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# Metrogyl (metronidazole)
## Overview
Metronidazole is a synthetic nitroimidazole antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of trichomoniasis.
* **Amoebiasis:** Treatment of amoebic infections of the intestinal tract (intestinal amoebiasis) and extraintestinal amoebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of various anaerobic bacterial infections, including intra-abdominal infections, skin and skin structure infections, gynecologic infections, bacteremia, endocarditis, and bone and joint infections. Often used in combination therapy.
* **Pseudomembranous Colitis:** Treatment of *Clostridioides difficile*-associated diarrhea.
* **Surgical Prophylaxis:** Perioperative prophylaxis for colorectal surgery.
* **H. pylori Eradication:** Part of multi-drug regimens for *Helicobacter pylori* eradication.
## Adult Dosing
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days, or 2 g orally as a single dose.
* **Trichomoniasis:** 2 g orally as a single dose, or 250 mg orally three times daily for 7 days, or 375 mg orally twice daily for 7 days.
* **Amoebiasis:**
* Intestinal: 500-750 mg orally three times daily for 5-10 days.
* Extra-intestinal: 500-750 mg orally three times daily for 5-10 days, followed by a luminal amoebicide.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days.
* **Anaerobic Bacterial Infections:** Typically 500 mg to 1 g intravenously or orally every 6 to 8 hours. Duration varies based on infection site and severity. Maximum dose generally 4 g/day.
* **Pseudomembranous Colitis:** 250-500 mg orally every 6-8 hours.
* **Surgical Prophylaxis:** 1 g orally or IV 1-2 hours before surgery, followed by 500 mg orally or IV every 8 hours for up to 24 hours postoperatively.
* **H. pylori Eradication:** Varies by regimen, often 500 mg orally twice daily in combination with other agents.
## Pediatric Dosing
Dosing is weight-based and depends on the indication. Consult specific pediatric guidelines or product information.
* **Amoebiasis (Intestinal and Hepatic Abscess):** 35-50 mg/kg/day orally or IV divided into 3 doses, not to exceed 750 mg per dose or 4 g/day, for 10 days.
* **Giardiasis:** 15 mg/kg/day orally divided into 3 doses for 5 days, not to exceed 250 mg per dose.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose IV or orally every 8 hours. Duration varies. Maximum dose generally 4 g/day.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment is typically required for renal impairment. Hemodialysis removes metronidazole; supplemental doses may be needed after dialysis if the patient is on chronic intermittent hemodialysis.
* **Hepatic Impairment:** Use with caution and consider dose reduction in severe hepatic impairment.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (relative contraindication, risk vs. benefit for certain indications).
* Concurrent use of disulfiram or alcohol.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, anorexia.
* **Serious:** Peripheral neuropathy (especially with prolonged use), central nervous system effects (seizures, encephalopathy, ataxia, dizziness), Stevens-Johnson syndrome, toxic epidermal necrolysis, severe allergic reactions, opportunistic infections.
* **Other:** Darkening of urine, vaginal candidiasis.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, headache, tachycardia). Avoid alcohol during treatment and for at least 3 days after.
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Disulfiram:** Concurrent use is contraindicated due to potential for psychotic reactions.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels by increasing metabolism.
* **5-Fluorouracil (5-FU):** Metronidazole may increase the toxicity of 5-FU.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain). Discontinue if neuropathy occurs.
* Monitor for CNS effects.
* Monitor stool for resolution of diarrhea in *C. difficile*-associated diarrhea.
* Monitor INR if co-administered with warfarin.
* Monitor lithium levels if co-administered with lithium.
## Clinical Pearls
* Metallic taste is common and usually transient.
* Urine may turn a reddish-brown color.
* Advise patients to avoid alcohol during therapy and for at least 3 days after the last dose.
* For trichomoniasis, sexual partners should also be treated concurrently.
* Use with caution in patients with CNS disorders.
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*This information is for educational purposes only and does not substitute for professional medical advice. Always verify current prescribing information with the official drug product labeling and consult with a qualified healthcare provider for any medical concerns or before making any decisions related to your health or treatment.*
