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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain parasites.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of vaginal bacterial infections.
* **Trichomoniasis:** Treatment of urogenital protozoal infections.
* **Amebiasis:** Treatment of intestinal and extraintestinal amebic infections.
* **Giardiasis:** Treatment of intestinal protozoal infections.
* **Anaerobic Bacterial Infections:** Treatment of various infections caused by susceptible anaerobic organisms, including intra-abdominal infections, gynecologic infections, skin and soft tissue infections, and bone and joint infections.
* **Pseudomembranous Colitis:** Treatment of *Clostridioides difficile* infection (often reserved for mild cases or as an alternative).
* **Surgical Prophylaxis:** Preoperative prophylaxis in specific surgical procedures (e.g., colorectal surgery).
## Adult Dosing
Dosing is highly dependent on the specific indication and severity of infection.
* **Bacterial Vaginosis:**
* 2 grams orally as a single dose.
* 500 mg orally twice daily for 7 days.
* Vaginal gel 0.75% (one applicatorful intravaginally once or twice daily for 5 days).
* **Trichomoniasis:**
* 2 grams orally as a single dose.
* 400 mg orally twice daily for 7 days.
* **Amebiasis:**
* **Intestinal:** 500-650 mg orally 3 times daily for 7-10 days.
* **Extra-intestinal (e.g., hepatic abscess):** 500-650 mg orally 3 times daily for 7-10 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 IV every 8 hours. Duration varies widely based on infection site and severity, often 7-14 days or longer. Intra-abdominal infections may require 10-14 days.
* **Pseudomembranous Colitis:** 500 mg orally 3 times daily for 10-14 days.
* **Surgical Prophylaxis:** 500 mg orally or IV 1 hour before surgery, and then 500 mg every 8 hours for up to 24 hours post-operatively.
## Pediatric Dosing
Dosing is weight-based and depends on the indication.
* **Amebiasis:** 35-50 mg/kg/day orally divided into 3 doses for 7-10 days. Maximum daily dose is 750 mg.
* **Giardiasis:** 15 mg/kg/day orally divided into 3 doses for 5-7 days. Maximum daily dose is 250 mg.
* **Anaerobic Bacterial Infections:** 30 mg/kg/day IV divided into 3 doses. Maximum daily dose is 4 grams. For specific indications and duration, consult pediatric infectious disease resources.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally needed for oral or IV metronidazole. However, some sources recommend reduced doses for severe renal impairment (CrCl < 10 mL/min) if on hemodialysis, though data is limited.
* **Hepatic Impairment:** Dose reduction may be necessary in severe hepatic insufficiency. Consider halving the daily dose.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use with disulfiram (within 2 weeks).
* Use with alcohol (disulfiram-like reaction).
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal pain, metallic taste, anorexia, headache, dizziness.
Serious: Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, neutropenia, optic neuropathy.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, palpitations, shortness of breath). Advise patients to avoid alcohol during therapy and for at least 3 days after.
* **Disulfiram:** Can cause acute psychosis, confusion. Avoid concurrent use.
* **Warfarin:** Metronidazole can potentiate the anticoagulant effect of warfarin. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole can increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole efficacy.
* **5-Fluorouracil (5-FU):** Metronidazole can increase the toxicity of 5-FU.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain). Discontinue if neuropathy occurs.
* Monitor for central nervous system effects (seizures, encephalopathy).
* Monitor for hypersensitivity reactions.
* Monitor for gastrointestinal distress.
* If prolonged therapy, consider monitoring complete blood count.
## Clinical Pearls
* Metronidazole has a metallic taste which can be a deterrent for some patients.
* Urine may turn a reddish-brown color; this is harmless.
* For vaginal use, avoid intercourse during treatment and for the duration of treatment with the gel.
* For bacterial vaginosis, partner treatment is generally not recommended unless symptomatic.
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***Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and clinical guidelines before administering any medication.*
