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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 urogenital trichomoniasis.
* **Amoebiasis:** Intestinal and extraintestinal amoebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections, often in combination with other agents.
* **_Clostridioides difficile_ Infection (CDI):** Used for mild to moderate CDI.
* **Surgical Prophylaxis:** Prophylaxis in colorectal surgery.
* **Helicobacter pylori Eradication:** Part of multi-drug regimens.
## Adult Dosing
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days, or 2 g as a single dose.
* Vaginal gel 0.75%: Apply one applicatorful (5g) intravaginally once daily for 5 days.
* **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 (e.g., liver 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 every 8 hours orally or IV. Duration varies with infection severity (typically 7-14 days). Maximum dose: 4 g daily.
* **_Clostridioides difficile_ Infection (Mild/Moderate):** 250 mg orally four times daily for 10 days.
* **Surgical Prophylaxis:** 1 g orally or IV 1 hour before surgery, or 500 mg orally or IV every 8 hours starting before surgery.
* **_H. pylori_ Eradication:** Typically 250-500 mg orally twice or three times daily in combination regimens.
## Pediatric Dosing
Dosing is weight-based and depends on the indication. Consult specific pediatric guidelines.
* **Giardiasis:** 5 mg/kg/dose orally three times daily for 5 days. Maximum 250 mg/dose.
* **Amoebiasis:** 35-50 mg/kg/day orally divided into 3 doses for 5-10 days. Maximum 750 mg/dose.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose orally or IV every 8 hours. Maximum 4 g daily.
## Dose Adjustments
* **Renal Impairment:** No dose adjustment generally needed for hemodialysis or peritoneal dialysis. However, consider reduced frequency in severe renal impairment.
* **Hepatic Impairment:** Use with caution. Reduce dosage by 30-50% in severe hepatic disease.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (risk vs. benefit).
* Concomitant use with disulfiram or alcohol (within 3 days of last dose).
## Adverse Effects
* **Common:** Nausea, vomiting, metallic taste, anorexia, abdominal discomfort, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, Stevens-Johnson syndrome, hypersensitivity reactions, pancreatitis.
* **Disulfiram-like reaction** with alcohol.
* Darkening of urine.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, nausea, vomiting, tachycardia). Avoid alcohol during and for at least 3 days after treatment.
* **Disulfiram:** Increased risk of psychotic reactions. Avoid coadministration.
* **Warfarin:** Enhanced anticoagulant effect. Monitor INR closely.
* **Lithium:** Increased lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Busulfan:** May increase busulfan levels, leading to toxicity.
## Monitoring
* Signs and symptoms of infection.
* Signs of peripheral neuropathy (numbness, tingling) and CNS toxicity (seizures, encephalopathy), especially with prolonged therapy.
* Renal and hepatic function (if impaired).
* INR if co-administered with warfarin.
* Lithium levels if co-administered with lithium.
## Clinical Pearls
* Metronidazole can cause a disulfiram-like reaction with alcohol; patients must be counseled to avoid alcohol.
* A metallic taste is a common side effect.
* Prolonged therapy increases the risk of peripheral neuropathy and CNS effects.
* The vaginal gel formulation may cause local irritation.
* Consider prescribing oral metronidazole for _H. pylori_ eradication with meals to minimize GI upset.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols for complete details and to confirm dosages and indications.
