Neostigmine reverses neuromuscular blockade by non-depolarizing agents. Its primary mechanism is:

• A Direct agonism at nicotinic NMJ receptors
• B Stimulation of presynaptic ACh synthesis and release
• C Reversible inhibition of acetylcholinesterase, increasing synaptic ACh ✓
• D Displacement of non-depolarizing blocker from the receptor by competitive antagonism

Explanation

Neostigmine is a quaternary carbamate inhibitor of acetylcholinesterase; it binds to both the anionic and esteratic sites of the enzyme reversibly. By preventing ACh hydrolysis, it raises acetylcholine concentration at the NMJ, which outcompetes the non-depolarizing blocker for the nicotinic receptor. Neostigmine itself has some direct nicotinic agonist action as a minor mechanism, but AChE inhibition is dominant. It is always co-administered with an anticholinergic (atropine/glycopyrrolate) to counter muscarinic side effects.

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

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