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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 symptomatic trichomoniasis. * **Amebiasis:** Treatment of intestinal amebiasis (amebic dysentery) and extraintestinal amebiasis (e.g., amebic liver abscess). * **Giardiasis:** Treatment of giardiasis. * **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis). Often used in combination with other antibiotics. * **Pseudomembranous Colitis:** Treatment of *Clostridioides difficile*-associated diarrhea (CDAD). * **Surgical Prophylaxis:** Prophylaxis against anaerobic infection in specific surgical procedures (e.g., colorectal surgery). * **Rosacea:** Topical formulation for inflammatory lesions of rosacea. ## Adult Dosing * **Bacterial Vaginosis:** * Oral: 500 mg twice daily for 7 days OR 2 g as a single dose. * Vaginal gel 0.75%: 5 g (one applicatorful) intravaginally once daily for 5 days. * **Trichomoniasis:** * Oral: 2 g as a single dose OR 250 mg twice daily for 7 days OR 375 mg twice daily for 7 days. * **Amebiasis:** * Intestinal: 500-650 mg orally three times daily for 5-10 days. * Extra-intestinal: 500-650 mg orally three times daily for 5-10 days, followed by a luminal amebicide if hepatic abscess is treated without drainage. * **Giardiasis:** * Oral: 250 mg three times daily for 5 days OR 375 mg three times daily for 5 days. * **Anaerobic Bacterial Infections:** * Oral/IV: 500 mg every 6-8 hours. Typical duration 7-14 days, but may be longer. * Maximum oral dose: 4 g per day. * **Pseudomembranous Colitis (CDAD):** * Oral: 500 mg three times daily. Duration typically 10-14 days. * **Surgical Prophylaxis:** * Oral/IV: 1 g as a single dose given 1 hour before surgery, or 500 mg every 8 hours starting before surgery and continuing for up to 24 hours postoperatively. ## Pediatric Dosing Dosing is highly dependent on indication and weight. Consult specific guidelines. * **Giardiasis:** * Oral: 15 mg/kg/day divided into 3 doses for 5 days. Maximum 250 mg per dose or 750 mg per day. * **Anaerobic Infections:** * Oral/IV: 7.5 mg/kg per dose every 8 hours. Maximum 400 mg per dose. Duration typically 7-14 days. * **Amebiasis:** * Oral: 35-50 mg/kg/day divided into 3 doses for 5-10 days. Maximum 750 mg per day. ## Dose Adjustments * **Hepatic Impairment:** Use with caution. Consider reducing dose by 30-50% in severe hepatic insufficiency. Monitor for toxicity. * **Renal Impairment:** No dose adjustment generally needed for standard doses. However, consider reducing the dose or extending the interval in severe renal impairment (CrCl < 10 mL/min) if dialysis is not performed, as the half-life may be prolonged. ## Contraindications * Hypersensitivity to metronidazole or other nitroimidazole derivatives. * Concurrent use of disulfiram (within 2 weeks). * Concurrent use of alcohol. ## 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, leukopenia, pancreatitis, disulfiram-like reaction with alcohol. ## Key Drug Interactions * **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, palpitations, shortness of breath). Avoid alcohol during therapy and for at least 3 days after. * **Disulfiram:** Potentially severe psychotic reactions. Avoid concurrent use. * **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed. * **Lithium:** May increase lithium levels, leading to toxicity. Monitor lithium levels. * **Phenytoin/Phenobarbital:** May decrease metronidazole levels. * **5-Fluorouracil (5-FU):** May increase 5-FU toxicity. ## Monitoring * **Clinical:** Monitor for signs and symptoms of infection resolution. * **Adverse Effects:** Assess for neurological symptoms (numbness, tingling, weakness, coordination issues), gastrointestinal upset, and hypersensitivity reactions. * **Laboratory:** Consider complete blood count (CBC) for prolonged therapy or high doses, especially if risk factors for neutropenia exist. Monitor lithium and INR levels if used concomitantly. ## Clinical Pearls * The metallic taste is a common and often bothersome side effect. * Advise patients to avoid alcohol during treatment and for at least 72 hours after the last dose due to the disulfiram-like reaction. * Peripheral neuropathy is a serious adverse effect that can be irreversible. Counsel patients to report any new onset of numbness, tingling, or weakness immediately. * Metronidazole can turn urine a reddish-brown color; this is benign. * For topical formulations, avoid sun exposure and use sunscreen. *** *This information is for educational purposes only and does not substitute for professional medical advice. Always consult current prescribing information and relevant guidelines for definitive patient care decisions.*