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# Metrogyl (Metronidazole)
## Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent. It is bactericidal against most obligate anaerobes and active against several protozoa.
## Primary Indications
* Anaerobic bacterial infections (e.g., intra-abdominal, skin/soft tissue, gynecologic).
* *Clostridioides difficile* infection (non-severe).
* Protozoal infections: Trichomoniasis, giardiasis, amebiasis.
* Bacterial vaginosis.
## Adult Dosing
* **Anaerobic Infections:** 500 mg IV/oral every 8 hours. Maximum: 4 g/day.
* **C. difficile:** 500 mg orally every 8 hours for 10–14 days.
* **Trichomoniasis:** 2 g orally as a single dose (or 500 mg BID for 7 days).
* **Bacterial Vaginosis:** 500 mg orally BID for 7 days.
## Pediatric Dosing
* **Anaerobic Infections:** 30 mg/kg/day divided every 6–8 hours. Maximum single dose: 500 mg. Maximum daily dose: 2,250 mg.
* **Amebiasis:** 35–50 mg/kg/day divided every 8 hours for 10 days.
* *Note: Dosing varies significantly by indication; always consult institutional protocols for neonatal/pediatric weight-based adjustments.*
## Dose Adjustments
* **Hepatic Impairment:** Reduce dosage by 50% in patients with severe hepatic impairment (Child-Pugh C).
* **Renal Impairment:** Generally no adjustment required for CrCl >10 mL/min. For hemodialysis, administer a supplemental dose post-dialysis if indicated by specific infection type.
## Contraindications
* First trimester of pregnancy (for trichomoniasis).
* Hypersensitivity to metronidazole or other nitroimidazoles.
* Concurrent use of disulfiram within the last 2 weeks.
* Consumption of alcohol or propylene glycol-containing products during and 3 days after therapy.
## Adverse Effects
* **Common:** Metallic taste, nausea, headache, dizziness, dark-colored urine.
* **Serious:** Peripheral neuropathy (prolonged use), seizures, encephalopathy, aseptic meningitis, and leukopenia.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (nausea, vomiting, tachycardia, flushing).
* **Warfarin:** Potentiates 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
* Monitor CBC (leukocytes) during prolonged therapy.
* Assess for neurological symptoms (numbness, tingling, ataxia).
* Monitor INR if patient is on warfarin.
## Clinical Pearls
* **Metallic Taste:** Advise patients this is a common side effect and not necessarily an allergy.
* **Administration:** Oral tablets may be taken with food to minimize GI upset.
* **Duration:** Avoid chronic, unnecessary therapy to reduce the risk of cumulative neurotoxicity.
* **Local Policy:** Specific empirical regimens for pelvic inflammatory disease or surgical prophylaxis depend on institutional antibiograms.
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**Disclaimer:** This information is for educational purposes for healthcare professionals. Clinical practice guidelines and local resistance patterns change frequently. Always verify current prescribing information in a trusted clinical resource (e.g., Lexicomp, UpToDate) and adhere to institutional policies before dosing.
