A heroin-dependent man takes his first supervised dose of buprenorphine 30 minutes after using heroin. Within an hour he develops vomiting, abdominal cramps, myalgia, sweating, and piloerection. Which property of buprenorphine explains this reaction?

• A It is a full agonist at kappa receptors causing dysphoria
• B It induces rapid metabolism of heroin through cytochrome P450 induction
• C It irreversibly inhibits monoamine oxidase in the gut
• D Its very high mu-receptor affinity displaces heroin from receptors while providing only partial agonism ✓

Explanation

Buprenorphine binds mu receptors with far higher affinity than heroin or methadone but has only partial agonist activity. Given while a full agonist still occupies receptors, it competitively displaces them and lowers net opioid tone, producing precipitated withdrawal. This is why buprenorphine must be started only after the patient shows objective moderate withdrawal signs. Kappa antagonism actually contributes to its low dysphoria, and the reaction is pharmacodynamic, not metabolic.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

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