antimuscarinic
Summary
Drugs that competitively block muscarinic acetylcholine receptors (M1-M5), producing parasympatholytic effects. Classic toxidrome: 'hot as a hare, dry as a bone, red as a beet, mad as a hatter, blind as a bat.'
Detail
Antimuscarinics competitively inhibit muscarinic ACh receptors on smooth muscle, glands, and the heart, blocking parasympathetic tone. Effects: mydriasis and cycloplegia, tachycardia, dry mouth, decreased sweat/secretions, urinary retention, constipation, and CNS effects (delirium, agitation in elderly). Common drugs: atropine (bradycardia, organophosphate poisoning), scopolamine (motion sickness), ipratropium/tiotropium (COPD/asthma), oxybutynin/tolterodine (overactive bladder), benztropine (Parkinson tremor, EPS), glycopyrrolate (secretions). Contraindicated in narrow-angle glaucoma and BPH. Reversal of toxicity: physostigmine (crosses BBB). Boards: TCA, antihistamine, antipsychotic overdoses share this toxidrome.
Sources
- First Aid for USMLE Step 1 2024
- Sketchy Pharmacology
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