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## Metronidazole (Metrogyl)
### Overview
Metronidazole is an antibiotic and antiprotozoal agent.
### Primary Indications
* Treatment of anaerobic bacterial infections.
* Treatment of protozoal infections (e.g., trichomoniasis, giardiasis, amebiasis).
* Part of multi-drug regimens for *Helicobacter pylori* eradication.
* Treatment of bacterial vaginosis.
* Topical treatment for rosacea.
### Adult Dosing
* **Anaerobic Infections:** Typically 500 mg IV or PO every 8 hours for 7-10 days. Dosing varies significantly based on infection site and severity.
* **Bacterial Vaginosis:** 500 mg PO twice daily for 7 days, or a single 2 g PO dose.
* **Trichomoniasis:** 2 g PO as a single dose, or 250 mg PO three times daily for 7 days, or 375 mg PO twice daily for 7 days.
* ***H. pylori* Eradication:** 250-500 mg PO twice daily in combination with other agents. Duration typically 10-14 days.
* **Amebiasis:**
* Intestinal: 500-750 mg PO three times daily for 5-10 days.
* Hepatic Abscess: 500-750 mg PO three times daily for 5-10 days.
* **Giardiasis:** 250 mg PO three times daily for 5 days, or 500 mg PO twice daily for 7-10 days.
* **Rosacea (Topical):** Apply a thin layer to affected areas once or twice daily.
### Pediatric Dosing
Dosing in pediatrics is highly variable and depends on the indication, weight, and severity of infection. Consult pediatric-specific guidelines.
* **Anaerobic Infections:** Generally 7.5-15 mg/kg/dose PO or IV every 8 hours. Maximum dose usually 4 g daily.
* **Amebiasis:** 35-50 mg/kg/day PO divided into 3 doses for 5-10 days. Maximum 750 mg/dose or 4 g/day.
### Dose Adjustments
No dose adjustment is typically required for renal impairment. In severe hepatic impairment, consider reducing the dose by 30-50% and dosing every 12 hours due to decreased metabolism.
### Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concurrent use with disulfiram or alcohol (within 3 days).
### Adverse Effects
Common: Nausea, metallic taste, headache, anorexia, vomiting, diarrhea, abdominal pain, dark urine.
Serious: Peripheral neuropathy, seizures, encephalopathy, Stevens-Johnson syndrome, pancreatitis, candidiasis.
### Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia). Avoid alcohol during and for at least 72 hours after treatment.
* **Disulfiram:** Concurrent use can lead to psychotic reactions.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Lithium:** Metronidazole may increase lithium levels. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole efficacy.
### Monitoring
* Monitor for signs and symptoms of infection resolution.
* Assess for adverse effects, particularly neurological symptoms (numbness, tingling, ataxia, seizures) and gastrointestinal upset.
* For patients on warfarin, monitor INR.
### Clinical Pearls
* Metronidazole has a metallic taste that can be bothersome. Taking with food may help mitigate gastrointestinal upset.
* Advise patients to avoid alcohol during treatment and for at least 72 hours after completion.
* IV metronidazole is a vesicant; monitor infusion site closely.
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*This information is intended as a quick reference and does not replace comprehensive drug information resources. Always verify current prescribing information and guidelines before making clinical decisions.*
