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# Metronidazole
## Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent. It is bactericidal against most anaerobic bacteria and active against various protozoa.
## Primary Indications
* Anaerobic bacterial infections (intra-abdominal, skin/skin structure, gynecological).
* *Clostridioides difficile* infection (second-line).
* Protozoal infections: Trichomoniasis, giardiasis, amebiasis.
* Bacterial vaginosis.
## Adult Dosing
* **Anaerobic Infections:** 500 mg orally or IV every 8 hours. Maximum: 4 g/day.
* **C. difficile (off-label):** 500 mg orally every 8 hours for 10–14 days.
* **Trichomoniasis:** 2 g orally as a single dose or 500 mg orally twice daily for 7 days.
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days.
## Pediatric Dosing
* **Anaerobic Infections:** 30 mg/kg/day divided every 6 hours (Max: 4 g/day).
* **Amebiasis:** 35–50 mg/kg/day divided every 8 hours for 7–10 days.
* **Giardiasis:** 15 mg/kg/day divided every 8 hours for 5–7 days.
## Dose Adjustments
* **Hepatic Impairment:** Reduce dosage by 50% in patients with severe hepatic impairment (Child-Pugh Class C).
* **Renal Impairment:** Generally no adjustment required for CrCl >10 mL/min; consider dose reduction in end-stage renal disease if adverse effects occur.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* First trimester of pregnancy (for trichomoniasis).
* Concurrent use of disulfiram or alcohol-containing products during and for 3 days after therapy.
## Adverse Effects
* **Common:** Nausea, metallic taste, headache, dark-colored urine.
* **Serious:** Peripheral neuropathy, seizure, encephalopathy, pancreatitis, and severe disulfiram-like reaction if alcohol is consumed.
## Key Drug Interactions
* **Alcohol:** Causes severe disulfiram-like reactions (vomiting, tachycardia, flushing).
* **Warfarin:** Significant increase in INR; requires empiric reduction of warfarin dose and frequent monitoring.
* **Lithium:** May increase serum lithium concentrations and toxicity.
* **CYP450 Inducers (e.g., Phenytoin, Phenobarbital):** May decrease metronidazole levels.
## Monitoring
* Monitor CBC in patients undergoing long-term therapy (risk of neutropenia).
* Monitor INR closely if on warfarin.
* Assess for neurological symptoms (numbness, tingling, ataxia).
## Clinical Pearls
* **Alcohol Precautions:** Ensure patients understand to avoid alcohol intake during therapy and for 72 hours post-completion.
* **Administration:** May take with food to minimize GI upset.
* **IV to PO:** Converting from IV to oral is 1:1 due to excellent bioavailability.
* **Resistance:** Not a first-line agent for *C. difficile* due to decreased susceptibility and poor penetration into the colon compared to oral vancomycin or fidaxomicin.
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**Educational Disclaimer:** This information is for educational purposes and does not substitute for professional medical advice. Always consult the most current prescribing information, institutional protocols, and clinical guidelines before prescribing or administering medication.
