Oral Antibiotics for MRSA Infections
For MRSA skin and soft tissue infections, trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets twice daily, clindamycin 300-450 mg three times daily (if local resistance <10%), or doxycycline/minocycline 100 mg twice daily are the recommended first-line oral options. 1, 2
First-Line Oral Antibiotic Options
Trimethoprim-Sulfamethoxazole (TMP-SMX)
- TMP-SMX is a preferred first-line agent for purulent cellulitis and uncomplicated MRSA skin infections 1, 2
- Adult dosing: 1-2 double-strength tablets (160/800 mg) orally twice daily 1
- Pediatric dosing: 4-6 mg/kg/dose (trimethoprim component) every 12 hours 1, 2
- Critical limitation: TMP-SMX does not provide adequate coverage for beta-hemolytic streptococci, so consider adding a beta-lactam if streptococcal infection is suspected 2, 3
- Contraindicated in third trimester pregnancy and children <2 months of age 1
Clindamycin
- Clindamycin provides dual coverage for both MRSA and beta-hemolytic streptococci, making it ideal for nonpurulent cellulitis 1, 2
- Adult dosing: 300-450 mg orally three times daily 1
- Pediatric dosing: 10-13 mg/kg/dose every 6-8 hours, not to exceed 40 mg/kg/day 1, 2
- Only use clindamycin if local erythromycin resistance rates are <10% due to risk of inducible resistance 1, 2
- Higher risk of Clostridium difficile infection compared to other oral agents 1
Tetracyclines (Doxycycline/Minocycline)
- Doxycycline: 100 mg orally twice daily 1
- Minocycline: 200 mg loading dose, then 100 mg orally twice daily 1
- Not recommended for children under 8 years of age or pregnant women (pregnancy category D) 1, 2
- Bacteriostatic activity with limited recent clinical experience 1
Linezolid
- Linezolid 600 mg orally twice daily is highly effective but significantly more expensive than alternatives 1, 4
- Pediatric dosing: 10 mg/kg/dose every 8 hours, not to exceed 600 mg/dose 1, 4
- Cure rates for MRSA skin infections: 79% in clinical trials 4
- Bacteriostatic with no cross-resistance to other antibiotic classes 1
- FDA-approved for complicated skin and soft tissue infections 4
Treatment Duration and Monitoring
- Uncomplicated MRSA skin infections: 5-10 days of therapy 2, 3
- Complicated skin and soft tissue infections: 7-14 days 1, 2
- Clinical reassessment within 48-72 hours is essential to ensure appropriate response 2
Special Clinical Scenarios
Osteomyelitis
- Oral options include TMP-SMX 4 mg/kg/dose twice daily combined with rifampin 600 mg once daily, linezolid 600 mg twice daily, or clindamycin 600 mg every 8 hours 1
- Minimum 8-week course recommended, with consideration for additional 1-3 months of rifampin-based combination therapy 1
- Surgical debridement remains the mainstay of therapy 1
Pneumonia
- Oral clindamycin 600 mg three times daily can be used if the strain is susceptible and local resistance is low 1
- Linezolid 600 mg twice daily is an alternative oral option for MRSA pneumonia 1
- Duration: 7-21 days depending on extent of infection 1
Critical Pitfalls to Avoid
- Never use beta-lactam antibiotics alone for MRSA—they are completely ineffective 3
- Do not use rifampin as monotherapy; resistance develops rapidly 1, 3
- Failure to drain abscesses leads to treatment failure regardless of antibiotic choice 2, 3
- For simple abscesses, incision and drainage alone may be adequate without antibiotics 1, 2
- Clindamycin should not be used for endocarditis or endovascular infections 1
Pediatric Considerations
- For children with musculoskeletal infections in MRSA-prevalent communities, oral clindamycin 30 mg/kg/day has shown effectiveness 5
- Vancomycin is preferred for serious pediatric MRSA infections including bacteremia 1, 2
- TMP-SMX dosing in children: 4-6 mg/kg/dose (trimethoprim component) every 12 hours 1, 2