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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal medication effective against anaerobic bacteria and certain parasites.
## Primary Indications
* **Bacterial infections:** Intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis, and *Clostridioides difficile*-associated diarrhea (CDAD).
* **Protozoal infections:** Trichomoniasis, amebiasis, and giardiasis.
* **Other:** As part of multidrug regimens for *Helicobacter pylori* eradication.
## Adult Dosing
Dosing varies significantly by indication. Common adult doses include:
* **Bacterial Vaginosis:** 500 mg orally BID for 7 days or 1 g orally once.
* **Trichomoniasis:** 2 g orally once or 250 mg orally TID for 7 days.
* **Amebiasis:** 500-750 mg orally TID for 7-10 days.
* **Giardiasis:** 250 mg orally TID for 5 days.
* **CDAD:** 500 mg orally TID or QID for 10-14 days.
* **Anaerobic bacterial infections (general):** 500 mg IV or orally every 8 hours. Typical duration is 7-14 days.
* ***H. pylori* eradication:** Typically 500 mg orally BID in combination with other agents for 10-14 days.
Maximum oral dose: Generally 4 g per day.
## Pediatric Dosing
Dosing is weight-based and varies by indication.
* **Amebiasis:** 35-50 mg/kg/day orally divided TID, not to exceed 750 mg/dose, for 7-10 days.
* **Giardiasis:** 15 mg/kg/day orally divided TID, not to exceed 250 mg/dose, for 5 days.
* **Anaerobic bacterial infections:** 7.5 mg/kg/dose IV or orally every 8 hours. Maximum dose is typically 500 mg per dose.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment necessary for hemodialysis or peritoneal dialysis.
* **Hepatic Impairment:** Consider reducing dose or extending interval in severe hepatic impairment due to potential accumulation.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use in the first trimester of pregnancy for trichomoniasis.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, Stevens-Johnson syndrome, encephalopathy, pancreatitis, dark urine.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (severe nausea, vomiting, flushing, headache, tachycardia). Advise patients to avoid alcohol during and for at least 3 days after treatment.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Potential for increased lithium levels and toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** Metronidazole may be less effective.
* **Cyclosporine:** Increased cyclosporine levels. Monitor cyclosporine levels.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for efficacy and adverse effects.
* Monitor INR if co-administered with warfarin.
* Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* Metronidazole has activity against many common anaerobic bacteria and protozoa.
* The metallic taste is a common and often bothersome side effect.
* Patients should be advised to avoid alcohol during treatment and for at least 72 hours after the last dose due to the risk of a disulfiram-like reaction.
* Prolonged use is associated with peripheral neuropathy.
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*This information is intended for healthcare professionals and does not substitute for professional clinical judgment. Always consult current prescribing information and relevant guidelines for complete and up-to-date details.*
