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# Metronidazole (Metrogyl)
## Overview
Metronidazole is a nitroimidazole antibiotic effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of symptomatic trichomoniasis.
* **Amebiasis:** Treatment of amebiasis (intestinal and extraintestinal).
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis).
* **_Clostridioides difficile_ Infection (CDI):** While historically used, oral vancomycin or fidaxomicin are now preferred for initial CDI treatment, especially for severe cases. Metronidazole may be considered for mild CDI or in specific resource-limited settings.
* **Prophylaxis:** Surgical prophylaxis in specific procedures (e.g., colorectal surgery).
* **_Helicobacter pylori_ Eradication:** As part of combination therapy.
## Adult Dosing
Dosing is highly dependent on the indication and severity of infection.
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days OR 2 g as a single dose.
* Vaginal gel 0.75%: One applicatorful (5 g) inserted intravaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 2 g as a single dose OR 250 mg twice daily for 7 days OR 500 mg twice daily for 7 days.
* **Amebiasis:**
* Invasive intestinal amebiasis: 500-600 mg orally three times daily for 5-10 days.
* Amebic liver abscess: 500-600 mg orally three times daily for 5-10 days.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5 days OR 2 g as a single dose.
* **Anaerobic Bacterial Infections:**
* Oral/IV: Typically 500 mg every 8 hours. Doses can range from 500 mg to 1 gram every 8-12 hours, depending on severity. Duration varies (7-14 days or longer).
* Maximum dose: Generally 4 grams per day.
* **CDI (Mild):**
* Oral: 500 mg three times daily for 10-14 days. (Note: Not first-line).
* **Surgical Prophylaxis (Colorectal):**
* Oral/IV: 1 gram given as a single dose 1 hour before surgery, or 500 mg every 8 hours starting 4 hours before surgery and continuing for 24 hours postoperatively.
## Pediatric Dosing
Dosing is weight-based and depends on the indication.
* **Trichomoniasis/Giardiasis:**
* Oral: 15 mg/kg/day divided into three doses for 7 days (maximum 250 mg per dose). Alternatively, 35-50 mg/kg as a single dose (maximum 2 g).
* **Amebiasis:**
* Oral: 35-50 mg/kg/day divided into three doses for 5-10 days (maximum 750 mg/dose).
* **Anaerobic Bacterial Infections:**
* Oral/IV: 7.5 mg/kg per dose every 8 hours OR 15 mg/kg per dose every 12 hours. Doses can range up to 30 mg/kg/day divided into doses, not to exceed 4 grams per day. Duration 7-14 days or longer.
* **CDI:**
* Oral: 10-15 mg/kg/day divided into three doses for 10-14 days (maximum 500 mg per dose). (Note: Not first-line).
## Dose Adjustments
* **Renal Impairment:** No dose adjustment typically needed for moderate renal impairment. For severe renal impairment (CrCl < 10 mL/min), dosing interval may need to be extended (e.g., every 12 hours instead of every 8 hours for IV formulations). Consider consulting pharmacokinetics.
* **Hepatic Impairment:** Use with caution. Reduce dose in severe hepatic insufficiency. Consider halving the usual maintenance dose.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazoles.
* Concomitant use of disulfiram.
* Concomitant use of alcohol (within 3 days of last dose).
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), CNS effects (seizures, encephalopathy, cerebellar toxicity), Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis, severe allergic reactions, pseudomembranous colitis.
* **Other:** Darkening of urine (harmless), oral/vaginal candidiasis, rash, urticaria, pruritus.
## Key Drug Interactions
* **Alcohol:** Disulfiram-like reaction (flushing, headache, nausea, vomiting, palpitations). Avoid alcohol during and for at least 3 days after treatment.
* **Disulfiram:** May cause acute psychosis or confusional state. Avoid concurrent use.
* **Warfarin:** Metronidazole can potentiate the anticoagulant effect. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** May increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Busulfan:** Metronidazole can increase busulfan levels, potentially causing toxicity.
## Monitoring
* Monitor for signs and symptoms of peripheral neuropathy (numbness, tingling, pain).
* Monitor for CNS toxicity (dizziness, confusion, seizures).
* Monitor for hypersensitivity reactions.
* If used for CDI, monitor stool frequency and consistency.
* If used with warfarin, monitor INR.
## Clinical Pearls
* The metallic taste is common and often resolves after treatment completion.
* Avoid alcohol during and for 3 days after therapy due to a disulfiram-like reaction.
* Prolonged use of metronidazole can increase the risk of peripheral neuropathy.
* For vaginal gel, avoid intercourse and do not use tampons or douches during treatment.
* IV metronidazole is often administered undiluted or diluted in compatible IV solutions. Check specific product labeling.
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*This information is intended for clinical use and does not replace a thorough review of the current prescribing information and patient-specific factors. Always verify the most up-to-date drug information with official sources.*
