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# Metronidazole ## Overview Metronidazole is a nitroimidazole antibiotic used to treat anaerobic bacterial and protozoal infections. ## Primary Indications * **Bacterial Vaginosis:** Treatment of bacterial vaginosis. * **Trichomoniasis:** Treatment of urogenital trichomoniasis. * **Amebiasis:** Treatment of amebiasis (intestinal amebiasis and amebic liver abscess). * **C. difficile Infection (CDI):** Treatment of *Clostridioides difficile*-associated diarrhea. * **Bacterial Infections:** Treatment of serious infections caused by susceptible anaerobic bacteria (e.g., intra-abdominal infections, gynecologic infections, skin and soft tissue infections, CNS infections, bone and joint infections, lower respiratory tract infections, endocarditis). * **Surgical Prophylaxis:** Preoperative or postoperative prophylaxis for colorectal surgery. * **Peptic Ulcer Disease:** Part of a combination regimen for *Helicobacter pylori* eradication. ## Adult Dosing * **Bacterial Vaginosis:** * Oral: 500 mg twice daily for 7 days; or 2 g single dose. * Vaginal gel (0.75%): 5 g intravaginally once daily for 5 days. * **Trichomoniasis:** * Oral: 2 g as a single dose; or 250 mg three times daily for 7 days; or 500 mg twice daily for 7 days. * **Amebiasis:** * Intestinal: Oral 500-650 mg three times daily for 7-10 days. * Hepatic abscess: Oral 500-650 mg three times daily for 7-10 days; or IV. * ***C. difficile* Infection:** * Oral: 500 mg three times daily for 10-14 days. Consider alternative agents for initial severe CDI or recurrent CDI. * **Anaerobic Bacterial Infections (Systemic):** * Oral: 500 mg every 8 hours. * IV: 15 mg/kg loading dose, followed by 7.5 mg/kg every 6-8 hours. Maximum daily dose typically 4 g. Dosing duration depends on severity and site of infection. * **Surgical Prophylaxis:** * Oral/IV: 1 g administered approximately 1 hour before surgery, followed by 500 mg every 8 hours for the first 24 hours postoperatively. * ***H. pylori* Eradication:** Oral 500 mg twice daily for 10-14 days as part of a multi-drug regimen. ## Pediatric Dosing Dosing is weight-based and depends on the indication and severity. * ***C. difficile* Infection:** Oral 7.5-15 mg/kg/day divided every 8 hours for 10-14 days. Maximum daily dose typically 4 g. * **Anaerobic Bacterial Infections (Systemic):** Oral/IV 7.5-15 mg/kg every 8 hours. Maximum daily dose typically 4 g. * **Amebiasis:** Oral/IV 35-50 mg/kg/day divided every 8 hours for 7-10 days. Maximum daily dose typically 4 g. Consult specific pediatric guidelines or local protocols for precise dosing and duration. ## Dose Adjustments * **Renal Impairment:** No dose adjustment typically needed for renal impairment. However, if used during dialysis, consider giving the usual dose after dialysis. * **Hepatic Impairment:** For severe hepatic impairment, reduce maintenance dose by 30-50% and administer every 12 hours. Monitor drug concentrations if possible. ## Contraindications * Hypersensitivity to metronidazole or other nitroimidazoles. * First trimester of pregnancy (although generally considered safe in the second and third trimesters for specific indications, risk-benefit should be assessed). * Use with disulfiram or alcohol (disulfiram-like reaction). ## Adverse Effects * **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness, dark urine. * **Serious:** Peripheral neuropathy (especially with prolonged use), CNS effects (seizures, encephalopathy, cerebellar toxicity), Stevens-Johnson syndrome, toxic epidermal necrolysis, hepatic dysfunction. * **Disulfiram-like reaction:** With concurrent alcohol use. ## Key Drug Interactions * **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia). Advise patients to avoid alcohol during treatment and for at least 3 days after. * **Warfarin:** Potentiates anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed. * **Lithium:** Can increase lithium levels. Monitor lithium levels. * **Disulfiram:** Coadministration is contraindicated. * **Phenobarbital, Phenytoin:** May decrease metronidazole levels. * **Cyclosporine:** Can increase cyclosporine levels. ## Monitoring * **Clinical:** Assess for improvement of signs and symptoms of infection. * **Adverse Effects:** Monitor for peripheral neuropathy (numbness, tingling), CNS symptoms (seizures, confusion), and hepatic function. * **INR:** If coadministered with warfarin. * **Lithium levels:** If coadministered with lithium. ## Clinical Pearls * Metronidazole has activity against anaerobic bacteria and protozoa. * A metallic taste is a common and expected adverse effect. * Avoid alcohol and products containing alcohol during therapy and for at least 72 hours after the last dose due to potential for a disulfiram-like reaction. * Prolonged therapy may increase the risk of peripheral neuropathy and CNS toxicity. * For IV administration, metronidazole is typically diluted in saline or dextrose solutions. --- ***Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information, institutional protocols, and professional judgment before making clinical decisions. Drug information can change rapidly.*