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# Metronidazole
## Overview
Metronidazole is an antimicrobial agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of symptomatic trichomoniasis.
* **Amoebiasis:** Treatment of intestinal and extraintestinal amoebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis).
* **Prophylaxis:** Prophylaxis against anaerobic bacterial infection in specific surgical procedures (e.g., colorectal surgery).
* **Pseudomembranous Colitis:** Treatment of *Clostridium difficile*-associated diarrhea (though other agents may be preferred).
## Adult Dosing
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days, OR 2 g as a single dose.
* Vaginal gel 0.75%: 5 g inserted vaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 2 g as a single dose, OR 250 mg three times daily for 7 days, OR 375 mg twice daily for 7 days.
* **Amoebiasis:**
* Intestinal: Oral: 500-650 mg three times daily for 5-10 days.
* Extra-intestinal: Oral: 500-650 mg three times daily for 5-10 days. IV: 500 mg every 8 hours.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5-7 days.
* **Anaerobic Bacterial Infections:**
* Oral: 500 mg every 8 hours.
* IV: 500 mg every 6-8 hours. Maximum IV dose: 4 g per day.
* **Prophylaxis (Colorectal Surgery):**
* Oral: 1 g given 8-12 hours before surgery.
* IV: 1 g given within 1 hour before surgery.
* **C. difficile-associated diarrhea:**
* Oral: 500 mg three times daily for 10-14 days.
## Pediatric Dosing
Dosing in children often depends on weight and indication. Specific dosing should be confirmed with current guidelines or a pediatric formulary. General guidelines include:
* **Amoebiasis:**
* Oral: 35-50 mg/kg/day divided into 3 doses for 5-10 days. Maximum: 750 mg per dose or 2 g per day.
* **Giardiasis:**
* Oral: 15 mg/kg/day divided into 3 doses for 5-7 days. Maximum: 250 mg per dose or 750 mg per day.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 7.5 mg/kg per dose every 8 hours. Maximum: 500 mg per dose or 4 g per day.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally recommended. Metronidazole and its metabolites are removed by hemodialysis. Extended or higher doses may require consideration for dialysis patients.
* **Hepatic Impairment:** Use with caution. In severe hepatic impairment, consider reducing the dose by one-third to one-half and dosing every 12 hours.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use with alcohol or disulfiram-containing products due to potential disulfiram-like reaction.
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness, rash, pruritus.
Serious: Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, Stevens-Johnson syndrome, neutropenia, pancreatitis, thrombophlebitis (IV).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache, tachycardia). Avoid alcohol during treatment and for at least 3 days after.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Busulfan:** Metronidazole may increase busulfan levels, leading to toxicity.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain). Discontinue if neuropathy occurs.
* Monitor for signs of central nervous system effects (dizziness, ataxia, seizures).
* Monitor blood counts with prolonged or high-dose therapy.
* Monitor for therapeutic response.
## Clinical Pearls
* Metronidazole has a metallic taste that can be unpleasant for patients.
* Urine may turn reddish-brown.
* IV administration can be given as a bolus or infusion. If infused, dilute in an appropriate IV fluid (e.g., NS, D5W).
* For anaerobic infections, combination therapy with an agent effective against aerobic bacteria may be necessary.
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*Disclaimer: This information is intended for healthcare professionals. Always verify current prescribing information and consult relevant clinical guidelines before making therapeutic decisions.*
