Which property of ketamine underlies its role as an adjuvant in refractory cancer pain and opioid-tolerant patients?
- A Selective agonism at mu-opioid receptors with minimal respiratory depression
- B Non-competitive antagonism at the phencyclidine site of the N-methyl-D-aspartate receptor ✓
- C Irreversible inhibition of prostaglandin synthesis in the dorsal horn
- D Blockade of voltage-gated calcium channels at presynaptic terminals
Correct answer: B. Non-competitive antagonism at the phencyclidine site of the N-methyl-D-aspartate receptor
Explanation
Ketamine is a non-competitive NMDA receptor antagonist acting at the phencyclidine binding site. By reducing NMDA-mediated central sensitisation and wind-up, subanaesthetic doses restore opioid responsiveness in refractory cancer pain and attenuate opioid-induced hyperalgesia. Option A describes a pure opioid agonist profile, option C describes NSAIDs acting on cyclooxygenase, and option D describes the action of ziconotide or gabapentinoids, which makes those distractors mechanistically plausible but incorrect for ketamine.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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