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# Metronidazole
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Anaerobic bacterial infections:** Intra-abdominal infections, skin and soft tissue infections, gynecological infections, bone and joint infections, central nervous system infections, lower respiratory tract infections, endocarditis, and septicemia.
* **Protozoal infections:** Trichomoniasis, amebiasis, and giardiasis.
* **Bacterial vaginosis.**
* **_Clostridioides difficile_ associated diarrhea.**
* **Surgical prophylaxis:** Particularly in colorectal surgery.
* **_Helicobacter pylori_ eradication** (in combination regimens).
## Adult Dosing
* **Anaerobic bacterial infections:** Typically 500 mg IV or PO every 8 hours. Duration varies based on infection severity and site, often 7-14 days. For severe infections, doses up to 1 gram IV every 8 hours may be used.
* **Bacterial vaginosis:** 500 mg PO BID for 7 days or 2 grams PO single dose.
* **Trichomoniasis:** 2 grams PO single dose or 250 mg PO TID for 7 days.
* **Amebiasis:**
* **Invasive intestinal amebiasis:** 500-750 mg PO TID for 5-10 days.
* **Amebic liver abscess:** 500-750 mg PO TID for 5-10 days.
* **Giardiasis:** 250 mg PO TID for 5-7 days or 2 grams PO once daily for 3 days.
* **_C. difficile_ associated diarrhea:** 500 mg PO TID for 10-14 days (IV if PO not tolerated).
* **_H. pylori_ eradication:** Typically 500 mg PO BID in combination with other agents for 10-14 days.
* **Surgical prophylaxis:** 500 mg IV 1 hour preoperatively.
## Pediatric Dosing
* **Anaerobic bacterial infections:** 15 mg/kg/day IV or PO divided every 8 hours, not to exceed 400 mg per dose. Maintenance: 7.5-10 mg/kg/dose IV or PO every 8 hours. Duration varies.
* **Bacterial vaginosis:** Not typically recommended in this age group without specific indication and expert consultation.
* **Trichomoniasis:** Not approved for use in children.
* **Amebiasis:** 35-50 mg/kg/day PO divided every 8 hours for 5-10 days.
* **Giardiasis:** 15 mg/kg/day PO divided every 8 hours for 5-7 days.
* **_C. difficile_ associated diarrhea:** 10-20 mg/kg/day PO divided TID for 10-14 days.
## Dose Adjustments
* **Hepatic impairment:** Use with caution. Reduce total daily dose by 30-50% in severe hepatic disease.
* **Renal impairment:** No dose adjustment typically needed for moderate renal impairment. For severe renal impairment (CrCl < 10 mL/min), consider reducing the maintenance dose by 50% if not on hemodialysis. If on hemodialysis, a supplemental dose may be needed after dialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Active central nervous system disease.
* Use within 14 days of disulfiram.
* Concomitant use with alcohol (disulfiram-like reaction).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, leukopenia, thrombophlebitis (with IV administration), Stevens-Johnson syndrome, anaphylaxis.
* **Disulfiram-like reaction** with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, dyspnea). Avoid alcohol during and for at least 3 days after treatment.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole can increase serum lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole efficacy.
* **Disulfiram:** Concomitant use can lead to psychosis and confusion. Avoid within 14 days of disulfiram.
## Monitoring
* **Signs and symptoms of infection:** Clinical response.
* **Renal and hepatic function:** Especially in patients with pre-existing impairment or those receiving high doses.
* **Neurological status:** Monitor for signs of peripheral neuropathy or CNS effects.
* **Prothrombin time/INR:** If used concurrently with warfarin.
* **Lithium levels:** If used concurrently with lithium.
## Clinical Pearls
* Metronidazole has a metallic taste, which can be a significant side effect for some patients.
* IV metronidazole can be a significant irritant; ensure adequate venous access and consider dilution.
* Patients should be advised to avoid alcohol during and for at least 72 hours after completing metronidazole therapy due to the potential for a disulfiram-like reaction.
* The risk of peripheral neuropathy increases with duration and dose of therapy.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional guidelines before making clinical decisions.*
