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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 vaginal infections caused by anaerobic bacteria.
* **Trichomoniasis:** Treatment of urogenital tract infections caused by *Trichomonas vaginalis*.
* **Amebiasis:** Treatment of intestinal and extraintestinal amebiasis.
* **Giardiasis:** Treatment of intestinal infections caused by *Giardia lamblia*.
* **Anaerobic Bacterial Infections:** Treatment of intra-abdominal infections, skin and skin structure infections, gynecologic infections, bacteremia, bone and joint infections, CNS infections, and lower respiratory tract infections caused by susceptible anaerobic bacteria.
* **Pseudomembranous Colitis:** Alternative agent for *Clostridioides difficile* infection.
* **Surgical Prophylaxis:** Perioperative prophylaxis, particularly in colorectal surgery.
* **Helicobacter pylori Eradication:** As part of a multi-drug regimen.
## Adult Dosing
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days, or a single 2-gram dose orally.
* **Trichomoniasis:** 2 grams orally as a single dose, or 250 mg orally three times daily for 7 days.
* **Amebiasis:**
* **Intestinal:** 500-750 mg orally three times daily for 7-10 days.
* **Extra-intestinal (e.g., liver abscess):** 500-750 mg orally three times daily for 7-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5 days.
* **Anaerobic Bacterial Infections:** 500 mg IV or orally every 8 hours. Duration varies by infection site and severity.
* **Pseudomembranous Colitis:** 500 mg orally every 8 hours.
* **Surgical Prophylaxis:** 1 gram orally or IV 1-2 hours before surgery, then 500 mg orally or IV every 8 hours for up to 24 hours postoperatively.
* **H. pylori Eradication:** Dosing varies widely within combination regimens. Consult specific guidelines.
## Pediatric Dosing
Dosing is based on weight and indication. Refer to specific pediatric infectious disease guidelines.
* **Amebiasis/Giardiasis:** 35-50 mg/kg/day orally, divided into 3 doses, not to exceed 750 mg/dose, for 7-10 days.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg IV or orally every 8 hours. Maximum adult dose generally not to exceed 4 g/day.
## Dose Adjustments
* **Hepatic Impairment:** Reduced doses may be necessary in severe hepatic impairment. Maximum dose of 1 g/day orally or IV.
* **Renal Impairment:** No dose adjustment generally needed for mild to moderate renal impairment. In severe renal impairment (CrCl < 10 mL/min), consider halving the daily dose after initial loading dose if on chronic hemodialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* First trimester of pregnancy (relative contraindication, risk/benefit assessment needed).
## 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), Stevens-Johnson syndrome, anaphylaxis, pancreatitis, liver dysfunction, thrombophlebitis (with IV administration).
* **Disulfiram-like reaction:** Severe nausea, vomiting, flushing, headache, and palpitations when taken with alcohol. Advise patients to avoid alcohol during and for at least 3 days after therapy.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Lithium:** Increased lithium levels, potentially leading to toxicity.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** May increase cyclosporine levels.
* **Fluorouracil:** Increased toxicity of fluorouracil.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for CNS adverse effects.
* Monitor INR if patient is on warfarin.
* Monitor lithium levels if concomitant use.
* Monitor stool for resolution of *C. difficile* if applicable.
## Clinical Pearls
* The metallic taste is a common side effect and can affect adherence.
* Advise patients to avoid alcohol during and for at least 3 days after treatment due to the disulfiram-like reaction.
* For vaginal infections, both oral and vaginal formulations exist.
* IV formulation can be administered as a bolus or infused over 20-60 minutes.
* Use with caution in patients with active CNS disease.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information or a comprehensive drug reference before making clinical decisions.*
