A patient receiving oral metronidazole for amoebic liver abscess attends a social event and consumes three drinks. Two hours later she develops flushing, throbbing headache, nausea and palpitations. The underlying mechanism of this reaction is:

• A Metronidazole-induced inhibition of mitochondrial monoamine oxidase causing tyramine accumulation
• B Additive central nervous system depression through GABA potentiation
• C Inhibition of aldehyde dehydrogenase leading to acetaldehyde accumulation ✓
• D Metronidazole-mediated induction of gastric ADH increasing ethanol metabolism rate

Explanation

Metronidazole produces a disulfiram-like reaction by inhibiting aldehyde dehydrogenase, so ethanol metabolism stalls at acetaldehyde, whose accumulation causes flushing, headache, vomiting and hypotension. Patients must avoid alcohol during therapy and for at least a day after stopping. Monoamine oxidase inhibition is the mechanism of the cheese reaction with MAO inhibitors, and GABA potentiation describes benzodiazepines and ethanol itself.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.