Loperamide controls diarrhoea without producing central opioid effects at therapeutic doses because:

• A It is a selective delta-opioid receptor agonist restricted to the gut
• B It antagonizes mu receptors centrally while agonizing them peripherally
• C It is completely destroyed by gastric acid before systemic absorption
• D It is a substrate for P-glycoprotein and does not cross the intact blood-brain barrier appreciably ✓

Explanation

Loperamide is a mu-receptor agonist acting on gut wall opioid receptors to reduce peristalsis and secretion. At normal doses it is actively pumped out of the CNS by P-glycoprotein, so it does not cross the intact blood-brain barrier and lacks analgesic or euphoric effects. It is well absorbed enough to act systemically, and it is a pure agonist, not a mixed antagonist. Massive overdoses can overcome the efflux pump and cause cardiac arrhythmia and CNS effects.

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.