Dextromethorphan, a common antitussive, is the d-isomer of the codeine analog levorphanol. Its antitussive effect is mediated primarily by:

• A Mu opioid receptor agonism in the cough center
• B Delta opioid receptor antagonism reducing cough reflex sensitivity
• C Sigma-1 receptor agonism and NMDA receptor antagonism in the medullary cough center ✓
• D Anticholinergic action reducing airway secretions

Explanation

Dextromethorphan is not a mu opioid agonist. It acts as an NMDA receptor antagonist and sigma-1 receptor agonist, depressing the medullary cough center through these mechanisms. It is the dextro isomer; its mirror image levorphanol is a potent mu opioid analgesic. This isomerism explains why dextromethorphan suppresses cough without significant analgesia or addiction potential at therapeutic doses.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.