Bactrim Dosage for Cellulitis
For purulent cellulitis with suspected MRSA, prescribe Bactrim (trimethoprim-sulfamethoxazole) 1-2 double-strength tablets (160/800 mg) orally twice daily for 5-6 days. 1
Dosing by Cellulitis Type
Purulent Cellulitis (with drainage, pus, or abscess)
- Adult dose: 1-2 double-strength (DS) tablets (160/800 mg) orally twice daily 1
- Pediatric dose: Trimethoprim 4-6 mg/kg/dose, sulfamethoxazole 20-30 mg/kg/dose orally every 12 hours 1
- Duration: 5-6 days 1
Nonpurulent Cellulitis (no drainage or pus)
Bactrim is NOT recommended as first-line therapy for nonpurulent cellulitis because its activity against β-hemolytic streptococci (the primary pathogen) is not well-defined. 1 Beta-lactams like cephalexin (500 mg orally four times daily) should be used instead. 1
Key Clinical Considerations
When to Use Bactrim
Bactrim is appropriate when:
- Purulent drainage is present (indicates likely MRSA involvement) 1
- Patient has failed beta-lactam therapy for nonpurulent cellulitis 1
- Systemic toxicity is present in nonpurulent cellulitis (consider adding MRSA coverage) 1
- Local MRSA prevalence is high and clinical suspicion warrants coverage 2
Important Contraindications
- Pregnancy: Category C/D - not recommended in third trimester 1
- Infants: Not recommended for children <2 months of age 1
Treatment Duration Evidence
Five days of antibiotic therapy is as effective as 10 days for uncomplicated cellulitis. 1, 3, 4 The American College of Physicians recommends 5-6 days for nonpurulent cellulitis in patients who can self-monitor with close follow-up. 1 Research demonstrates no additional benefit from courses longer than 5 days. 3, 4
Common Pitfalls to Avoid
Coverage Gap for Streptococci
The most critical pitfall is using Bactrim alone for typical (nonpurulent) cellulitis. 1 TMP-SMX has excellent activity against community-associated MRSA but unreliable activity against β-hemolytic streptococci, which cause most nonpurulent cellulitis. 1 A randomized trial showed that adding TMP-SMX to cephalexin provided no benefit over cephalexin alone for nonpurulent cellulitis. 5
When Bactrim Monotherapy Fails
If a patient with purulent cellulitis on Bactrim is not improving, consider:
- Inadequate source control (abscess requiring drainage) 1
- Streptococcal co-infection requiring beta-lactam addition 1
- Complicated infection requiring IV therapy (vancomycin 15-20 mg/kg IV every 8-12 hours) 1
Severity Indicators Requiring Hospitalization
Do not use oral Bactrim if the patient has: 1
- Systemic toxicity or sepsis
- Rapidly progressive infection despite oral antibiotics
- Multiple infection sites
- Significant comorbidities (diabetes, immunosuppression, HIV/AIDS)
- Extremes of age with severe disease
- Inability to take oral medications
Alternative Regimens for Purulent Cellulitis
If Bactrim cannot be used: