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# Metronidazole (Metrogyl)
## 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 trichomoniasis.
* **Amoebiasis:** Treatment of intestinal and extraintestinal amoebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections, often in combination with other antibiotics.
## Adult Dosing
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days, or a single 2-gram dose orally. Alternatively, 0.75% vaginal gel applied intravaginally once daily for 5 days.
* **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.
* **Amoebiasis:**
* *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.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days, or 2 grams orally once daily for 3 days.
* **Anaerobic Bacterial Infections:** Dosing varies significantly based on the type and severity of infection. Typical adult doses range from 500 mg to 1 gram intravenously or orally every 6-8 hours.
## Pediatric Dosing
Dosing is weight-based and depends on the indication. Consult specific pediatric guidelines.
* **Amoebiasis:** 35-50 mg/kg/day orally divided into three doses for 5-10 days (maximum 750 mg per dose).
* **Giardiasis:** 15 mg/kg/day orally divided into three doses for 5-7 days (maximum 250 mg per dose).
* **Anaerobic Bacterial Infections:** Dosing is variable. A common regimen is 7.5 mg/kg/dose IV or orally every 8 hours (maximum 500 mg per dose).
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally needed. Hemodialysis may reduce metronidazole levels, necessitating redosing.
* **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in severe hepatic impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (use cautiously in the second and third trimesters if benefits outweigh risks).
* Concomitant use with disulfiram or alcohol (due to disulfiram-like reaction).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, Stevens-Johnson syndrome, hypersensitivity reactions, pancreatitis, candidiasis of the vagina.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, shortness of breath). Avoid alcohol during treatment and for at least 3 days after.
* **Disulfiram:** Can cause psychomotor episodes. Avoid co-administration.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole effectiveness.
* **Cyclosporine:** Increased cyclosporine levels. Monitor cyclosporine levels.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for signs of central nervous system effects (dizziness, confusion, seizures).
* Monitor for hypersensitivity reactions.
* If used for anaerobic infections, monitor for clinical signs of infection resolution.
* If used with warfarin, monitor INR.
## Clinical Pearls
* The metallic taste is common and can be mitigated by taking with food or using flavored agents.
* Advise patients to avoid alcohol and products containing alcohol during therapy and for at least 72 hours after the last dose.
* For trichomoniasis, sexual partners should also be treated to prevent reinfection.
* Prolonged treatment may lead to overgrowth of non-susceptible organisms, including fungi.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines for complete details and to ensure patient safety.*
