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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of trichomoniasis.
* **Amebiasis:** Treatment of amebiasis (intestinal and extraintestinal).
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, gynecological infections, bacteremia, bone and joint infections, CNS infections, respiratory tract infections). Often used in combination with other antibiotics.
* **Clostridioides difficile Infection (CDI):** Treatment of mild to moderate CDI.
* **Prophylaxis:** Surgical prophylaxis, particularly in colorectal surgery.
* **Rosacea:** Topical formulations for treatment of inflammatory lesions of rosacea.
## Adult Dosing
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days, OR 2 g as a single dose.
* Vaginal gel 0.75%: Apply one applicatorful (approx. 5g) intravaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 2 g as a single dose, OR 250 mg twice daily for 7 days, OR 375 mg twice daily for 7 days.
* **Amebiasis:**
* *Intestinal:* Oral: 500-750 mg three times daily for 5-10 days.
* *Extra-intestinal (e.g., liver abscess):* Oral: 500-750 mg three times daily for 5-10 days. IV: 15 mg/kg loading dose, then 7.5 mg/kg every 8 hours for 5-10 days.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5-7 days.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 500 mg every 8 hours. Duration varies by infection severity and site, typically 7-10 days.
* IV: 15 mg/kg loading dose, then 7.5 mg/kg every 8 hours.
* **Clostridioides difficile Infection (CDI):**
* Oral: 500 mg three times daily for 10-14 days (for mild to moderate disease).
* **Surgical Prophylaxis:**
* IV: 1 g as a single dose given 30-60 minutes before surgery.
* **Rosacea (Topical):**
* Gel 0.75% or Cream 1%: Apply thin layer to affected areas twice daily.
## Pediatric Dosing
* **Bacterial Infections (Anaerobic):**
* Oral/IV: 7.5 mg/kg per dose every 8 hours. Maximum adult dose typically applies.
* **Amebiasis:**
* Oral: 35-50 mg/kg/day in 3 divided doses for 5-10 days. Maximum 750 mg/dose.
* **Giardiasis:**
* Oral: 15 mg/kg/day in 3 divided doses for 5-7 days. Maximum 250 mg/dose.
* **Trichomoniasis:**
* Oral: Not generally recommended in children.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally needed.
* **Hepatic Impairment:** Reduce dose by 30-50% in severe hepatic impairment. Monitor drug concentrations.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use in the first trimester of pregnancy for trichomoniasis (risk-benefit assessment needed for other indications).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness, dark urine.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, Stevens-Johnson syndrome, leukopenia, pancreatitis, drug rash with eosinophilia and systemic symptoms (DRESS).
* **Disulfiram-like reaction:** Avoid alcohol during and for at least 3 days after treatment.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, headache).
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Lithium:** May increase lithium levels, leading to toxicity.
* **Phenobarbital, Phenytoin:** May decrease metronidazole levels.
* **Busulfan:** Metronidazole may increase busulfan levels.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels.
## Monitoring
* Monitor for signs of peripheral neuropathy (numbness, tingling, pain) with prolonged therapy.
* Monitor for therapeutic response and signs of superinfection.
* Monitor CBC with differential in patients receiving prolonged therapy.
* Monitor lithium levels if used concurrently.
* Monitor INR if used concurrently with warfarin.
## Clinical Pearls
* Metronidazole can cause a harmless dark or reddish-brown discoloration of urine.
* Ensure adequate hydration and avoid alcohol during therapy and for at least 3 days after completion.
* For anaerobic infections, consider combining with an agent covering aerobic Gram-positive organisms.
* IV metronidazole is a vesicant; ensure proper IV access and administration.
* The metallic taste can be a significant side effect for some patients.
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*This information is intended for healthcare professionals. Please verify current prescribing information with the official product monograph or other reliable sources before making clinical decisions.*
