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# Metrogyl (metronidazole)
## Overview
Metronidazole is a nitroimidazole antibiotic effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of symptomatic trichomoniasis.
* **Amebiasis:** Treatment of amebiasis (intestinal amebiasis and amebic liver abscess).
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic bacterial infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis, bacteremia). Often used in combination with other antibiotics.
* **Pseudomembranous colitis:** Treatment of antibiotic-associated colitis caused by *Clostridium difficile*.
* **Surgical prophylaxis:** Prophylaxis against anaerobic infection in specific surgical procedures (e.g., 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%: One applicatorful (5g) inserted vaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 2 g as a single dose OR 250 mg three times daily for 7 days OR 375 mg twice daily for 7 days.
* **Amebiasis:**
* *Intestinal:* Oral: 500-750 mg three times daily for 5-10 days.
* *Liver Abscess:* Oral: 500-750 mg three times daily for 5-10 days. Parenteral followed by oral therapy may be preferred in severe cases.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5 days OR 375 mg twice daily for 7 days OR 500 mg twice daily for 5 days.
* **Anaerobic bacterial infections:**
* Oral: 500 mg every 8 hours.
* Parenteral: 500 mg every 8 hours (IV infusion over 20-60 minutes).
* Maximum dose: Generally 4 g daily.
* **Pseudomembranous colitis:**
* Oral: 250 mg four times daily OR 500 mg three times daily. Duration depends on clinical response, typically 7-14 days.
* **Surgical prophylaxis:**
* Oral/IV: 1 g as a single dose administered 1-2 hours before surgery, or 500 mg every 8 hours starting before surgery and continuing for up to 24 hours postoperatively.
## Pediatric Dosing
Dosing is highly dependent on indication and patient weight. Specific protocols may vary.
* **Bacterial Infections:**
* Oral/Parenteral: 15-30 mg/kg/day divided into 3 doses. Maximum dose typically 4 g/day.
* **Amebiasis:**
* Oral/Parenteral: 35-50 mg/kg/day divided into 3 doses for 5-10 days.
* **Giardiasis:**
* Oral: 15 mg/kg/day divided into 3 doses for 5 days. Maximum dose typically 250 mg three times daily.
* **Trichomoniasis/Bacterial Vaginosis:** Generally not recommended in children < 12 years old. Safety and efficacy not established.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution. Reduce dose in severe hepatic insufficiency (e.g., cirrhosis) by one-third to one-half and administer less frequently.
* **Renal Impairment:** No specific dose adjustment is typically required for oral or IV administration in adults. However, consider the inactive metabolites which can accumulate in renal failure. Some sources suggest reducing dose or extending interval in severe renal impairment (CrCl < 10 mL/min) if on hemodialysis, as metronidazole is removed by dialysis.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Active central nervous system disease.
* First trimester of pregnancy (though benefits may outweigh risks for certain infections).
## Adverse Effects
Common: Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness, rash, pruritus.
Serious: Seizures, peripheral neuropathy (especially with prolonged use or high doses), Stevens-Johnson syndrome, toxic epidermal necrolysis, encephalopathy, aseptic meningitis, pancreatitis, optic neuropathy, leukopenia, thrombophlebitis (with IV).
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (severe nausea, vomiting, flushing, headache, tachycardia). Advise patients to avoid alcohol during treatment and for at least 3 days after.
* **Warfarin:** Potentiates 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.
* **Cyclosporine:** May increase cyclosporine levels. Monitor cyclosporine levels.
* **Disulfiram:** Concurrent use is contraindicated due to potential for psychotic reactions.
## Monitoring
* Monitor for signs and symptoms of neurotoxicity (e.g., dizziness, ataxia, numbness, tingling, seizures).
* Monitor for gastrointestinal adverse effects.
* Monitor for signs of secondary infection or yeast overgrowth.
* For prolonged therapy, consider periodic monitoring of blood counts.
* Monitor INR if used concurrently with warfarin.
* Monitor lithium levels if used concurrently with lithium.
## Clinical Pearls
* The metallic taste is a common and often bothersome side effect.
* Avoid alcohol during treatment and for at least 72 hours after the last dose.
* Metronidazole can turn urine a reddish-brown color.
* For IV administration, infuse slowly over 20-60 minutes to minimize vein irritation.
* Consider anaerobic coverage for polymicrobial infections, especially intra-abdominal, pelvic, and certain skin/soft tissue infections.
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**Disclaimer:** This information is intended for clinical decision support and does not replace individual clinical judgment or comprehensive prescribing information. Always consult the most current product monograph or other authoritative sources for complete and up-to-date information before prescribing.
