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# Metronidazole (Metrogyl)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* Treatment of anaerobic bacterial infections (e.g., intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis).
* Treatment of *Clostridioides difficile* infection (CDI).
* Treatment of protozoal infections (e.g., trichomoniasis, giardiasis, amebiasis).
* Prophylaxis against anaerobic infection in surgical procedures (e.g., colorectal surgery).
* Management of inflammatory conditions associated with rosacea (topical).
## Adult Dosing
Dosing varies widely based on indication.
* **Anaerobic Bacterial Infections:**
* Intravenous: 500 mg every 8 hours. Typical duration 7-10 days.
* Oral: 250-500 mg every 8 hours. Typical duration 7-10 days.
* Maximum daily dose generally 4 grams.
* ***C. difficile* Infection:**
* Oral: 500 mg every 8 hours for 10-14 days. (Note: Fidaxomicin or vancomycin are preferred for initial episodes based on current guidelines, especially for severe CDI).
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days, or 2 g as a single dose.
* Vaginal gel 0.75%: One full applicator (5g) inserted vaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 2 g as a single dose, or 250 mg three times daily for 7 days, or 375 mg twice daily for 7 days.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5-7 days.
* **Amebiasis:**
* Oral: 500-750 mg every 8 hours for 5-10 days.
* **Surgical Prophylaxis:**
* Intravenous: 1 gram given as a single dose within 1 hour before surgery, or 500 mg every 8 hours starting within 12 hours before surgery and continued for up to 24 hours postoperatively.
## Pediatric Dosing
Dosing is weight-based and depends on the indication.
* **Serious Anaerobic Infections:**
* Intravenous/Oral: 15 mg/kg/day divided into 3 doses, not to exceed 400 mg per dose. Maintenance dose: 7.5-10 mg/kg every 8 hours. Typical duration 7-10 days.
* **Cystic Fibrosis Exacerbations (Anaerobic Coverage):**
* Oral: 20-30 mg/kg/day divided into 3 doses, maximum 400 mg per dose.
* ***C. difficile* Infection:**
* Oral: 15 mg/kg/day divided into 3 doses, maximum 500 mg per dose for 10 days. (Note: Oral vancomycin is generally preferred for pediatric CDI).
* **Giardiasis:**
* Oral: 15 mg/kg/day divided into 3 doses for 5-7 days, maximum 250 mg per dose.
* **Trichomoniasis:**
* Oral: 15 mg/kg/day divided into 3 doses for 7 days, maximum 250 mg per dose.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in severe hepatic impairment.
* **Renal Impairment:** No dose adjustment generally required for hemodialysis or peritoneal dialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use during the first trimester of pregnancy for trichomoniasis.
* Concomitant use with disulfiram.
* Concomitant use with alcohol (within 3 days of last dose).
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness, rash.
Serious: Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, leukopenia, pancreatitis, hepatotoxicity.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, dyspnea). Avoid alcohol during and for at least 3 days after treatment.
* **Disulfiram:** Can cause psychotic reactions. Avoid concurrent use.
* **Warfarin:** May potentiate anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase lithium levels. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Fluorouracil:** Metronidazole may increase fluorouracil toxicity.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling) and CNS effects (dizziness, confusion, seizures), especially with prolonged or high-dose therapy.
* Monitor for gastrointestinal side effects.
* Monitor INR if patient is on warfarin.
* Monitor lithium levels if patient is on lithium.
## Clinical Pearls
* Metallic taste is a common and expected side effect.
* Advise patients to avoid alcohol during and for at least 72 hours after treatment due to the potential for a disulfiram-like reaction.
* Oral metronidazole has a bitter taste; it can be masked with food or flavored liquids.
* For vaginal gel, patients should abstain from intercourse during treatment.
* Consider topical options for rosacea to minimize systemic side effects.
**Disclaimer:** This information is intended for clinical pharmacy professionals. Always consult the most current prescribing information and relevant clinical guidelines for definitive guidance. Drug dosing and recommendations can vary based on patient-specific factors and institutional protocols.
