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# Metronidazole (Metrogyl)
## Overview
Metronidazole is an antibiotic and antiprotozoal medication effective against anaerobic bacteria and certain parasites.
## Primary Indications
* **Bacterial infections:** Intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, central nervous system infections, lower respiratory tract infections, endocarditis, and C. difficile infection.
* **Protozoal infections:** Trichomoniasis, amebiasis, and giardiasis.
* **Bacterial vaginosis.**
* **H. pylori eradication.**
* **Surgical prophylaxis.**
## Adult Dosing
* **Bacterial infections:** 500 mg intravenously (IV) or orally every 8 hours. Dosing varies by indication and severity; for serious infections, doses may be higher, up to 4000 mg per day divided into doses. Duration of therapy depends on the type and severity of infection.
* **C. difficile infection:** 500 mg orally every 8 hours for 10-14 days.
* **Trichomoniasis:** 2 g orally as a single dose, or 200 mg orally every 8 hours for 7 days.
* **Amebiasis:**
* **Intestinal:** 500-750 mg orally every 8 hours for 7-10 days.
* **Hepatic abscess:** 500-750 mg orally every 8 hours for 5-10 days.
* **Giardiasis:** 250 mg orally every 8 hours for 5-7 days, or 500 mg orally every 12 hours for 3 days.
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days, or a single 2 g dose orally.
* **H. pylori eradication:** Typically part of a combination regimen. Common regimens include 500 mg orally twice daily with other agents for 10-14 days.
* **Surgical prophylaxis:** 500 mg orally or IV 1 hour before surgery, may be repeated every 8 hours postoperatively for up to 24 hours.
## Pediatric Dosing
Dosing in children is based on weight and indication, and specific protocols may vary.
* **Bacterial infections:** 7.5 mg/kg/dose IV or orally every 8 hours. Maximum dose generally 500 mg per dose.
* **C. difficile infection:** 10-20 mg/kg/day orally divided every 8 hours.
* **Intestinal amebiasis:** 35-50 mg/kg/day orally divided every 8 hours for 7-10 days.
* **Giardiasis:** 15 mg/kg/day orally divided every 8 hours for 5-7 days.
## Dose Adjustments
* **Hepatic impairment:** Use with caution and consider reduced doses due to impaired metabolism.
* **Renal impairment:** No dose adjustment generally required for hemodialysis patients if given after dialysis. For other severe renal impairment, some sources suggest caution and potential dose reduction, though data is limited.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use within 14 days of disulfiram therapy.
* Active central nervous system disease.
## Adverse Effects
Common: Nausea, vomiting, diarrhea, metallic taste, stomatitis, headache, dizziness, rash, pruritus.
Serious: Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, leukopenia, pancreatitis, hepatic dysfunction, disulfiram-like reaction with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, palpitations, headache). Advise patients to avoid alcohol during and for at least 3 days after therapy.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Lithium:** May increase lithium levels, potentially leading to toxicity.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
* **Busulfan:** Metronidazole may increase busulfan toxicity.
* **Cyclosporine:** May increase cyclosporine levels.
## Monitoring
* Monitor for signs and symptoms of C. difficile infection recurrence.
* Monitor for neurological adverse effects (numbness, tingling, seizures).
* Monitor for signs of hypersensitivity reactions.
* For prolonged therapy, consider periodic CBCs.
* For H. pylori regimens, monitor for treatment success.
## Clinical Pearls
* A metallic taste is common and usually transient.
* Urine may turn a reddish-brown color.
* Patients should be advised to avoid alcohol during and for 3 days after treatment.
* Topical metronidazole is used for rosacea.
* Metronidazole is a prodrug that is activated by anaerobic organisms.
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*This information is intended for healthcare professionals. Always consult the current prescribing information and relevant clinical guidelines for complete details and to confirm suitability for individual patients.*
