A 28-year-old woman started on erythromycin for mycoplasma pneumonia calls complaining of cramping abdominal pain, nausea, and diarrhea beginning after the first dose. The mechanism responsible for these gastrointestinal symptoms is:

• A Agonist action at motilin receptors in the gastrointestinal tract ✓
• B Direct irritation of gastric mucosa by acidic degradation products
• C Inhibition of gut CYP3A4 causing accumulation of bile acids
• D Antibiotic-induced disruption of colonic anaerobic flora

Explanation

Erythromycin is an agonist at motilin receptors on gastrointestinal smooth muscle, which increases peristalsis and produces cramping, nausea, and diarrhea even at antibacterial doses. This property is exploited pharmacologically when erythromycin is used as a prokinetic agent in gastroparesis. Antibiotic-associated colitis involves toxin-producing C. difficile and takes days to weeks, not hours, to develop.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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