What is the dosage and treatment duration of Bactrim (trimethoprim/sulfamethoxazole) for bacterial infections?

Trimethoprim/Sulfamethoxazole (Bactrim) Dosage and Treatment Duration for Bacterial Infections

For bacterial infections, trimethoprim-sulfamethoxazole (Bactrim) is typically dosed as 1-2 double-strength tablets (160mg/800mg) twice daily for adults, with treatment duration ranging from 5-14 days depending on the specific infection type. 1

Adult Dosing Recommendations

Oral Administration

• Standard adult dose: 1-2 double-strength tablets (160mg/800mg) twice daily 2
• Duration by infection type:
  • Urinary tract infections: 10-14 days 1
  • Skin and soft tissue infections: 7 days (depending on clinical response) 2
  • Acute exacerbations of chronic bronchitis: 14 days 1
  • Traveler's diarrhea: 5 days 1
  • Shigellosis: 5 days 1

Intravenous Administration

• Dosage: 8-12 mg/kg/day (based on trimethoprim component) in 4 divided doses 2

Pediatric Dosing Recommendations

• Standard pediatric dose: 8-12 mg/kg/day (based on trimethoprim component) in either 4 divided doses IV or 2 divided doses PO 2
• For children ≥2 months of age (weight-based dosing) 1:
  • 10 kg: 1 teaspoonful (5 mL) every 12 hours
  • 20 kg: 2 teaspoonfuls (10 mL) every 12 hours
  • 30 kg: 3 teaspoonfuls (15 mL) every 12 hours
  • 40 kg: 4 teaspoonfuls (20 mL) every 12 hours
• Duration: Same as adults based on infection type
• Note: Contraindicated in children less than 2 months of age 1

Special Indications

Pneumocystis jirovecii Pneumonia

• Treatment dose: 75-100 mg/kg/day sulfamethoxazole and 15-20 mg/kg/day trimethoprim in equally divided doses every 6 hours for 14-21 days 1
• Prophylaxis dose:
  • Adults: 1 double-strength tablet daily 1
  • Children: 750 mg/m²/day sulfamethoxazole with 150 mg/m²/day trimethoprim in equally divided doses twice daily, 3 consecutive days per week 1

MRSA Skin and Soft Tissue Infections

• Dosage: 1-2 double-strength tablets twice daily 2
• Duration: 7 days (depending on clinical response) 2

Dosage Adjustment for Renal Impairment

• CrCl >30 mL/min: Standard regimen
• CrCl 15-30 mL/min: Half the usual regimen
• CrCl <15 mL/min: Not recommended 1

Clinical Considerations and Cautions

• TMP-SMX is bactericidal but has limited published efficacy data for some infections 2
• Consider resistance patterns in your geographic area before prescribing, as resistance has increased over time 3
• Monitor for adverse effects, particularly with longer treatment courses:
  • Common side effects include rash, gastrointestinal disturbances, and photosensitivity
  • Serious but rare effects include bone marrow suppression, Stevens-Johnson syndrome, and hepatotoxicity 4
• For skin and soft tissue infections, surgical drainage remains the primary treatment for purulent infections, with TMP-SMX as adjunctive therapy 5

Pitfalls to Avoid

1. Inappropriate duration: Avoid underdosing or extending treatment unnecessarily
2. Use in contraindicated populations: Do not use in children <2 months, pregnant women near term, or patients with severe renal impairment
3. Failure to adjust for renal function: Always check creatinine clearance and adjust dosing accordingly
4. Ignoring resistance patterns: Consider local resistance patterns before prescribing
5. Drug interactions: Be aware of potential interactions with warfarin, phenytoin, methotrexate, and other medications

By following these guidelines, you can optimize the use of trimethoprim-sulfamethoxazole for bacterial infections while minimizing the risk of treatment failure and adverse effects.