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# Metronidazole (Metrogyl)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent. It is effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of urogenital trichomoniasis.
* **Amebiasis:** Treatment of intestinal amebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic bacterial infections:** Treatment of serious anaerobic bacterial infections, often in combination with other agents.
* **Prophylaxis:** Surgical prophylaxis, particularly in colorectal surgery.
* **_Helicobacter pylori_ eradication:** As part of a multi-drug regimen.
## Adult Dosing
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days OR 2 grams orally as a single dose.
* **Trichomoniasis:** 2 grams orally as a single dose OR 250 mg orally twice daily for 7 days OR 375 mg orally twice daily for 7 days.
* **Amebiasis (intestinal):** 500-650 mg orally three times daily for 5-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5 days OR 500 mg orally twice daily for 3 days.
* **Anaerobic bacterial infections:** 500 mg IV or orally every 8 hours. Duration varies based on infection severity and patient response, typically 7-14 days.
* **Surgical Prophylaxis:** 1 gram IV 1-2 hours before surgery, then 500 mg orally or IV every 8 hours for up to 24 hours postoperatively.
* **_H. pylori_ eradication:** Typically 500 mg orally twice daily in combination with a proton pump inhibitor and another antibiotic (e.g., amoxicillin or clarithromycin) for 10-14 days.
## Pediatric Dosing
Dosing in children is typically weight-based and depends on the indication. Local pediatric protocols should be consulted for specific dosing. Examples include:
* **Giardiasis:** 15 mg/kg/day orally divided into 3 doses, not to exceed 250 mg per dose, for 5 days.
* **Amebiasis:** 35-50 mg/kg/day orally divided into 3 doses, not to exceed 750 mg per dose, for 5-10 days.
* **Anaerobic infections:** 7.5 mg/kg/dose IV or orally every 8 hours. Maximum dose typically 500 mg per dose.
## Dose Adjustments
* **Hepatic Impairment:** Reduce dose by 30-50% in severe hepatic impairment. Use with caution.
* **Renal Impairment:** No dose adjustment generally needed for standard intermittent hemodialysis. For continuous renal replacement therapy (CRRT), consult specific protocols as clearance can be variable.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Active central nervous system disease.
* First trimester of pregnancy (relative contraindication, consider risks and benefits).
## Adverse Effects
* **Common:** Nausea, metallic taste, headache, anorexia, vomiting, diarrhea, abdominal cramping, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, leukopenia, thrombocytopenia, hepatotoxicity, disulfiram-like reaction with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache, tachycardia). Advise patients to avoid alcohol during and for at least 3 days after treatment.
* **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase serum lithium levels. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** May increase cyclosporine levels. Monitor cyclosporine levels.
* **5-Fluorouracil (5-FU):** Metronidazole may increase the toxicity of 5-FU.
## Monitoring
* Monitor for signs and symptoms of neuropathy (numbness, tingling, pain) and discontinue if it occurs.
* Monitor for psychiatric side effects (e.g., confusion, hallucinations).
* Monitor for signs of superinfection (e.g., fungal overgrowth).
* Monitor complete blood count if prolonged therapy or significant anemia is suspected.
* Monitor INR if co-administered with warfarin.
## Clinical Pearls
* Advise patients to avoid alcohol during treatment and for at least 72 hours after the last dose.
* A metallic taste is common and generally transient.
* Urine may turn a reddish-brown color; this is harmless.
* For _H. pylori_ eradication, compliance with the full multi-drug regimen is crucial for success.
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**Disclaimer:** This information is intended for clinical use and is not a substitute for professional medical advice. Always consult the most current prescribing information and local protocols before making treatment decisions.
