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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain parasites.
## Primary Indications
* **Bacterial vaginosis:** Treatment of vaginal infections.
* **Trichomoniasis:** Treatment of sexually transmitted infections.
* **Amebiasis:** Intestinal and extraintestinal infections.
* **Giardiasis:** Intestinal infection.
* **Anaerobic bacterial infections:** Intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis, and pseudomembranous colitis (C. difficile).
* **Surgical prophylaxis:** Preoperative prophylaxis in specific colorectal surgeries.
## Adult Dosing
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days, or 2 g orally as a single dose. Alternatively, 0.75% vaginal gel 5 g applied vaginally once daily for 5 days.
* **Trichomoniasis:** 2 g orally as a single dose, or 250 mg orally three times daily for 7 days, or 375 mg orally twice daily for 7 days.
* **Amebiasis:**
* **Intestinal:** 500-675 mg orally three times daily for 5-10 days.
* **Extra-intestinal (e.g., liver abscess):** 500-675 mg orally three times daily for 5-10 days. Higher doses may be required.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days, or 2 g orally once daily for 3 days.
* **Anaerobic bacterial infections:** 500 mg IV or orally every 8 hours. Duration varies by infection severity and site. For severe infections, higher doses (e.g., up to 1 g IV every 8 hours) may be used.
* **Surgical prophylaxis (colorectal):** 1 g IV 30-60 minutes before surgery, or 500 mg orally 4 hours before surgery and then every 8 hours for 24 hours postoperatively.
## Pediatric Dosing
Pediatric dosing is weight-based and depends on the indication. Consult specific guidelines or product information.
* **Amebiasis:** 35-50 mg/kg/day orally divided into three doses for 5-10 days. Maximum 750 mg/dose.
* **Giardiasis:** 15 mg/kg/day orally divided into three doses for 5-7 days. Maximum 250 mg/dose.
* **Anaerobic bacterial infections:** 7.5 mg/kg/dose IV or orally every 8 hours. For severe infections, 15 mg/kg/dose IV or orally every 8 hours. Neonatal dosing varies based on gestational and postnatal age.
## Dose Adjustments
* **Renal impairment:** No dose adjustment is typically needed for mild to moderate renal impairment. In severe renal impairment or during dialysis, dosage reduction and/or extension of dosing interval may be considered, though data are limited.
* **Hepatic impairment:** Use with caution. Severe hepatic impairment may warrant dose reduction, especially with prolonged or high-dose therapy.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* History of hypersensitivity reaction to metronidazole.
* Concomitant use of disulfiram.
* Concomitant use of alcohol during therapy and for at least 3 days after discontinuation.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, dizziness, ataxia, encephalopathy, Stevens-Johnson syndrome, toxic epidermal necrolysis, leukopenia, pancreatitis, darkening of urine.
* **Disulfiram-like reaction:** With alcohol.
## Key Drug Interactions
* **Alcohol:** Severe disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, dyspnea). Avoid alcohol.
* **Disulfiram:** May cause delirium, psychosis. Avoid concurrent use.
* **Warfarin:** Potentiates 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 efficacy.
* **Fluorouracil (5-FU):** Metronidazole may increase fluorouracil toxicity.
* **Cyclosporine:** May increase cyclosporine levels.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for central nervous system side effects (dizziness, seizures).
* Monitor for signs of C. difficile-associated diarrhea.
* For patients on warfarin, monitor INR regularly.
* For patients on lithium, monitor lithium levels.
## Clinical Pearls
* Take oral metronidazole with food to minimize gastrointestinal upset.
* Advise patients to avoid alcohol during treatment and for at least 3 days after the last dose due to the potential for a disulfiram-like reaction.
* Metronidazole can cause a harmless darkening of the urine (reddish-brown).
* Treatment for trichomoniasis should include partner treatment to prevent reinfection.
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*This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the current prescribing information and relevant clinical guidelines before making any treatment decisions.*
