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## Metronidazole (Metrogyl)
### Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
### Primary Indications
* Treatment of **anaerobic bacterial infections**: intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, CNS infections, lower respiratory tract infections, and endocarditis.
* Treatment of **protozoal infections**: trichomoniasis, amebiasis, and giardiasis.
* Treatment of **_Clostridioides difficile_ associated diarrhea**.
* **Surgical prophylaxis** in specific procedures (e.g., colorectal surgery).
### Adult Dosing
Dosing is highly dependent on the indication and severity of infection. Typical doses range from **250 mg to 500 mg every 6 to 12 hours orally or intravenously**.
* For **trichomoniasis**: 2 grams as a single dose or 200 mg three times daily for 7 days.
* For **amebiasis**: 500-750 mg three times daily for 5-10 days.
* For **giardiasis**: 250 mg three times daily for 5-7 days or 500 mg twice daily for 3 days.
* For **_C. difficile_**: 500 mg every 8 hours orally for 10-14 days.
* Maximum dose generally **4 grams per day**.
### Pediatric Dosing
Dosing in children is typically based on weight and indication.
* For **anaerobic infections**: **15-30 mg/kg/day orally or IV, divided into 3 doses**, not to exceed adult maximum.
* For **trichomoniasis**: **5 mg/kg/day orally, divided into 3 doses**, for 7 days.
* For **amebiasis**: **35-50 mg/kg/day orally or IV, divided into 3 doses**, for 5-10 days.
* For **giardiasis**: **15-25 mg/kg/day orally, divided into 3 doses**, for 5-7 days.
* Consult specific pediatric guidelines for precise dosing.
### Dose Adjustments
No dose adjustment is generally required for renal impairment.
For **hepatic impairment**, reduce the dose by one-third to one-half, as metronidazole is primarily metabolized in the liver.
### Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use during the first trimester of pregnancy is generally avoided unless absolutely necessary.
### Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness.
Serious: Peripheral neuropathy, seizures, Stevens-Johnson syndrome, encephalopathy, leukopenia, pancreatitis, disulfiram-like reaction with alcohol.
### Key Drug Interactions
* **Alcohol**: Disulfiram-like reaction (severe nausea, vomiting, flushing, tachycardia, palpitations). Avoid alcohol during and for at least 72 hours after treatment.
* **Warfarin**: Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium**: Increased lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital**: May decrease metronidazole levels.
* **Cyclosporine**: May increase cyclosporine levels.
### Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for CNS effects (seizures, dizziness).
* Monitor for gastrointestinal side effects.
* Monitor INR if patient is on warfarin.
* Monitor lithium levels if patient is on lithium.
### Clinical Pearls
* Metronidazole has a strong metallic taste which can affect patient compliance.
* Alcohol should be strictly avoided during therapy and for 72 hours after discontinuation.
* Long-term or high-dose therapy may increase the risk of peripheral neuropathy.
* May discolor urine a dark or reddish-brown color.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information or a reliable drug reference for complete details, including specific indications, dosing nuances, and safety warnings, before making any clinical decisions.*
