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# Metronidazole (Metrogyl) ## Overview Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent. It acts by disrupting DNA synthesis in susceptible anaerobic bacteria and protozoa. It possesses significant anaerobic antibacterial activity and is effective against certain parasites. ## Primary Indications * **Anaerobic Bacterial Infections:** Intra-abdominal infections, skin/soft tissue, gynecologic, bone/joint, CNS, and lower respiratory tract infections. * **Protozoal Infections:** Trichomoniasis, amebiasis, and giardiasis. * **Clostridioides difficile infection (CDI):** Adjunctive or alternative treatment for mild-to-moderate initial episodes (if preferred agents are unavailable). * **Bacterial Vaginosis.** ## Adult Dosing * **Anaerobic Infections:** 500 mg IV/PO every 8 hours. Maximum: 4 g/day. * **Trichomoniasis:** 2 g PO as a single dose or 500 mg PO BID for 7 days. * **Giardiasis:** 250 mg PO TID for 5–7 days. * **Amebiasis:** 500–750 mg PO TID for 5–10 days. * **Bacterial Vaginosis:** 500 mg PO BID for 7 days or 750 mg ER once daily for 7 days. ## Pediatric Dosing * **Anaerobic Infections:** 30 mg/kg/day divided into doses every 6 hours (max 4 g/day). * **Giardiasis/Amebiasis:** 15–35 mg/kg/day PO in 3 divided doses for 5–10 days. * **Trichomoniasis:** 15–30 mg/kg/day divided into 3 doses for 7 days (max 2 g/day). * *Note: Always verify pediatric dosing against local institutional protocols or weight-based guidelines.* ## Dose Adjustments * **Hepatic Impairment:** Reduce dosage in severe hepatic impairment (Child-Pugh Class C) due to decreased clearance; monitor for increased toxicity. * **Renal Impairment:** No dose adjustment usually required for creatinine clearance >10 mL/min. In patients undergoing hemodialysis, administer a supplemental dose post-dialysis. ## Contraindications * Hypersensitivity to metronidazole or other nitroimidazoles. * First trimester of pregnancy (for trichomoniasis). * Use of disulfiram within the last 2 weeks. * Consumption of alcohol during therapy and for 72 hours after completion (disulfiram-like reaction). ## Adverse Effects * **Common:** Metallic taste, nausea, headache, dizziness, dark-colored urine. * **Serious:** Peripheral neuropathy (with prolonged use), seizures, encephalopathy, aseptic meningitis, and leukopenia. ## Key Drug Interactions * **Alcohol:** Severe disulfiram-like reaction (flushing, vomiting, tachycardia). * **Warfarin:** Significant increase in INR; preemptively reduce warfarin dose by 30–50% when starting metronidazole. * **Lithium/Cyclosporine:** May increase serum concentrations/toxicity. ## Monitoring * **Baseline/Routine:** Complete blood count (CBC) if long-term therapy (>10 days) is planned. * **Neurological:** Monitor for signs of peripheral neuropathy, numbness, or ataxia. * **Therapeutic:** Monitor INR closely when co-administered with anticoagulants. ## Clinical Pearls * **Metallic Taste:** Advise patients this is a common, harmless side effect. * **CNS Toxicity:** If ataxia, confusion, or difficulty speaking occurs, discontinue the drug immediately and evaluate for metronidazole-induced encephalopathy. * **Formulation:** IV to PO conversion is typically 1:1, as oral bioavailability is excellent (near 100%). *** **Educational Disclaimer:** This information is for educational purposes only. Drug dosing, indications, and safety profiles may change. Always verify current prescribing information in official resources (e.g., Lexicomp, UpToDate) or with a clinical pharmacist before prescribing or administering medication.