Metrogyl%252525252525252525252525252525252525252525252525252525252525252520%252525252525252525252525252525252525252525252525252525252525252528metronidazole%252525252525252525252525252525252525252525252525252525252525252529

# Metrogyl (metronidazole) ## Overview - **Class:** Nitroimidazole antimicrobial and antiprotozoal. - **Available forms:** Oral tablets/capsules/suspension, IV infusion, vaginal gel, topical gel/cream, and other local formulations. - **Activity:** Anaerobic bacteria and protozoa; does **not** reliably treat aerobic bacteria. - Dosing depends on infection, formulation, renal/hepatic function, and local protocol. ## Primary Indications - Anaerobic bacterial infections, including intra-abdominal, pelvic, dental, bone/joint, CNS, and severe skin/soft-tissue infections. - Bacterial vaginosis. - Trichomoniasis. - Giardiasis. - Amebiasis. - *Clostridioides difficile* infection when preferred agents are unavailable or unsuitable; oral vancomycin or fidaxomicin is generally preferred. - Surgical prophylaxis for procedures with significant anaerobic risk. - Part of selected *Helicobacter pylori* eradication regimens. - Topical treatment of rosacea or vaginal infections, depending on formulation. ## Adult Dosing Doses below are typical systemic regimens; confirm the indication-specific local protocol. - **Serious anaerobic infections, oral or IV:** **500 mg every 8 hours**. Severe infections may require **500 mg every 6 hours**. Usual maximum: **4 g/day**. - **Surgical prophylaxis:** **500 mg IV once**, administered within 60 minutes before incision. Repeat dosing depends on procedure duration and local protocol. - **Bacterial vaginosis:** **500 mg orally every 12 hours for 7 days**, or metronidazole vaginal gel **0.75%: 5 g intravaginally once daily for 5 days**. - **Trichomoniasis:** - Women: **500 mg orally every 12 hours for 7 days**. - Men: **2 g orally once** or **500 mg every 12 hours for 7 days**, depending on recurrence risk and local guidance. Treat sexual partners concurrently and avoid sex until treatment is completed and symptoms resolve. - **Giardiasis:** **250 mg orally three times daily for 5–7 days**, or **500 mg twice daily for 5–7 days**. - **Amebiasis:** **500–750 mg orally three times daily for 5–10 days**, followed by a **luminal amebicide** such as paromomycin when indicated. - **Initial nonsevere *C. difficile* infection when alternatives are unavailable:** **500 mg orally three times daily for 10 days**. This is not preferred when fidaxomicin or oral vancomycin is appropriate. - **H. pylori eradication:** Regimens vary; a common bismuth quadruple regimen uses **500 mg orally three or four times daily for 10–14 days** with a proton-pump inhibitor, bismuth, and tetracycline. Follow current local resistance-based guidance. ## Pediatric Dosing Use weight-based dosing and verify the maximum dose and indication-specific protocol. - **Anaerobic infections:** **7.5 mg/kg/dose orally or IV every 6 hours** (approximately **30 mg/kg/day**). Maximum: commonly **4 g/day**. - **Surgical prophylaxis:** **15 mg/kg IV once** within 60 minutes before incision. Maximum: commonly **500 mg/dose**. - **Giardiasis:** **5–10 mg/kg/dose orally every 8 hours for 5–7 days**. Maximum: commonly **250 mg/dose**. - **Amebiasis:** **11.7–16.7 mg/kg/dose orally every 8 hours for 5–10 days** (35–50 mg/kg/day). Maximum: commonly **750 mg/dose** or **2.25 g/day**, depending on protocol. A luminal agent is usually required afterward. - ***C. difficile* infection when metronidazole is specifically selected:** **7.5 mg/kg/dose orally every 8 hours for 10 days**. Maximum: **500 mg/dose**. Preferred therapy depends on age, severity, recurrence, and current guidelines. - **Trichomoniasis:** Pediatric dosing should be directed by a specialist or local protocol; commonly **15 mg/kg/day orally divided every 8 hours for 7 days**, with a maximum of **500 mg/dose**. ## Dose Adjustments - **Renal impairment:** Usually **no adjustment** is required, including severe renal impairment. - **Hemodialysis:** Metronidazole and metabolites may be removed. Give the scheduled dose **after dialysis** when timing requires; follow local protocol. - **Severe hepatic impairment, particularly Child-Pugh C:** Reduce the total daily dose by approximately **50%** and monitor closely. - **Mild-to-moderate hepatic impairment:** Usually no adjustment, but use caution with prolonged courses. - **Older adults:** No routine adjustment; assess hepatic function, polypharmacy, and neuropathy risk. - **Topical or vaginal products:** Systemic exposure is lower but not absent; follow the specific product