• Metronidazole (250–750 mg PO/IV q6–12h) is only active against anaerobic bacteria and some protozoa. The drug exerts its bactericidal effect through accumulation of toxic metabolites that interfere with multiple biologic processes. It has excellent tissue penetration, including abscess cavities, bone, and the CNS.
  • It has greater activity against gram-negative than gram-positive anaerobes but is active against Clostridium perfringens and Clostridioides difficile; however, it is no longer a preferred treatment for C. difficile colitis. Metronidazole is a treatment of choice for bacterial vaginosis and can be used in combination with other antibiotics to treat intra-abdominal infections and brain abscesses. Protozoal infections that are routinely treated with metronidazole include Giardia, Entamoeba histolytica, and Trichomonas vaginalis. Dose reduction may be warranted for patients with decompensated liver disease.

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