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# Metronidazole
## Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent.
## Primary Indications
* Treatment of anaerobic bacterial infections (e.g., intra-abdominal infections, gynecological infections, skin and soft tissue infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis).
* Treatment of protozoal infections (e.g., trichomoniasis, amebiasis, giardiasis).
* Management of *Clostridioides difficile* infection (CDI).
* Surgical prophylaxis (e.g., colorectal surgery).
* H. pylori eradication.
## Adult Dosing
* **Anaerobic Infections:** 500 mg IV or PO every 8 hours for 7-10 days, or longer depending on infection severity and site. Typical doses range from 500 mg to 1000 mg every 8-12 hours. Max dose generally 4000 mg/day.
* **Trichomoniasis:** 2 grams PO single dose, or 250 mg PO every 12 hours for 7 days, or 500 mg PO every 12 hours for 5-7 days.
* **Amebiasis (Intestinal):** 500-750 mg PO every 8 hours for 5-10 days.
* **Amebiasis (Hepatic Abscess):** 500-750 mg PO or IV every 8 hours for 5-10 days.
* ***C. difficile* Infection:** 500 mg PO every 8 hours for 10-14 days. (Note: Vancomycin is often preferred for severe or initial episodes).
* **Surgical Prophylaxis:** 1000 mg IV 1-2 hours before surgery, or 500 mg PO 12-24 hours before surgery.
## Pediatric Dosing
Dosing is typically weight-based. Consult specific pediatric guidelines or infectious disease specialists.
* **Anaerobic Infections:** 15 mg/kg/day IV or PO divided every 8 hours, not to exceed 4000 mg/day.
* **Amebiasis:** 35-50 mg/kg/day PO divided every 8 hours for 5-10 days.
* **Giardiasis:** 15 mg/kg/day PO divided every 8 hours for 5 days.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment necessary in mild to moderate renal impairment. In severe impairment (CrCl < 10 mL/min), the extended-interval or maintenance dose may need to be reduced. Hemodialysis removes metronidazole; administer dose after dialysis.
* **Hepatic Impairment:** Use with caution. Reduce dose in severe hepatic insufficiency.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* Use with disulfiram or alcohol within 3 days.
## Adverse Effects
Common: Nausea, vomiting, diarrhea, metallic taste, headache, anorexia, abdominal pain, stomatitis.
Serious: Seizures, peripheral neuropathy, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, dark urine, pancreatitis, leukopenia, thrombophlebitis (IV).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache, palpitations). Advise patient to avoid alcohol during and for at least 3 days after therapy.
* **Disulfiram:** Concurrent use may cause psychosis or confusion. Avoid concurrent use.
* **Warfarin:** May potentiate anticoagulant effect. Monitor INR closely.
* **Lithium:** Metronidazole may increase serum lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole efficacy.
* **5-Fluorouracil (5-FU):** Metronidazole may increase 5-FU toxicity.
## Monitoring
* Monitor for signs and symptoms of C. difficile infection recurrence.
* Monitor for neurological side effects (e.g., peripheral neuropathy, dizziness, ataxia) especially with prolonged therapy.
* Monitor INR if co-administered with warfarin.
* Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* Metronidazole has excellent activity against anaerobic bacteria and protozoa.
* Metallic taste is a common and often bothersome side effect.
* Advise patients to avoid alcohol due to the potential for a disulfiram-like reaction.
* IV formulation can be administered undiluted or diluted in normal saline or dextrose 5% in water.
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*Disclaimer: This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and relevant clinical guidelines for definitive dosing and management decisions.*
