Neostigmine administered post-operatively to reverse neuromuscular blockade is always co-administered with atropine. The specific muscarinic effect that makes this co-administration MOST critical for patient safety is:

• A Bradycardia from increased cardiac vagal tone causing asystole ✓
• B Urinary retention from detrusor muscle relaxation
• C Mydriasis impairing pupillary light reflex
• D Dry mouth reducing secretion-related aspiration risk

Explanation

Neostigmine inhibits acetylcholinesterase, increasing ACh at all cholinergic synapses. At the heart, the resulting M2-mediated vagal bradycardia can be severe enough to cause life-threatening bradyarrhythmias or asystole. Atropine blocks this cardiac muscarinic effect while neostigmine still reverses neuromuscular blockade at the nicotinic junction. Atropine is given 1–2 minutes before neostigmine.

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

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Written and medically reviewed by the StethoPrep medical team.