A 35-year-old opioid-dependent patient is maintained on buprenorphine/naloxone (Suboxone). A colleague asks why naloxone is combined with buprenorphine in this formulation. The rationale is:

• A Naloxone enhances buprenorphine's analgesic effect by blocking kappa opioid receptors
• B When taken sublingually as intended, naloxone has poor bioavailability and is inactive; if injected, naloxone is absorbed and precipitates withdrawal, deterring IV misuse ✓
• C Naloxone accelerates buprenorphine's hepatic clearance, preventing dose accumulation
• D Naloxone blocks mu receptor tolerance to buprenorphine, maintaining efficacy during maintenance therapy

Explanation

Naloxone has very poor sublingual and oral bioavailability (<10%) due to extensive first-pass metabolism, so it is essentially inactive when the Suboxone tablet/film is used sublingually as prescribed. However, if a patient attempts to dissolve and inject the formulation to get a euphoric effect from buprenorphine, the intravenously administered naloxone achieves high blood levels, competitively displaces buprenorphine from mu receptors, and precipitates acute withdrawal in opioid-dependent patients. This pharmacokinetic deterrence discourages diversion and IV misuse.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.