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# Metrogyl (metronidazole)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent.
## Primary Indications
* **Anaerobic bacterial infections:** Intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis, septicemia.
* **Protozoal infections:** Trichomoniasis, amebiasis, giardiasis.
* **Other:** Bacterial vaginosis, *Clostridioides difficile* infection (adjunctive therapy).
## Adult Dosing
Dosing is highly variable depending on the indication and site of infection. Consult specific guidelines or institutional protocols.
* **Bacterial infections:** Typical intravenous doses range from 500 mg every 8 hours to 1 g every 12 hours. Oral doses are often similar.
* **Trichomoniasis:** 2 g 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. Invasive: 500-750 mg orally or IV every 8 hours for 7-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days or 500 mg orally once daily for 5 days.
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days.
* ***Clostridioides difficile* infection:** 500 mg orally three times daily for 10-14 days (often used for recurrent or severe non-`C. diff toxin` positive C. diff).
**Maximum cumulative dose:** Not universally established, but prolonged high-dose therapy requires careful risk-benefit assessment.
## Pediatric Dosing
Dosing is based on weight and indication. Consult specific pediatric guidelines.
* **Anaerobic bacterial infections:** 15-30 mg/kg/day (divided every 8 hours), not to exceed 1500 mg/day.
* **Trichomoniasis:** Not established in children.
* **Amebiasis:**
* Intestinal: 35-50 mg/kg/day (divided every 8 hours) for 7-10 days, not to exceed 750 mg/dose.
* Abscess: 50 mg/kg/day (divided every 8 hours), not to exceed 1.5 g/day.
* **Giardiasis:** 15 mg/kg/day (divided every 8 hours) for 5-7 days, not to exceed 250 mg/day.
## Dose Adjustments
* **Hepatic Impairment:** Reduce dose by 50% in severe hepatic disease. Caution in moderate impairment.
* **Renal Impairment:** No specific dose adjustment typically required for intermittent hemodialysis or peritoneal dialysis. May consider dose reduction or increased frequency with continuous renal replacement therapy (CRRT), consult guidelines.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (relative contraindication due to theoretical risks; risk-benefit assessment warranted, especially for non-emergent indications).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, hepatotoxicity, neutropenia, darkened urine.
* **Disulfiram-like reaction:** Nausea, vomiting, flushing, palpitations, chest pain, headache when taken with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction. Advise avoidance during and for at least 3 days after treatment.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenobarbital, Phenytoin, Carbamazepine:** May decrease metronidazole levels.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels.
## Monitoring
* **Clinical signs and symptoms of infection.**
* **Renal and hepatic function (especially with prolonged therapy or severe impairment).**
* **Neurological status (especially with prolonged therapy).**
* **INR (if on warfarin).**
* **Lithium levels (if on lithium).**
## Clinical Pearls
* Administer intravenous metronidazole over 30-60 minutes to reduce risk of phlebitis.
* Avoid alcohol consumption during and for at least 72 hours after completing therapy.
* Peripheral neuropathy is a risk, especially with long-term use; patients should report numbness or tingling.
* The metallic taste is common but usually resolves after treatment.
* For *C. difficile* infection, consider vancomycin or fidaxomicin as first-line agents per current guidelines.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and institutional protocols before making clinical decisions.
