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# Metronidazole ## Overview Metronidazole is an antimicrobial agent effective against anaerobic bacteria and certain protozoa. ## Primary Indications * Bacterial vaginosis * Trichomoniasis * Amebiasis * Giardiasis * Anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, bone and joint infections, gynecologic infections, CNS infections, lower respiratory tract infections, endocarditis, sepsis) * *Clostridioides difficile* infection (CDI) - often a second-line agent or for mild-moderate CDI. * Prophylaxis in specific surgical procedures (e.g., colorectal surgery). * Treatment of inflammatory lesions of rosacea. ## Adult Dosing * **Bacterial Vaginosis:** * Oral: 500 mg twice daily for 7 days OR 2 g as a single dose. * Vaginal gel 0.75%: One full applicator (5 g) vaginally once daily for 5 days. * **Trichomoniasis:** * Oral: 2 g as a single dose OR 250 mg three times daily for 7 days OR 500 mg twice daily for 7 days. * **Amebiasis:** * Intestinal: 500-750 mg three times daily for 5-10 days. * Hepatic abscess: 500-750 mg three times daily for 5-10 days. * **Giardiasis:** * Oral: 250 mg three times daily for 5-7 days OR 2 g once daily for 3 days. * **Anaerobic Bacterial Infections:** * Intravenous: 500 mg every 8 hours. Dosing may be adjusted based on severity and pathogen. Duration varies (typically 7-14 days). * Oral: 500 mg every 8 hours. Duration varies. * Maximum oral dose is generally 4 g daily. * ***Clostridioides difficile* Infection (CDI):** * Oral: 500 mg three times daily for 10-14 days (often reserved for mild-moderate CDI or as an alternative to vancomycin). * **Surgical Prophylaxis (Colorectal):** * Intravenous or Oral: 1 g as a single dose or 500 mg every 8 hours before surgery, continuing postoperatively for up to 24 hours. * **Rosacea:** * Oral: 250 mg twice daily to 500 mg twice daily, gradually tapering dose and duration as tolerated (often weeks to months). ## Pediatric Dosing Dosing varies significantly by indication and weight. Consult specialized pediatric guidelines or a pediatrician. General examples: * **Bacterial Infections (Anaerobes):** * Intravenous/Oral: 7.5 mg/kg per dose every 8 hours (max 500 mg/dose). * **Giardiasis:** * Oral: 5 mg/kg per dose every 8 hours (max 250 mg/dose) for 5-7 days, or 15-30 mg/kg as a single dose (max 1 g). * **Trichomoniasis:** * Oral: 5 mg/kg per dose every 8 hours (max 250 mg/dose) for 7 days. ## Dose Adjustments * **Hepatic Impairment:** Use with caution. Reduced doses may be considered in severe hepatic impairment or hepatic encephalopathy. Some sources suggest halving the usual maintenance dose. * **Renal Impairment:** No dose adjustment typically required for hemodialysis or peritoneal dialysis patients. For severe renal impairment (CrCl < 10 mL/min), consider reducing the maintenance dose by 25-50% and administering after dialysis if applicable. ## Contraindications * Hypersensitivity to metronidazole or other nitroimidazole derivatives. * Disulfiram-like reaction with alcohol during therapy and for at least 3 days after. ## Adverse Effects * **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness. * **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, leukopenia, pancreatitis. * **Other:** Darkened urine (harmless), superinfections (e.g., candidiasis). ## Key Drug Interactions * **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache, palpitations). Avoid alcohol during and for 3 days after therapy. * **Warfarin:** Potentiated anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed. * **Lithium:** Increased lithium levels, potentially leading to toxicity. Monitor lithium levels and renal function. * **Busulfan:** Metronidazole may increase busulfan levels, leading to toxicity. * **Phenytoin/Phenobarbital:** May decrease metronidazole efficacy and increase risk of peripheral neuropathy. * **Cyclosporine:** Increased cyclosporine levels. Monitor cyclosporine levels. ## Monitoring * Assess for signs and symptoms of infection resolution. * Monitor for adverse effects, particularly neuropathy with prolonged use. * Monitor INR if co-administered with warfarin. * Monitor lithium levels if co-administered with lithium. * Monitor for superinfections. ## Clinical Pearls * Administer oral metronidazole with or without food. Taking with food may reduce gastrointestinal upset. * Intravenous metronidazole is typically infused over 30-60 minutes. * IV to PO switch can be made when clinically appropriate. * Avoid alcohol during treatment and for at least 3 days after stopping the drug due to the disulfiram-like reaction. * Warn patients about potential metallic taste and darkened urine. * Neuropathy is a serious concern with prolonged therapy; monitor patients closely. --- **Disclaimer:** This information is intended for clinical pharmacists and healthcare professionals. It is essential to consult the most current prescribing information and local protocols for definitive guidance, as drug information can change.