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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal agent.
## Primary Indications
* Treatment of anaerobic bacterial infections.
* Treatment of protozoal infections such as trichomoniasis, giardiasis, and amebiasis.
* Management of inflammatory conditions like Crohn's disease and rosacea (topical).
* Prophylaxis against anaerobic infection in surgical procedures.
## Adult Dosing
* **Anaerobic Infections:** Doses vary widely based on infection site and severity. Typical doses range from 500 mg intravenously or orally every 8 hours. For severe infections, higher doses may be used, but a common maximum is 4 grams per day.
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days, or a single 2-gram dose orally.
* **Trichomoniasis:** 2 grams orally as a single dose, or 250 mg orally twice daily for 7 days, or 375 mg orally twice daily for 7 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days.
* **Amebiasis:** 500-750 mg orally three times daily for 5-10 days (intestinal) or 1.5-2 grams orally once daily for 2-3 days (hepatic abscess, often followed by a luminal agent).
* **Surgical Prophylaxis:** 1 gram orally or IV 1-2 hours before surgery, often with an aminoglycoside.
* **Clostridioides difficile Infection (CDI):** 500 mg orally three times daily for 10-14 days. *Note: Oral vancomycin is generally preferred for initial episodes of severe CDI.*
* **Rosacea (Topical):** Apply a thin layer of 0.75% or 1% gel/cream to affected areas once or twice daily.
## Pediatric Dosing
Dosing is typically weight-based and depends on the indication.
* **Anaerobic Infections:** 15-30 mg/kg/day orally or IV, divided into 3 doses, not to exceed 4 grams/day.
* **Giardiasis:** 5 mg/kg orally three times daily for 5-7 days (maximum 250 mg/dose).
* **Amebiasis:** 35-50 mg/kg/day orally or IV, divided into 3 doses, for 5-10 days.
## Dose Adjustments
* **Hepatic Impairment:** Reduce dose by 30-50% in severe hepatic insufficiency. Monitor for toxicity.
* **Renal Impairment:** No dose adjustment is generally needed for standard doses. However, if using high doses or in patients on chronic dialysis, consultation may be warranted.
## Contraindications
* Known hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (although often used if benefits outweigh risks).
* Concomitant use of disulfiram or alcohol (within 3 days of last dose).
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness.
Serious: Peripheral neuropathy (especially with prolonged use), central nervous system effects (seizures, encephalopathy), Stevens-Johnson syndrome, leukopenia, pancreatitis, dark urine.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, dyspnea). Avoid alcohol during and for at least 3 days after treatment.
* **Warfarin:** May potentiate anticoagulant effect. Monitor INR closely.
* **Lithium:** May increase lithium levels, leading to toxicity. Monitor lithium levels.
* **Disulfiram:** Avoid concurrent use due to potential for psychotic reactions.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
* **5-Fluorouracil:** Metronidazole may increase the toxicity of 5-FU.
## Monitoring
* Monitor for signs of C. difficile infection recurrence or development.
* Assess for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for CNS adverse effects.
* For patients on warfarin, monitor INR regularly.
## Clinical Pearls
* The metallic taste is common and can lead to decreased oral intake.
* Advise patients to avoid alcohol during and for at least 72 hours after therapy.
* For topical formulations, avoid sun exposure and use of UV light.
* Ensure adequate hydration, especially when administered intravenously.
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*This information is intended for healthcare professionals and does not substitute for a thorough review of the complete prescribing information or clinical judgment. Always verify current prescribing information before use.*
