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# Metronidazole
## Overview
Metronidazole is an antimicrobial agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial vaginosis:** Treatment of vaginal infections.
* **Trichomoniasis:** Treatment of urogenital protozoal infections.
* **Amebiasis:** Treatment of intestinal and extraintestinal amebiasis.
* **Giardiasis:** Treatment of intestinal protozoal infections.
* **Anaerobic bacterial infections:** Treatment of serious infections caused by susceptible anaerobes (e.g., intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis).
* **_Clostridium difficile_-associated diarrhea (CDAD):** While often a second-line agent, it can be used for mild to moderate cases.
* **Surgical prophylaxis:** Prophylaxis against anaerobic infection in specific surgical procedures (e.g., colorectal surgery).
## Adult Dosing
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days, OR 2 g orally as a single dose. Topical formulations also available.
* **Trichomoniasis:** 2 g orally as a single dose, OR 250 mg orally twice daily for 7 days, OR 375 mg orally twice daily for 7 days.
* **Amebiasis (intestinal):** 500-675 mg orally 3 times daily for 5-10 days.
* **Amebiasis (extra-intestinal):** 500-675 mg orally 3 times daily for 5-10 days, followed by a luminal agent.
* **Giardiasis:** 250 mg orally 3 times daily for 5 days.
* **Anaerobic bacterial infections:** 500 mg orally or IV every 8 hours. Typical duration 7-14 days. For severe infections, doses up to 1 g IV every 8 hours may be used.
* **_Clostridium difficile_-associated diarrhea (CDAD):** 500 mg orally 3 times daily for 10 days. (Vancomycin is often preferred for initial episodes).
* **Surgical prophylaxis:** 1 g orally or IV 1-2 hours before surgery, followed by 500 mg every 8 hours for up to 24 hours postoperatively.
## Pediatric Dosing
Dosing in children is typically based on weight and indication. Specific protocols may vary.
* **Giardiasis:** 15 mg/kg/day orally, divided into 3 doses, for 5 days. Maximum daily dose: 750 mg.
* **Amebiasis:** 35-50 mg/kg/day orally or IV, divided into 3 doses, for 5-10 days. Maximum daily dose: 2 g.
* **Anaerobic bacterial infections:** 7.5 mg/kg/dose orally or IV every 8 hours. Maximum dose: 2 g per day for adolescents. Neonatal dosing is more complex and weight-based, often with longer dosing intervals.
## Dose Adjustments
* **Renal impairment:** No dose adjustment is typically required for moderate to severe renal impairment. Hemodialysis may necessitate supplemental dosing.
* **Hepatic impairment:** Use with caution. Severe hepatic impairment may require dose reduction.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (relative contraindication; used only if essential).
## Adverse Effects
* **Common:** Nausea, vomiting, metallic taste, anorexia, abdominal discomfort, diarrhea, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, leukopenia, pancreatitis, disulfiram-like reaction with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache, palpitations). Advise patients to avoid alcohol during treatment and for at least 72 hours after discontinuation.
* **Warfarin:** May potentiate the anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase serum lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels. Monitor cyclosporine levels.
## Monitoring
* Monitor for signs of peripheral neuropathy (numbness, tingling, pain).
* Monitor for central nervous system effects (dizziness, seizures).
* Monitor for gastrointestinal side effects.
* Monitor INR if co-administered with warfarin.
* Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* Metronidazole has a metallic taste, which can affect patient adherence.
* Advise patients to avoid alcohol during and for 72 hours after treatment due to the disulfiram-like reaction.
* Urine may turn a reddish-brown color.
* Neuropathic side effects can be irreversible, especially with prolonged or high-dose therapy.
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*This information is intended as a quick reference and does not replace comprehensive drug information resources. Always verify current prescribing information with the official product labeling and consult relevant guidelines.*
