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# Metrogyl (metronidazole)
## Overview
Metronidazole is an antimicrobial agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* Bacterial vaginosis
* Trichomoniasis
* Giardiasis
* Amoebiasis
* Anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, gynecologic infections, intra-abdominal sepsis)
* *Clostridioides difficile* infection (CDI) - typically second-line or for mild cases.
## Adult Dosing
* **Bacterial vaginosis:** 500 mg orally twice daily for 7 days, OR 2 g orally as a single dose.
* **Trichomoniasis:** 2 g orally as a single dose, OR 250 mg orally three times daily for 7 days.
* **Giardiasis:** 250 mg orally three times daily for 5 days, OR 2 g orally once daily for 3 days.
* **Amoebiasis (intestinal):** 500-750 mg orally three times daily for 5-10 days.
* **Amoebiasis (hepatic abscess):** 500-750 mg orally three times daily for 5-10 days, followed by a luminal agent.
* **Anaerobic bacterial infections:** Dosing is highly variable depending on site and severity. Common regimens include 500 mg IV or orally every 8 hours. Maximum dose generally 4 g/day.
* ***Clostridioides difficile* infection (mild-moderate):** 500 mg orally three times daily for 10 days. Avoid in severe CDI.
## Pediatric Dosing
Dosing varies by indication and weight. Specific pediatric guidelines should be consulted.
* **Bacterial vaginosis, Trichomoniasis, Giardiasis:** Generally not indicated in children under 12 years for these conditions unless specific circumstances warrant.
* **Amoebiasis:** 35-50 mg/kg/day orally divided into 3 doses, maximum 750 mg/dose, for 5-10 days.
* **Anaerobic bacterial infections:** 7.5 mg/kg IV or orally every 8 hours (30 mg/kg/day divided into 3 doses), maximum 4 g/day.
## Dose Adjustments
No dose adjustment is necessary for hepatic impairment for standard treatment durations. However, caution is advised in severe hepatic disease, and total daily dose may need to be reduced. No dose adjustment needed for renal impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Disulfiram-like reaction with alcohol; patients should avoid alcohol during and for at least 3 days after treatment.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, hepatotoxicity, severe allergic reactions.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia). Avoid concurrent use.
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose.
* **Lithium:** Increased lithium levels. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** Decreased metronidazole levels.
* **Cyclosporine:** Increased cyclosporine levels. Monitor cyclosporine levels.
* **Disulfiram:** Concurrent use can lead to psychotic reactions. Avoid.
## Monitoring
* Monitor for signs and symptoms of adverse effects, particularly peripheral neuropathy and central nervous system effects.
* Monitor INR if co-administered with warfarin.
* Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* A metallic taste is a common, though usually transient, side effect.
* Patients should be advised to avoid alcohol during treatment and for at least 3 days after.
* Long-term or high-dose therapy increases the risk of peripheral neuropathy.
* For IV use, dilute and administer as an infusion.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols for complete details and to verify dosage and safety.
