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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 *Trichomonas vaginalis* infection.
* **Giardiasis:** Treatment of *Giardia lamblia* infection.
* **Amebiasis:** Treatment of amebiasis (intestinal and extraintestinal).
* **Anaerobic Bacterial Infections:** Treatment of serious infections caused by susceptible anaerobic bacteria, such as intra-abdominal infections, skin and soft tissue infections, gynecological infections, bone and joint infections, central nervous system infections, lower respiratory tract infections, and endocarditis. Often used in combination with other antibiotics.
* ** *Clostridioides difficile* Infection (CDI):** Treatment of CDI.
* **Surgical Prophylaxis:** Preoperative prophylaxis in specific surgical procedures (e.g., colorectal surgery).
* **Rosacea:** Topical treatment for inflammatory lesions of rosacea.
## Adult Dosing
Dosing varies significantly by indication.
* **Bacterial Vaginosis:**
* Vaginal gel 0.75%: One application (5g gel containing 37.5 mg metronidazole) intravaginally once daily for 5 days.
* Oral: 500 mg orally twice daily for 7 days.
* **Trichomoniasis:**
* Oral: Single dose of 2 grams orally, or 250 mg orally three times daily for 7 days, or 500 mg orally twice daily for 7 days.
* **Giardiasis:**
* Oral: 250 mg orally three times daily for 5 days.
* **Amebiasis:**
* *Intestinal:* 500-750 mg orally three times daily for 5-10 days.
* *Extra-intestinal (e.g., liver abscess):* 500-750 mg orally three times daily for 5-10 days.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 500 mg every 8 hours. Duration varies based on severity and site of infection.
* IV: Higher doses may be used for severe infections, up to 15 mg/kg loading dose followed by 7.5 mg/kg every 6 hours, not to exceed 4 grams daily.
* ** *Clostridioides difficile* Infection (CDI):**
* Oral: 500 mg orally three times daily for 10-14 days. (Note: Fidaxomicin or vancomycin are often preferred for initial episodes of CDI).
* **Surgical Prophylaxis:**
* Oral/IV: 500 mg orally or IV within 2 hours before surgery. May be repeated every 8 hours postoperatively for up to 24 hours.
* **Rosacea (Topical):**
* Gel 0.75%, Cream 1%: Apply a thin layer to affected areas once or twice daily.
## Pediatric Dosing
Dosing is weight-based and varies by indication. Always consult specific pediatric guidelines.
* **Giardiasis:**
* Oral: 15 mg/kg/day divided into three doses for 5 days, not to exceed 250 mg per dose.
* **Amebiasis:**
* Oral: 35-50 mg/kg/day divided into three doses for 5-10 days, not to exceed 750 mg per dose.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 7.5 mg/kg per dose every 8 hours. Maximum daily dose typically 4 grams.
## Dose Adjustments
* **Hepatic Impairment:** Caution is advised in severe hepatic impairment. Some sources recommend reducing the maintenance dose by 30-50% and monitoring for adverse effects.
* **Renal Impairment:** No dose adjustment is typically needed for moderate to severe renal impairment. Metronidazole and its metabolites are removed by hemodialysis, so an additional dose may be required after dialysis if used.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concomitant use of disulfiram or alcohol (within 3 days of last dose).
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness, darkening of urine.
Serious: Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, Stevens-Johnson syndrome, hypersensitivity reactions, pancreatitis, severe mucositis.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache, palpitations). Avoid alcohol during and for at least 3 days after metronidazole therapy.
* **Disulfiram:** Can cause acute psychosis or confusion.
* **Warfarin:** Metronidazole can potentiate the anticoagulant effect of warfarin. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels. Monitor cyclosporine levels.
## Monitoring
* Signs and symptoms of infection.
* Signs of peripheral neuropathy (numbness, tingling, pain in extremities).
* Mental status changes.
* Signs of hypersensitivity reactions.
* INR if co-administered with warfarin.
* Lithium levels if co-administered with lithium.
## Clinical Pearls
* Metallic taste is common and often bothersome for patients.
* Advise patients to avoid alcohol during treatment and for at least 3 days after completing therapy to prevent a disulfiram-like reaction.
* For vaginal gel, instruct patients on proper insertion technique and advise against intercourse during treatment.
* Due to potential for CNS effects, use caution when operating machinery or driving.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines for definitive recommendations. This summary does not replace professional medical judgment.*
