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# Metronidazole
## Overview
Metronidazole is an antimicrobial agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of trichomoniasis.
* **Giardiasis:** Treatment of giardiasis.
* **Amebiasis:** Treatment of amebiasis.
* **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).
## 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.
* **Giardiasis:** 250 mg orally three times daily for 5 days, or 500 mg orally twice daily for 5-7 days.
* **Amebiasis:**
* *Intestinal amebiasis:* 500-650 mg orally three times daily for 5-10 days.
* *Extraintestinal amebiasis (e.g., liver abscess):* 500-650 mg orally three times daily for 5-10 days, followed by a luminal agent if intestinal parasites are present.
* **Anaerobic Bacterial Infections:** 500 mg intravenously or orally every 8 hours. Dosing may vary based on severity and site of infection.
* **Pseudomembranous Colitis:** 500 mg orally three times daily for 10-14 days.
## Pediatric Dosing
* **Bacterial Vaginosis:** Not typically used in children.
* **Trichomoniasis:** Not typically used in children.
* **Giardiasis:** 15 mg/kg/day orally in 3 divided doses for 5-7 days. Maximum dose: 250 mg per dose or 750 mg/day.
* **Amebiasis:** 35-50 mg/kg/day orally in 3 divided doses for 5-10 days. Maximum dose: 750 mg/day.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose intravenously or orally every 8 hours. Maximum dose: 4 g/day.
* **Pseudomembranous Colitis:** 10 mg/kg/dose orally every 8 hours for 10-14 days. Maximum dose: 500 mg/dose.
## Dose Adjustments
* **Hepatic Impairment:** Reduce maintenance dose by 50% in severe hepatic disease.
* **Renal Impairment:**
* *Hemodialysis:* Additional dose may be needed after dialysis.
* *Peritoneal Dialysis:* No supplemental dose recommended.
* *CrCl < 10 mL/min:* Consider reducing maintenance dose by 50% for longer courses, although data is limited. For single-dose regimens, no adjustment is generally needed.
## Contraindications
* Known hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use during the first trimester of pregnancy for trichomoniasis is generally avoided unless no other suitable treatment is available.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness, dark urine.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, leukopenia, thrombophlebitis (IV).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (severe nausea, vomiting, flushing, tachycardia, shortness of breath). Patients should avoid alcohol during therapy and for at least 3 days after completion.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** May increase cyclosporine levels. Monitor cyclosporine levels.
* **5-Fluorouracil (5-FU):** Metronidazole may increase the toxicity of 5-FU.
## Monitoring
* **Signs and symptoms of infection resolution.**
* **Adverse effects:** Neurological status, gastrointestinal symptoms.
* **Liver function tests (LFTs)** in patients with severe hepatic impairment.
* **Lithium levels** if co-administered.
* **INR** if co-administered with warfarin.
## Clinical Pearls
* Administer orally with or without food. For IV administration, infuse over 30-60 minutes.
* Metallic taste is common and usually resolves after discontinuation.
* Peripheral neuropathy is a serious adverse effect that can be irreversible. Advise patients to report numbness or tingling.
* For the treatment of anaerobic infections, metronidazole is often used in combination with other agents that cover aerobic organisms.
* The disulfiram-like reaction with alcohol is a significant interaction to counsel patients on.
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*This information is for educational purposes and does not substitute for professional medical advice. Always consult the most current prescribing information and a qualified healthcare provider for any medical decisions.*
