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# Metronidazole ## Overview Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa. ## Primary Indications * **Bacterial Vaginosis:** Primary treatment. * **Trichomoniasis:** Primary treatment. * **Giardiasis:** Primary treatment. * **Amebiasis:** Intestinal and extraintestinal infections. * **Anaerobic Bacterial Infections:** Intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections, bacterial vaginosis, C. difficile infection (in select cases). * **Helicobacter pylori Eradication:** Part of combination therapy. * **Surgical Prophylaxis:** Particularly in colorectal surgery. ## Adult Dosing * **Bacterial Vaginosis:** * Oral: 500 mg twice daily for 7 days OR 2 g as a single dose. * Vaginal Gel 0.75%: One applicatorful (5 g) intravaginally once daily for 5 days. * **Trichomoniasis:** * Oral: 2 g as a single dose OR 250 mg three times daily for 7 days OR 375 mg twice daily for 7 days. * **Giardiasis:** * Oral: 250 mg three times daily for 5 days. * **Amebiasis:** * Oral: 500-750 mg three times daily for 5-10 days. * **Anaerobic Bacterial Infections:** * Oral/IV: 500 mg every 8 hours. Usual duration 7-10 days. * **C. difficile Infection:** * Oral: 500 mg every 8 hours for 10-14 days (alternative to vancomycin for initial episode, mild-to-moderate disease). * **H. pylori Eradication:** * Oral: 500 mg twice daily for 10-14 days as part of a triple or quadruple therapy regimen. * **Surgical Prophylaxis:** * Oral/IV: 500 mg to 1 g before surgery, repeated every 8-12 hours for up to 24 hours post-operatively. ## Pediatric Dosing Dosing is weight-based and depends on the indication. Consult specific pediatric guidelines. * **Bacterial Infections:** 15-30 mg/kg/day divided into 3 doses (maximum 400 mg per dose or 2 g/day). * **Amebiasis:** 35-50 mg/kg/day divided into 3 doses (maximum 750 mg/dose) for 5-10 days. ## Dose Adjustments * **Renal Impairment:** No dose adjustment typically needed. However, if using IV formulations with high sodium content, monitor fluid status. * **Hepatic Impairment:** Use with caution. May require dose reduction in severe hepatic dysfunction. ## Contraindications * Hypersensitivity to metronidazole or other nitroimidazoles. * First trimester of pregnancy (though often used if benefits outweigh risks and alternatives are unsuitable). * Concomitant use of disulfiram or alcohol (within 3 days of last dose). ## Adverse Effects * **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dark urine. * **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, Stevens-Johnson syndrome, aseptic meningitis, pancreatitis, dizziness, ataxia. ## Key Drug Interactions * **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache, tachycardia). Avoid alcohol during and for at least 3 days after therapy. * **Disulfiram:** Concomitant use can lead to psychosis, confusion. Avoid. * **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed. * **Lithium:** May increase lithium levels. Monitor lithium levels. * **Phenytoin/Phenobarbital:** May decrease metronidazole levels. * **Fluorouracil (5-FU):** May increase fluorouracil toxicity. ## Monitoring * Signs and symptoms of infection resolution. * Adverse effects, particularly peripheral neuropathy (numbness, tingling) and CNS effects. * INR if patient is on warfarin. * Lithium levels if concomitantly used. ## Clinical Pearls * Advise patients to avoid alcohol during treatment and for at least 3 days after finishing. * The metallic taste is common and usually resolves after discontinuation. * Neuropathy can be irreversible; report any signs or symptoms immediately. * For vaginal gel, avoid sexual intercourse during treatment. * Ensure adequate hydration when administering IV metronidazole. --- *Disclaimer: This information is intended for clinical professionals. Always consult the most current prescribing information and local protocols for definitive guidance.*