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# Metrogyl (metronidazole)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* Treatment of anaerobic bacterial infections (e.g., intra-abdominal infections, pelvic inflammatory disease, bacterial vaginosis, *C. difficile* infection).
* Treatment of protozoal infections (e.g., trichomoniasis, giardiasis, amebiasis).
* Surgical prophylaxis.
## Adult Dosing
Dosing varies significantly based on indication. Common regimens include:
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days, or a single 2-gram dose orally.
* ***C. difficile* infection:** 500 mg orally every 8 hours for 10-14 days.
* **Trichomoniasis:** 2 gram single dose orally, or 250 mg orally three times daily for 7 days, or 500 mg orally twice daily for 7 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days, or a single 2-gram dose orally.
* **Amebiasis:** 500-750 mg orally every 8 hours for 7-10 days.
* **Surgical prophylaxis:** 500 mg orally or IV 1 hour before surgery, may be repeated intraoperatively if procedure >12 hours.
Maximum oral dose is generally 4 grams per day.
## Pediatric Dosing
Dosing is weight-based and indication-specific.
* **Anaerobic infections:** 15-30 mg/kg/day orally or IV, divided into 3 doses. Maximum dose: 4 grams/day.
* **Trichomoniasis:** 5 mg/kg/day orally, divided into 3 doses for 7 days. Maximum dose: 250 mg/day.
* **Giardiasis:** 5 mg/kg/day orally, divided into 3 doses for 5-7 days. Maximum dose: 250 mg/day.
## Dose Adjustments
No dose adjustment is typically needed for renal impairment. In severe hepatic impairment, dose reduction may be considered due to impaired metabolism.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (relative contraindication for non-emergent use).
## Adverse Effects
Common: Nausea, vomiting, metallic taste, diarrhea, abdominal pain, headache, dizziness.
Serious: Peripheral neuropathy (especially with prolonged use), seizures, Stevens-Johnson syndrome, encephalopathy, pancreatitis, darkening of urine.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (severe nausea, vomiting, flushing, headache). Advise patients to 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:** Can increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
## Monitoring
* Monitor for signs and symptoms of infection resolution.
* Monitor for adverse effects, particularly peripheral neuropathy (numbness, tingling) and central nervous system effects.
* For patients on warfarin, monitor INR.
## Clinical Pearls
* Metronidazole has a bitter taste; oral formulations may be given with food to minimize GI upset.
* Advise patients to avoid alcohol during therapy.
* Neuropathy can be irreversible; discontinue if symptoms occur.
* Used in combination therapy for *H. pylori* eradication and as adjunctive therapy for inflammatory bowel disease.
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Please verify this information with the most current prescribing information or other reliable resources before clinical use.
