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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 symptomatic trichomoniasis.
* **Amebiasis:** Treatment of amebiasis (intestinal and extraintestinal).
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and skin structure infections, gynecologic infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis). Often used in combination with other antibiotics.
* **Pseudomembranous Colitis:** Treatment of *Clostridium difficile*-associated diarrhea (CDAD).
* **Surgical Prophylaxis:** Prophylaxis against anaerobic bacterial infection in specific surgical procedures (e.g., colorectal surgery).
## Adult Dosing
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days, OR 2 g as a single dose.
* Vaginal Gel (0.75%): Insert one full applicator (5 g) intravaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 2 g as a single dose, OR 250 mg three times daily for 7 days, OR 375 mg twice daily for 7 days.
* **Amebiasis:**
* Intestinal: Oral: 500-750 mg three times daily for 5-10 days.
* Extra-intestinal (e.g., liver abscess): Oral: 500-750 mg three times daily for 5-10 days.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5 days.
* **Anaerobic Bacterial Infections:**
* Oral: 500 mg every 8 hours.
* IV: 15 mg/kg loading dose, followed by 7.5 mg/kg every 6-8 hours. Maximum IV dose: 4 g/day.
* Duration varies based on severity and site of infection, typically 7-14 days.
* **Pseudomembranous Colitis (CDAD):**
* Oral: 500 mg every 8 hours for 10-14 days. Note: Vancomycin is generally preferred for initial episodes, especially if severe.
* **Surgical Prophylaxis:**
* Oral or IV: 1 g within 12 hours before surgery, then 500 mg every 8 hours for up to 24 hours post-operatively.
## Pediatric Dosing
Dosing is weight-based and depends on the indication. Consult specific pediatric guidelines or manufacturer's labeling.
* **Bacterial Infections:** Oral or IV: 7.5 mg/kg every 8 hours. Maximum: 400 mg/dose.
* **Trichomoniasis/Giardiasis/Amebiasis:**
* Oral: 15-35 mg/kg/day divided into 3 doses for 5-10 days. Maximum: 750 mg/dose or 2 g/day depending on indication.
## Dose Adjustments
* **Hepatic Impairment:** Caution advised. Severe hepatic impairment may require dose reduction. Data is limited.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (especially for systemic use) due to potential risk, though risk-benefit is considered for specific indications.
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness, rash, urticaria.
Serious: Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, Stevens-Johnson syndrome, dark urine, opportunistic infections (e.g., candidiasis).
Disulfiram-like reaction with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, headache, nausea, vomiting, chest pain). Advise patients to avoid alcohol during treatment and for at least 3 days after.
* **Warfarin:** Metronidazole can potentiate the anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase serum lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole efficacy.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels. Monitor cyclosporine levels.
* **5-Fluorouracil:** Metronidazole may increase toxicity of 5-FU.
## Monitoring
* **Clinical response:** Assess for improvement in signs and symptoms of infection.
* **Adverse effects:** Monitor for nausea, vomiting, diarrhea, metallic taste, headache, dizziness. Assess for signs of peripheral neuropathy (numbness, tingling) and seizures, especially with prolonged or high-dose therapy.
* **Lab tests:** Monitor CBC. Monitor LFTs if hepatic impairment is present.
* **Drug interactions:** Monitor INR if co-administered with warfarin. Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* Administer oral metronidazole with or without food.
* A metallic taste is common and usually resolves after treatment.
* Advise patients to avoid alcohol during therapy and for at least 72 hours after the last dose.
* Urine may become reddish-brown in color; this is harmless.
* For parenteral administration, infuse over 20-60 minutes.
* Consider prescribing an antiemetic for patients experiencing significant nausea.
* Use with caution in patients with CNS disorders or blood dyscrasias.
**Disclaimer:** This information is intended for clinical use and does not replace the official prescribing information or the need for clinical judgment. Always consult the most current drug information available from the manufacturer and relevant clinical guidelines before prescribing.
