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# Metronidazole (Metrogyl)
## Overview
Metronidazole is a nitroimidazole antibiotic effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of *Trichomonas vaginalis* infection.
* **Amoebiasis:** Treatment of amoebic dysentery and amoebic liver abscess.
* **Giardiasis:** Treatment of *Giardia lamblia* infection.
* **Anaerobic bacterial infections:** Treatment of serious anaerobic infections, such as intra-abdominal infections, skin and soft tissue infections, gynecologic infections, and central nervous system infections. Often used in combination with other antibiotics.
* **Pseudomembranous colitis:** Treatment of antibiotic-associated *Clostridioides difficile* infection.
* **Surgical prophylaxis:** Prophylaxis against anaerobic infection in specific surgical procedures (e.g., colorectal surgery).
## Adult Dosing
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days OR 2 g orally as a single dose OR 0.75% vaginal gel, one applicatorful (5 g) inserted vaginally once daily for 5 days.
* **Trichomoniasis:** 2 g orally as a single dose OR 250 mg orally three times daily for 7 days OR 375 mg orally twice daily for 7 days.
* **Amoebiasis:**
* Dysentery: 500-650 mg orally three times daily for 5-10 days.
* Abscess: 500-650 mg orally three times daily for 5-10 days, followed by a luminal agent.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days OR 500 mg orally twice daily for 5 days OR 2 g orally as a single dose for 3 days.
* **Anaerobic bacterial infections:** 500 mg IV or orally every 8 hours. Duration varies based on severity and site of infection (typically 7-14 days).
* **Pseudomembranous colitis:** 500 mg orally every 8 hours. Duration typically 10-14 days.
* **Surgical prophylaxis:** 1 g IV or orally 1-2 hours before surgery, followed by 500 mg IV or orally every 8 hours for up to 24 hours postoperatively.
## Pediatric Dosing
Dosing is weight-based and depends on the indication. Consult specific pediatric guidelines.
* **Giardiasis:** 15 mg/kg/day orally, divided into 3 doses, for 5-7 days (maximum 250 mg per dose, 750 mg/day).
* **Anaerobic bacterial infections:** 7.5 mg/kg/dose IV or orally every 8 hours (maximum 500 mg/dose).
## Dose Adjustments
* **Hepatic Impairment:** Use with caution. Consider reducing the dose in severe hepatic insufficiency.
* **Renal Impairment:** No dose adjustment generally recommended for hemodialysis or peritoneal dialysis, though some sources suggest dose reduction in severe impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* First trimester of pregnancy (especially for protozoal infections; oral use in second and third trimesters may be considered if benefits outweigh risks).
## 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, toxic epidermal necrolysis, pancreatitis, hepatotoxicity, neutropenia.
* **Disulfiram-like reaction:** Alcohol should be avoided during treatment and for at least 3 days after.
## Key Drug Interactions
* **Alcohol:** Severe disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, palpitations, shortness of breath).
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Lithium:** Increased lithium levels, potentially leading to toxicity.
* **Phenytoin, Phenobarbital:** Decreased efficacy of metronidazole.
* **Cyclosporine:** Increased cyclosporine levels.
* **Busulfan:** Increased busulfan levels.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for psychiatric effects (mood changes, hallucinations).
* Monitor for signs of hypersensitivity reactions.
* Monitor for gastrointestinal upset.
* For long-term therapy, consider complete blood counts.
## Clinical Pearls
* A metallic taste is a common and often bothersome side effect.
* Advise patients to avoid alcohol during therapy and for at least 3 days after the last dose.
* Oral therapy may be substituted for IV therapy when clinically indicated.
* For vaginal infections, ensure patient understanding of proper application technique for vaginal gel.
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*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 treatment decisions. Dosing may vary based on local protocols and individual patient factors.*
