Bactrim DS for Staph Skin Infection
Bactrim DS (trimethoprim-sulfamethoxazole 160/800 mg twice daily) is highly effective as first-line oral therapy for MRSA skin infections and should be used for 7-10 days, but for methicillin-susceptible staph aureus (MSSA), dicloxacillin or cephalexin are superior choices. 1
Treatment Algorithm Based on Methicillin Susceptibility
For MRSA Skin Infections:
- TMP-SMX (Bactrim DS) 1-2 double-strength tablets (160/800 mg) twice daily for 7-10 days is the most effective first-line oral option 1
- Alternative agents include doxycycline 100 mg twice daily when TMP-SMX fails or is contraindicated 1
- Minocycline 200 mg loading dose, then 100 mg twice daily may be more reliable than doxycycline for community-acquired MRSA 1, 2
- Clindamycin 300-600 mg every 8 hours is preferred when coverage for both MRSA and β-hemolytic streptococci is needed, though resistance rates are now very common 3
For MSSA Skin Infections:
- Dicloxacillin or cephalexin for 7 days is first-line treatment, NOT Bactrim DS 1
- Bactrim DS should be reserved for MRSA or penicillin-allergic patients 1
Critical Management Principles
Incision and Drainage:
- Incision and drainage is mandatory for any abscess or purulent wound infection and must be performed before or concurrent with antibiotic therapy 1
- Continue warm compresses even when using antibiotics to promote drainage 4
Culture Guidance:
- Obtain cultures from purulent drainage before starting antibiotics to confirm the pathogen and guide definitive therapy 1
- In vitro susceptibilities do not always predict in vivo effectiveness with MRSA 2
Dosing Considerations for Bactrim DS
Standard vs. High Dose:
- Standard dose (160/800 mg twice daily) and high dose (320/1600 mg twice daily) show similar clinical resolution rates for MRSA skin infections 5
- Use standard dose (1-2 double-strength tablets twice daily) as recommended by guidelines 3, 1
Treatment Duration:
- 7-10 days of therapy is recommended for uncomplicated skin infections 3, 1
- Duration should be individualized based on clinical response 3
Efficacy Evidence
Comparative Effectiveness:
- TMP-SMX, doxycycline, and minocycline are effective for community-acquired MRSA skin infections based on observational studies and small randomized trials 3
- In pediatric patients, TMP-SMX and clindamycin show no significant differences in outcomes for MRSA skin infections 6
- For serious MRSA infections with high bacterial burden, vancomycin remains superior to TMP-SMX 7
Important Caveat:
- TMP-SMX may be effective for infections with low bacterial burdens of susceptible strains 8
- All treatment failures with TMP-SMX in one major study occurred in patients with MSSA infection, particularly tricuspid valve endocarditis 7
When to Escalate Therapy
Indications for IV Antibiotics:
- Systemic signs of infection persisting despite oral therapy 4
- Rapid progression despite appropriate oral antibiotics 4
- Severe or necrotizing infections requiring immediate IV therapy 3
- IV options for MRSA include vancomycin 15 mg/kg every 12 hours, daptomycin 4-6 mg/kg daily, linezolid 600 mg every 12 hours, or ceftaroline 600 mg every 12 hours 3
Transition to Oral Therapy:
- Switch from IV to oral when criteria of clinical stability have been reached 3
- Oral therapy is recommended for mild infections; moderate infections may be treated with 1-2 IV doses then transition to oral 3
Special Populations
Pediatric Patients:
- Clindamycin 10-13 mg/kg/dose every 6-8 hours is preferred for children with MRSA infections 1
- Avoid doxycycline in children <8 years old due to tooth discoloration and bone growth effects 1, 4
Combination Therapy:
- If coverage for both streptococci and MRSA is desired, combine TMP-SMX with a beta-lactam (penicillin, cephalexin, or amoxicillin) 3
Common Pitfalls to Avoid
- Do not use Bactrim DS empirically for MSSA when dicloxacillin or cephalexin are appropriate 1
- Do not use clindamycin empirically for MRSA without susceptibility testing due to increasing resistance rates 3, 4
- Do not rely on antibiotics alone without incision and drainage for abscesses 1
- Nausea and vomiting are common side effects with TMP-SMX (23% toxicity rate) 7