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# Metrogyl (metronidazole)
## Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent. It is bactericidal against most obligate anaerobes and active against several protozoa.
## Primary Indications
* Anaerobic bacterial infections (intra-abdominal, gynecologic, skin/soft tissue, bone/joint, CNS, lower respiratory).
* *Clostridioides difficile* infection (non-severe, though oral vancomycin/fidaxomicin are preferred).
* Protozoal infections: Trichomoniasis, giardiasis, amebiasis.
* Bacterial vaginosis.
## Adult Dosing
* **Anaerobic infections:** 500 mg IV/PO every 8 hours. Maximum: 4 g/day.
* **Trichomoniasis:** 2 g PO as a single dose OR 500 mg PO twice daily for 7 days.
* **Giardiasis:** 250 mg PO three times daily for 5–7 days.
* **Bacterial vaginosis:** 500 mg PO twice daily for 7 days OR 2 g PO single dose.
## Pediatric Dosing
* **Anaerobic infections:** 30 mg/kg/day divided every 6 hours (Max: 4 g/day).
* **Giardiasis:** 15 mg/kg/day divided in 3 doses for 5–7 days.
* **Amebiasis:** 35–50 mg/kg/day divided in 3 doses for 10 days.
## Dose Adjustments
* **Hepatic Impairment:** Reduce dosage by 50% in patients with severe hepatic impairment (Child-Pugh Class C).
* **Renal Impairment:** No standard adjustment required for CrCl >10 mL/min. For ESRD/hemodialysis patients, consider supplemental dosing post-dialysis depending on clinical stability.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (for trichomoniasis).
* Concurrent use of disulfiram within the last 2 weeks.
* Concurrent use of alcohol or propylene glycol-containing products (risk of disulfiram-like reaction).
## Adverse Effects
* **Common:** Metallic taste, nausea, headache, dark-colored urine.
* **Serious:** Peripheral neuropathy (prolonged use), seizures, encephalopathy, aseptic meningitis, leukopenia, QT prolongation.
## Key Drug Interactions
* **Warfarin/Coumarins:** Significantly increases INR (monitor closely).
* **Alcohol:** Causes a disulfiram-like reaction (flushing, tachycardia, nausea, vomiting).
* **Lithium:** May increase lithium levels/toxicity.
* **CYP450 Inducers (e.g., Phenytoin, Phenobarbital):** May decrease metronidazole levels.
## Monitoring
* Baseline and periodic CBC (if prolonged therapy >10 days).
* Neurological status (watch for signs of peripheral neuropathy or ataxia).
* INR/PT if co-administered with warfarin.
* Signs of resolution of infection.
## Clinical Pearls
* **Metallic Taste:** Advise patients this is a common side effect and not necessarily an allergy.
* **Alcohol Avoidance:** Patients must be counseled to avoid alcohol during therapy and for at least 48 hours after the last dose.
* **Administration:** Oral bioavailability is high; IV to oral conversion is generally 1:1.
* **Local Variations:** Dosing for *C. difficile* and common off-label uses may vary by institutional antimicrobial stewardship protocols.
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*Disclaimer: This information is for educational purposes for healthcare professionals. Clinical practice varies; always verify current prescribing information, institutional guidelines, and patient-specific factors before administration.*
