A 28-year-old man is brought to the emergency department after ingesting a large quantity of buprenorphine obtained illicitly. He is drowsy with miosis but maintains adequate spontaneous ventilation. Compared with a comparable overdose of fentanyl, his outcome is better mainly because:

• A Buprenorphine dissociates from the mu receptor much faster than fentanyl
• B As a partial mu agonist, buprenorphine has a ceiling effect on respiratory depression ✓
• C Buprenorphine is a kappa receptor antagonist and lacks central depressant activity
• D Buprenorphine undergoes extensive first-pass metabolism so oral overdose is ineffective

Explanation

Buprenorphine binds the mu receptor with very high affinity but has intrinsic activity well below unity, so beyond a certain dose further escalation adds little respiratory depression. This partial agonist ceiling effect makes overdose less likely to cause fatal apnea compared with full agonists such as fentanyl. Its dissociation is actually slower, contributing to its long duration, and the danger here concerns parenteral or sublingual overdose, not oral bioavailability.

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

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