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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 used for bacterial vaginosis.
* **Trichomoniasis:** Treatment of symptomatic trichomoniasis.
* **Amebiasis:** Intestinal and extraintestinal amebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections, lower respiratory tract infections, and endocarditis when caused by susceptible anaerobic bacteria.
* **Pseudomembranous Colitis:** Alternative agent for C. difficile infections.
* **Surgical Prophylaxis:** Surgical prophylaxis, particularly in colorectal surgery.
* **Helicobacter pylori Eradication:** Component of multi-drug regimens.
## Adult Dosing
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days, OR 2 g orally as a single dose, OR 0.75% vaginal gel intravaginally once daily for 5 days.
* **Trichomoniasis:** 2 g orally as a single dose, OR 500 mg orally twice daily for 7 days.
* **Amebiasis:**
* Intestinal: 500-650 mg orally three times daily for 7-10 days.
* Extra-intestinal (e.g., liver abscess): 500-650 mg orally three times daily for 7-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5 days.
* **Anaerobic Bacterial Infections:** 500 mg orally or IV every 8 hours. Duration varies by indication, typically 7-14 days.
* **Pseudomembranous Colitis:** 500 mg orally three times daily.
* **Surgical Prophylaxis:** 1 g orally or IV 1-2 hours before surgery, or 500 mg orally or IV every 8 hours starting 4 hours before surgery and continuing for up to 12 hours postoperatively.
* **H. pylori Eradication:** Dosing varies significantly within combination regimens. Often 500 mg orally twice daily as part of a 10-14 day regimen.
## Pediatric Dosing
Dosing is weight-based and depends on the indication and severity. Specific protocols may vary.
* **Amebiasis:** 35-50 mg/kg/day orally divided into three doses for 10 days. Maximum: 750 mg/day.
* **Giardiasis:** 15 mg/kg/day orally divided into three doses for 5 days. Maximum: 750 mg/day.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose orally or IV every 8 hours. Maximum: 400 mg/dose. Duration varies.
## Dose Adjustments
* **Hepatic Impairment:** No dose adjustment necessary for mild to moderate hepatic impairment. Caution and potential dose reduction may be warranted in severe hepatic impairment.
* **Renal Impairment:** No dose adjustment is typically required for oral therapy. For IV therapy, consider reducing the dose in severe renal impairment (CrCl < 30 mL/min), although data is limited.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* History of hypersensitivity to any component of the formulation.
* Concurrent use of disulfiram or alcohol.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, Stevens-Johnson syndrome, toxic epidermal necrolysis, encephalopathy, aseptic meningitis, pancreatitis, hepatotoxicity, neutropenia, disulfiram-like reaction with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, headache). Advise avoidance of alcohol during and for at least 72 hours after treatment.
* **Disulfiram:** Concurrent use can cause acute psychosis or confusion.
* **Warfarin:** May potentiate anticoagulant effect. 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.
* **Fluorouracil (5-FU):** Metronidazole may increase the toxicity of 5-FU.
## Monitoring
* Assess for signs and symptoms of infection resolution.
* Monitor for adverse effects, particularly neurological symptoms (neuropathy, dizziness, seizures).
* Monitor for signs of superinfection.
* If used for prolonged periods, consider baseline and periodic CBC.
* Monitor INR if co-administered with warfarin.
## Clinical Pearls
* Advise patients to avoid alcohol during and for at least 72 hours after metronidazole therapy due to the potential for a disulfiram-like reaction.
* A metallic taste is a common and expected side effect.
* Neurological side effects, including peripheral neuropathy, can occur, especially with prolonged or high-dose therapy. Advise patients to report any numbness, tingling, or weakness.
* Metronidazole can cause dark or reddish-brown urine.
* For IV administration, reconstitute and dilute as per manufacturer instructions.
**Disclaimer:** This information is intended for healthcare professionals. Always verify current prescribing information and consult with a pharmacist or physician for patient-specific guidance.
