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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal medication effective against anaerobic bacteria and certain parasites.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of trichomoniasis.
* **Giardiasis:** Treatment of giardiasis.
* **Amebiasis:** Treatment of amebiasis.
* **Anaerobic Bacterial Infections:** Treatment of various infections caused by susceptible anaerobic bacteria, including intra-abdominal infections, skin and soft tissue infections, gynecologic infections, and central nervous system infections.
* **_Clostridioides difficile_ Infection (CDI):** Historically used for CDI, but vancomycin is now preferred for initial episodes, especially severe ones.
## Adult Dosing
* **Bacterial Vaginosis:**
* 500 mg orally twice daily for 7 days.
* Or, a single 2-gram dose orally.
* **Trichomoniasis:**
* 2 grams orally as a single dose.
* Or, 250 mg orally twice daily for 7 days.
* Or, 375 mg orally twice daily for 7 days.
* **Giardiasis:**
* 250 mg orally three times daily for 5-7 days.
* **Amebiasis:**
* **Intestinal amebiasis:** 500-750 mg orally three times daily for 5-10 days.
* **Hepatic amebiasis:** 500-750 mg orally three times daily for 5-10 days (may require a follow-up course of a luminal amebicide).
* **Anaerobic Bacterial Infections:**
* 500 mg to 1 gram intravenously or orally every 6-8 hours. Duration varies based on infection severity and patient response.
* Maximum dose generally 4 grams per day.
* **_Clostridioides difficile_ Infection (CDI):**
* 500 mg orally three times daily for 10-14 days (less preferred option).
## Pediatric Dosing
Dosing for children depends on the indication and weight. Consult specific pediatric guidelines or drug compendia.
* **Trichomoniasis, Giardiasis, Amebiasis:** Doses vary, often calculated per kg. For example, for Giardiasis, a common regimen is 15 mg/kg/day divided into 3 doses for 5-7 days, with a maximum of 250 mg per dose.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose intravenously or orally every 8 hours.
* **Neonates:** Dosing requires careful consideration due to immature hepatic function; doses are typically lower and given less frequently.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution and consider reduced doses in severe hepatic insufficiency.
* **Renal Impairment:** No specific dose adjustment is usually needed for hemodialysis or peritoneal dialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use in the first trimester of pregnancy for trichomoniasis (though benefits may outweigh risks in some cases).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, anaphylaxis, dark urine, pancreatitis.
* **Disulfiram-like reaction:** Severe nausea, vomiting, flushing, and palpitations with concurrent alcohol ingestion. Advise patients to avoid alcohol during treatment and for at least 3 days after.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Lithium:** Increased lithium levels and potential toxicity.
* **Phenytoin, Phenobarbital:** Metronidazole may decrease phenytoin/phenobarbital levels.
* **Cyclosporine:** Increased cyclosporine levels.
* **5-Fluorouracil:** Increased toxicity of 5-FU.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for signs of central nervous system toxicity (seizures, encephalopathy).
* Monitor for therapeutic response and signs of infection.
* Monitor INR if co-administered with warfarin.
## Clinical Pearls
* Advise patients to avoid alcohol during treatment and for at least 72 hours after the last dose due to the disulfiram-like reaction.
* The metallic taste is common and often bothersome; patients should be counseled about this.
* For topical preparations (e.g., for rosacea), systemic absorption is minimal, and systemic side effects are rare.
* Ensure appropriate duration of therapy for all indications.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols before administering any medication.*
