First-Line Treatment for Methicillin-Sensitive Staphylococcus aureus (MSSA)
The first-line treatment for MSSA infections is a β-lactam antibiotic, specifically an anti-staphylococcal penicillin (such as oxacillin or nafcillin) or cefazolin. 1, 2
Preferred Agents for MSSA Infections
Intravenous options:
Oral options:
Rationale for β-lactam Preference
- β-lactam antibiotics demonstrate superior efficacy compared to vancomycin for MSSA infections 1, 4
- Studies comparing nafcillin/oxacillin with cefazolin show similar clinical outcomes, making both excellent first-line choices 5
- Penicillinase-resistant penicillins (flucloxacillin, dicloxacillin) remain the antibiotics of choice for serious MSSA infections 4
Treatment by Infection Type
Skin and Soft Tissue Infections
- For minor skin infections: Dicloxacillin 125mg every 6 hours or cephalexin 500mg every 6 hours 2, 6
- For moderate infections: Dicloxacillin 250mg every 6 hours 3
- For abscesses: Incision and drainage plus empirical antibiotic coverage 2
Bacteremia and Serious Infections
- For uncomplicated bacteremia: Oxacillin, nafcillin, or cefazolin for at least 2 weeks 1
- For complicated bacteremia or endocarditis: 4-6 weeks of therapy 1
- For pyomyositis: Cefazolin or antistaphylococcal penicillin (nafcillin or oxacillin) 2
Alternative Options for Penicillin-Allergic Patients
- For non-immediate hypersensitivity: First-generation cephalosporins (cefazolin, cephalexin) 4
- For immediate hypersensitivity (urticaria, angioedema, bronchospasm, anaphylaxis): Clindamycin or lincomycin 4
- Note: Cephalosporins are contraindicated in patients with immediate penicillin hypersensitivity 4
Important Clinical Considerations
- Blood cultures should be obtained before initiating therapy to confirm the causative organism 2
- For serious infections, therapy should be continued for at least 14 days 3
- Treatment should continue for at least 48 hours after the patient becomes afebrile, asymptomatic, and cultures are negative 3
- Dicloxacillin is best absorbed when taken on an empty stomach (1 hour before or 2 hours after meals) 3
Common Pitfalls to Avoid
- Using vancomycin for MSSA when β-lactams are available (vancomycin is less effective) 1, 2
- Using broad-spectrum antibiotics like piperacillin/tazobactam as monotherapy for MSSA bacteremia (associated with higher mortality compared to nafcillin/oxacillin/cefazolin) 5
- Inadequate duration of therapy, especially for complicated infections 3
- Failure to obtain follow-up cultures in bacteremia to document clearance 1
- Inadequate source control (drainage of abscesses, removal of infected devices) 1
By following these evidence-based recommendations, clinicians can optimize outcomes for patients with MSSA infections while practicing appropriate antimicrobial stewardship.