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# Metrogyl (metronidazole)
## Overview
Metronidazole is an antimicrobial agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of symptomatic bacterial vaginosis.
* **Trichomoniasis:** Treatment of *Trichomonas vaginalis* infection.
* **Amebiasis:** Treatment of amebiasis (intestinal and extraintestinal).
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Used in the treatment of serious anaerobic bacterial infections, often as part of combination therapy (e.g., intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections). It is also used for *Clostridioides difficile* infection (CDI), though oral vancomycin is often preferred for initial treatment.
## 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%: 5 grams (one applicatorful) intravaginally once daily for 5 days.
* **Trichomoniasis:** 2 grams orally as a single dose OR 250 mg orally three times daily for 7 days.
* **Amebiasis:**
* Intestinal: 500-750 mg orally three times daily for 7-10 days.
* Extraintestinal (e.g., liver abscess): 500-750 mg orally three times daily for 7-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5 days OR 2 grams orally once daily for 3 days.
* **Anaerobic Bacterial Infections:** Dosing varies significantly by infection site and severity. Commonly ranges from 500 mg to 1 gram IV or orally every 6-12 hours. **Specific dosing often depends on local antibiogram data and institutional protocols.**
* ***C. difficile* Infection (CDI):** If used, typically 500 mg orally three times daily for 10-14 days (though oral vancomycin is preferred for initial episodes).
## Pediatric Dosing
Dosing for pediatric patients is complex and depends on the indication, weight, and severity of infection. Consult specific pediatric guidelines or drug information resources.
* **Trichomoniasis/Giardiasis:** Often dosed at 15 mg/kg/day orally in 3 divided doses for 7 days (maximum 250 mg/dose or 2 g/day).
* **Amebiasis:** Frequently dosed at 35-50 mg/kg/day orally in 3 divided doses for 7-10 days (maximum 750 mg/dose or 2 g/day).
* **Anaerobic Bacterial Infections:** Typically 7.5 mg/kg/dose IV or orally every 8 hours (or 15 mg/kg/dose every 12 hours), with a maximum dose of 1 gram per dose.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally recommended for mild to moderate renal impairment. Accumulation may occur in severe impairment or with prolonged dialysis, though data is limited. Monitor for adverse effects.
* **Hepatic Impairment:** Dose reduction may be necessary in severe hepatic impairment. Consider reducing the maintenance dose by 30-50% and monitoring drug concentrations if possible.
## Contraindications
* Hypersensitivity to metronidazole, other nitroimidazoles, or any excipient.
* Active central nervous system (CNS) disease.
* Active hepatic disease.
* First trimester of pregnancy (relative contraindication for some indications due to limited data, especially for other nitroimidazoles).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, stomatitis, headache, dizziness, dark/reddish urine.
* **Serious:** Peripheral neuropathy (may be irreversible), CNS effects (seizures, encephalopathy, cerebellar dysfunction), Stevens-Johnson syndrome, toxic epidermal necrolysis, hypersensitivity reactions, pancreatitis.
* **Alcohol Interaction:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, shortness of breath) when taken with alcohol. Advise patients to avoid alcohol during treatment and for at least 3 days after completion.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction.
* **Warfarin:** Potentiates anticoagulant effect; requires close INR monitoring and potential warfarin dose adjustment.
* **Lithium:** May increase serum lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May increase metronidazole metabolism, decreasing efficacy.
* **Busulfan:** Metronidazole can significantly increase busulfan toxicity. Avoid concurrent use.
* **Tofacitinib:** May increase tofacitinib levels.
## Monitoring
* Monitor for signs and symptoms of neuropathy (numbness, tingling, pain in extremities). Discontinue if neuropathy occurs.
* Monitor for CNS effects.
* Monitor for signs of hypersensitivity reactions.
* Monitor INR in patients taking warfarin.
* Monitor lithium levels if co-administered.
* With IV administration, monitor for thrombophlebitis.
## Clinical Pearls
* Administer orally with or without food. Oral suspensions may have an unpleasant taste; consider flavoring or taking with a palatable vehicle.
* Intravenous administration is preferred for severe infections or when oral route is not feasible.
* The metallic taste can be mitigated by sucking on sugarless candy or chewing gum.
* Avoid concurrent use with alcohol to prevent disulfiram-like reactions.
* Treatment duration should be as short as clinically indicated.
* For protozoal infections, ensure patients complete the full course of therapy.
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*This information is intended for healthcare professionals and does not substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines for complete details and to verify dosage, indications, and safety information before prescribing.*
