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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* Treatment of 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).
* Treatment of trichomoniasis.
* Treatment of amebiasis.
* Treatment of giardiasis.
* Bacterial vaginosis.
* *Clostridioides difficile* infection (CDI).
* Prophylaxis against anaerobic infection in colorectal surgery.
## Adult Dosing
Dosing varies widely based on indication.
* **Anaerobic Bacterial Infections:** Common regimens include 500 mg IV or PO every 8 hours for 7-10 days. Doses can range from 500 mg to 1 g every 8 hours, with a typical maximum of 4 g daily.
* **Trichomoniasis:** 2 g PO single dose or 250 mg PO every 12 hours for 7 days.
* **Amebiasis (intestinal):** 500-600 mg PO every 8 hours for 7-10 days.
* **Amebiasis (hepatic abscess):** 500-600 mg PO every 8 hours for 7-10 days, often in conjunction with a luminal amebicide.
* **Giardiasis:** 250 mg PO every 8 hours for 5-7 days or 2 g PO once daily for 3 days.
* **Bacterial Vaginosis:** 500 mg PO BID for 7 days or 2 g PO single dose.
* ***Clostridioides difficile* Infection (CDI):** For non-severe CDI, 500 mg PO every 8 hours for 10 days. For severe CDI, vancomycin is generally preferred.
* **Surgical Prophylaxis:** 1 g IV or PO administered 4 hours prior to surgery, followed by 500 mg PO every 8 hours for up to 24 hours post-operatively.
## Pediatric Dosing
Dosing is weight-based and varies by indication. Dosing is often based on specific protocols.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose IV or PO every 8 hours. Maximum daily dose typically 2 g.
* **Intestinal Amebiasis:** 35-50 mg/kg/day PO divided every 8 hours for 7-10 days. Maximum daily dose 2 g.
* **Giardiasis:** 5 mg/kg/dose PO every 8 hours for 5-7 days. Maximum daily dose 250 mg.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution. Reduced doses may be necessary in severe hepatic impairment.
* **Renal Impairment:** No dose adjustment is typically required for hemodialysis or peritoneal dialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Active CNS disease.
* First trimester of pregnancy (relative contraindication, use only if benefits outweigh risks).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, metallic taste, anorexia, abdominal discomfort, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, dark urine, hepatotoxicity, pancreatitis, candidiasis.
* **Disulfiram-like reaction:** With alcohol consumption. Advise patients to avoid alcohol during treatment and for at least 3 days after.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Lithium:** Increased lithium levels.
* **Phenytoin, Phenobarbital:** Decreased metronidazole levels.
* **Cyclosporine:** Increased cyclosporine levels.
* **5-Fluorouracil:** Increased toxicity of 5-FU.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for central nervous system effects (seizures, dizziness, encephalopathy).
* Monitor liver function tests if used in patients with pre-existing hepatic disease or for prolonged courses.
* Monitor INR if co-administered with warfarin.
* Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* Metronidazole has a metallic taste that can lead to poor adherence.
* Advise patients to avoid alcohol during therapy and for at least 72 hours after the last dose to prevent a disulfiram-like reaction.
* The parenteral formulation contains sodium, which should be considered in patients requiring sodium restriction.
* For the treatment of trichomoniasis, sexual partners should also be treated.
* For the treatment of CDI, metronidazole is generally reserved for initial episodes of non-severe disease; vancomycin is preferred for severe or recurrent CDI.
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*Please verify current prescribing information before use. This information is intended for educational purposes and does not substitute for professional medical advice.*
