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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal medication used to treat a variety of infections caused by anaerobic bacteria and certain parasites.
## Primary Indications
* **Bacterial vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of symptomatic trichomoniasis.
* **Amebiasis:** Intestinal amebiasis and amebic liver abscess.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic bacterial infections:** Intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, central nervous system infections, lower respiratory tract infections, and endocarditis, particularly when caused by susceptible anaerobic organisms. Often used in combination therapy.
* **Pseudomembranous colitis:** Treatment of *Clostridioides difficile*-associated diarrhea (CDAD).
* **Surgical prophylaxis:** Preoperative prophylaxis for colorectal surgery.
* **Helicobacter pylori eradication:** In combination with other agents.
## Adult Dosing
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days, or 2 g orally as a single dose.
* **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: 500-750 mg orally three times daily for 5-10 days.
* Hepatic abscess: 500-750 mg orally three times daily for 5-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5 days, or 2 g orally once daily for 3 days.
* **Anaerobic bacterial infections:** 500 mg IV or orally every 8 hours. Duration varies based on infection severity and response.
* **Pseudomembranous colitis:** 250-500 mg orally every 6-8 hours.
* **Surgical prophylaxis:** 1 g IV once, or 500 mg orally/IV every 8 hours starting prior to surgery and continuing for up to 24 hours postoperatively.
* **H. pylori eradication:** Varies based on regimen, typically 250-500 mg orally twice daily for 10-14 days in combination with other agents.
**Maximum dose:** Generally 4 g/day for IV therapy. Oral maximum may vary based on indication.
## Pediatric Dosing
Dosing in pediatrics is highly dependent on indication and weight. Consult specific pediatric guidelines or infectious disease specialists.
* **Bacterial vaginosis/Trichomoniasis:** Safety and efficacy not established in pediatric patients.
* **Amebiasis:**
* Intestinal: 35-50 mg/kg/day orally divided into 3 doses for 5-10 days. Maximum dose 750 mg/dose.
* Hepatic abscess: 35-50 mg/kg/day orally or IV divided into 3 doses for 5-10 days. Maximum dose 750 mg/dose.
* **Giardiasis:** 5 mg/kg/dose orally every 8 hours for 5 days. Maximum dose 250 mg/dose.
* **Anaerobic bacterial infections:** 7.5 mg/kg/dose IV or orally every 8 hours. Maximum dose 15 mg/kg/dose or 4 g/day.
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustment typically recommended for mild to moderate impairment. In severe renal impairment (CrCl < 30 mL/min), consider reducing the maintenance dose by 50% if administering IV, as the metabolite can accumulate. Dialysis may or may not remove metronidazole effectively; consult specific guidelines.
* **Hepatic Impairment:** Use with caution. Consider reducing the dose in severe hepatic insufficiency due to impaired metabolism.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (relative contraindication; benefit vs. risk must be carefully assessed).
* Concomitant use of disulfiram or alcohol (within 3 days of last dose) due to disulfiram-like reaction.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, severe allergic reactions, neutropenia, pancreatitis.
* **Other:** Darkened urine, yeast overgrowth (superinfection).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, headache, nausea, vomiting, chest pain, palpitations). Avoid alcohol during treatment and for at least 3 days after discontinuation.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase serum lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole efficacy by increasing its metabolism.
* **Disulfiram:** Co-administration is contraindicated.
* **Certain Antineoplastics (e.g., busulfan):** Metronidazole may increase busulfan levels, leading to toxicity.
## Monitoring
* **Clinical response:** Monitor for signs and symptoms of infection resolution.
* **Adverse effects:** Watch for neurological symptoms (numbness, tingling, paresthesia, dizziness, ataxia, seizures), gastrointestinal distress, and signs of hypersensitivity.
* **Laboratory tests:** Complete blood count (CBC) may be monitored with prolonged therapy or in patients with a history of blood dyscrasias. Lithium levels if co-administered. INR if co-administered with warfarin.
## Clinical Pearls
* A metallic taste is a common and often bothersome side effect.
* Advise patients to avoid alcohol during treatment and for at least 72 hours after the last dose.
* Peripheral neuropathy is a risk with prolonged or high-dose therapy; monitor for symptoms.
* For vaginal infections, oral therapy is generally preferred over vaginal suppositories/gels for systemic treatment of partners, though local treatment may be considered.
* When treating *C. difficile*, it is important to avoid antiperistaltic agents (e.g., loperamide) as they can worsen the condition.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for clinical judgment. Always consult the most current prescribing information and relevant guidelines for definitive patient management.
