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# Metronidazole (Metrogyl)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of symptomatic trichomoniasis.
* **Amebiasis:** Treatment of amebiasis (intestinal and extraintestinal).
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious 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).
* **Pseudomembranous Colitis:** Treatment of *Clostridioides difficile*-associated diarrhea (CDAD).
* **Surgical Prophylaxis:** Prophylaxis against anaerobic infection in specific surgical procedures (e.g., colorectal surgery).
## Adult Dosing
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days OR 2 g as a single dose.
* Vaginal gel 0.75%: 5 g intravaginally 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.
* **Amebiasis:**
* *Intestinal:* Oral: 500-675 mg three times daily for 5-10 days.
* *Extra-intestinal (e.g., liver abscess):* Oral: 500-675 mg three times daily for 5-10 days. Intravenous: 15 mg/kg loading dose, then 7.5 mg/kg every 6 hours for 5-10 days.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5-7 days OR 500 mg twice daily for 5 days.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 500 mg every 8 hours. Usual duration 7-10 days, but depends on severity and type of infection.
* IV: Loading dose of 15 mg/kg, followed by 7.5 mg/kg every 6 hours.
* **Pseudomembranous Colitis (CDAD):**
* Oral: 500 mg three times daily for 10-14 days. *Vancomycin is generally preferred for initial episodes, especially if severe.*
* **Surgical Prophylaxis:**
* Oral/IV: 500 mg to 1 g given 1 hour before surgery, may be repeated every 8 hours for up to 24 hours post-operatively.
## Pediatric Dosing
Dosing in pediatrics is weight-based and depends heavily on the indication and local protocols.
* **General Pediatric Dosing for Anaerobic Infections:**
* Oral/IV: 7.5 mg/kg per dose every 8 hours.
* Maximum dose: Generally 400 mg per dose for oral, 15 mg/kg loading dose and 7.5 mg/kg every 6 hours IV. Actual maximums may vary by protocol.
* **Amebiasis:**
* Oral: 35-50 mg/kg/day divided into 3 doses for 5-10 days.
* **Giardiasis:**
* Oral: 5 mg/kg three times daily for 5-7 days.
* **Trichomoniasis:**
* Oral: Not generally recommended for children due to lack of data.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment is typically needed. However, high doses of IV metronidazole may accumulate in severe renal failure and dialysis may remove it.
* **Hepatic Impairment:** Use with caution. Reduce dose in severe hepatic disease, particularly for IV administration.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Active CNS disease.
* First trimester of pregnancy (although widely used later in pregnancy when benefits outweigh risks).
* Use with disulfiram or alcohol (within 3 days of last dose) due to potential disulfiram-like reaction.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, anaphylaxis, leukopenia, thrombocytopenia, pancreatitis, hepatotoxicity.
* **Disulfiram-like reaction:** Flushing, vomiting, tachycardia when taken with alcohol.
* **Urine discoloration:** Darkening of urine (harmless).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction. Avoid alcohol during and for at least 3 days after therapy.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Potential for increased lithium levels and toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Disulfiram:** Concurrent use is contraindicated.
* **Busulfan:** Metronidazole may increase busulfan levels, potentially leading to toxicity.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain) and CNS effects (seizures, confusion).
* Monitor for signs of hypersensitivity reactions.
* Monitor for efficacy and signs of secondary infections.
* Monitor INR if patient is on warfarin.
* Consider baseline and periodic CBC with differential and platelet count in patients receiving prolonged therapy.
## Clinical Pearls
* Metronidazole has a metallic taste which can affect compliance. Taking with food may reduce gastrointestinal upset.
* Advise patients to avoid alcohol during treatment and for at least 72 hours after the last dose.
* Treatment duration should be guided by clinical response and specific indication.
* For vaginal use, avoid intercourse and douches during treatment.
* IV administration is typically given over 20-60 minutes.
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*Disclaimer: This information is intended for clinical use and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines before making any treatment decisions. Drug information can change, and individual patient factors must be considered.*
