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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.
* **Amebiasis:** Intestinal and extraintestinal amebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and skin structure infections, gynecologic infections, bacteremia, bone and joint infections, CNS infections, lower respiratory tract infections). Often used in combination with other agents.
* **Pseudomembranous Colitis:** Treatment of *Clostridium difficile*-associated diarrhea (CDAD).
* **Surgical Prophylaxis:** Preoperative prophylaxis in certain surgeries (e.g., colorectal surgery).
* **H. pylori Eradication:** Part of multi-drug regimens for *Helicobacter pylori* eradication.
## Adult Dosing
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days.
* Vaginal Gel 0.75%: 5 grams (one applicatorful) intravaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: Single dose of 2 grams, 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 5-10 days.
* Extra-intestinal (e.g., liver abscess): Oral 500-650 mg three times daily for 5-10 days. IV may be preferred for severe disease.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5-7 days.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 500 mg every 8 hours.
* IV: Duration varies based on infection severity and response. Typically 7-10 days, but can be longer.
* **Pseudomembranous Colitis (CDAD):**
* Oral: 250 mg four times daily or 500 mg three times daily for 10-14 days. Vancomycin is generally preferred for initial episodes, especially severe ones.
* **Surgical Prophylaxis:**
* Oral/IV: 500 mg to 1 g IV or orally 1 hour before surgery, followed by doses every 8 hours for up to 24 hours post-operatively.
* **H. pylori Eradication:**
* Oral: Varies by regimen, often 250-500 mg twice or three times daily in combination with other agents for 10-14 days.
## Pediatric Dosing
Dosing is often weight-based and depends on the indication. Consult specific pediatric guidelines or literature.
* **Amebiasis:**
* Oral: 35-50 mg/kg/day divided into 3 doses for 5-10 days (maximum 750 mg/dose).
* **Giardiasis:**
* Oral: 15 mg/kg/day divided into 3 doses for 5-7 days (maximum 250 mg/dose).
* **Anaerobic Bacterial Infections:**
* Oral/IV: 7.5 mg/kg/dose every 8 hours (maximum 400 mg/dose for pediatric and 500 mg/dose for adolescent patients). Duration varies.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution in severe hepatic impairment. Reduced doses may be necessary due to impaired metabolism.
* **Renal Impairment:** No specific dose adjustment is generally required for intermittent hemodialysis or peritoneal dialysis. However, for continuous renal replacement therapy, consult specific guidelines as clearance can be significant.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concomitant use with disulfiram.
* Concomitant use with alcohol (due to disulfiram-like reaction).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, anorexia, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, severe hypersensitivity reactions, thrombophlebitis (IV formulation).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, palpitations, headache). Advise patients to avoid alcohol during therapy and for at least 3 days after.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels.
## Monitoring
* **Clinical Response:** Monitor for improvement of signs and symptoms of infection.
* **Adverse Effects:** Monitor for signs of peripheral neuropathy, CNS effects, and hypersensitivity reactions.
* **Laboratory Tests:** Liver function tests may be considered in prolonged therapy or in patients with pre-existing liver disease. Monitor INR if co-administered with warfarin. Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* Instruct patients to avoid alcohol during treatment and for at least 72 hours after the last dose.
* A metallic taste is common and usually resolves after treatment.
* Neurological side effects can be serious; patients should report any numbness, tingling, or coordination problems immediately.
* When used for trichomoniasis, sexual partners should be treated concurrently to prevent reinfection.
* The IV formulation can cause thrombophlebitis; use slow infusion and rotate sites.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines for complete details and to confirm dosages and safety before administering any medication.
