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# Metronidazole (Metrogyl)
## Overview
Metronidazole is a nitroimidazole antibiotic effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Anaerobic 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.
* **Protozoal infections:** Trichomoniasis, giardiasis, amebiasis.
* **_Clostridium difficile_ infection (CDI):** Alternative to vancomycin for initial episodes.
* **_Helicobacter pylori_ eradication:** Part of multi-drug regimens.
* **Bacterial vaginosis.**
* **Surgical prophylaxis:** Particularly for colorectal surgery.
## Adult Dosing
Dosing varies significantly by indication. General ranges include:
* **Anaerobic infections:** 500 mg IV or PO every 8 hours. Typical duration is 7-10 days. Higher doses may be used for severe infections (e.g., CNS).
* **Bacterial vaginosis:** 500 mg PO BID for 7 days, or 2 g PO single dose.
* **Trichomoniasis:** 2 g PO single dose, or 250 mg PO TID for 7 days.
* **Giardiasis:** 250 mg PO TID for 5-7 days.
* **Amebiasis:** 500-750 mg PO TID for 7-10 days (intestinal amebiasis) or 750 mg PO TID for 5-10 days (extraintestinal amebiasis).
* **CDI:** 500 mg PO TID for 10-14 days (often reserved for non-severe initial episodes or as an alternative).
* **_H. pylori_ eradication:** Typically 250-500 mg PO BID or TID as part of a multi-drug regimen.
* **Surgical prophylaxis:** 1 g IV 1-2 hours before surgery, or 500 mg PO/IV every 8 hours for 24 hours.
## Pediatric Dosing
Dosing is weight-based and varies by indication.
* **Anaerobic infections:** 7.5 mg/kg/dose IV or PO every 8 hours. Maximum dose usually 500 mg/dose or 40 mg/kg/day.
* **Babesiosis:** 5 mg/kg/dose IV every 8 hours for 7 days (often combined with quinine).
* **Giardiasis:** 5 mg/kg/dose PO TID for 5-7 days. Maximum 250 mg/dose.
* **Intestinal amebiasis:** 35-50 mg/kg/day PO divided TID for 10 days. Maximum 750 mg/dose.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution. Reduce dose by 50% in severe hepatic disease.
* **Renal Impairment:** Dose adjustment is generally not required for standard doses. However, for doses exceeding 1 g or in patients on hemodialysis, consult specific guidelines as metronidazole can be removed by dialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* First trimester of pregnancy (relative contraindication for trichomoniasis, use may be considered for other indications if benefits outweigh risks).
* Concurrent use of disulfiram or alcohol (within 3 days of last dose) due to disulfiram-like reaction.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, Stevens-Johnson syndrome, erythema multiforme, neutropenia, pancreatitis, darkening of urine.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, tachycardia, nausea, vomiting). Avoid alcohol during treatment and for at least 3 days after discontinuation.
* **Warfarin:** May increase INR. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase serum lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole efficacy.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels. Monitor cyclosporine levels.
* **Disulfiram:** Concomitant use is contraindicated due to potential for psychotic reactions.
## Monitoring
* **Clinical response:** Assess for improvement in signs and symptoms of infection.
* **Renal and hepatic function:** Especially in patients with pre-existing impairment or receiving prolonged therapy.
* **Neurologic status:** Monitor for signs of neuropathy or central nervous system effects.
* **INR:** If co-administered with warfarin.
* **Lithium levels:** If co-administered with lithium.
## Clinical Pearls
* A metallic taste is a common side effect and can impact compliance.
* Advise patients to avoid alcohol during and for 3 days after therapy.
* Peripheral neuropathy is a risk, particularly with prolonged or high-dose therapy. Discontinue if symptoms occur.
* Oral metronidazole has good absorption and can be used interchangeably with IV therapy unless parenteral route is specifically indicated.
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*This information is intended for healthcare professionals. Always verify current prescribing information with the official product labeling or a reliable drug information resource.*
