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# Metrogyl (Metronidazole)
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of symptomatic trichomoniasis.
* **Amebiasis:** Treatment of intestinal amebiasis (amebic dysentery) and amebic liver abscess.
* **Giardiasis:** Treatment of symptomatic 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, central nervous system infections, lower respiratory tract infections, endocarditis, C. difficile infection).
## Adult Dosing
Dosing varies significantly by indication.
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days OR 2 g as a single dose.
* Vaginal gel 0.75%: Insert one applicatorful (37.5 mg) vaginally once daily for 5 days.
* **Trichomoniasis:** 2 g as a single oral dose OR 250 mg orally three times daily for 7 days OR 375 mg orally twice daily for 7 days. Repeat therapy may be required.
* **Amebiasis:**
* Intestinal: 500-750 mg orally three times daily for 5-10 days.
* Liver Abscess: 500-750 mg orally three times daily for 5-10 days, often followed by a luminal agent.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days OR 2 g once daily for 3 days.
* **Anaerobic Bacterial Infections:** 500 mg orally or IV every 8 hours. Duration varies (typically 7-14 days). For severe infections, doses up to 1 g every 12 hours are used.
* **C. difficile Infection:** 500 mg orally three times daily for 10-14 days.
## Pediatric Dosing
Dosing is typically based on weight and indication.
* **Trichomoniasis/Giardiasis:** 15 mg/kg/day orally in 3 divided doses, not to exceed 250 mg per dose, for 7-10 days. Maximum dose not well-established for repeated courses.
* **Bacterial Infections (Anaerobic):** 7.5 mg/kg/dose orally or IV every 8 hours OR 15 mg/kg/dose every 12 hours. Maximum dose often cited as 4 g/day.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution in severe hepatic impairment. May require dose reduction. Consider specific protocols.
* **Renal Impairment:** No dose adjustment is generally recommended for hemodialysis or peritoneal dialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* Use in the first trimester of pregnancy for trichomoniasis (risk vs. benefit assessment needed).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, anorexia, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, hepatotoxicity, dark urine.
* **Alcohol Interaction:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, headache) with concurrent alcohol use. Advise patients to avoid alcohol during treatment and for at least 3 days after.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Lithium:** May increase lithium levels, potentially leading to toxicity.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** May increase cyclosporine levels.
* **5-Fluorouracil (5-FU):** Metronidazole may increase the toxicity of 5-FU.
## Monitoring
* **Clinical Response:** Assess for improvement in signs and symptoms of infection.
* **Neurological Status:** Monitor for signs of peripheral neuropathy or central nervous system effects.
* **Renal Function:** Especially if given IV in high doses or in patients with existing renal compromise.
* **Hepatic Function:** Particularly in patients with liver disease or those receiving long-term therapy.
* **INR:** If co-administered with warfarin.
## Clinical Pearls
* The metallic taste is common and can be a sign of therapeutic effect or toxicity.
* Advise patients to avoid alcohol during therapy and for at least 72 hours after discontinuation due to the disulfiram-like reaction.
* Long-term or high-dose use increases the risk of peripheral neuropathy.
* Can cause a dark or reddish-brown urine.
* For vaginal administration, systemic absorption does occur and potential drug interactions should still be considered.
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*Disclaimer: This information is intended for clinical use and is not a substitute for professional medical advice. Always consult the current official prescribing information and relevant clinical guidelines before making any treatment decisions.*
