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# Metrogyl (metronidazole)
## Overview
Metronidazole is a synthetic nitroimidazole antimicrobial agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* Treatment of anaerobic bacterial infections (e.g., intra-abdominal infections, gynecologic infections, skin and soft tissue infections, bone and joint infections, CNS infections, bacteremia, endocarditis).
* Treatment of trichomoniasis.
* Treatment of amebiasis.
* Treatment of giardiasis.
* Bacterial vaginosis.
* *Clostridioides difficile*-associated diarrhea (CDAD).
## Adult Dosing
* **Anaerobic Infections:** Typically 500 mg every 8 hours or 15 mg/kg loading dose followed by 7.5 mg/kg every 8 hours (or 500 mg every 8 hours) for 7-10 days. IV administration: 500 mg every 8 hours.
* **Trichomoniasis:** 2 grams as a single dose, OR 500 mg twice daily for 7 days, OR 250 mg three times daily for 7 days.
* **Amebiasis:**
* Dysentery: 500-750 mg three times daily for 5-10 days.
* Abscess: 500-750 mg three times daily for 5-10 days, followed by a luminal amebicide (e.g., iodoquinol, paromomycin).
* **Giardiasis:** 250 mg three times daily for 5 days, OR 500 mg twice daily for 7 days.
* **Bacterial Vaginosis:** 500 mg twice daily for 7 days OR 2 grams as a single dose OR 0.75% vaginal gel applied once daily for 5 days.
* ***C. difficile*-associated diarrhea (CDAD):** 500 mg every 8 hours for 10-14 days. This indication is generally reserved for non-severe CDAD.
## Pediatric Dosing
Dosing can be weight-based and may depend on the specific indication and institutional protocol.
* **Anaerobic Infections:** 7.5 mg/kg every 8 hours (IV or PO). Typical max dose is 500 mg per dose.
* **Trichomoniasis:** Not established.
* **Amebiasis:** 35-50 mg/kg/day divided into 3 doses for 5-10 days (max 750 mg/dose).
* **Giardiasis:** 5 mg/kg three times daily for 5 days (max 250 mg/dose).
* ***C. difficile*-associated diarrhea (CDAD):** 20 mg/kg/day divided into 3 doses for 10 days (max 500 mg/dose).
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally needed. Metronidazole and its metabolites are removed by hemodialysis. If given during hemodialysis, supplemental doses may be required.
* **Hepatic Impairment:** Use with caution. Reduce total daily dose in severe hepatic insufficiency.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Concomitant use with disulfiram.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache.
* **Serious:** Peripheral neuropathy (with prolonged use or high doses), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, severe hypersensitivity reactions.
* **Disulfiram-like reaction:** With alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia, dyspnea). Avoid alcohol during therapy and for at least 3 days after completion.
* **Disulfiram:** Risk of psychotic reactions. Avoid coadministration.
* **Warfarin:** Potentiates 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.
* **5-Fluorouracil (5-FU):** Metronidazole may increase the toxicity of 5-FU.
## Monitoring
* Clinical signs and symptoms of infection.
* Neurologic status, especially with prolonged or high-dose therapy.
* Prothrombin time/INR if patient is on warfarin.
* Lithium levels if coadministered.
## Clinical Pearls
* Metronidazole has activity against anaerobic bacteria and protozoa, but not most aerobic bacteria.
* A metallic taste is a common side effect.
* Urine may turn reddish-brown.
* Advise patients to avoid alcohol during treatment and for at least 72 hours after the last dose.
* Prolonged use should be reserved for specific indications due to the risk of peripheral neuropathy.
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*Disclaimer: This information is intended for clinical reference only and does not replace comprehensive drug information resources. Always consult the most current prescribing information and institutional guidelines before making clinical decisions.*
