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# Metronidazole
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic with activity against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of symptomatic trichomoniasis.
* **Amebiasis:** Treatment of intestinal and extraintestinal amebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections, including intra-abdominal infections, skin and soft tissue infections, gynecologic infections, and central nervous system infections. Often used in combination with other agents.
* **_Clostridioides difficile_ Infection:** Alternative agent for _C. difficile_ infection, particularly in mild to moderate cases or when other agents are contraindicated.
* **Prophylaxis:** Surgical prophylaxis in specific procedures, particularly colorectal surgery.
## Adult Dosing
* **Bacterial Vaginosis:**
* Vaginal gel 0.75%: 5 g intravaginally once daily for 5 days.
* Oral 500 mg twice daily for 7 days.
* **Trichomoniasis:**
* Oral 2 g as a single dose, or 250 mg three times daily for 7 days, or 500 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, or IV 500 mg every 8 hours.
* **Giardiasis:**
* Oral 250 mg three times daily for 5 days.
* **Anaerobic Bacterial Infections:**
* Oral: 500 mg every 8 hours.
* IV: 500 mg every 6-8 hours.
* **Maximum dose:** Generally 4 g per day.
* **_Clostridioides difficile_ Infection:**
* Oral 500 mg three times daily for 10 days. (Considered second-line to vancomycin in severe cases).
* **Surgical Prophylaxis:**
* IV 1 g as a single dose or 500 mg every 8 hours initiated before surgery.
## Pediatric Dosing
Dosing in pediatric patients should be based on weight and specific indication, often determined by local protocols.
* **Amebiasis:**
* Oral 35-50 mg/kg/day divided into three doses for 5-10 days (maximum 750 mg/dose).
* **Giardiasis:**
* Oral 15 mg/kg/day divided into three doses for 5 days (maximum 250 mg/dose).
* **Anaerobic Bacterial Infections:**
* Oral or IV 30-40 mg/kg/day divided into three doses (maximum 750 mg/dose).
* **_Clostridioides difficile_ Infection:**
* Oral 15-30 mg/kg/day divided into three doses for 10 days (maximum 500 mg/dose).
## Dose Adjustments
* **Renal Impairment:** No dose adjustment typically needed. Hemodialysis may enhance clearance; consult prescribing information.
* **Hepatic Impairment:** Dose reduction may be necessary in severe hepatic impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (relative contraindication, use with caution and only if benefits outweigh risks).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), central nervous system effects (seizures, encephalopathy), Stevens-Johnson syndrome, leukopenia, pancreatitis, dark urine.
* **Disulfiram-like reaction:** Severe flushing, vomiting, tachycardia when taken with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction. Avoid alcohol during and for at least 72 hours after therapy.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** May increase cyclosporine levels.
## Monitoring
* Assess for signs and symptoms of infection resolution.
* Monitor for adverse effects, especially neurological symptoms and gastrointestinal disturbances.
* Monitor INR if co-administered with warfarin.
* Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* Advise patients to avoid alcohol during treatment and for at least 72 hours after completion to prevent a disulfiram-like reaction.
* A metallic taste is a common side effect and may affect adherence.
* For vaginal use, avoid tampons and douches during treatment.
* Use IV formulation for severe infections or when oral route is not feasible.
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*This information is intended for healthcare professionals. Always consult the official prescribing information and relevant guidelines for complete details before making clinical decisions.*
