A 29-year-old woman being treated with metronidazole for Trichomonas vaginitis attends a wedding, consumes two glasses of wine, and within minutes develops flushing, throbbing headache, palpitations, nausea and vomiting. What is the explanation?

• A Metronidazole inhibits aldehyde dehydrogenase, causing acetaldehyde accumulation ✓
• B Metronidazole induces hepatic microsomal ethanol oxidation, generating excess acetate
• C An idiosyncratic mast-cell degranulation triggered by the nitroimidazole ring
• D Metronidazole potentiates ethanol absorption from the stomach

Explanation

Metronidazole produces a disulfiram-like reaction by inhibiting aldehyde dehydrogenase, so ingested alcohol accumulates as acetaldehyde, causing flushing, headache, vomiting and hypotension. Patients must be warned to avoid alcohol during therapy and for a period afterwards. It is not an allergic reaction and does not alter ethanol absorption. The same caution applies to cephalosporins with the methylthiotetrazole side chain.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.