Which condition is the most likely indication for a single oral dose of metronidazole 2 g?

• A. Trichomonas vaginalis infection
• B. Bacterial vaginosis
• C. Pelvic inflammatory disease
• D. Chlamydia trachomatis infection

Answer: (B)

When you use a single high-dose of metronidazole, you’re targeting infections caused by anaerobic organisms where a one-time exposure can achieve effective antimicrobial levels. Metronidazole works by being activated inside anaerobic cells and then damaging their DNA, which makes it particularly active against anaerobic bacteria and certain protozoa.

Bacterial vaginosis is a condition driven by overgrowth of anaerobic bacteria in the vagina. It’s a classic situation where a 2 g single oral dose of metronidazole is a well-established, convenient regimen. It delivers rapid, effective treatment in one dose, which improves adherence compared with longer courses. In contrast, the other conditions listed either rely on different pathogens or are more commonly managed with multi-day regimens or different antibiotics: pelvic inflammatory disease typically requires combination therapy over several days, and chlamydia is primarily treated with doxycycline or azithromycin. Trichomonas infection can be treated with metronidazole as well, but the single-dose 2 g approach is most consistently highlighted as the standard option for BV in many practice guidelines.