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# Metronidazole (Metrogyl)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain parasites.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of vaginal infections.
* **Trichomoniasis:** Treatment of parasitic infections.
* **Amebiasis:** Treatment of amebic dysentery and liver abscesses.
* **Giardiasis:** Treatment of intestinal infections.
* **Anaerobic Bacterial Infections:** Including intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections, and endocarditis.
* **Pseudomembranous Colitis:** Alternative agent.
* **Surgical Prophylaxis:** Particularly in colorectal surgery.
* **Helicobacter pylori Eradication:** As part of a multi-drug regimen.
## Adult Dosing
Dosing varies significantly by indication.
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days, or a single 2-gram dose orally. Alternatively, 0.75% vaginal gel inserted once daily for 5 days.
* **Trichomoniasis:** 2 grams 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):** 500-675 mg orally three to four times daily for 5-10 days.
* **Amebiasis (hepatic abscess):** 500-750 mg orally three times daily for 5-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days.
* **Anaerobic Bacterial Infections (non-CNS):** 500 mg IV or orally every 8 hours. Doses may range from 1.5 g to 2 g daily, divided.
* **Anaerobic CNS Infections:** 15 mg/kg IV initially, followed by 7.5 mg/kg every 8 hours. Maximum daily dose is typically 4 g.
* **Surgical Prophylaxis:** 1 gram IV 1-2 hours pre-operatively, or 500 mg orally every 8 hours starting pre-operatively.
* **H. pylori Eradication:** Typically 250-500 mg orally twice daily as part of a multi-drug regimen for 10-14 days.
## Pediatric Dosing
Dosing is based on weight and indication.
* **Amebiasis:** 35-50 mg/kg/day orally or IV, divided into three doses for 5-10 days. Maximum daily dose 750 mg.
* **Giardiasis:** 15 mg/kg/day orally, divided into three doses for 5-7 days. Maximum daily dose 250 mg.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg IV or orally every 8 hours. Neonates require specific dosing due to immature metabolism; consult pediatric infectious disease guidelines.
## Dose Adjustments
No dose adjustment is typically required for renal impairment, though prolonged therapy in hemodialysis patients may require dose replenishment. Metronidazole is removed by hemodialysis. Use with caution in severe hepatic impairment; reduce dose by 30-50%.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (though benefits may outweigh risks in certain severe infections).
* Concomitant use of disulfiram or alcohol (due to disulfiram-like reaction).
## Adverse Effects
Common: Nausea, vomiting, diarrhea, metallic taste, headache, dizziness.
Serious: Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, Stevens-Johnson syndrome, pancreatitis, opportunistic infections.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, headache, nausea, vomiting, tachycardia). Avoid alcohol during and for at least 3 days after therapy.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Lithium:** Can increase lithium levels, potentially leading to toxicity.
* **Phenytoin/Phenobarbital:** May decrease metronidazole effectiveness and increase risk of toxicity.
* **Disulfiram:** Avoid concomitant use due to potential for psychotic reactions.
* **Theophylline/Aminophylline:** Metronidazole may inhibit metabolism, increasing serum levels.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain) with prolonged therapy.
* Monitor for signs of opportunistic infections.
* Monitor liver function tests if hepatic impairment is present.
* Monitor INR if patient is on warfarin.
## Clinical Pearls
* Metronidazole has a metallic taste which can be bothersome.
* Urine may turn a reddish-brown color.
* Take oral doses with or without food.
* For vaginal gel, avoid intercourse during treatment and for several days after.
* Use cautiously in patients with CNS disorders.
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**Disclaimer:** This information is intended for clinical pharmacists and healthcare professionals. It is essential to consult current prescribing information, institutional protocols, and drug interaction databases for complete and up-to-date guidance before making any treatment decisions.
