A 34-year-old woman receiving metronidazole for pelvic inflammatory disease attends a wedding and consumes two glasses of wine. She soon develops flushing, throbbing headache, palpitations, nausea and hypotension. The underlying mechanism of this reaction is:

• A Histamine content of alcoholic beverages acting on sensitized mast cells
• B Induction of hepatic alcohol dehydrogenase causing rapid ethanol clearance
• C Serotonergic excess due to impaired serotonin metabolism
• D Disulfiram-like inhibition of aldehyde dehydrogenase causing acetaldehyde accumulation ✓

Explanation

Metronidazole produces a disulfiram-like reaction by inhibiting the enzyme aldehyde dehydrogenase. Ethanol metabolism stalls at acetaldehyde, whose accumulation causes flushing, headache, nausea, vomiting, palpitations and hypotension. Patients must be warned to avoid alcohol during therapy and for at least 24 to 48 hours after the last dose. The reaction is pharmacological, not allergic, and does not involve serotonin pathways or beverage histamine.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.