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# Metronidazole (Metrogyl)
## Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent. It acts by inducing DNA strand breakage and inhibiting nucleic acid synthesis in susceptible anaerobes and protozoa.
## Primary Indications
* Amebiasis, giardiasis, and trichomoniasis.
* Anaerobic bacterial infections (e.g., intra-abdominal, skin/skin structure, gynecological).
* *Clostridioides difficile* infection (off-label/alternative for mild cases).
* 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 BID for 7 days).
* **Amebiasis:** 500–750 mg PO every 8 hours for 7–10 days.
* **Bacterial Vaginosis:** 500 mg PO BID for 7 days.
## Pediatric Dosing
* **Anaerobic Infections:** 30 mg/kg/day divided every 6–8 hours. Maximum: 4 g/day or 500 mg per dose.
* **Amebiasis:** 35–50 mg/kg/day divided every 8 hours for 10 days.
* **Giardiasis:** 15–30 mg/kg/day divided every 8 hours for 5–7 days.
## Dose Adjustments
* **Hepatic Impairment:** Severe impairment (Child-Pugh C) requires a 50% dose reduction.
* **Renal Impairment:** No standard adjustment required for CrCl >10 mL/min. In patients undergoing hemodialysis, administer dose after the session.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (for trichomoniasis treatment).
* Concurrent use of disulfiram within the last 2 weeks.
* Use of alcohol or propylene glycol-containing products during and for 3 days after therapy (disulfiram-like reaction).
## Adverse Effects
* **Common:** Metallic taste, nausea, headache, dizziness, dark urine.
* **Serious:** Peripheral neuropathy, seizure, encephalopathy, aseptic meningitis, and leukopenia.
## Key Drug Interactions
* **Alcohol:** Triggers severe disulfiram-like reaction (nausea, vomiting, flushing, tachycardia).
* **Warfarin:** Significantly enhances anticoagulant effect (monitor INR closely).
* **Lithium:** May increase serum levels and risk of toxicity.
* **CYP450 Inducers (e.g., Phenytoin, Phenobarbital):** May decrease metronidazole efficacy.
## Monitoring
* Baseline and periodic CBC (if prolonged course).
* Neurological status (assess for ataxia or paresthesia).
* Signs of resolution of the infection.
* INR monitoring if on warfarin.
## Clinical Pearls
* **GI Tolerance:** Administer with food to minimize metallic taste and gastrointestinal irritation.
* **Dark Urine:** Inform patients that urine discoloration is harmless.
* **Local Protocols:** Treatment duration and dosage for specific anaerobic infections may vary significantly by institution; always consult local antibiogram and infectious disease guidelines.
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**Educational Disclaimer:** This information is for educational purposes and does not substitute for clinical judgment. Always verify current prescribing information, institutional protocols, and patient-specific factors before administration.