instructions. ## Contraindications - Serious hypersensitivity to metronidazole, other nitroimidazoles, or formulation excipients. - Concomitant **disulfiram use within the previous 14 days** because of possible psychotic reactions. - **Cockayne syndrome:** Avoid when possible because of reported severe, sometimes fatal hepatotoxicity. - Avoid unnecessary use in patients with active neurologic disease, severe hepatic dysfunction, or prior metronidazole-associated encephalopathy. - Pregnancy is **not an absolute contraindication** when treatment is clinically indicated; consult current obstetric guidance. ## Adverse Effects - **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, anorexia, headache, dizziness, metallic taste, dry mouth, and dark urine. - **Oral/vaginal:** Candidiasis, vaginal irritation, or local discomfort. - **Neurologic:** Peripheral neuropathy, paresthesias, ataxia, seizures, encephalopathy, or confusion—more likely with prolonged or high-dose therapy. - **Hepatic:** Elevated transaminases, hepatitis, cholestatic injury, or rare severe liver failure. - **Hematologic:** Leukopenia or neutropenia, usually reversible. - **Hypersensitivity:** Rash, urticaria, angioedema, or rare severe cutaneous reactions. - Discontinue and urgently evaluate for new numbness, weakness, ataxia, seizures, severe rash, jaundice, or confusion. ## Key Drug Interactions - **Alcohol or propylene glycol:** Avoid during treatment and for at least **48–72 hours after the final dose** because of possible severe nausea, vomiting, flushing, and tachycardia. Check liquid formulations for propylene glycol. - **Warfarin and other vitamin K antagonists:** May substantially increase INR. Monitor INR closely and adjust anticoagulant dosing as needed. - **Disulfiram:** Avoid within **14 days**. - **Lithium:** May increase lithium concentrations and toxicity; monitor lithium and renal function. - **Phenytoin:** Metronidazole may increase phenytoin concentrations; phenytoin may reduce metronidazole exposure. Monitor levels and clinical response. - **Phenobarbital and other strong enzyme inducers:** May reduce metronidazole concentrations. - **Busulfan:** May markedly increase busulfan exposure; avoid or use specialist-directed monitoring. - **Tacrolimus or cyclosporine:** May increase concentrations; monitor levels. - **Fluorouracil:** May increase fluorouracil toxicity. - **QT-prolonging drugs:** Use caution in patients with additional QT-risk factors or multiple QT-prolonging medicines. ## Monitoring - Clinical response, fever, pain, diarrhea, wound findings, and infection-specific cultures when appropriate. - CBC for prolonged therapy or patients at hematologic risk. - Liver function tests at baseline and periodically during prolonged therapy, in hepatic disease, or if symptoms develop. - Neurologic assessment during prolonged or high-dose courses. - INR within several days of starting and after stopping therapy in patients receiving warfarin. - Lithium, phenytoin, tacrolimus, or cyclosporine concentrations when clinically indicated. - For trichomoniasis: test for other sexually transmitted infections and retest women approximately **3 months after treatment** because reinfection is common. ## Clinical Pearls - Use only when anaerobic or protozoal coverage is indicated; metronidazole has no dependable activity against aerobic bacteria. - Oral and IV dosing are generally interchangeable on a milligram-for-milligram basis when gastrointestinal absorption is reliable. - Do not use metronidazole alone for infections likely to include aerobic or facultative organisms unless the regimen provides additional coverage. - Treatment of amebiasis generally requires a **luminal agent after metronidazole** to eradicate intestinal cysts. - For bacterial vaginosis and trichomoniasis, topical therapy does not reliably treat extragenital infection or all sexual partners. - Avoid prolonged courses when an effective shorter course is appropriate because cumulative neurotoxicity risk increases with exposure. - Do not stop anticoagulation or antiseizure therapy without prescriber guidance; interactions may require monitoring and dose adjustment. - Product concentrations and dosing instructions vary, especially for oral suspensions, vaginal products, and topical formulations. > **Educational disclaimer:** This information is for educational use and does not replace patient-specific clinical judgment. Verify the current product labeling, local antimicrobial guidelines, formulation strength, renal/hepatic status, pregnancy considerations, and indication-specific dosing before prescribing or dispensing.