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# Metronidazole
## Overview
Metronidazole is an antibiotic and antiprotozoal medication effective against anaerobic bacteria and certain parasites.
## Primary Indications
* **Bacterial vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of symptomatic 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, 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.
* **Clostridioides difficile infection (CDI):** Treatment of mild to moderate CDI.
* **Prophylaxis:** Surgical prophylaxis, particularly in colorectal surgery.
* **Rosacea:** Topical metronidazole for inflammatory lesions of rosacea.
## Adult Dosing
* **Bacterial Vaginosis:**
* Oral: 500 mg orally twice daily for 7 days OR 2 grams orally as a single dose.
* Vaginal Gel 0.75%: One applicatorful (5g) intravaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 2 grams orally as a single dose OR 250 mg orally twice daily for 7 days OR 375 mg orally twice daily for 7 days.
* **Amebiasis:**
* Invasive amebiasis (dysentery): 500-650 mg orally three times daily for 5-10 days.
* Amebic liver abscess: 500-650 mg orally three times daily for 5-10 days.
* **Giardiasis:**
* Oral: 250 mg orally three times daily for 5-7 days.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 500 mg every 8 hours.
* Duration varies based on infection severity and patient response. For intra-abdominal infections, often combined with an aerobic antibiotic.
* **Clostridioides difficile infection (CDI):**
* Oral: 500 mg orally three times daily. Duration of therapy is typically 10-14 days, but longer courses may be considered based on local guidelines and patient response.
* **Surgical Prophylaxis (Colorectal Surgery):**
* Oral/IV: 1 gram orally or IV 1-2 hours before surgery, often combined with an oral aminoglycoside or fluoroquinolone.
* **Rosacea (Topical Gel/Cream 0.75% or 1%):**
* Apply a thin layer to affected areas once or twice daily.
## Pediatric Dosing
Dosing for pediatric patients can be highly variable based on indication and weight. Consult specific pediatric guidelines or a pediatrician.
* **Bacterial Infections:**
* Intravenous: 7.5 mg/kg/dose every 8 hours (max 500 mg/dose) or 15 mg/kg/dose every 12 hours (max 1000 mg/dose).
* **Amebiasis:**
* Intestinal: 35-50 mg/kg/day orally divided into three doses for 5-10 days (max 750 mg/dose).
* Extra-intestinal: 35-50 mg/kg/day orally or IV divided into three doses for 5-10 days (max 750 mg/dose).
* **Giardiasis:**
* Oral: 15 mg/kg/day divided into three doses for 5-7 days (max 250 mg/dose).
* **Trichomoniasis:**
* Not typically recommended in children due to lack of data.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution. For severe hepatic impairment, consider reducing the maintenance dose by 33-50% and administering every 8-12 hours.
* **Renal Impairment:** No dose adjustment is generally necessary for standard doses. However, if using hemodialysis, an additional dose may be required after dialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concurrent use of disulfiram.
* Concurrent use of alcohol.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness, rash.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, leukopenia, thrombophlebitis (with IV administration), Stevens-Johnson syndrome, anaphylaxis, pancreatitis.
* **Disulfiram-like reaction:** Severe nausea, vomiting, flushing, tachycardia, and dyspnea with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction. Avoid alcohol during and for at least 3 days after treatment.
* **Disulfiram:** May cause psychotic reactions. Avoid concurrent use.
* **Warfarin:** Metronidazole can potentiate the anticoagulant effect of warfarin. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole can increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenobarbital:** May increase metronidazole metabolism and decrease its efficacy.
* **Cyclosporine:** Metronidazole 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:** Clinical response to therapy.
* **Adverse effects:** Particularly peripheral neuropathy (numbness, tingling, pain in extremities) and neurological symptoms (dizziness, confusion).
* **INR:** If co-administered with warfarin.
* **Lithium levels:** If co-administered with lithium.
* **Complete blood count (CBC):** May be considered in patients receiving prolonged therapy.
## Clinical Pearls
* The metallic taste is a common and often bothersome side effect.
* Oral metronidazole should be taken with food to minimize gastrointestinal upset.
* A disulfiram-like reaction with alcohol can be severe. Patients must be counselled to avoid alcohol consumption.
* Prolonged use of metronidazole may lead to peripheral neuropathy. Advise patients to report symptoms promptly.
* For IV administration, dilute and infuse over 30-60 minutes.
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*Disclaimer: This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and local protocols for definitive guidance. This information does not replace clinical judgment.*
