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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 anaerobic bacteria and protozoa.
## Primary Indications
* Anaerobic bacterial infections (intra-abdominal, gynecological, skin/soft tissue)
* *Clostridioides difficile* infection (second-line)
* Protozoal infections: Trichomoniasis, giardiasis, amebiasis
* Bacterial vaginosis
## Adult Dosing
* **Anaerobic Infections:** 500 mg IV or PO every 8 hours. Max: 4 g/day.
* **Bacterial Vaginosis:** 500 mg PO twice daily for 7 days.
* **Trichomoniasis:** 2 g PO as a single dose (or 500 mg twice daily for 7 days).
* **Giardiasis:** 250 mg PO three times daily for 5–7 days.
* **Amebiasis:** 500–750 mg PO three times daily for 5–10 days.
## Pediatric Dosing
* **Anaerobic Infections:** 7.5 mg/kg IV or PO every 6–8 hours. Max: 500 mg/dose.
* **Giardiasis:** 15 mg/kg/day PO divided in 3 doses for 5–7 days.
* **Amebiasis:** 35–50 mg/kg/day PO divided in 3 doses for 10 days.
## Dose Adjustments
* **Renal impairment:** Generally no adjustment required for CrCl >10 mL/min, though removal by hemodialysis requires supplemental dosing post-dialysis.
* **Hepatic impairment:** Reduce dose by 50% in patients with severe hepatic impairment (Child-Pugh C).
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (for trichomoniasis treatment).
* Concurrent use of disulfiram within the last 2 weeks.
* Concurrent use of alcohol or alcohol-containing products (disulfiram-like reaction).
## Adverse Effects
* **Common:** Metallic taste, nausea, headache, dry mouth.
* **Serious:** Peripheral neuropathy (with long-term use), seizures, encephalopathy, pancreatitis, leukopenia.
## Key Drug Interactions
* **Warfarin:** Increases INR significantly; monitor closely and adjust anticoagulant dose.
* **Alcohol:** Triggers dangerous disulfiram-like reactions (flushing, tachycardia, vomiting).
* **Busulfan:** Metronidazole increases busulfan plasma levels; risk of severe toxicity.
* **CYP450 Inducers (e.g., Phenytoin, Phenobarbital):** May decrease metronidazole efficacy.
## Monitoring
* Baseline and periodic CBC (if prolonged use).
* Monitor INR if on concurrent warfarin.
* Neurological assessment for signs of peripheral neuropathy or CNS effects.
## Clinical Pearls
* IV to PO conversion is 1:1.
* Always advise patients to avoid alcohol during and for at least 48 to 72 hours after completing therapy.
* Metronidazole may cause dark or reddish-brown urine; reassure the patient this is benign.
* *Note: Dosing can vary by institution and specific clinical guidelines (e.g., IDSA); always verify against local hospital protocols.*
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice guidelines and drug information change frequently. Always consult the most current prescribing information, institutional formulary, and official product monographs before prescribing or administering medication.
