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# Metronidazole
## Overview
Metronidazole is an antimicrobial agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* Treatment of anaerobic bacterial infections (e.g., intra-abdominal infections, gynecological infections, skin and soft tissue infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis).
* Treatment of protozoal infections (e.g., trichomoniasis, amebiasis, giardiasis).
* Treatment of *Clostridioides difficile* infection (CDI).
* Surgical prophylaxis.
## Adult Dosing
* **Anaerobic bacterial infections:** 500 mg intravenously (IV) or orally every 8 hours. Dosing may vary based on infection severity and site. For severe infections, doses up to 1 g IV every 8 hours have been used. Usual duration is 7-14 days.
* **Trichomoniasis:** 2 g orally as a single dose, or 200 mg orally every 12 hours for 7 days.
* **Amebiasis (intestinal):** 500-650 mg orally every 8 hours for 5-10 days.
* **Amebiasis (extraintestinal):** 500-800 mg orally or IV every 8 hours for 5-10 days.
* ***Giardiasis:*** 250 mg orally every 8 hours for 5-7 days.
* ***Clostridioides difficile* infection (CDI):** 500 mg orally every 8 hours for 10-14 days.
## Pediatric Dosing
* **Anaerobic bacterial infections:** 15 mg/kg orally or IV every 8 hours, not to exceed 4 g per day. Dosing is highly dependent on the specific indication and patient weight.
* ***Giardiasis:*** 5 mg/kg orally every 8 hours for 5-7 days (maximum 250 mg/dose).
* **Other indications:** Consult specialized pediatric resources for specific dosing guidelines.
## Dose Adjustments
No dose adjustment is typically needed for renal impairment.
In hepatic impairment, consider reducing the dose by 30-50% and monitoring for toxicity, especially with prolonged use.
## Contraindications
* Known hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (relative contraindication, weigh risks and benefits).
* Concurrent use of disulfiram or alcohol (due to disulfiram-like reaction).
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
Serious: Seizures, peripheral neuropathy (especially with prolonged use), Stevens-Johnson syndrome, toxic epidermal necrolysis, encephalopathy, leukopenia, pancreatitis.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, dyspnea). Advise patients to avoid alcohol during and for at least 3 days after treatment.
* **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.
* **Disulfiram:** Concurrent use can lead to psychotic reactions. Avoid concurrent use.
## Monitoring
* Monitor for signs and symptoms of neuropathy (numbness, tingling, pain).
* Monitor for CNS effects (dizziness, confusion, seizures).
* Monitor for gastrointestinal upset.
* In CDI, monitor for clinical improvement.
## Clinical Pearls
* Metronidazole has a distinct metallic taste which can affect patient adherence.
* Advise patients to avoid alcohol during therapy and for 72 hours after the last dose.
* For vaginal infections (trichomoniasis), treating the sexual partner is crucial to prevent reinfection.
* The oral formulation can be crushed and mixed with food or liquid if needed, but verify before administration.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional guidelines for definitive dosing and management.*
