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# Metronidazole
## Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent.
## Primary Indications
* **Bacterial infections:** Treatment of anaerobic bacterial infections, including intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bacterial vaginosis, and *Clostridium difficile*-associated diarrhea (CDAD).
* **Protozoal infections:** Treatment of trichomoniasis, amebiasis, and giardiasis.
* **Surgical prophylaxis:** Prevention of anaerobic infection in certain surgical procedures.
## Adult Dosing
* **Bacterial infections:** 500 mg to 1 g intravenously (IV) or orally every 6-8 hours. Dosing varies significantly by indication and severity.
* **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 250 mg orally three times daily for 7 days.
* **Amebiasis:**
* **Intestinal:** 500-750 mg orally every 8 hours for 7-10 days.
* **Hepatic abscess:** 500-750 mg orally every 8 hours for 7-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days.
* **CDAD:** 500 mg orally or IV every 8 hours for 10-14 days.
* **Surgical prophylaxis:** 1 g IV 1 hour before surgery, then 500 mg orally or IV every 8 hours for up to 24 hours postoperatively.
* **Maximum dose:** Generally, no more than 4 g per day should be administered.
## Pediatric Dosing
Dosing is weight-based and varies by indication. Consult specific pediatric guidelines.
* **Bacterial infections:** Typically 7.5 mg/kg/dose every 8 hours (maximum 400 mg/dose).
* **Amebiasis:** 35-50 mg/kg/day orally in 3 divided doses for 7-10 days.
* **Giardiasis:** 5 mg/kg/dose orally every 8 hours for 5-7 days (maximum 250 mg/dose).
## Dose Adjustments
* **Renal impairment:** No dose adjustment is generally needed for mild to moderate impairment. In severe impairment, consider extending the dosing interval or reducing the dose, although data are limited. Metronidazole is removed by hemodialysis.
* **Hepatic impairment:** Use with caution in severe hepatic impairment; consider reducing the dose.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* Use in the first trimester of pregnancy for trichomoniasis.
## Adverse Effects
* **Common:** Nausea, vomiting, metallic taste, anorexia, diarrhea, abdominal pain, headache, dizziness, dark urine.
* **Serious:** Peripheral neuropathy, central nervous system effects (seizures, encephalopathy), Stevens-Johnson syndrome, leukopenia, thrombophlebitis (IV administration), pancreatitis.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia). Avoid alcohol during and for at least 3 days after treatment.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase serum lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole efficacy.
## Monitoring
* Monitor for signs and symptoms of neuropathy (numbness, tingling, pain).
* Monitor for signs and symptoms of CNS toxicity.
* Monitor for therapeutic response and signs of infection recurrence.
* Monitor INR if co-administered with warfarin.
## Clinical Pearls
* Administer IV metronidazole over 20-60 minutes to reduce the risk of phlebitis.
* A metallic taste is a common side effect and can impact adherence.
* Urine may turn reddish-brown in color.
* Avoid concurrent alcohol use due to the disulfiram-like reaction.
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*Disclaimer: This information is intended for clinical decision support and does not replace professional judgment. Always refer to the current official prescribing information and institutional protocols for complete and up-to-date guidance.*
