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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.
* **Amebiasis:** Treatment of intestinal amebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bacterial vaginosis, endocarditis, bone and joint infections, central nervous system infections, lower respiratory tract infections, and C. difficile infection).
## Adult Dosing
* **Bacterial Vaginosis:**
* Vaginal gel 0.75%: One applicatorful (5 grams) inserted vaginally once daily for 5 days.
* Oral: 500 mg twice daily for 7 days.
* **Trichomoniasis:**
* Oral: A single 2-gram dose, or 250 mg three times daily for 7 days, or 500 mg twice daily for 7 days.
* **Amebiasis:**
* Intestinal: 500 mg to 650 mg orally three times daily for 7 to 10 days.
* Hepatic abscess: 500 mg to 650 mg orally three times daily for 7 to 10 days, often followed by a tissue amoebicide.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5 to 7 days.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 500 mg every 8 hours. Duration varies by infection site and severity, typically 7 to 14 days.
* Maximum dose: Generally not to exceed 4 grams per day.
## Pediatric Dosing
Dosing varies by indication and weight. Consult specific pediatric guidelines.
* **Giardiasis:**
* Oral: 15 mg/kg/day divided into three doses for 5 to 7 days. Maximum daily dose: 250 mg.
* **Amebiasis:**
* Oral: 35-50 mg/kg/day divided into three doses for 5 to 10 days. Maximum daily dose: 750 mg.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 7.5 mg/kg/dose every 8 hours, or 15 mg/kg/dose every 12 hours. Maximum dose: 4 grams per day. Duration varies.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution. Consider reducing the dose by 30-50% in severe hepatic insufficiency.
* **Renal Impairment:** No dose adjustment typically required for oral or IV use. However, some sources suggest a dose reduction in severe renal impairment (CrCl < 10 mL/min) for IV administration to avoid accumulation of metabolites, though data is limited.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use of disulfiram within the last 2 weeks.
* Concurrent use of alcohol due to disulfiram-like reaction.
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness.
Serious: Peripheral neuropathy, central nervous system effects (seizures, encephalopathy), Stevens-Johnson syndrome, toxic epidermal necrolysis, myelosuppression, pancreatitis, hepatic dysfunction.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache, palpitations). Avoid alcohol during and for at least 3 days after treatment.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** May increase cyclosporine levels. Monitor cyclosporine levels.
* **Disulfiram:** Concomitant use is contraindicated due to risk of psychosis and confusion.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling).
* Monitor for CNS adverse effects (dizziness, confusion, seizures).
* Monitor for hypersensitivity reactions.
* For long-term therapy, consider complete blood counts.
* For amebiasis, monitor for clinical improvement.
## Clinical Pearls
* Metronidazole has a distinct metallic taste that may affect patient compliance.
* Advise patients to avoid alcohol during and for at least 3 days after completing therapy.
* Urine may become reddish-brown in color.
* When treating C. difficile infection, metronidazole may be less effective than vancomycin for severe disease, but is a viable alternative for mild-to-moderate disease.
* Vaginal gel is for local use and systemic absorption is minimal.
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*This information is intended for clinical use and does not replace comprehensive drug references. Always verify current prescribing information and consult with a healthcare provider.*
