Loperamide is preferred over diphenoxylate for self-medication of acute diarrhoea because:

• A Loperamide has a broader spectrum of antimicrobial activity
• B Loperamide acts on 5-HT3 receptors unlike the mu-opioid mechanism of diphenoxylate
• C Loperamide does not cross the blood-brain barrier at therapeutic doses and has negligible CNS opioid effects ✓
• D Loperamide increases intestinal water absorption while diphenoxylate reduces motility only

Explanation

Both loperamide and diphenoxylate act on mu-opioid receptors in the myenteric plexus to reduce intestinal motility and increase sphincter tone. However, loperamide is a substrate for P-glycoprotein efflux transporters at the blood-brain barrier, preventing CNS penetration at therapeutic doses. This eliminates addiction potential, respiratory depression and euphoria, making it an OTC drug. Diphenoxylate has CNS penetrability and abuse potential, requiring combination with atropine (to discourage misuse).

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

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Written and medically reviewed by the StethoPrep medical team.