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## Metronidazole
### 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.
* **Amebiasis:** Intestinal and extraintestinal amebiasis.
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, gynecological infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis).
* **_Clostridioides difficile_ Infection:** Alternative therapy for _C. difficile_ infection (CDI).
* **Surgical Prophylaxis:** Prophylaxis in specific surgical procedures (e.g., colorectal surgery).
* **Helicobacter pylori Eradication:** Part of combination therapy for _H. pylori_ eradication.
### Adult Dosing
Dosing varies significantly by indication. Refer to specific guidelines for each.
* **Bacterial Vaginosis:**
* Oral: 500 mg twice daily for 7 days.
* Vaginal gel 0.75%: One full applicator (5 g) intravaginally once daily for 5 days.
* **Trichomoniasis:**
* Oral: 2 g as a single dose or 250 mg three times daily for 7 days or 500 mg twice daily for 7 days.
* **Amebiasis:**
* Intestinal: Oral 500-750 mg three times daily for 7-10 days.
* Extra-intestinal (e.g., liver abscess): Oral 500-750 mg three times daily for 7-10 days, or IV 500 mg every 8 hours.
* **Giardiasis:**
* Oral: 250 mg three times daily for 5-7 days.
* **Anaerobic Bacterial Infections:**
* Oral/IV: 500 mg every 8 hours. Duration varies by infection severity and site.
* Maximum dose typically 4 g daily.
* **_Clostridioides difficile_ Infection (CDI):**
* Oral: 500 mg three times daily for 10-14 days (generally reserved for non-severe disease or as an alternative).
* **Surgical Prophylaxis:**
* Oral/IV: 1 g administered 1 hour before surgery, followed by 500 mg every 8 hours for up to 24 hours postoperatively.
* **_H. pylori_ Eradication:**
* Oral: Typically 500 mg twice daily for 10-14 days as part of a multi-drug regimen.
### Pediatric Dosing
Dosing is weight-based and indication-dependent. Consult pediatric infectious disease guidelines.
* **_General Anaerobic Infections_:** Oral/IV 7.5 mg/kg per dose every 8 hours.
* Maximum pediatric dose: 500 mg per dose or 4 g daily.
* **_Amebiasis_:** Oral/IV 12.5 mg/kg per dose every 8 hours for 7-10 days.
* Maximum pediatric dose: 750 mg per dose.
* **_Giardiasis_:** Oral 5 mg/kg per dose three times daily for 5-7 days.
* Maximum pediatric dose: 250 mg per dose.
* **_Trichomoniasis_:** Oral 5 mg/kg per dose twice daily for 7 days.
* Maximum pediatric dose: 250 mg per dose.
* **_Bacterial Vaginosis (Adolescents)_:** As per adult dosing.
### Dose Adjustments
* **Renal Impairment:** No dose adjustment is generally required in renal impairment. However, use caution in severe impairment.
* **Hepatic Impairment:** Dose reduction may be necessary in severe hepatic impairment.
### Contraindications
* Known hypersensitivity to metronidazole or other nitroimidazole derivatives.
* First trimester of pregnancy (though often used if benefits outweigh risks).
### Adverse Effects
* **Common:** Nausea, metallic taste, anorexia, vomiting, diarrhea, abdominal discomfort, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, leukopenia, thrombophlebitis (with IV administration), Stevens-Johnson syndrome, toxic epidermal necrolysis, pancreatitis.
* **Disulfiram-like reaction:** With alcohol.
### Key Drug Interactions
* **Alcohol:** Severe disulfiram-like reaction (flushing, vomiting, tachycardia). Avoid alcohol consumption during therapy 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, leading to toxicity. Monitor lithium levels.
* **Phenytoin, Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** May increase cyclosporine levels. Monitor cyclosporine levels.
### Monitoring
* Monitor for signs and symptoms of neuropathy (numbness, tingling, pain).
* Monitor complete blood counts with prolonged therapy.
* Monitor for signs of hypersensitivity reactions.
* For _H. pylori_ regimens, monitor for treatment efficacy.
* For warfarin interaction, monitor INR.
### Clinical Pearls
* Metronidazole can cause dark or red-brown urine.
* Advise patients to avoid alcohol during treatment.
* IV metronidazole should be infused slowly.
* Oral formulations may be taken with or without food.
* Consider metronidazole's activity against specific anaerobic organisms when selecting therapy.
**Disclaimer:** This information is for clinical reference only. Always consult the most current prescribing information and institutional protocols for complete drug details, dosing, and safety.
