Bactrim Dosage for Cellulitis
For purulent cellulitis with suspected MRSA, prescribe Bactrim 1-2 double-strength tablets (160/800 mg) orally twice daily for 5-6 days. 1
Dosing by Patient Population
Adults
- Standard dose: 1-2 double-strength tablets (160/800 mg) orally twice daily 1
- Treatment duration: 5-6 days for uncomplicated cases 1
- This dosing is specifically recommended by the Infectious Diseases Society of America for purulent cellulitis 1
Pediatric Patients
- Trimethoprim 4-6 mg/kg/dose plus sulfamethoxazole 20-30 mg/kg/dose orally every 12 hours 1
- Contraindicated in infants under 2 months of age 1
Critical Context: When Bactrim Is Appropriate
Bactrim is specifically indicated for purulent cellulitis, not non-purulent cellulitis. This distinction is crucial because the evidence shows different bacterial etiologies:
- For purulent cellulitis (with drainage, exudate, or abscess): MRSA coverage with Bactrim is appropriate 1
- For non-purulent cellulitis (simple erythema without drainage): Adding trimethoprim-sulfamethoxazole to cephalexin provided no benefit over cephalexin alone in a large randomized trial of 496 patients (clinical cure 83.5% vs 85.5%, difference -2.0%, 95% CI -9.7% to 5.7%) 2
Important Contraindications
- Pregnancy, especially third trimester (Category C/D classification) 1, 3
- Infants under 2 months of age 1
Monitoring and Expected Response
- Clinical improvement should be evident within 48-72 hours 3
- If no improvement occurs, consider MRSA resistance or need for incision and drainage if abscess has formed 3
Alternative Regimens for MRSA Coverage
If Bactrim is contraindicated or not tolerated:
- Clindamycin 300-450 mg orally three times daily (higher risk of C. difficile infection) 1, 3
- Doxycycline 100 mg orally twice daily (avoid in children under 8 years and pregnancy) 1, 3
- Linezolid 600 mg orally twice daily (more expensive option) 1, 3
Common Pitfalls to Avoid
- Do not use Bactrim for non-purulent cellulitis: The evidence demonstrates no added benefit when combined with beta-lactams for simple cellulitis without purulent features 4, 2
- Do not prescribe for extended durations: 5-6 days is sufficient for uncomplicated cases; longer courses are unnecessary 1
- Monitor for serious adverse effects: While rash, nausea, and GI disturbances are common, Stevens-Johnson syndrome is a rare but serious complication 3