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# Metronidazole
## 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, central nervous system infections, lower respiratory tract infections, endocarditis).
* Treatment of trichomoniasis, amebiasis, and giardiasis.
* Treatment of bacterial vaginosis.
* Prophylaxis against anaerobic infection in surgical procedures.
* *Clostridioides difficile* infection (CDI) - typically reserved for mild to moderate cases when initial therapy with vancomycin is not suitable or as a second-line agent.
## Adult Dosing
* **Anaerobic Bacterial Infections (Systemic):**
* Intravenous: 500 mg every 8 hours.
* Oral: 500 mg every 8 hours.
* Duration varies based on infection severity and site, typically 7-14 days.
* **Trichomoniasis:**
* Single dose: 2 grams orally.
* Alternatively: 500 mg orally twice daily for 7 days.
* **Amebiasis:**
* Invasive amebic dysentery: 500-650 mg orally three times daily for 5-10 days.
* Amebic liver abscess: 500-650 mg orally three times daily for 5-10 days, often followed by a luminal amebicide.
* **Giardiasis:**
* 250 mg orally three times daily for 5-7 days.
* **Bacterial Vaginosis:**
* 2 grams orally as a single dose.
* Alternatively: 500 mg orally twice daily for 7 days.
* **Surgical Prophylaxis:**
* Intravenous: 500 mg given within 1 hour before surgery, may be repeated every 8 hours for up to 24 hours postoperatively.
* **CDI (Mild to Moderate):**
* 500 mg orally three times daily for 10-14 days. (Note: Vancomycin is generally preferred for initial CDI therapy).
## Pediatric Dosing
Dosing is weight-based and depends on the indication. Always consult specific pediatric guidelines.
* **Anaerobic Bacterial Infections (Systemic):**
* Intravenous/Oral: 7.5 mg/kg per dose every 8 hours.
* Maximum dose: 500 mg per dose or 40 mg/kg/day, whichever is less.
* Duration varies.
* **Intestinal Amebiasis:**
* Oral: 35-50 mg/kg/day divided into three doses for 5-10 days.
* Maximum dose: 750 mg/day.
* **Giardiasis:**
* Oral: 15 mg/kg/day divided into three doses for 5-7 days.
* Maximum dose: 250 mg/day.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment is typically needed for moderate to severe renal impairment. However, metronidazole and its metabolites are removed by hemodialysis, so a supplemental dose may be required after dialysis.
* **Hepatic Impairment:** Use with caution in severe hepatic impairment. Dosing may need to be reduced, particularly with prolonged therapy. Consider consulting specialized resources for specific recommendations.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concomitant use with disulfiram or alcohol.
## 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, exfoliative dermatitis, leukopenia, thrombocytopenia, pancreatitis, hepatotoxicity.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, palpitations). Advise patients to avoid alcohol during therapy and for at least 3 days after.
* **Disulfiram:** Acute psychosis and confusion. Avoid coadministration.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Increased lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole efficacy and increase phenytoin/phenobarbital levels.
* **5-Fluorouracil (5-FU):** Increased toxicity of 5-FU.
## Monitoring
* Monitor for signs and symptoms of infection resolution.
* Monitor for adverse effects, particularly neuropathy (numbness, tingling) with prolonged use.
* Monitor CBC if prolonged therapy or high doses are used.
* Monitor INR if used concurrently with warfarin.
* Monitor lithium levels if used concurrently with lithium.
## Clinical Pearls
* Metronidazole has a metallic taste which can be a common complaint.
* Urine may turn a reddish-brown color; this is harmless.
* For trichomoniasis, all sexual partners should be treated concurrently to prevent reinfection, even if asymptomatic.
* Ensure adequate hydration when using IV metronidazole.
* Caution patients against driving or operating machinery until they know how metronidazole affects them, due to potential dizziness and neurological effects.
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*Disclaimer: This information is intended for healthcare professionals. Always verify current prescribing information and consult relevant clinical guidelines before making treatment decisions.*
