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# Metrogyl (metronidazole)
## Overview
- Nitroimidazole antibiotic with bactericidal activity against anaerobes and certain parasites.
- Available in oral, intravenous, rectal, and topical formulations.
## Primary Indications
- Anaerobic bacterial infections (e.g., intra-abdominal, pelvic, dental)
- Protozoal infections: trichomoniasis, giardiasis, amebiasis
- *C. difficile* infection
- Perioperative prophylaxis (colorectal surgery)
## Adult Dosing
- **Anaerobic infections**: 500 mg IV/PO every 8 hours
- **C. difficile** (mild-moderate): 500 mg PO three times daily for 10–14 days
- **Trichomoniasis**: 2 g PO single dose (or 500 mg twice daily for 7 days)
- **Giardiasis**: 250 mg PO three times daily for 5–7 days
- **Amebiasis**: 750 mg PO three times daily for 10 days
*Max single dose: 4 g/day (some protocols limit to 2–3 g/day).*
## Pediatric Dosing
- **Anaerobic infections**: 30 mg/kg/day IV/PO divided every 6–8 hours. Max 2 g/day.
- **Giardiasis**: 15 mg/kg/day PO divided three times daily for 5–7 days (max 750 mg/day).
- **Amebiasis**: 35–50 mg/kg/day PO divided three times daily for 10 days (max 2 g/day).
- **C. difficile**: 30 mg/kg/day PO divided four times daily for 10 days. Avoid in infants <1 month due to lack of safety data.
## Dose Adjustments
- **Renal**: No adjustment for mild-moderate impairment. In severe (CrCl <10 mL/min), reduce dose by 50% or extend interval to 12 hourly.
- **Hepatic**: Severe hepatic impairment (Child-Pugh C): reduce dose to 50% of normal.
- **Hemodialysis**: Give after dialysis; drug is removed.
## Contraindications
- Hypersensitivity to metronidazole or nitroimidazoles
- First trimester of pregnancy (avoid unless essential; use with caution in later pregnancy)
- Concomitant use with disulfiram (psychotic reactions)
## Adverse Effects
- Common: metallic taste, nausea, headache, dark urine (harmless)
- Serious: peripheral neuropathy (long courses), CNS effects (seizures, encephalopathy), pancreatitis, hypersensitivity
- IV site: phlebitis
## Key Drug Interactions
- **Warfarin**: potentiates anticoagulation (monitor INR)
- **Lithium**: may increase lithium levels (toxicity)
- **Disulfiram**: psychosis, avoid concurrent use
- **Alcohol**: disulfiram-like reaction (nausea, flushing, headache) – avoid during therapy and 48 hours after
- **CYP3A4 inducers** (e.g., phenytoin, rifampin): reduce metronidazole levels
## Monitoring
- CBC with differential (prolonged courses; risk of neutropenia)
- Liver function tests (if hepatic impairment)
- Serum drug levels only for severe toxicity or unresponsive infection
- Neurologic assessment for peripheral neuropathy or CNS symptoms
## Clinical Pearls
- Bioavailability >80% orally; IV to PO conversion is routine when tolerated.
- Prolonged use (>10 days) increases neuropathy risk; reassess necessity after 7 days.
- Dark urine is due to an inactive metabolite and is harmless.
- Do not use alcohol or alcohol-containing products during therapy and for 48 hours after last dose.
- Metronidazole is a first-line for *C. difficile* but avoid for severe or complicated cases (oral vancomycin preferred).
- Topical metronidazole is used for rosacea; systemic absorption is minimal.
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*This information is for educational purposes only. Always verify current prescribing information from a reliable drug reference or local formulary, as dosing and recommendations may vary by region and clinical context.*
