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# Metronidazole
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* Treatment of anaerobic bacterial infections (e.g., intra-abdominal infections, pelvic inflammatory disease, gynecologic infections, intra-abdominal sepsis, 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.
* Treatment of *Clostridioides difficile*-associated diarrhea (CDAD).
* Prophylaxis against anaerobic infection in colorectal surgery.
* Part of multi-drug regimens for *Helicobacter pylori* eradication.
## Adult Dosing
* **Anaerobic Infections:**
* Mild to moderate: 500 mg IV or orally every 8 hours for 7-10 days.
* Severe: 15 mg/kg IV or orally loading dose, then 7.5 mg/kg every 6-8 hours. Maximum daily dose 4 g.
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days or 2 g orally single dose.
* **Trichomoniasis:** 2 g orally single dose or 500 mg orally twice daily for 7 days.
* **Amebiasis:**
* Invasive intestinal amebiasis: 500-750 mg orally three times daily for 5-10 days.
* Amebic liver abscess: 500-750 mg orally three times daily for 5-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days or 2 g orally once daily for 3 days.
* **CDAD:** 500 mg orally every 8 hours for 10-14 days.
* **Surgical Prophylaxis (Colorectal):** 1 g IV or orally 1-2 hours preoperatively. May repeat doses intraoperatively and postoperatively as needed.
* ***H. pylori* Eradication:** Typically 500 mg orally twice daily in combination with other agents for 10-14 days.
## Pediatric Dosing
* **Anaerobic Infections:**
* Newborns ( $< $40 weeks gestation): 7.5 mg/kg IV or orally every 12 hours.
* Newborns ( $> $40 weeks gestation) and older infants/children: 15 mg/kg IV or orally as a loading dose, followed by 7.5 mg/kg every 8 hours. Maximum daily dose 4 g.
* **Trichomoniasis:** 35 mg/kg orally single dose or 15 mg/kg orally twice daily for 7 days. Maximum 2 g per dose.
* **Amebiasis:** 35-50 mg/kg/day orally divided into 3 doses for 5-10 days. Maximum 750 mg per dose.
* **Giardiasis:** 15 mg/kg/day orally divided into 3 doses for 5-7 days. Maximum 250 mg per dose.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally recommended for hemodialysis or peritoneal dialysis.
* **Hepatic Impairment:** Use with caution. Consider reducing dose in severe hepatic impairment.
## Contraindications
* Known hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use within 14 days of disulfiram therapy (due to potential for psychosis).
* Use with alcohol during and for at least 3 days after therapy (disulfiram-like reaction).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, anorexia, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, hypersensitivity reactions, pancreatitis.
* **Other:** Darkened urine (harmless).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia). Advise patients to avoid alcohol.
* **Warfarin:** Increased INR and bleeding risk. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Increased lithium levels and toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
* **Disulfiram:** Potential for psychosis. Avoid concurrent use.
* **Cyclosporine:** May increase cyclosporine levels.
## Monitoring
* Clinical signs and symptoms of infection.
* For prolonged therapy (>10 days), consider monitoring for peripheral neuropathy.
* For patients on warfarin, monitor INR.
* For patients on lithium, monitor lithium levels.
## Clinical Pearls
* Administer IV metronidazole over at least 1 hour to minimize risk of phlebitis.
* Patients should be advised to avoid alcohol during treatment and for at least 3 days after completion.
* A metallic taste is a common side effect and usually resolves after therapy completion.
* Peripheral neuropathy is a risk, particularly with long-term therapy; discontinue if symptoms occur.
**Disclaimer:** This information is intended for clinical use and does not replace professional judgment. Always verify current prescribing information from reliable sources before administering any medication.
