with marked bradycardia (slowing of heart rate), AV or ventricular block (slowing of heart rate by blocking of cardiac electrical conduction), escape rhythms (rapid rhythms to escape cardiac conduction block) or pulmonary edema, give 1.5 mg IV at once and titrate from there. The pediatric dose is not strictly according to weight; the range is 0.25-1.0 mg total for children under 12. Dr. Denis Benjamin, a US physician, gives the pediatric dose as 0.01-0.3 mg/kg body weight with a repeat dose at 10 minute intervals up to a total of 1 mg in children. (82),(101)

Always consider the possibility of insecticide poisoning. The organophosphates, some carbamates and at least one organochloride (Malathion) also produce muscarinic symptoms, but do so by interfering with acetylcholinesterase. This enzyme inactivates acetylcholine. The toxicity is usually severe and may require very high doses of atropine. These insecticides are also able to enter the central nervous system. In skeletal muscle, in addition to acetylcholine receptors, there are also receptors responsive to nicotine. Some of these insectides bind to these nicotinic receptors and cause such skeletal muscle symptoms as weakness, fasciculations and paralysis. (156,157) Since atropine does not bind to nicotinic receptors, treatment of skeletal muscle symptoms requires the use of pralidoxime hydrochloride, a cholinesterase reactivator.