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# Metronidazole
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic and antiprotozoal agent.
## Primary Indications
* Treatment of anaerobic bacterial infections.
* Treatment of protozoal infections (e.g., trichomoniasis, amebiasis, giardiasis).
* Management of *Clostridioides difficile* infection.
* Surgical prophylaxis (colorectal surgery).
* Management of inflammatory bowel disease (e.g., Crohn's disease, ulcerative colitis).
* Treatment of bacterial vaginosis.
* Topical treatment of rosacea.
## Adult Dosing
* **Anaerobic Infections:** 500 mg every 8 hours IV or PO. Duration varies by infection site.
* **_C. difficile_ Infection:** 500 mg every 8 hours PO for 10-14 days.
* **Trichomoniasis:** 2 g single PO dose, or 250 mg PO every 12 hours for 7 days, or 375 mg PO every 12 hours for 7 days.
* **Amebiasis:**
* *Intestinal:* 500-675 mg PO every 8 hours for 5-10 days.
* *Hepatic Abscess:* 500-675 mg PO every 8 hours for 5-10 days.
* **Giardiasis:** 250 mg PO every 8 hours for 5-7 days.
* **Bacterial Vaginosis:** 500 mg PO every 12 hours for 7 days, or 2 g PO single dose. Vaginal gel 0.75% applied once daily for 5 days.
* **Surgical Prophylaxis:** 1 g IV 1-2 hours before surgery, then 500 mg IV or PO every 8 hours for up to 24 hours post-operatively.
* **Rosacea (Topical):** Gel 0.75% or cream 1% applied to affected areas once or twice daily.
**Maximum Dose:** Generally 4 g daily.
## Pediatric Dosing
Dosing in children requires careful consideration and is often based on weight and specific indication.
* **Anaerobic Infections:** 7.5 mg/kg per dose PO or IV every 8 hours. Maximum dose: 500 mg per dose.
* **Intestinal Amebiasis:** 35-50 mg/kg/day divided every 8 hours PO for 5-10 days. Maximum dose: 750 mg per dose.
* **Giardiasis:** 5 mg/kg per dose PO every 8 hours for 5-7 days. Maximum dose: 250 mg per dose.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally needed for intermittent hemodialysis or peritoneal dialysis. Continuous renal replacement therapy (CRRT) may require dose adjustment based on protocol.
* **Hepatic Impairment:** Dose reduction may be necessary for severe hepatic impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (though often used if benefits outweigh risks).
* Active central nervous system disease.
* Use with disulfiram or alcohol (within 3 days of last dose).
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
Less Common/Serious: Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, leukopenia, thrombocytopenia, Stevens-Johnson syndrome, pancreatitis, dark urine.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, palpitations). Avoid alcohol during and for at least 3 days after treatment.
* **Disulfiram:** Avoid concurrent use; can cause psychosis.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
* **5-Fluorouracil (5-FU):** Increased toxicity of 5-FU.
## Monitoring
* Signs and symptoms of infection.
* Signs of peripheral neuropathy (numbness, tingling) or central nervous system effects (dizziness, seizures).
* Complete blood count (CBC) with differential, especially with prolonged therapy.
* Liver function tests (LFTs) if hepatic impairment is present or during prolonged therapy.
* Renal function tests.
* Lithium levels if co-administered.
* INR if co-administered with warfarin.
## Clinical Pearls
* Administer IV metronidazole without dilution or with compatible IV fluids (e.g., NS, D5W).
* A metallic taste is a common and expected side effect.
* Advise patients to avoid alcohol during treatment and for at least 72 hours after the last dose.
* Oral metronidazole can be taken with or without food.
* Ensure adequate hydration, especially with IV administration.
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*This information is intended for healthcare professionals. Please consult the most current prescribing information and relevant guidelines for definitive patient care decisions. Dosing may vary based on specific clinical situations, patient factors, and local protocols.*
