A 40-year-old man receiving metronidazole for a dental abscess attends a wedding and consumes three glasses of wine. He soon develops flushing, throbbing headache, palpitations, nausea, and hypotension. This reaction occurs because metronidazole:

• A Inhibits aldehyde dehydrogenase, causing acetaldehyde accumulation ✓
• B Induces hepatic microsomal alcohol oxidation, generating excess acetaldehyde
• C Forms a toxic adduct with ethanol in the circulation
• D Inhibits gastric alcohol dehydrogenase, increasing ethanol bioavailability

Explanation

Metronidazole produces a disulfiram-like reaction by inhibiting aldehyde dehydrogenase, so ingested ethanol is metabolized to acetaldehyde which then accumulates and causes flushing, headache, vomiting, and hypotension. Patients must be warned to avoid alcohol during therapy and for at least a day after stopping it. Disulfiram itself works by the same enzyme inhibition, hence the eponym. Induction of alcohol oxidation would lower acetaldehyde, and the other proposed mechanisms are not established.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.