Bactrim Dosing for Skin Infections
For uncomplicated skin and soft tissue infections in adults, prescribe trimethoprim-sulfamethoxazole (Bactrim) 1-2 double-strength tablets (160mg/800mg TMP-SMX) twice daily for 7-10 days. 1, 2
Adult Dosing
- Standard dose: 1-2 double-strength tablets (160mg/800mg) twice daily orally 1, 2
- Duration: 5-10 days based on clinical response 2
- Intravenous option: 8-12 mg/kg/day (based on trimethoprim component) in 4 divided doses for severe infections 1
The Infectious Diseases Society of America (IDSA) guidelines establish Bactrim as a bactericidal agent with proven efficacy against MRSA skin infections, which is critical given that MRSA accounts for approximately 40-55% of skin abscess cultures in contemporary practice. 1, 3, 4
Pediatric Dosing
- Oral: 8-12 mg/kg/day (based on trimethoprim component) in 2 divided doses 1, 2
- Intravenous: 8-12 mg/kg/day in 4 divided doses 1
- Duration: 5-10 days, with 10 days preferred for MRSA infections 2, 5
Critical caveat: Pediatric patients with MRSA abscesses treated for only 3 days showed significantly higher treatment failure rates (10.1% difference) and recurrence within 1 month (10.3% difference) compared to 10-day treatment, making the full 10-day course essential for MRSA infections. 5
Clinical Context and Evidence Quality
The recommendation for Bactrim is supported by high-quality randomized controlled trial data showing superiority over placebo for drained abscesses. In a large multicenter trial, Bactrim achieved 92.9% cure rates versus 85.7% for placebo (7.2% difference, P<0.001), and significantly reduced subsequent surgical drainage procedures (3.4% vs 8.6%), new site infections (3.1% vs 10.3%), and household member infections (1.7% vs 4.1%). 3
When compared head-to-head with clindamycin, Bactrim showed equivalent cure rates (91.9% vs 92.1%), though clindamycin demonstrated lower recurrence rates at 6-8 weeks (2.0% vs 7.1%, P<0.05). 4 This suggests clindamycin may be preferable for patients with high recurrence risk, though both are IDSA-recommended first-line agents. 1, 2
When to Use Bactrim
Indications for antibiotic therapy (in addition to incision and drainage): 2
- Severe or extensive disease with surrounding cellulitis
- Rapid progression of infection
- Signs of systemic illness or sepsis
- Immunocompromised patients
- Extremes of age (very young or elderly)
- Difficult-to-drain locations (face, hands, genitals)
- Multiple abscesses or recurrent infections
Important Caveats
- Incision and drainage remains the primary treatment for purulent abscesses; antibiotics are adjunctive 2
- Bactrim lacks reliable streptococcal coverage—if non-purulent cellulitis without abscess is present, consider beta-lactams instead 1
- Most common side effect is mild gastrointestinal upset 3
- For severe/complicated infections requiring hospitalization, use intravenous vancomycin (30 mg/kg/day in 2 divided doses) as first-line for MRSA coverage 1