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# Metronidazole (Metrogyl)
## Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent. It is effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of trichomoniasis.
* **Amebiasis:** Intestinal and extraintestinal amebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious 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). Often used in combination with other antibiotics.
* **Pseudomembranous Colitis:** Treatment of *Clostridioides difficile*-associated diarrhea.
* **Surgical Prophylaxis:** Preoperative prophylaxis in specific gynecologic and colorectal procedures.
* **H. pylori Eradication:** Part of multi-drug regimens for *Helicobacter pylori* eradication.
## Adult Dosing
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days, or a single 2-g dose orally.
* **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.
* *Extra-intestinal (e.g., liver abscess):* 500-750 mg orally three times daily for 5-10 days. Followed by a luminal agent if intestinal involvement is confirmed.
* **Giardiasis:** 250 mg orally three times daily for 5 days, or 500 mg orally twice daily for 5-7 days.
* **Anaerobic Bacterial Infections:** 500 mg intravenously or orally every 8 hours. Dosing duration varies based on infection severity and patient response, typically 7-14 days. Higher doses may be used for severe infections, up to 4 g/day intravenously.
* **Pseudomembranous Colitis:** 500 mg orally every 8 hours. For severe cases, 500 mg intravenously every 8 hours.
* **Surgical Prophylaxis:** 1 g orally or intravenously 1 hour before surgery.
* **H. pylori Eradication:** Typically 500 mg orally twice daily in combination with other agents for 10-14 days.
## Pediatric Dosing
Dosing is typically based on weight and indication. Consult specific pediatric guidelines.
* **Giardiasis:** 15 mg/kg/day orally divided into three doses, not to exceed 250 mg per dose, for 5-7 days. Maximum daily dose is 750 mg.
* **Amebiasis:** 35-50 mg/kg/day orally divided into three doses for 5-10 days. Maximum daily dose is 750 mg.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose orally or intravenously every 8 hours. Maximum dose is 15-30 mg/kg/day, not to exceed 4 g/day.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally recommended. However, hemodialysis removes metronidazole, so it may need to be re-dosed after dialysis.
* **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in severe hepatic impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concurrent use of disulfiram or alcohol (within 3 days of last dose).
## Adverse Effects
Common: Nausea, vomiting, diarrhea, metallic taste, stomatitis, headache, dizziness, rash, pruritus.
Serious: Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, dark urine, pancreatitis, thrombophlebitis (IV formulation).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, shortness of breath). Avoid alcohol during and for at least 3 days after treatment.
* **Disulfiram:** Risk of psychosis and confusion. Avoid concurrent use.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole efficacy.
* **5-Fluorouracil (5-FU):** Metronidazole may increase the toxicity of 5-FU.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for signs of CNS toxicity (seizures, encephalopathy).
* Monitor for hypersensitivity reactions.
* Monitor INR if patient is on warfarin.
* Monitor lithium levels if patient is on lithium.
## Clinical Pearls
* The metallic taste is a common and often bothersome side effect.
* Advise patients to avoid alcohol.
* For IV administration, metronidazole is compatible with normal saline and D5W.
* A luminal agent is recommended after treating intestinal amebiasis to eradicate cysts.
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*Disclaimer: This information is intended for clinical decision support and does not replace professional judgment. Always verify current prescribing information, guidelines, and product literature before making clinical decisions.*
