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# Metronidazole
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic and antiprotozoal agent active against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of trichomoniasis.
* **Amebiasis:** Intestinal and extraintestinal 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, CNS infections, lower respiratory tract infections, endocarditis). Often used in combination with other antibiotics.
* **_Clostridioides difficile_ Infection (CDI):** Treatment of CDI, though vancomycin is often preferred for severe disease.
* **Surgical Prophylaxis:** Preoperative prophylaxis, particularly in colorectal surgery.
* **_Helicobacter pylori_ Eradication:** Part of multi-drug regimens.
## Adult Dosing
Dosing varies significantly by indication.
* **Bacterial Vaginosis:**
* Oral: 500 mg orally twice daily for 7 days OR 2 g orally as a single dose.
* Vaginal gel 0.75%: One applicatorful (5 g) intravaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 2 g orally as a single dose OR 250 mg orally three times daily for 7 days OR 375 mg orally twice daily for 7 days.
* **Amebiasis:**
* Oral: 500-750 mg orally three times daily for 5-10 days.
* IV: 500 mg to 1 g IV every 8 hours for 5-10 days.
* **Giardiasis:**
* Oral: 250 mg orally three times daily for 5-7 days.
* **Anaerobic Bacterial Infections:**
* Oral: 500 mg orally every 8 hours.
* IV: 500 mg to 1 g IV every 6-8 hours.
* Duration varies based on infection severity, typically 7-14 days.
* **_Clostridioides difficile_ Infection (CDI):**
* Oral: 500 mg orally three times daily for 10-14 days (generally for non-severe CDI).
* **Surgical Prophylaxis:**
* Oral/IV: 1 g orally or IV 30-60 minutes before surgery, may repeat 8 hours later.
* **_Helicobacter pylori_ Eradication:**
* Oral: Typically 500 mg orally twice daily in combination with other agents (e.g., omeprazole and clarithromycin or amoxicillin) for 10-14 days.
Maximum daily oral dose generally not to exceed 4 g.
## Pediatric Dosing
Dosing is weight-based and depends on the indication. Consult specific pediatric guidelines.
* **Amebiasis:** 35-50 mg/kg/day orally divided into 3 doses for 5-10 days. Maximum 750 mg/dose.
* **Giardiasis:** 15 mg/kg/day orally divided into 3 doses for 5-7 days. Maximum 250 mg/dose.
* **Anaerobic Bacterial Infections:** 7.5-15 mg/kg/dose IV or orally every 6-8 hours. Maximum 4 g/day.
## Dose Adjustments
No dose adjustment is typically necessary for renal impairment. Use with caution in severe hepatic impairment; consider reducing the dose by 50% and monitoring closely.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (though debated for specific indications).
* Concomitant use with disulfiram (within 2 weeks).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, anaphylaxis, dark urine (harmless), vulvovaginal candidiasis.
* **Disulfiram-like reaction:** Severe flushing, vomiting, tachycardia with alcohol. Advise patients to avoid alcohol during therapy and for at least 3 days after completion.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction.
* **Warfarin:** May potentiate anticoagulant effect. Monitor INR closely.
* **Lithium:** May increase lithium levels, leading to toxicity.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
* **Disulfiram:** Risk of psychosis or confusion.
* **Busulfan:** Metronidazole can increase busulfan toxicity.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for signs of hypersensitivity reactions.
* Monitor for efficacy and resolution of infection.
* In patients on warfarin, monitor INR.
* In patients on lithium, monitor lithium levels.
## Clinical Pearls
* Administer IV metronidazole over at least 20-60 minutes to reduce the risk of phlebitis.
* The metallic taste is common and can lead to poor adherence.
* Advise patients to avoid alcohol during treatment and for at least 72 hours after the last dose.
* For _C. difficile_ infection, oral administration is preferred over IV if the patient can tolerate it.
* Ensure adequate hydration.
* Use of metronidazole during breastfeeding is generally considered compatible with breastfeeding, but discuss with patient.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and clinical guidelines for definitive patient management.
