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# Metrogyl (metronidazole)
## Overview
Metronidazole is a nitroimidazole antibiotic effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of symptomatic trichomoniasis.
* **Amebiasis:** Treatment of amebiasis, including amebic dysentery and amebic liver abscess.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis). Often used in combination therapy.
* **C. difficile Infection (CDI):** Treatment of *Clostridioides difficile*-associated diarrhea. (Note: Oral vancomycin or fidaxomicin are preferred agents for initial CDI treatment).
## Adult Dosing
Dosing varies significantly by indication.
* **Bacterial Vaginosis:**
* Oral: 500 mg orally twice daily for 7 days, OR 2 g orally as a single dose.
* Vaginal gel 0.75%: One full applicator (5 g) inserted vaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 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.
* Hepatic 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.
* **Anaerobic Bacterial Infections:** Typically 500 mg IV or orally every 8 hours. Duration depends on severity and site of infection, often 7-14 days. May be dosed higher (up to 1 g every 8 hours) for severe infections.
* **C. difficile Infection:** 500 mg orally three times daily for 10-14 days. (Not preferred first-line therapy).
## Pediatric Dosing
Dosing is weight-based and varies by indication. Consult specific pediatric guidelines.
* **Trichomoniasis/Giardiasis:** 15 mg/kg orally once daily for 2-3 days, OR 5 mg/kg orally every 8 hours for 7-10 days. Maximum dose: 250 mg per dose for trichomoniasis or 40 mg/kg/day for giardiasis.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg IV or orally every 8 hours. For severe infections, may increase to 15 mg/kg every 8 hours. Maximum dose: 4 g/day.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally needed for hemodialysis or peritoneal dialysis. For severe renal impairment (CrCl < 10 mL/min), some sources recommend reducing the maintenance dose by 50% or extending the dosing interval, though this is not universally agreed upon.
* **Hepatic Impairment:** Use with caution. May require dose reduction in severe hepatic impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* Use in the first trimester of pregnancy for trichomoniasis (although risk is low, alternatives are preferred). May be used in later pregnancy or breastfeeding if clearly indicated.
## 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, leukopenia, thrombocytopenia, pancreatitis, hepatotoxicity, disulfiram-like reaction with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache, palpitations). Advise patients to avoid alcohol during therapy and for at least 72 hours after completion.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole efficacy.
* **5-Fluorouracil (5-FU):** May increase toxicity of 5-FU.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for signs of CNS effects (dizziness, confusion, seizures).
* Monitor complete blood count (CBC) if treatment is prolonged or in patients with a history of blood dyscrasias.
* Monitor INR if patient is on warfarin.
* Monitor lithium levels if patient is on lithium.
## Clinical Pearls
* The metallic taste is common and can be bothersome.
* Advise patients to avoid alcohol during treatment and for 72 hours after.
* Oral metronidazole can be taken with or without food.
* For vaginal gel, ensure proper insertion technique.
* Be aware of the potential for cross-reactivity with other nitroimidazoles.
* Prolonged use may increase the risk of peripheral neuropathy.
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*This information is intended for healthcare professionals. Please consult the current prescribing information for complete details and to ensure accuracy before use.*
