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# Metronidazole
## Overview
Metronidazole is a nitroimidazole antibiotic and antiprotozoal agent.
## Primary Indications
* **Bacterial vaginosis:** Treatment of vaginal infections caused by bacteria.
* **Trichomoniasis:** Treatment of sexually transmitted infections caused by *Trichomonas vaginalis*.
* **Amebiasis:** Treatment of intestinal and extraintestinal amebiasis.
* **Giardiasis:** Treatment of intestinal infections caused by *Giardia lamblia*.
* **Anaerobic bacterial infections:** Treatment of serious anaerobic infections, often in combination with other agents. Examples include intra-abdominal infections, skin and soft tissue infections, gynecological infections, and CNS infections.
* **_Clostridioides difficile_ infection (CDI):** Although not first-line for most cases, it can be used for mild to moderate CDI.
* **Surgical prophylaxis:** Primarily in colorectal surgery.
## Adult Dosing
* **Bacterial vaginosis:**
* Oral: 500 mg twice daily for 7 days, or 2 g as a single dose.
* Vaginal gel 0.75%: 5 g (one applicatorful) inserted vaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 2 g as a single dose, or 250 mg twice daily for 7 days.
* **Amebiasis:**
* Oral: 500-750 mg three times daily for 5-10 days.
* Pediatric: See Pediatric Dosing.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5 days.
* Pediatric: See Pediatric Dosing.
* **Anaerobic bacterial infections:**
* Oral/IV: 500 mg every 8 hours.
* IV: Usual duration is 7-10 days, but may be longer depending on clinical response and site of infection. Maximum dose generally 4 g daily.
* **CDI:**
* Oral: 500 mg three times daily for 10-14 days. Note: Fidaxomicin or vancomycin are preferred first-line agents for initial CDI episodes.
* **Surgical Prophylaxis:**
* Oral/IV: 1 g given as a single dose just prior to surgery, or 500 mg every 8 hours starting before surgery and continuing for up to 12 hours post-operatively.
## Pediatric Dosing
Dosing is weight-based and depends on the indication. Consult specific pediatric guidelines for precise dosing.
* **Amebiasis:**
* Oral: 35-50 mg/kg/day divided into three doses for 5-10 days. Maximum 750 mg per dose.
* **Giardiasis:**
* Oral: 15 mg/kg/day divided into three doses for 5 days. Maximum 250 mg per dose.
* **Anaerobic bacterial infections:**
* Oral/IV: 7.5 mg/kg/dose every 8 hours (30 mg/kg/day total). Maximum 4 g daily.
## Dose Adjustments
* **Renal impairment:** No dose adjustment generally needed for oral or IV metronidazole. However, caution is advised as some metabolites are renally excreted.
* **Hepatic impairment:** Use with caution. No specific dose adjustment guidelines are universally established, but reduced doses may be considered in severe hepatic disease.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use of disulfiram within the last 2 weeks.
* Use of alcohol during and for at least 3 days after treatment.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), central nervous system effects (seizures, encephalopathy, aseptic meningitis), Stevens-Johnson syndrome, toxic epidermal necrolysis, leukopenia, thrombocytopenia, pancreatitis, dark urine.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, headache). Avoid alcohol during and for at least 3 days after treatment.
* **Disulfiram:** Concurrent use can lead to psychosis or confusional states.
* **Warfarin:** May increase the anticoagulant effect of warfarin. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole may increase serum lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease the efficacy of metronidazole.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels. Monitor cyclosporine levels.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for CNS effects, especially in patients with pre-existing neurological conditions or receiving high doses.
* Monitor CBC if prolonged therapy or high doses are used.
* Monitor INR if used concurrently with warfarin.
* Monitor lithium levels if used concurrently with lithium.
## Clinical Pearls
* Metronidazole has activity against anaerobic bacteria and certain protozoa.
* A metallic taste is a common and expected side effect.
* Urine may become reddish-brown in color.
* Advise patients to avoid alcohol during treatment and for at least 72 hours after the last dose due to the potential for a disulfiram-like reaction.
* For trichomoniasis and giardiasis, treatment of sexual partners is essential to prevent reinfection.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines before making treatment decisions.
