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# Metronidazole (Metrogyl)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain parasites.
## 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 (e.g., intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bacterial vaginosis, *C. difficile* infection - though often reserved for specific scenarios).
## 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, OR 375 mg orally twice daily for 7 days.
* **Amebiasis:**
* **Intestinal (Amebic dysentery):** 500-750 mg orally three times daily for 5-10 days.
* **Hepatic abscess:** 500-750 mg orally three times daily for 5-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days.
* **Anaerobic Bacterial Infections:** Dosing varies significantly based on indication and severity. A common regimen is 500 mg IV or orally every 8 hours. Duration depends on clinical response.
## Pediatric Dosing
Dosing in children is generally based on weight and indication. Calculations should be performed based on the specific clinical guidelines or product information.
* **Trichomoniasis:** Not generally recommended for children under 12 years of age.
* **Giardiasis:** 15 mg/kg/day orally in 3 divided doses, not to exceed 250 mg per dose, for 5-7 days. Maximum daily dose is generally 750 mg.
* **Anaerobic Bacterial Infections:** Generally 7.5 mg/kg/dose orally or IV every 8 hours.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment is typically necessary for mild to moderate renal impairment. In severe renal impairment, accumulation may occur. Consider extending dosing interval or reducing dose, especially with prolonged therapy.
* **Hepatic Impairment:** In severe hepatic impairment, reduce the usual maintenance dose by one-third to one-half and administer less frequently.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use in the first trimester of pregnancy for trichomoniasis (though benefits may outweigh risks in some situations and alternatives may be limited).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), central nervous system effects (seizures, encephalopathy, aseptic meningitis), Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, disulfiram-like reaction with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, headache, nausea, vomiting, chest pain, palpitations). 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 lithium levels. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole effectiveness and increase phenytoin/phenobarbital levels.
* **Busulfan:** Metronidazole may increase busulfan levels, leading to toxicity.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for CNS effects.
* Monitor for hypersensitivity reactions.
* For patients on warfarin, monitor INR.
## Clinical Pearls
* Metronidazole can cause dark urine (reddish-brown).
* The metallic taste is common and can affect adherence.
* Ensure adequate hydration, especially with oral administration.
* Use with caution in patients with active CNS disease.
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***Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines before making treatment decisions.*
