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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 trichomoniasis.
* **Amebiasis:** Treatment of amebiasis (intestinal and extraintestinal).
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, gynecological infections, bacterial vaginosis, C. difficile-associated diarrhea).
## Adult Dosing
* **Bacterial Vaginosis:**
* 2 grams orally once.
* Alternatively, 500 mg orally twice daily for 7 days.
* **Trichomoniasis:**
* 2 grams orally once.
* Alternatively, 250 mg orally three times daily for 7 days.
* Alternatively, 375 mg orally twice daily for 7 days.
* **Amebiasis:**
* **Intestinal:** 500 mg to 650 mg orally three times daily for 7 to 10 days.
* **Extra-intestinal (e.g., liver abscess):** 500 mg to 750 mg orally three times daily for 5 to 10 days.
* **Giardiasis:**
* 250 mg orally three times daily for 5 to 7 days.
* **Anaerobic Bacterial Infections:**
* **General:** 500 mg orally or IV every 8 hours. Duration varies by infection severity and site.
* **C. difficile-associated diarrhea (CDAD):** 500 mg orally every 8 hours for 10 to 14 days. *Note: Oral vancomycin is often preferred for initial episodes of severe CDAD or for recurrent episodes.*
## Pediatric Dosing
Dosing in children is based on weight and indication and may require specific calculations. Consult pediatric infectious disease guidelines.
* **Trichomoniasis:** Not typically recommended for children.
* **Giardiasis:** 15 mg/kg/day orally in 3 divided doses for 5 to 7 days. Maximum 250 mg per dose or 750 mg/day.
* **Anaerobic Bacterial Infections:** Doses vary. For example, 7.5 mg/kg/dose orally or IV every 8 hours.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally needed for mild to moderate renal impairment. In severe renal impairment (CrCl < 10 mL/min), the dosing interval may need to be extended (e.g., every 12 hours) or the dose reduced, though data is limited. Metronidazole and its metabolites are removed by hemodialysis.
* **Hepatic Impairment:** Caution and potentially dose reduction in severe hepatic impairment due to reduced clearance.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use in the first trimester of pregnancy for trichomoniasis (oral therapy is generally avoided).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, leukopenia, thrombocytopenia, Stevens-Johnson syndrome, disulfiram-like reaction with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, headache, nausea, vomiting, palpitations, shortness of breath). Patients should avoid alcohol during treatment and for at least 3 days after completion.
* **Warfarin:** Potentiates the effect of warfarin, leading to an increased risk of bleeding. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase serum lithium levels, leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease the efficacy of metronidazole.
* **Succinylcholine:** Metronidazole may prolong the neuromuscular blockade.
## Monitoring
* **Clinical response:** Assess for improvement in signs and symptoms of infection.
* **Neurological symptoms:** Monitor for peripheral neuropathy or central nervous system effects.
* **Complete blood count (CBC):** Consider monitoring CBC, especially with prolonged or high-dose therapy, to detect leukopenia.
* **INR:** If co-administered with warfarin.
## Clinical Pearls
* The metallic taste is common and may be managed by offering ice chips or sugar-free candy.
* Advise patients to avoid alcohol during and for at least 72 hours after completing therapy.
* Oral metronidazole can be taken with or without food.
* Intravenous administration can be irritating; ensure adequate venous access.
* For the treatment of *Clostridioides difficile* infection (CDI), oral vancomycin is generally preferred for initial treatment of severe or fulminant CDI and for recurrent CDI.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant guidelines before making clinical decisions.*
