Muscarine

Muscarine is a naturally occurring alkaloid that acts as a potent agonist of muscarinic acetylcholine receptors (M1–M5). It is a quaternary ammonium compound, which means it largely stays outside the central nervous system and produces predominantly peripheral effects.

Natural occurrence and sources include certain poisonous mushrooms, especially species in the genera Inocybe and Clitocybe. Examples of muscarine-containing mushrooms include Inocybe geophylla, Inocybe fastigiata, Clitocybe dealbata, and Clitocybe rivulosa. Poisoning occurs after ingestion of these mushrooms or their improperly prepared preparations.

Pharmacology and mechanism of action involve stimulation of parasympathetic (muscarinic) receptors, leading to increased secretions and smooth muscle activity. This produces the characteristic cholinergic or "SLUDGE" effects: sweating, salivation, lacrimation, urination, defecation, gastrointestinal cramps, miosis, bronchorrhea, and bronchospasm. Bradycardia and hypotension may occur due to excessive vagal tone. Central nervous system effects are usually minimal because muscarine does not readily cross the blood–brain barrier.

Clinical presentation often begins within 15 to 60 minutes of ingestion and includes copious sweating and salivation, tearing, bronchial secretions, bronchospasm, abdominal cramps, vomiting, diarrhea, pinpoint pupils, and slow heart rate. Distinguishing features from other mushroom toxins are the pronounced muscarinic signs and the absence of significant central or neurological symptoms.

Diagnosis is clinical, supported by identification of the mushroom species in suspected cases. Detection of muscarine in mushrooms is available in specialized laboratories but is not typically required.

Treatment is supportive and focuses on counteracting muscarinic effects. Atropine, a muscarinic receptor antagonist, is the primary antidote. Additional measures include airway management, hydration, and, if ingestion was recent, activated charcoal. With prompt treatment, prognosis is generally favorable.