Partial Agonist Buprenorphine — FRCA Primary MCQ

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ModeratePharmacology - General PrinciplesPartial Agonist BuprenorphineFRCA Primary

Which drug is a partial agonist at the mu-opioid receptor and may precipitate withdrawal if administered before the effects of a recently used full mu-opioid agonist have subsided?

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Correct answer: A — Buprenorphine

Buprenorphine is a partial agonist at the mu-opioid receptor and an antagonist at the kappa-opioid receptor. Compared with a full agonist, it has lower intrinsic efficacy at the mu receptor, although its slowly reversible receptor binding allows it to displace other opioids. Consequently, giving it while a full agonist is still active can reduce net receptor activation and precipitate withdrawal in an opioid-dependent patient. Opioid agonist ceiling effects, including a ceiling in respiratory depression in clinical pharmacology studies, do not eliminate the risk of severe or fatal respiratory depression. Naloxone is an opioid antagonist, whereas methadone, morphine and fentanyl are full mu-opioid agonists.

Reference: Camurus AB. Buvidal 64 mg prolonged-release solution for injection, Summary of Product Characteristics, sections 4.4 and 5.1. Updated 29 June 2026. https://www.medicines.org.uk/emc/product/9706/smpc