Cefazolin is Effective Against MSSA
Yes, cefazolin is effective against methicillin-sensitive Staphylococcus aureus (MSSA) and is considered an appropriate treatment option for MSSA infections. 1, 2
Evidence Supporting Cefazolin for MSSA
- Cefazolin is FDA-approved for the treatment of serious infections due to Staphylococcus aureus, including beta-lactamase-producing strains (which includes MSSA) 1
- The Infectious Diseases Society of America (IDSA) recommends cefazolin as an appropriate treatment option for pyomyositis caused by MSSA 2
- Many experts regularly use cefazolin for S. aureus infections instead of nafcillin due to better drug tolerability and cost, particularly for MSSA infections 2
- Cefazolin is specifically listed as a reasonable alternative in patients with a well-defined history of nonanaphylactoid reactions to penicillins (e.g., simple skin rash) who have MSSA infections 2
Comparative Effectiveness with Other Anti-MSSA Agents
- A large retrospective cohort study found no significant difference in 30-day mortality between patients with MSSA bacteremia treated with flucloxacillin (an antistaphylococcal penicillin) versus cefazolin (10.7% vs 11.2%) 3
- A systematic review and meta-analysis demonstrated that cefazolin was associated with significant reduction in mortality (OR 0.69) and clinical failure (OR 0.56) compared to antistaphylococcal penicillins for MSSA bacteremia 4
- When comparing nafcillin/oxacillin with cefazolin for MSSA bacteremia, 30-day mortality was similar between groups, supporting cefazolin as an effective treatment option 5
Clinical Considerations When Using Cefazolin for MSSA
- Cefazolin is often preferred over antistaphylococcal penicillins due to its better safety profile, with significantly lower rates of nephrotoxicity (OR 0.36) and hepatotoxicity (OR 0.12) 4
- In cases of brain abscess resulting from MSSA infective endocarditis, guidelines recommend nafcillin instead of cefazolin due to concerns about CNS penetration 2
- Although cefazolin may be more susceptible to β-lactamase–mediated hydrolysis than nafcillin in laboratory testing (known as the cefazolin inoculum effect), the clinical significance of this observation remains uncertain 2
Important Distinction Between MSSA and MRSA
- While cefazolin is effective against MSSA, it is important to note that methicillin-resistant S. aureus (MRSA) strains are uniformly resistant to cefazolin 1, 6
- When empiric coverage for both MSSA and MRSA is needed before culture results are available, appropriate options include vancomycin, daptomycin, or linezolid, not cefazolin 6
- Once culture results confirm MSSA, therapy can be narrowed to cefazolin as an appropriate targeted therapy 2, 7
Dosing and Administration
- For serious MSSA infections, cefazolin is typically administered intravenously at doses of 0.5-1g every 8 hours, with adjustments based on infection severity and renal function 2, 1
- Cefazolin achieves high serum concentrations (approximately 185 mcg/mL peak after 1g IV dose) with a serum half-life of approximately 1.8 hours 1
In summary, cefazolin is an effective and often preferred treatment option for MSSA infections due to its proven efficacy, favorable safety profile, and cost advantages compared to antistaphylococcal penicillins.