Loperamide produces effective antidiarrhoeal action without central opioid effects at therapeutic doses because:

• A It is completely destroyed by gastric acid before absorption
• B It acts on sigma receptors rather than mu receptors
• C It is actively pumped out of the brain by P-glycoprotein at the blood-brain barrier ✓
• D It antagonizes mu receptors in the myenteric plexus

Explanation

Loperamide is a mu receptor agonist acting on enteric neurons to slow gut transit. At normal doses it is excluded from the CNS by P-glycoprotein efflux at the blood-brain barrier, so it retains peripheral action without euphoria or respiratory depression. In massive overdose, P-glycoprotein is overwhelmed and loperamide crosses into the brain and also blocks cardiac hERG channels, causing arrhythmias.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.