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# Metronidazole (Metrogyl)
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic and antiprotozoal agent. It is effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* Bacterial vaginosis
* Trichomoniasis
* Amebiasis
* Giardiasis
* Bacterial infections caused by susceptible anaerobic organisms (e.g., intra-abdominal infections, skin and soft tissue infections, gynecological infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis).
* *Clostridioides difficile*-associated diarrhea (CDAD) - generally reserved for mild to moderate cases or as an alternative to vancomycin.
* Prophylaxis against anaerobic infection in specific surgical procedures.
* H. pylori eradication (in combination regimens).
## 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.
* **Amebiasis:**
* Invasive amebiasis: 500-750 mg orally three times daily for 5-10 days.
* Amebic liver abscess: 500-750 mg orally three times daily for 5-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5 days.
* **Anaerobic Bacterial Infections:** Typically 500 mg orally or intravenously every 8 hours. Duration varies by infection site and severity, often 7-14 days.
* **CDAD (Mild-Moderate):** 500 mg orally three times daily for 10-14 days.
* **Surgical Prophylaxis:** 1 g orally or intravenously 1-2 hours before surgery, followed by 500 mg orally or intravenously every 8 hours for up to 24 hours post-operatively.
* **H. pylori Eradication:** Regimens vary, often 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. Consult specific pediatric guidelines or a pediatric infectious disease specialist.
* **Giardiasis:** 15 mg/kg/day orally in 3 divided doses, not to exceed 250 mg per dose, for 5 days.
* **Amebiasis:** 35-50 mg/kg/day orally in 3 divided doses, not to exceed 750 mg per dose, for 5-10 days.
* **Serious Anaerobic Infections:** 7.5 mg/kg/dose intravenously every 8 hours.
## Dose Adjustments
No dose adjustment is typically required for hepatic impairment. Metronidazole is renally excreted, but accumulation is not usually significant in mild to moderate renal impairment. In severe renal impairment or in patients on hemodialysis, dosing interval may need to be extended or dose reduced, though data is limited.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (relative contraindication, use if risk-benefit favors).
* Concomitant use with disulfiram or alcohol (within 3 days of alcohol cessation).
## 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, ataxia), Stevens-Johnson syndrome, severe allergic reactions, liver enzyme elevations, pancreatitis.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia). Avoid alcohol during treatment and for at least 3 days after discontinuation.
* **Disulfiram:** Acute psychotic reactions may occur. Avoid concomitant use.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase lithium levels. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole efficacy.
* **Cyclosporine:** May increase cyclosporine levels. Monitor cyclosporine levels.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for CNS adverse effects.
* Monitor liver function tests if prolonged therapy.
* Monitor INR if patient is on warfarin.
* Monitor lithium levels if patient is on lithium.
## Clinical Pearls
* The metallic taste is a common and often bothersome side effect.
* Metronidazole can cause dark urine (reddish-brown).
* Use with caution in patients with CNS disorders.
* For treating anaerobic infections, oral and IV routes are generally considered equally effective.
* Consider topical metronidazole for rosacea.
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*This information is intended for clinical decision-making support and does not replace a thorough review of the most current prescribing information, guidelines, or consultation with a specialist.*
