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# Metronidazole (Metrogyl)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of infections caused by *Trichomonas vaginalis*.
* **Amoebiasis:** Treatment of amoebic infections, including amoebic dysentery and amoebic liver abscess.
* **Giardiasis:** Treatment of infections caused by *Giardia lamblia*.
* **Anaerobic bacterial infections:** Treatment of intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bacterial vaginosis, and *C. difficile*-associated diarrhea. Often used in combination therapy.
* **Prophylaxis:** Surgical prophylaxis, particularly in colorectal surgery.
* **Helicobacter pylori eradication:** Part of combination therapy for *H. pylori* infection.
## 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.
* **Amoebiasis:**
* **Intestinal:** 500-750 mg orally three times daily for 5-10 days.
* **Hepatic Abscess:** 500-750 mg orally three times daily for 5-10 days.
* **Giardiasis:** 250 mg orally three times daily for 5 days, OR 2 g orally once daily for 3 days.
* **Anaerobic Bacterial Infections:** 500 mg intravenously or orally every 8 hours. Duration varies by infection site and severity, typically 7-14 days.
* **Prophylaxis (Colorectal Surgery):** 500 mg intravenously before surgery, followed by 500 mg orally or intravenously every 8 hours for up to 24 hours post-operatively.
* ***H. pylori* Eradication:** Typically 500 mg orally twice daily in combination with other agents for 10-14 days.
## Pediatric Dosing
Dosing in pediatric patients is highly dependent on indication and weight. Consult specific pediatric guidelines or manufacturer information.
* **Giardiasis:** 15 mg/kg/day orally in 3 divided doses, not to exceed 250 mg per dose, for 5 days. Maximum dose: 750 mg/day.
* **Amoebiasis:** 35-50 mg/kg/day orally or IV in 3 divided doses, not to exceed 750 mg per dose, for 5-10 days. Maximum dose: 2.25 g/day.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose IV or orally every 8 hours. Maximum dose: 15 mg/kg/dose or 500 mg per dose.
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustment typically required for mild to moderate impairment. In severe impairment (CrCl < 10 mL/min), consider reducing the dose by 50% and extending the dosing interval, although data is limited. Metronidazole is dialyzable.
* **Hepatic Impairment:** In severe hepatic impairment, consider reducing the dose by 30-50% and extending the dosing interval.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use during the first trimester of pregnancy for trichomoniasis (risk vs. benefit).
* Concurrent use with disulfiram.
* Concurrent use with alcohol (disulfiram-like reaction).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, metallic taste, headache, dark urine.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, Stevens-Johnson syndrome, toxic epidermal necrolysis, encephalopathy, dizziness, ataxia, pancreatitis, neutropenia.
* **Disulfiram-like reaction:** Flushing, headache, nausea, vomiting, palpitations, and chest pain when combined with alcohol.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction. Avoid concurrent use.
* **Disulfiram:** Avoid concurrent use due to potential for psychotic reactions.
* **Warfarin:** Metronidazole can potentiate the 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 efficacy and increase phenytoin/phenobarbital levels.
* **5-Fluorouracil (5-FU):** Metronidazole may increase the toxicity of 5-FU.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for signs of central nervous system effects (dizziness, seizures).
* Monitor for signs of hypersensitivity reactions.
* If used for prolonged periods or in severe hepatic impairment, consider monitoring blood counts.
* For *H. pylori* eradication, assess for symptom resolution and consider repeat testing.
## Clinical Pearls
* Metronidazole has activity against anaerobic bacteria and protozoa.
* Oral administration is generally well-absorbed.
* A metallic taste is a common side effect.
* Patients should be advised to avoid alcohol during and for at least 3 days after treatment to prevent a disulfiram-like reaction.
* Peripheral neuropathy is a risk with prolonged or high-dose therapy.
* For vaginal gel formulations, absorption is significantly less than oral therapy.
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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, clinical guidelines, and institutional protocols before making clinical decisions.*
