What is the appropriate dosage of Bactrim (sulfamethoxazole and trimethoprim) for treating a suspected bacterial skin rash?

Bactrim Dosing for Bacterial Skin Infections

For suspected bacterial skin rash in adults, the recommended dosage of trimethoprim-sulfamethoxazole (Bactrim) is 1-2 double-strength tablets (160mg/800mg) twice daily for 7-10 days. 1, 2

Adult Dosing Options

• For mild to moderate skin infections: 1 double-strength tablet (160mg/800mg) twice daily 2
• For more severe infections: 2 double-strength tablets twice daily 2
• Standard duration of therapy is 7 days, depending on clinical response 1

Pediatric Dosing

• For children ≥2 months: 8-12 mg/kg/day of trimethoprim component (40-60 mg/kg/day of sulfamethoxazole) divided into 2 doses 1, 2
• Not recommended for children under 2 months of age 2
• Weight-based dosing guide:
  • 10-20 kg: 1/2 tablet every 12 hours
  • 20-40 kg: 1 tablet every 12 hours

  • 40 kg: adult dosing 2

Clinical Considerations

• TMP-SMX is bactericidal against many skin pathogens, including MRSA 1
• Good penetration into skin tissue has been demonstrated, with drug concentrations exceeding MIC for susceptible pathogens 3, 4
• Consider TMP-SMX particularly when:
  • MRSA is suspected or prevalent in your community 1
  • Previous treatment failure with beta-lactam antibiotics 1
  • Patient has risk factors for community-acquired MRSA 1

Monitoring and Precautions

• Monitor for adverse reactions, most commonly:

  • Gastrointestinal disturbances (usually mild) 1
  • Skin rashes (including rare but serious Stevens-Johnson syndrome) 1, 5
  • Hematologic abnormalities (neutropenia, thrombocytopenia) 1

• Contraindications:

  • Pregnancy (especially third trimester) 1
  • Known sulfa allergy 1
  • Severe renal impairment (creatinine clearance <15 mL/min) 2

Alternative Options

If TMP-SMX is contraindicated, consider these alternatives for skin infections:

• Clindamycin: 300-450 mg orally four times daily for adults 1
• Doxycycline: 100 mg orally twice daily (not for children <8 years) 1
• Linezolid: 600 mg orally twice daily (more expensive option) 1

Important Clinical Pearls

• Always obtain cultures in severe or non-responsive cases to guide therapy 1
• For simple skin abscesses, incision and drainage may be sufficient without antibiotics 1
• TMP-SMX has been used off-label for various skin conditions including bacterial skin infections 6, 7
• If mild rash develops, discontinue TMP-SMX temporarily; if severe rash (urticarial or Stevens-Johnson) occurs, permanently discontinue 1, 5