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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Typically treatment of choice.
* **Trichomoniasis:** Treatment of choice.
* **Amebiasis:** Intestinal and extraintestinal amebiasis.
* **Giardiasis:** Treatment of choice.
* **Anaerobic Bacterial Infections:** Intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis, C. difficile infection (alternative).
* **Surgical Prophylaxis:** Particularly in colorectal surgery.
* **Rosacea:** Topical formulation.
## Adult Dosing
* **Bacterial Vaginosis:**
* Oral: 500 mg orally twice daily for 7 days, or 2 g orally as a single dose.
* Vaginal gel 0.75%: 5 g vaginally 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:**
* Intestinal: 500-750 mg orally three times daily for 5-10 days.
* Extraintestinal (e.g., liver abscess): 500-750 mg orally three times daily for 5-10 days. Consider IV for severe disease.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 500 mg every 8 hours. Duration varies by infection site and severity, typically 7-14 days.
* Maximum oral dose generally 4 g/day.
* **Surgical Prophylaxis:**
* Oral/IV: 1 g orally or IV 1 hour before surgery, followed by 500 mg every 8 hours for up to 24 hours postoperatively.
* **C. difficile infection:** 500 mg orally three times daily for 10-14 days (reserved for non-severe cases or when vancomycin is not an option).
* **Rosacea (Topical 0.75% gel or 1% cream):** Apply thin layer to affected areas once or twice daily.
## Pediatric Dosing
Dosing is weight-based and depends on the indication. Always confirm with local protocol or specialized pediatric resources.
* **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:**
* Oral/IV: 7.5 mg/kg/dose every 8 hours, or 15 mg/kg/dose every 12 hours.
* Neonates: Dosing varies based on gestational age and postnatal age. Consult neonatology guidelines.
* Maximum dose generally 4 g/day.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution. Reduce dose by 50% in severe hepatic disease.
* **Renal Impairment:** No dose adjustment necessary for intermittent hemodialysis or peritoneal dialysis. For severe renal impairment (CrCl < 10 mL/min), consider reducing maintenance dose by 50% if therapy exceeds 4 days, though this is controversial.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* First trimester of pregnancy (use only if essential and benefits outweigh risks; generally avoided).
* Concurrent use with disulfiram.
* Concurrent use with alcohol (disulfiram-like reaction).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, leukopenia, Stevens-Johnson syndrome, dark urine.
* **Disulfiram-like reaction:** With alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, headache, nausea, vomiting, chest pain). Advise patients to avoid alcohol during and for at least 3 days after therapy.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Disulfiram:** Concurrent use is contraindicated due to risk of psychotic reactions.
* **Phenytoin, Phenobarbital:** May decrease metronidazole efficacy.
* **5-Fluorouracil (5-FU) and Capecitabine:** Metronidazole may increase toxicity of fluoropyrimidines.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling).
* Monitor for signs of C. difficile infection recurrence or development.
* Monitor lithium levels if co-administered.
* Monitor INR if co-administered with warfarin.
## Clinical Pearls
* Metronidazole is effective against a wide range of anaerobic organisms and protozoa.
* A metallic taste is a common and often bothersome side effect.
* Patients should be strongly advised to avoid alcohol during treatment and for at least 72 hours after the last dose due to the disulfiram-like reaction.
* For prolonged treatment courses, especially for C. difficile infection, consider the risk of peripheral neuropathy.
* The intravenous formulation is not effective against C. difficile colitis; oral administration is required.
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*This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and relevant clinical guidelines for complete details before making any treatment decisions.*
