Neostigmine reverses non-depolarizing neuromuscular blockade and is also used for postoperative ileus (Ogilvie syndrome). Its mechanism in treating Ogilvie syndrome is:

• A Direct acetylcholine receptor agonism at enteric smooth muscle M2 receptors
• B Acetylcholinesterase inhibition increasing ACh at enteric myenteric plexus M3 receptors, stimulating intestinal smooth muscle contraction and propulsion ✓
• C Motilin receptor agonism stimulating migrating motor complex
• D 5-HT4 receptor agonism at the serotonergic neurons of the myenteric plexus

Explanation

Neostigmine inhibits acetylcholinesterase, increasing ACh concentrations at parasympathetic cholinergic synapses in the myenteric plexus and at smooth muscle muscarinic receptors. Intestinal smooth muscle bears predominantly M3 muscarinic receptors; their activation by accumulated ACh increases smooth muscle tone, propulsive contractions, and rectosigmoid peristalsis. In Ogilvie syndrome (acute colonic pseudo-obstruction), where diminished parasympathetic tone allows colonic dilation, IV neostigmine 2 mg rapidly decompresses the colon by restoring cholinergic tone. Atropine should be available to counteract bradycardia.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.