Metronidazole can cause a disulfiram-like reaction due to inhibition of aldehyde dehydrogenase. In which clinical situations is metronidazole typically used?

• A. Inhibition of aldehyde dehydrogenase; used for anaerobic infections and protozoal infections.
• B. Induction of cytochrome P450 enzymes causing faster drug clearance.
• C. Blocks 30S ribosomal subunit; used for pneumonia.
• D. Inhibits DNA gyrase; used for urinary tract infections.

Answer: (A)

Metronidazole is active against anaerobic bacteria and certain protozoa, so it is typically used for infections where anaerobes or these protozoa are involved. This includes anaerobic infections such as intra-abdominal and pelvic infections, gynecologic infections, brain abscesses with anaerobic organisms, and odontogenic (dental) infections. It is also effective for protozoal infections like amoebiasis, giardiasis, and trichomoniasis. The drug’s use in these settings reflects its ability to be activated in anaerobic cells to damage DNA, rather than any role in inducing cytochrome P450, blocking the 30S ribosomal subunit, or inhibiting DNA gyrase, which are mechanisms associated with other drug classes.