Metro

# Metro ## Overview - **Classification**: Nitroimidazole antibiotic, antiprotozoal. - **Mechanism**: Reduced by susceptible organisms/protozoa to reactive metabolites that damage DNA and inhibit nucleic acid synthesis. ## Primary Indications 1. **Anaerobic Bacterial Infections**: Intra-abdominal, skin/soft tissue, gynecologic, bone/joint, CNS, lower respiratory tract. 2. **Trichomoniasis**: _Trichomonas vaginalis_ infection. 3. **Bacterial Vaginosis (BV)**: Polymicrobial infection (e.g., _Gardnerella vaginalis_). 4. **Amebiasis**: _Entamoeba histolytica_ (intestinal and extra-intestinal). 5. **Giardiasis**: _Giardia lamblia_ infection. 6. **_Clostridioides difficile_ Infection (CDI)**: Mild to moderate cases. ## Adult Dosing ### Standard Dosing **Anaerobic Bacterial Infections (e.g., intra-abdominal)** - **Dose**: **500 mg** - **Frequency**: Every **8 hours** (TID) - **Route**: Oral (PO) or Intravenous (IV) - **Duration**: Typically 7-14 days depending on infection severity. **Trichomoniasis** - **Dose**: **2 grams** - **Frequency**: Once (**single dose**) - **Route**: Oral (PO) **Bacterial Vaginosis (BV)** - **Dose**: **500 mg** - **Frequency**: Twice daily (BID) - **Route**: Oral (PO) - **Duration**: 7 days **_Clostridioides difficile_ Infection (CDI) - Mild to Moderate** - **Dose**: **500 mg** - **Frequency**: Every **8 hours** (TID) - **Route**: Oral (PO) - **Duration**: 10-14 days ### Dose Adjustments - **Renal Impairment**: No routine adjustment for CrCl >10 mL/min. - CrCl <10 mL/min: Consider reducing maintenance dose by **50%**. - Hemodialysis: Administer dose after dialysis session. - **Hepatic Impairment**: Severe hepatic dysfunction (Child-Pugh C): Reduce dose by **50%** or extend interval. - **Elderly Patients**: Monitor for adverse effects; may require lower end of dosing range. ## Pediatric Dosing ### Neonates (0-28 days) - **Anaerobic Infections** - **Dose**: **7.5 mg/kg** - **Frequency**: Every **12 hours** (gestational age <28 weeks or postnatal age <7 days). - **Frequency**: Every **8 hours** (gestational age >28 weeks AND postnatal age >7 days). - **Maximum**: Avoid exceeding 15 mg/kg/day total dose. - **Special Notes**: Use cautiously due to immature hepatic metabolism; monitor for neurotoxicity. ### Infants (1-12 months) - **Anaerobic Infections** - **Dose**: **15-30 mg/kg/day** (divided doses) - **Frequency**: Every **8 hours** (TID) - **Maximum**: **1 gram/day**. ### Children (1-12 years) - **Anaerobic Infections** - **Dose**: **30 mg/kg/day** (divided) - **Frequency**: Every **6-8 hours** (Q6-8H) - **Maximum**: **4 grams/day** (not to exceed adult maximum for severe infections). - **Amebiasis** - **Dose**: **35-50 mg/kg/day** (divided) - **Frequency**: Every **8 hours** (TID) - **Maximum**: **750 mg/dose**. - **Giardiasis** - **Dose**: **15 mg/kg/day** (divided) - **Frequency**: Every **8 hours** (TID) - **Maximum**: **250 mg/dose**. ### Adolescents (13-18 years) - **Dose**: Generally follows **adult dosing recommendations**. - **Maximum**: Do not exceed **adult maximum doses**. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to metronidazole or other nitroimidazole derivatives. - **Absolute**: Use of disulfiram within the last 14 days. - **Absolute**: Alcohol consumption during therapy and for at least 3 days after. ### Common Adverse Effects - **Very Common (>10%)**: Nausea, metallic taste, headache. - **Common (1-10%)**: Diarrhea, vomiting, abdominal cramps, dizziness, dark urine. - **Serious but Rare**: Seizures, peripheral neuropathy (with prolonged/high doses), aseptic meningitis, Stevens-Johnson Syndrome (SJS)/TEN. ### Key Drug Interactions - **Warfarin**: Potentiates anticoagulant effect; increases bleeding risk. Monitor **INR** closely, adjust warfarin dose. - **Alcohol**: Disulfiram-like reaction (flushing, headache, nausea, vomiting, abdominal cramps). **Avoid all alcohol** during and for 3 days post-treatment. - **Disulfiram**: Psychotic reactions (confusion, hallucinations). Do not use within 14 days of disulfiram. - **Lithium**: May increase lithium levels. Monitor lithium levels. - **Phenobarbital**: Decreases metronidazole levels (CYP450 induction). ## Monitoring & Follow-up - **Before Treatment**: Pregnancy test (if indicated for women of childbearing potential). - **During Treatment**: Monitor for CNS toxicity (seizures, neuropathy), especially with prolonged use. - Monitor WBC count, especially with prolonged or repeat courses. - **Clinical Signs**: Report new numbness/tingling (neuropathy), severe rash, or seizure activity immediately. ## Clinical Pearls - 💡 **Tip 1**: Take with food to minimize GI upset and metallic taste. - 💡 **Tip 2**: Advise patients to avoid ALL alcohol (including alcohol-containing products like mouthwash) during therapy and for **3 days** after. - 💡 **Tip 3**: May cause urine to turn dark reddish-brown; this is a harmless effect. - 💡 **Tip 4**: For trichomoniasis, concurrent treatment of all sexual partners is crucial to prevent re-infection. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.