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# Metronidazole (Metrogyl)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of urogenital trichomoniasis.
* **Amebiasis:** Treatment of intestinal amebiasis (amebic dysentery) and amebic liver abscess.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections, including intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections, lower respiratory tract infections, and endocarditis. Often used in combination with other antibiotics.
* **Pseudomembranous Colitis:** Treatment of *Clostridioides difficile*-associated diarrhea (CDAD).
* **Surgical Prophylaxis:** Prophylaxis against anaerobic infection in specific surgical procedures (e.g., colorectal surgery).
* **H. pylori Eradication:** Part of multi-drug regimens for *Helicobacter pylori* eradication.
## Adult Dosing
Dosing varies significantly by indication. Below are common examples:
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days OR 2 grams orally as a single dose.
* **Trichomoniasis:** 2 grams orally as a single dose OR 200 mg orally three times daily for 7 days OR 400 mg orally twice daily for 7 days.
* **Intestinal Amebiasis:** 500-600 mg orally three times daily for 7-10 days.
* **Amebic Liver Abscess:** 500-600 mg orally three times daily for 7-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days OR 2 grams orally once daily for 3 days.
* **Anaerobic Bacterial Infections:** 500 mg intravenously or orally every 8 hours. Typical duration 7-14 days.
* **CDAD:** 500 mg orally every 8 hours for 10-14 days. For severe CDAD, IV may be preferred.
* **Surgical Prophylaxis:** 1 gram orally or IV 1 hour before surgery, followed by 500 mg orally or IV every 8 hours for up to 24 hours post-operatively.
Maximum oral dose generally 4 grams daily.
## Pediatric Dosing
Dosing is weight-based and varies by indication. Refer to specific pediatric guidelines.
* **Intestinal Amebiasis:** 35-50 mg/kg/day orally divided into 3 doses for 7-10 days (max 750 mg/dose or 2 g/day).
* **Giardiasis:** 15 mg/kg/day orally divided into 3 doses for 5-7 days (max 250 mg/dose or 750 mg/day).
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose IV or orally every 8 hours (max 500 mg/dose or 4 g/day).
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally recommended for mild to moderate impairment. In severe impairment (CrCl < 10 mL/min), consider reducing dose or extending interval, as metabolite accumulation may occur.
* **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in severe hepatic impairment.
## Contraindications
* Known hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Active central nervous system disease.
* Active G.I. bleeding.
* First trimester of pregnancy (relative contraindication, risk vs. benefit).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), central nervous system effects (seizures, encephalopathy, aseptic meningitis), Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, hepatotoxicity, disulfiram-like reaction with alcohol.
* **Hematologic:** Leukopenia, neutropenia (rare).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, dyspnea). Advise patients to avoid alcohol during therapy and for at least 3 days after.
* **Warfarin:** Increased 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.
* **Cyclosporine:** May increase cyclosporine levels.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for signs and symptoms of CNS toxicity.
* Monitor for diarrhea, especially if severe or persistent, which may indicate CDAD.
* Monitor blood counts if prolonged therapy is anticipated.
* Monitor INR if co-administered with warfarin.
* Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* Instruct patients to avoid alcohol during treatment and for at least 72 hours after discontinuation.
* A metallic taste is common and usually resolves after treatment.
* Metronidazole can cause dark urine (reddish-brown).
* For bacterial vaginosis, trichomoniasis, and giardiasis, treatment of sexual partners is recommended.
* IV metronidazole should be infused slowly.
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*Please verify this information with the most current prescribing information and institutional protocols before use.*
