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# Metronidazole
## Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent.
## Primary Indications
* Treatment of anaerobic bacterial infections.
* Treatment of protozoal infections (e.g., *Trichomonas vaginalis*, *Giardia lamblia*, *Entamoeba histolytica*).
* Surgical prophylaxis (colorectal surgery).
* *Clostridioides difficile* infection (CDI) - typically reserved for non-severe cases or as an alternative if vancomycin is unavailable.
## Adult Dosing
Dosing varies widely based on indication. Typical regimens include:
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days, or 2 g orally as a single dose.
* **Trichomoniasis:** 2 g orally as a single dose, or 500 mg orally twice daily for 7 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days.
* **Amebiasis (intestinal):** 500-750 mg orally three times daily for 7-10 days.
* **Amebiasis (hepatic abscess):** 500-750 mg orally three times daily for 7-10 days.
* **Anaerobic infections:** 500 mg intravenously or orally every 8 hours. Duration varies based on infection severity and site.
* **CDI (non-severe):** 500 mg orally three times daily for 10-14 days.
* **Surgical prophylaxis:** 1 g orally or intravenously 1 hour before surgery, often combined with a cephalosporin.
## Pediatric Dosing
Dosing is typically weight-based and depends on the indication.
* **General anaerobic infections:** 15 mg/kg/day orally or intravenously, divided into three doses, not to exceed 400 mg per dose or 2 g/day.
* **Giardiasis:** 5 mg/kg orally three times daily for 5 days, not to exceed 250 mg per dose.
* **Trichomoniasis:** Similar to adults, though specific pediatric data is limited. Consult specialists.
## Dose Adjustments
* **Renal impairment:** No dose adjustment is typically required, but consider prolonged infusion for IV administration if renal replacement therapy is used.
* **Hepatic impairment:** Use with caution. May require dose reduction in severe hepatic disease.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* First trimester of pregnancy (relative contraindication, use only if benefits outweigh risks).
* Concomitant use with disulfiram (within 2 weeks).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, Stevens-Johnson syndrome, encephalopathy, pancreatitis, dark urine.
* **Disulfiram-like reaction:** With alcohol ingestion.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache). Advise patients to avoid alcohol during and for at least 72 hours after treatment.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely.
* **Lithium:** May increase lithium levels. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** May increase cyclosporine levels.
## Monitoring
* Signs and symptoms of infection.
* Peripheral neuropathy with prolonged use.
* Rarely, drug-induced hepatitis or pancreatitis.
* INR if co-administered with warfarin.
* Lithium levels if co-administered with lithium.
## Clinical Pearls
* Metallic taste is common and usually resolves after treatment.
* Urine may turn reddish-brown.
* Administer IV metronidazole over 30-60 minutes to minimize risk of phlebitis.
* Do not use to treat viral infections.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and local protocols for definitive guidance.*
