A 58-year-old man with paroxysmal supraventricular tachycardia requires urgent pharmacological cardioversion. The physician administers a drug that acts by stimulating cardiac M2 receptors, slowing AV nodal conduction. This drug most likely also causes which of the following peripheral effects?

• A Mydriasis and cycloplegia
• B Reduced gastrointestinal motility
• C Urinary retention
• D Increased bronchial secretions and bronchoconstriction ✓

Explanation

Muscarinic receptor stimulation (M3 in bronchi) increases bronchial gland secretions and causes smooth muscle contraction leading to bronchoconstriction. Mydriasis and cycloplegia are anticholinergic effects (muscarinic blockade of the iris and ciliary muscle). Reduced GI motility and urinary retention are also features of antimuscarinic agents, not muscarinic agonists.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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