A patient on long-term high-dose morphine for cancer pain is switched to equianalgesic buprenorphine for addiction concerns. Unexpectedly, the patient develops acute opioid withdrawal symptoms. The pharmacological basis for this is:

• A Buprenorphine metabolites compete with endorphins at delta-opioid receptors
• B Buprenorphine has low mu-opioid receptor intrinsic efficacy (partial agonist) and can displace full agonist morphine, precipitating relative withdrawal ✓
• C Buprenorphine's kappa antagonism causes dysphoria mimicking withdrawal symptoms
• D Buprenorphine inhibits CYP3A4 causing morphine accumulation with rebound

Explanation

Buprenorphine is a partial agonist at mu-opioid receptors with extremely high receptor affinity (higher than morphine) but submaximal intrinsic efficacy. When given to a patient with high mu-receptor occupancy by a full agonist (morphine), buprenorphine displaces morphine from receptors but activates them only partially, effectively reducing net mu-receptor activation and precipitating withdrawal. This is why buprenorphine induction for opioid use disorder must be initiated during mild-to-moderate withdrawal, not while the patient is in full opioid effect.

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

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