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# Metronidazole
## Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent.
## Primary Indications
* **Bacterial infections:** Intra-abdominal infections, skin and soft tissue infections, gynecological infections, CNS infections, bone and joint infections, endocarditis, and bacterial vaginosis.
* **Protozoal infections:** Trichomoniasis, amebiasis, giardiasis.
* **C. difficile infection (CDI)**
## Adult Dosing
* **Bacterial Infections:** Typically 500 mg IV or PO every 8 hours. Duration varies by infection.
* **Bacterial Vaginosis:** 500 mg PO twice daily for 7 days or a single 2 g dose.
* **Trichomoniasis:** Single 2 g PO dose.
* **Amebiasis (intestinal):** 500-750 mg PO every 8 hours for 7-10 days.
* **Amebiasis (hepatic abscess):** 500-750 mg PO every 8 hours for 5-10 days, often combined with a luminal amebicide.
* **Giardiasis:** 250 mg PO three times daily for 5-7 days or 500 mg PO twice daily for 5 days.
* **C. difficile Infection (CDI):** 500 mg PO every 8 hours for 10-14 days. (Note: Vancomycin is generally preferred for initial episodes of severe CDI).
## Pediatric Dosing
Dosing varies significantly by indication and weight. **Consult pediatric-specific guidelines or a pediatric infectious disease specialist.** General ranges include:
* **Bacterial Infections:** 7.5 mg/kg IV or PO every 8 hours, not to exceed adult doses.
* **Giardiasis:** 5 mg/kg PO three times daily for 5-7 days, maximum 250 mg/dose.
* **Intestinal Amebiasis:** 35-50 mg/kg/day PO divided into 3 doses for 7-10 days, maximum 750 mg/dose.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment typically needed. Metronidazole and its metabolites are removed by hemodialysis.
* **Hepatic Impairment:** Reduce dose by 33-50% in severe hepatic impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concomitant use with disulfiram or alcohol (within 3 days of last dose) due to disulfiram-like reaction.
## Adverse Effects
Common: Nausea, vomiting, diarrhea, metallic taste, abdominal pain, headache, dizziness.
Serious: Peripheral neuropathy (especially with prolonged use), seizures, Stevens-Johnson syndrome, anaphylaxis, leukopenia, pancreatitis, hepatic dysfunction.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, shortness of breath). Avoid alcohol during and for at least 3 days after treatment.
* **Disulfiram:** Can cause acute psychosis or confusional states. Avoid coadministration.
* **Warfarin:** Metronidazole may potentiate the anticoagulant effect of warfarin. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Ciclosporin:** May increase ciclosporin levels.
## Monitoring
* Assess for signs and symptoms of infection resolution.
* Monitor for adverse effects, particularly neurological symptoms (numbness, tingling, seizures) and gastrointestinal distress.
* Monitor INR if co-administered with warfarin.
* Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* A metallic taste is a common and expected side effect.
* Avoid alcohol and disulfiram during and for 3 days after therapy.
* For trichomoniasis, treat sexual partners concurrently.
* Metronidazole can turn urine a dark brown or reddish-brown color.
* Peripheral neuropathy is a risk with prolonged or high-dose therapy; patients should report any new neurological symptoms immediately.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines before making therapeutic decisions.*
