Medicine & USMLE


Anti-Infective Drugs
  1. Vancomycin
  2. Metronidazole
  3. Penicillins
  4. Cephalosporins
  5. Macrolides
  6. Fluoroquinolones
  7. Aminoglycosides
  8. Tetracyclines
  9. Sulfonamides
  10. Rifampin
  11. Isoniazid
  12. Ethambutol
  13. Chloroquine
  14. Acyclovir
  15. Oseltamivir
  16. Azoles
  17. Nystatin
  18. Amphotericin B


Metronidazole is an antibiotic used to treat bacterial infections, including clostridium difficile and trichomoniasis. When taken concurrently with alcohol, it can cause a disulfiram-like reaction so patients should avoid alcohol while taking the drug. Metronidazole can cause a host of harmless side effects, including metallic taste in the mouth and reddish-brown urine discoloration. Both of these side effects are expected and benign, so patients should be consoled to not worry about them when they occur.

Key Points

  • Metronidazole (Flagyl)
    • Mechanism
      • Antibiotic
        • Creates free radicals that damage bacterial DNA, causing cell death
    • Clinical Use
      • Gastrointestinal infections
        • C. difficile
          • First-line treatment
        • H. pylori
          • Associated with peptic and duodenal ulcers
        • Giardiasis
        • Amoebiasis
      • Gynecological infections
        • Trichomoniasis
          • Sexually-transmitted infection characterized by grey frothy vaginal discharge with a fishy odor
          • Partners should also be treated
        • Bacterial vaginosis
      • Prophylaxis for surgical infections
      • Acne rosacea
      • Anaerobic bacterial infections
    • SE and AR
      • (Disulfiram-Like) Reaction to alcohol
        • Flushing, headache, visual disturbance, confusion, dyspnea, nausea, vomiting
        • Alcohol should be avoided until at least 48 hours after treatment is completed
      • Metallic taste
        • This is an expected side effect, no need to report
      • Red/brown urine discoloration
        • This is an expected side effect, no need to report
      • Stevens-Johnson Syndrome
        • Immediately report any skin rash or peeling
        • Can be fatal if not treated
      • Peripheral neuropathy
        • Can appear with long-term use