Tricyclic anticholinergic effects — MRCPsych Paper A MCQ

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EasyPsychopharmacologyTricyclic anticholinergic effectsMRCPsych Paper A

A 68-year-old woman develops dry mouth, blurred vision, constipation and urinary hesitancy shortly after starting amitriptyline for neuropathic pain. Blockade of which receptor most directly explains this cluster of adverse effects?

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Correct answer: E — Muscarinic acetylcholine receptors

The correct answer is E: muscarinic acetylcholine receptor blockade. Amitriptyline has clinically important antimuscarinic activity. Reduced parasympathetic signalling causes decreased salivary secretion, impaired ocular accommodation, reduced gastrointestinal motility and impaired bladder emptying, producing dry mouth, blurred vision, constipation and urinary hesitancy. Older adults are particularly susceptible to the cumulative cognitive and peripheral effects of anticholinergic medicines. Histamine H1 receptor blockade mainly causes sedation and weight gain. Dopamine D2 blockade is associated with extrapyramidal adverse effects and hyperprolactinaemia. Serotonin 5-HT3 and GABA-B receptors do not explain this characteristic peripheral anticholinergic syndrome.

Reference: Electronic Medicines Compendium. Amitriptyline hydrochloride 50 mg film-coated tablets, Summary of Product Characteristics, sections 4.8 and 5.1. Revised 2025. https://www.medicines.org.uk/emc/product/100842/smpc