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# Metronidazole
## Overview
Metronidazole is an antimicrobial agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* Bacterial vaginosis
* Trichomoniasis
* Amebiasis
* Giardiasis
* *Clostridioides difficile* infection (CDI)
* Surgical prophylaxis (anaerobic coverage)
* Treatment of anaerobic infections (e.g., intra-abdominal, gynecological, skin/soft tissue)
## Adult Dosing
Dosing varies significantly by indication.
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days, OR 2 grams orally as a single dose. Topical options also available.
* **Trichomoniasis:** 2 grams orally as a single dose, OR 250 mg orally three times daily for 7 days.
* **Amebiasis (intestinal):** 500-675 mg orally three times daily for 5-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days, OR 2 grams orally once daily for 3 days.
* **CDI:** 500 mg orally three times daily for 10-14 days. (Note: Vancomycin is often preferred for initial episodes, especially severe ones).
* **Anaerobic infections:** Typical dose is 500 mg intravenously or orally every 8 hours. Duration depends on infection severity and site. Maximum dose generally 4 grams daily.
## Pediatric Dosing
Dosing is weight-based and varies by indication. Consult specific pediatric guidelines or institutional protocols.
* **Trichomoniasis:** Not typically used in children under 12 unless diagnosed.
* **Giardiasis:** 15 mg/kg/day orally in 3 divided doses for 5-7 days. Maximum 250 mg per dose or 750 mg daily.
* **Anaerobic infections:** 7.5-15 mg/kg/dose intravenously or orally every 6-8 hours. Maximum 4 grams daily.
## Dose Adjustments
No dose adjustment needed for renal impairment. Dose may need reduction in severe hepatic impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* Concurrent use with disulfiram (within 2 weeks).
* Concurrent use with alcohol.
## Adverse Effects
Common: Nausea, vomiting, diarrhea, metallic taste, headache, dizziness, dry mouth.
Serious: Seizures, peripheral neuropathy, Stevens-Johnson syndrome, encephalopathy, leukopenia.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia). Avoid alcohol during and for at least 3 days after therapy.
* **Disulfiram:** Potential for psychosis or confusion. Avoid concurrent use.
* **Warfarin:** Increased risk of bleeding. Monitor INR closely. Dose adjustments of warfarin may be needed.
* **Lithium:** Metronidazole may increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** Can decrease metronidazole efficacy.
## Monitoring
* Signs and symptoms of infection resolution.
* For prolonged therapy: Neurologic status (peripheral neuropathy, encephalopathy), signs of C. difficile recurrence.
* For patients on warfarin: INR.
* For patients on lithium: Lithium levels.
## Clinical Pearls
* Advise patients to avoid alcohol during treatment and for at least 3 days after completing therapy due to potential disulfiram-like reaction.
* A metallic taste is common and usually resolves after discontinuation.
* Peripheral neuropathy can be irreversible; discontinue if symptoms develop.
* Use with caution in patients with CNS disorders.
* For CDI, oral metronidazole is less effective than oral vancomycin for severe disease.
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*Please verify current prescribing information and institutional guidelines before administration.*
