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# Metronidazole
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of trichomoniasis.
* **Amoebiasis:** Treatment of intestinal and extraintestinal amoebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections, including intra-abdominal infections, skin and skin structure infections, gynecologic infections, and central nervous system infections. Often used in combination therapy.
* **Pseudomembranous Colitis:** Treatment of *Clostridioides difficile*-associated diarrhea.
* **Surgical Prophylaxis:** Prophylaxis against anaerobic infection in specific surgical procedures (e.g., colorectal surgery).
* **H. pylori Eradication:** Part of multi-drug regimens for *Helicobacter pylori* eradication.
## Adult Dosing
Dosing varies significantly by indication.
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days.
* Vaginal Gel 0.75%: One full applicator (5g) inserted vaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: Single dose of 2 grams, or 250 mg twice daily for 7 days, or 500 mg twice daily for 7 days.
* **Amoebiasis:**
* Intestinal: 500-750 mg three times daily for 5-10 days.
* Extra-intestinal (e.g., liver abscess): 500-750 mg three times daily for 5-10 days.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5 days, or a single dose of 2 grams.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 500 mg every 8 hours. Doses up to 1 gram every 8 hours have been used for severe infections. Usual duration 7-14 days.
* **Pseudomembranous Colitis:**
* Oral: 500 mg three or four times daily for 10-14 days. Vancomycin is often preferred for severe *C. difficile*.
* **Surgical Prophylaxis:**
* Oral/IV: 1 gram as a single dose given within 12 hours before surgery. Repeat dose of 500 mg may be given 6 and 12 hours after the initial dose.
* **H. pylori Eradication:**
* Oral: Typically 500 mg twice daily in combination with other agents for 10-14 days.
## Pediatric Dosing
Dosing is weight-based and varies by indication. Always consult specific guidelines.
* **General Anaerobic Infections:**
* Oral/IV: 7.5 mg/kg per dose every 8 hours. Maximum adult dose applies if less than 12 years old. For children >12 years, use adult doses.
* **Amoebiasis:**
* Oral: 35-50 mg/kg/day divided into 3 doses for 5-10 days. Maximum adult dose applies.
* **Giardiasis:**
* Oral: 15 mg/kg/day divided into 3 doses for 5 days. Maximum adult dose applies.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in severe hepatic impairment.
* **Renal Impairment:** No dose adjustment typically needed for oral or IV administration, though it is removed by hemodialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concomitant use of disulfiram (within the last 2 weeks).
* Concomitant use of alcohol.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, metallic taste, headache, dizziness, dark urine.
* **Serious:** Peripheral neuropathy (especially with prolonged use), central nervous system effects (seizures, encephalopathy), Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema multiforme, severe allergic reactions, candidiasis (oral or vaginal).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (severe nausea, vomiting, flushing, tachycardia, headache). Avoid alcohol during therapy and for at least 3 days after.
* **Disulfiram:** May cause psychosis or confusion. Avoid coadministration.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Increased serum lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole efficacy.
* **Fluorouracil:** May increase fluorouracil toxicity.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for central nervous system adverse effects.
* Monitor INR if patient is on warfarin.
* Monitor lithium levels if coadministered.
## Clinical Pearls
* A metallic taste is common and can be managed by sugar-free gum or candy.
* Advise patients to avoid alcohol during and for at least 3 days after treatment.
* For IV administration, metronidazole is a vesicant; infuse through a central line or well-functioning peripheral IV.
* Treatment duration depends on the specific infection and clinical response.
**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant guidelines for complete details and to confirm recommendations before making clinical decisions.
