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# Metronidazole (Metrogyl)
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic and antiprotozoal agent.
## Primary Indications
* Treatment of anaerobic bacterial infections (e.g., intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections).
* Treatment of protozoal infections (e.g., trichomoniasis, giardiasis, amebiasis).
* Treatment of *Clostridium difficile* infection (CDI).
* Surgical prophylaxis (colorectal surgery).
* Part of *Helicobacter pylori* eradication regimens.
## Adult Dosing
* **Anaerobic bacterial infections:** 500 mg IV or PO every 8 hours for 7-10 days, or longer depending on the infection. For severe infections, doses up to 1 g IV every 8 hours may be used.
* **Trichomoniasis:** 2 g PO single dose, or 200 mg PO every 12 hours for 7 days, or 400 mg PO every 12 hours for 5 days.
* **Giardiasis:** 250 mg PO three times daily for 5-7 days.
* **Amebiasis (intestinal):** 500-750 mg PO every 8 hours for 5-10 days.
* **Amebiasis (hepatic abscess):** 500-750 mg PO or IV every 8 hours for 5-10 days.
* ***C. difficile* infection:** 500 mg PO every 8 hours for 10-14 days. (Note: Oral vancomycin is generally preferred for severe or refractory CDI).
* **Surgical prophylaxis (colorectal):** 500 mg IV 30-60 minutes before surgery, often combined with a cephalosporin.
## Pediatric Dosing
Dosing varies significantly by indication and patient weight. Consult pediatric-specific guidelines.
* **Anaerobic bacterial infections:** 7.5 mg/kg/dose IV or PO every 8 hours. Maximum dose: 500 mg per dose.
* **Trichomoniasis:** Not typically used in children.
* **Giardiasis:** 5 mg/kg/dose PO three times daily for 5-7 days. Maximum dose: 250 mg per dose.
* **Amebiasis:** 10-20 mg/kg/dose PO or IV every 8 hours for 5-10 days. Maximum dose: 750 mg per dose.
## Dose Adjustments
* **Renal impairment:** No dose adjustment typically needed for mild to moderate impairment. In severe renal impairment (CrCl < 10 mL/min), consider halving the usual dose or extending the dosing interval.
* **Hepatic impairment:** No specific dose adjustments are universally recommended, but caution is advised. Monitor for adverse effects.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* Concurrent use of disulfiram or alcohol due to potential disulfiram-like reaction.
## Adverse Effects
Common: Nausea, vomiting, metallic taste, diarrhea, headache, dizziness.
Serious: Seizures, peripheral neuropathy (especially with prolonged use), Stevens-Johnson syndrome, anaphylaxis, pancreatitis, hepatotoxicity. A disulfiram-like reaction may occur with alcohol ingestion.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, headache). Advise patients to avoid alcohol during therapy and for at least 3 days after completion.
* **Disulfiram:** Concomitant use is contraindicated due to potential for psychosis or confusional state.
* **Warfarin:** Metronidazole can potentiate the anticoagulant effect of warfarin. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase lithium levels. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole efficacy.
* **5-Fluorouracil (5-FU):** Metronidazole may increase the toxicity of 5-FU.
## Monitoring
* Monitor for signs and symptoms of infection resolution.
* Monitor for signs of neurological toxicity (peripheral neuropathy, dizziness, seizures), especially with prolonged or high-dose therapy.
* Monitor INR if co-administered with warfarin.
* Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* Metronidazole has activity against anaerobic bacteria and protozoa.
* A metallic taste is a common and expected side effect.
* Advise patients to avoid alcohol during treatment and for at least 72 hours after the last dose due to the potential for a disulfiram-like reaction.
* IV administration should be followed by oral therapy when clinically appropriate.
* For *H. pylori* eradication, metronidazole is typically part of a multi-drug regimen and specific dosing depends on the chosen regimen.
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This information is intended for healthcare professionals. Always consult the most current prescribing information and consider individual patient factors before making therapeutic decisions.
