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# Metronidazole
## Overview
Metronidazole is an antimicrobial agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* Bacterial vaginosis
* *Clostridioides difficile* infection (CDI)
* Amoebiasis
* Giardiasis
* Trichomoniasis
* Surgical prophylaxis (certain procedures)
* Intra-abdominal infections
* Skin and soft tissue infections
* Bone and joint infections
* CNS infections
* Pelvic inflammatory disease
* Endocarditis
## Adult Dosing
Dosing varies significantly by indication.
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days, OR 2 grams orally once daily for 1-2 days.
* ***Clostridioides difficile* Infection (CDI):** 500 mg orally three times daily for 10-14 days. Consider higher doses for severe CDI if vancomycin is contraindicated or unavailable.
* **Amoebiasis (intestinal):** 500-800 mg orally three times daily for 5-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days.
* **Trichomoniasis:** 2 grams orally once daily for 1 day, OR 250 mg orally three times daily for 7 days.
* **Surgical Prophylaxis:** 1 g IV 1-2 hours before surgery, OR 500 mg PO/IV every 8 hours starting preoperatively.
## Pediatric Dosing
Dosing in children is often weight-based and varies by indication. Consult pediatric guidelines.
* **Intestinal Amoebiasis:** 35-50 mg/kg/day divided into three doses orally, not to exceed 400 mg per dose, for 5-10 days.
* **Giardiasis:** 15 mg/kg/day divided into three doses orally, not to exceed 250 mg per dose, for 5-7 days.
* **Bacterial Infections (anaerobic):** 7.5 mg/kg/dose IV/PO every 8 hours. Maximum 500 mg per dose.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution; reduce dose by 50% in severe hepatic disease.
* **Renal Impairment:** No dose adjustment typically needed for hemodialysis or peritoneal dialysis, but prolonging the dosing interval may be considered in severe renal impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use within 14 days of disulfiram therapy (due to potential for disulfiram-like reaction).
* Concurrent use with alcohol.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dark urine.
* **Serious:** Peripheral neuropathy (especially with prolonged use), central nervous system effects (seizures, encephalopathy, dizziness), Stevens-Johnson syndrome, toxic epidermal necrolysis, severe allergic reactions, pancreatitis.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, palpitations). Avoid alcohol during and for at least 3 days after therapy.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Increased lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole efficacy.
* **Disulfiram:** Concurrent use is contraindicated due to potential for psychotic reactions.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for CNS side effects.
* For CDI, monitor for clinical improvement.
* For GI infections, monitor for resolution of symptoms.
* For surgical prophylaxis, monitor for signs of surgical site infection.
* Monitor INR if co-administered with warfarin.
## Clinical Pearls
* Administer oral metronidazole with or without food.
* A metallic taste is a common side effect and can be managed with sugar-free gum or candy.
* Patients should be advised to avoid alcohol during treatment and for at least 3 days after completion.
* IV metronidazole can be given as a continuous infusion or intermittent infusion.
* Ensure adequate hydration, especially for patients receiving IV therapy.
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*This information is intended for healthcare professionals. Always consult the current official prescribing information and institutional protocols for complete and up-to-date guidance.*
