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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of urogenital trichomoniasis.
* **Amebiasis:** Treatment of intestinal amebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic bacterial infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, central nervous system infections, lower respiratory tract infections, endocarditis). Often used in combination therapy.
* **_Clostridioides difficile_ infection (CDI):** Treatment of mild to moderate CDI.
* **Surgical prophylaxis:** Surgical prophylaxis in specific procedures (e.g., colorectal surgery).
* **_Helicobacter pylori_ eradication:** Part of combination therapy for _H. pylori_ eradication.
## Adult Dosing
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days.
* Vaginal gel 0.75%: One applicatorful (5g) intravaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: Single dose of 2 grams, or 250 mg three times daily for 7 days, or 500 mg twice daily for 7 days.
* **Amebiasis:**
* Intestinal: 500-750 mg orally three times daily for 5-10 days.
* Hepatic abscess: 500-750 mg orally three times daily for 5-10 days, or 500 mg IV every 8 hours.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5 days, or a single dose of 2 grams.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 500 mg every 8 hours. Duration varies based on infection severity and site, typically 7-14 days.
* IV: Loading dose of 15 mg/kg, followed by 7.5 mg/kg every 6-8 hours. Do not exceed 4 grams per day.
* **_C. difficile_ Infection (CDI):**
* Oral: 500 mg three times daily for 10-14 days. *Note: Vancomycin is generally preferred for severe CDI.*
* **Surgical Prophylaxis (Colorectal Surgery):**
* Oral/IV: 500 mg every 8 hours, initiated before surgery and continued for up to 12 hours postoperatively.
* **_H. pylori_ Eradication:**
* Oral: Typically 500 mg twice daily as part of a multi-drug regimen for 10-14 days.
## Pediatric Dosing
* **General Dosing for Anaerobic Infections:**
* Oral/IV: 7.5 mg/kg per dose every 8 hours. Maximum dose: 500 mg per dose or 4 grams per day.
* **Trichomoniasis:** Not recommended for treatment of trichomoniasis in children.
* **Giardiasis:**
* Oral: 15 mg/kg/day in 3 divided doses for 5 days. Maximum 250 mg per dose.
* **Amebiasis:**
* Oral: 35-50 mg/kg/day in 3 divided doses for 5-10 days. Maximum 750 mg per dose.
Dosing for pediatric patients should be guided by specific indications and institutional protocols, as data may be limited for certain conditions.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment is typically needed in renal impairment. However, if the drug is administered with sodium-containing IV fluids, caution is advised due to potential sodium load.
* **Hepatic Impairment:** No dose adjustment is typically needed in mild to moderate hepatic impairment. For severe hepatic impairment, dose reduction may be considered due to reduced metabolism, though specific guidelines are not well-established.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concurrent use with disulfiram or alcohol (within 3 days of last dose) due to disulfiram-like reaction.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), central nervous system effects (seizures, encephalopathy, ataxia, aseptic meningitis), Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, peripheral neuritis.
* **Disulfiram-like reaction:** Flushing, palpitations, nausea, vomiting, shortness of breath when taken with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction. Advise patients to avoid alcohol during and for at least 3 days after treatment.
* **Disulfiram:** Risk of psychosis and confusion. Avoid concurrent use.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase serum lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** May increase cyclosporine levels. Monitor cyclosporine levels.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain) and CNS effects.
* Monitor for signs and symptoms of severe hypersensitivity reactions.
* For _H. pylori_ eradication, monitor for symptom resolution and consider repeat testing per guidelines.
* For _C. difficile_, monitor for improvement in diarrhea and associated symptoms.
* Monitor INR if co-administered with warfarin.
## Clinical Pearls
* Metronidazole has a metallic taste which can affect compliance.
* Urine may turn a reddish-brown color.
* Advise patients to avoid alcohol during and for at least 72 hours after completing therapy to prevent a disulfiram-like reaction.
* For bacterial vaginosis, oral therapy is generally preferred over vaginal gel for complete eradication.
* IV metronidazole is effective for severe anaerobic infections and can be used in patients unable to take oral medications.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines for definitive patient management decisions.*
