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# Metronidazole
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic and antiprotozoal agent. It is active against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of *Trichomonas vaginalis* infection.
* **Amebiasis:** Treatment of amebiasis (*Entamoeba histolytica*) intestinalis and extraintestinal infections.
* **Giardiasis:** Treatment of giardiasis (*Giardia lamblia*).
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and skin structure infections, gynecologic infections, bacterial vaginosis, and infections caused by *Bacteroides* species).
* **Pseudomembranous Colitis:** Treatment of antibiotic-induced pseudomembranous colitis caused by *Clostridium difficile*.
* **Surgical Prophylaxis:** Prophylaxis against anaerobic bacterial infection in patients undergoing certain surgical procedures (e.g., colorectal surgery).
* **H. pylori Eradication:** Component of multi-drug regimens for *Helicobacter pylori* eradication.
## 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 inserted once daily for 5 days.
* **Trichomoniasis:** 2 g orally as a single dose OR 250 mg orally three times daily for 7 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, followed by a luminal agent.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days OR 2 g orally once daily for 3 days.
* **Anaerobic Bacterial Infections:** 500 mg IV or orally every 8 hours. Duration varies based on infection severity and response, typically 7-14 days.
* **Pseudomembranous Colitis:** 250-500 mg orally every 6-8 hours for 10-14 days.
* **Surgical Prophylaxis:** 1 g IV 1-2 hours before surgery, followed by 500 mg IV or orally every 8 hours for up to 24 hours post-operatively.
* **H. pylori Eradication:** Dosing varies significantly based on the specific regimen. Common regimens include 500 mg orally twice daily in combination with other agents for 10-14 days.
## Pediatric Dosing
Dosing is weight-based and depends on the indication. Always confirm with current pediatric guidelines or consult a pediatric specialist.
* **Amebiasis:** 35-50 mg/kg/day orally divided into three doses for 5-10 days (maximum 750 mg/dose or 2000 mg/day).
* **Giardiasis:** 15-30 mg/kg/day orally divided into three doses for 5-7 days (maximum 250 mg/dose or 750 mg/day).
* **Anaerobic Bacterial Infections:** 30 mg/kg/day IV or orally divided into three doses (maximum 400 mg/dose or 1200 mg/day).
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally needed for mild to moderate renal impairment. In severe renal impairment (CrCl < 10 mL/min), dosing interval may be extended, or dose reduced, though data is limited. Metronidazole and its metabolites are removed by hemodialysis.
* **Hepatic Impairment:** Use with caution in severe hepatic impairment. Consider reducing the dose.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* Use of disulfiram within the last 2 weeks.
* Use of alcohol during and for at least 3 days after metronidazole therapy.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness, dark or reddish-brown urine.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, neutropenia, thrombophlebitis (IV), candidiasis (vaginal).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, abdominal cramps, headache). Avoid alcohol during and for at least 3 days after treatment.
* **Disulfiram:** Acute psychotic reactions may occur. Avoid concurrent use.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Increased lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
* **Fluorouracil (5-FU):** Metronidazole may increase 5-FU toxicity.
* **Cimetidine:** May decrease metronidazole metabolism and increase serum concentrations.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain) and central nervous system effects (dizziness, confusion, seizures), especially with prolonged therapy.
* Monitor for signs of superinfection, particularly *C. difficile*-associated diarrhea.
* Monitor INR if patient is on warfarin.
* Monitor lithium levels if concurrently used.
* Monitor for therapeutic response.
## Clinical Pearls
* A metallic taste is a common side effect and can impact patient adherence.
* Patients should be advised to avoid alcohol during and for at least 3 days after treatment due to the potential for a disulfiram-like reaction.
* The urine may turn a reddish-brown color; this is harmless.
* For IV administration, metronidazole is compatible with normal saline and D5W.
* For patients experiencing nausea, consider administering with food.
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*Disclaimer: This information is intended for healthcare professionals and does not replace the need to consult the most current prescribing information and local institutional protocols.*
