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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.
* **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).
* **Pseudomembranous Colitis:** Treatment of *Clostridioides difficile*-associated diarrhea (alternative agent).
* **Surgical Prophylaxis:** Prophylaxis against anaerobic infection in specific surgical procedures (e.g., colorectal surgery).
## Adult Dosing
* **Bacterial Vaginosis:** Oral: 500 mg twice daily for 7 days, or 2 g as a single dose. Vaginal gel: 0.75% applied intravaginally once daily for 5 days.
* **Trichomoniasis:** Oral: 2 g as a single dose, or 250 mg three times daily for 7 days, or 500 mg twice daily for 7 days.
* **Amebiasis:** Oral: 500-750 mg three times daily for 7-10 days.
* **Giardiasis:** Oral: 250 mg three times daily for 5 days, or 2 g as a single dose.
* **Anaerobic Bacterial Infections:** Oral/IV: 500 mg every 8 hours. Severe infections may require higher doses, up to 1 g every 8 hours. Duration is variable, typically 7-10 days or longer.
* **Pseudomembranous Colitis:** Oral: 250-500 mg every 6-8 hours. Dosing may vary based on local protocols and severity.
* **Surgical Prophylaxis:** Oral/IV: 1 g as a single dose or 500 mg every 8 hours starting prior to surgery.
## Pediatric Dosing
Dosing in pediatrics is highly variable and depends on indication, weight, and severity. Consult specific pediatric guidelines or infectious disease recommendations. Generally:
* **Trichomoniasis/Giardiasis:** Oral: 15 mg/kg/day divided into 3 doses for 7 days (max 250 mg/dose).
* **Amebiasis:** Oral: 35-50 mg/kg/day divided into 3 doses for 7-10 days.
* **Anaerobic Bacterial Infections:** Oral/IV: 30 mg/kg/day divided into 3 doses, maximum 2 g/day.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution and consider reduced doses in severe hepatic impairment due to potential accumulation.
* **Renal Impairment:** No dose adjustment necessary for mild to moderate renal impairment. Consider reduced frequency or dose in severe renal impairment or patients on hemodialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concurrent use of disulfiram (within 2 weeks).
* Concurrent use of alcohol.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, Stevens-Johnson syndrome, toxic epidermal necrolysis, encephalopathy, optic neuropathy.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, palpitations). Avoid alcohol during treatment and for at least 3 days after.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase serum lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole effectiveness.
* **Disulfiram:** Concurrent use can lead to psychotic reactions.
## Monitoring
* Clinical signs and symptoms of infection.
* For prolonged use: Neurological status, signs of peripheral neuropathy (numbness, tingling).
* For patients on warfarin: INR.
* For patients on lithium: Lithium levels.
## Clinical Pearls
* Administer oral metronidazole with food to minimize gastrointestinal upset.
* Intravenous metronidazole is a common component of regimens for intra-abdominal infections and other serious anaerobic infections.
* A metallic taste is a common and expected side effect.
* Patients should be advised to avoid alcohol during therapy and for at least 3 days after completion.
* The clinical efficacy of metronidazole for treatment of asymptomatic *Chlamydia trachomatis* is not established.
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*Disclaimer: This information is intended for clinical decision support and does not replace professional medical judgment or official prescribing information. Always consult the most current product monograph or relevant clinical guidelines for complete and up-to-date information before initiating or modifying therapy.*
