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# Metrogyl (metronidazole)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain parasites.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of vaginal infections caused by anaerobic bacteria.
* **Trichomoniasis:** Treatment of urogenital infections caused by *Trichomonas vaginalis*.
* **Amebiasis:** Treatment of intestinal amebiasis (amebic dysentery) and extraintestinal amebiasis (e.g., amebic liver abscess).
* **Giardiasis:** Treatment of intestinal infections caused by *Giardia lamblia*.
* **Anaerobic Bacterial Infections:** Treatment of intra-abdominal infections, skin and skin structure infections, gynecologic infections, bone and joint infections, CNS infections, lower respiratory tract infections, and endocarditis caused by susceptible anaerobic bacteria. Often used in combination therapy.
* **Pseudomembranous Colitis (Clostridioides difficile infection):** Treatment of *C. difficile*-associated diarrhea.
## Adult Dosing
* **Bacterial Vaginosis:**
* 2 grams (g) orally as a single dose.
* 500 mg orally twice daily for 7 days.
* **Trichomoniasis:**
* 2 g orally as a single dose.
* 400 mg orally twice daily for 7-10 days.
* **Amebiasis:**
* Intestinal: 500-650 mg orally 3 times daily for 5-10 days.
* Extraintestinal: 500-650 mg orally 3 times daily for 5-10 days, followed by a luminal agent.
* **Giardiasis:** 250 mg orally 3 times daily for 5-7 days.
* **Anaerobic Bacterial Infections:** Typically 500 mg orally or intravenously (IV) every 8 hours for 7-14 days. Duration depends on the site and severity of infection.
* **Pseudomembranous Colitis:** 500 mg orally every 8 hours for 10-14 days.
## Pediatric Dosing
Dosing in children depends on the indication and weight. **Consult specific pediatric guidelines or protocols.**
* **Amebiasis:** 35-50 mg/kg/day orally divided into 3 doses for 5-10 days. Maximum dose typically 750 mg per dose or 2 g/day.
* **Giardiasis:** 5 mg/kg/dose orally 3 times daily for 5-7 days. Maximum dose typically 250 mg per dose.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose orally or IV every 8 hours.
## Dose Adjustments
No dose adjustment is typically required for renal impairment.
For significant hepatic impairment, consider reducing the dose.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use in the first trimester of pregnancy for non-emergent indications (relative contraindication, risk-benefit assessment required).
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness, dark urine.
Less common: Rash, pruritus, stomatitis, peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, leukopenia, thrombocytopenia.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (severe nausea, vomiting, flushing, headache, tachycardia). Avoid alcohol during and for at least 72 hours after metronidazole therapy.
* **Warfarin:** May increase INR. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase serum lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole efficacy.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels. Monitor cyclosporine levels.
## Monitoring
* Monitor for signs and symptoms of infection resolution.
* Monitor for adverse effects, particularly peripheral neuropathy with prolonged therapy.
* In patients with hepatic impairment, monitor liver function tests.
* Monitor complete blood count (CBC) with prolonged therapy.
## Clinical Pearls
* Metronidazole has a metallic taste that can be bothersome for patients.
* Urine may turn reddish-brown; this is benign.
* Avoid muzzling devices for dogs receiving this medication.
* For anaerobic infections, combination therapy is often preferred.
* IV metronidazole can be infused undiluted or diluted in normal saline.
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*This information is intended as a quick reference and does not replace comprehensive drug information resources. Always verify current prescribing information with the manufacturer's product monograph or other authoritative sources before making clinical decisions.*
