From the Guidelines
For persistent methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia, I recommend prompt source control and high-dose intravenous cefazolin (2g IV every 8 hours) for at least 4-6 weeks, as supported by the most recent and highest quality study 1.
Key Considerations
- Source control involves removing infected devices, draining abscesses, and debriding infected tissues.
- Obtain follow-up blood cultures every 24-48 hours until clearance is documented.
- Consider adding gentamicin (1mg/kg IV every 8 hours) for the first 3-5 days in severe cases.
- For patients with persistent bacteremia despite appropriate therapy, consider obtaining an echocardiogram to rule out endocarditis.
- Daptomycin (6-10mg/kg IV daily) may be used for patients who cannot tolerate beta-lactams.
Rationale
The recommendation is based on the most recent study 1, which suggests that cefazolin or an anti-staphylococcal penicillin (ASP) is the preferred treatment for MSSA bacteremia.
Monitoring and Duration
Regular monitoring of renal function, liver enzymes, and complete blood counts is essential during prolonged antibiotic therapy. The extended duration of therapy is necessary because MSSA can form biofilms and persist in deep-seated infections, as noted in 2 and 3. However, the most recent study 1 takes precedence in guiding the treatment decision.
Additional Considerations
While other studies 4 and 5 provide valuable information on the treatment of MRSA bacteremia, the focus here is on MSSA bacteremia, and the recommendations are tailored accordingly. The use of vancomycin, daptomycin, linezolid, and trimethoprim-sulfamethoxazole (TMP-SMX) is discussed in the context of MRSA bacteremia, but the primary recommendation for MSSA bacteremia remains focused on cefazolin or ASP, as per 1.
From the FDA Drug Label
Cefazolin has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in INDICATIONS AND USAGE Gram-Positive Aerobes Staphylococcus aureus (including beta-lactamase-producing strains) Staphylococcus epidermidis Streptococcus pyogenes, Streptococcus agalactiae, and other strains of streptococci Streptococcus pneumoniae Methicillin-resistant staphylococci are uniformly resistant to cefazolin, and many strains of enterococci are resistant
Cefazolin is effective against Methicillin-Susceptible Staphylococcus aureus (MSSA). For persistent MSSA bacteremia, cefazolin can be considered as a treatment option, given its in vitro activity against MSSA. However, the clinical effectiveness of cefazolin in treating persistent MSSA bacteremia would depend on various factors, including the patient's overall health, the severity of the infection, and the presence of any underlying conditions. 6
From the Research
Treatment Options for Persistent MSSA Bacteremia
- The treatment of methicillin-sensitive Staphylococcus aureus (MSSA) bacteremia typically involves the use of beta-lactam antibiotics, such as nafcillin, oxacillin, or cefazolin 7, 8, 9.
- Cefazolin has been shown to be effective in the treatment of MSSA bacteremia, with some studies suggesting it may be associated with lower mortality rates compared to other beta-lactams 7, 8.
- The use of vancomycin, an antibiotic often used to treat methicillin-resistant Staphylococcus aureus (MRSA) infections, may be associated with poor outcomes in patients with MSSA bacteremia, including nephrotoxicity, persistent bacteremia, and treatment failure 9.
- Switching from vancomycin to a beta-lactam antibiotic, such as nafcillin or cefazolin, may be beneficial in patients with MSSA bacteremia, with some studies suggesting it may be associated with lower mortality rates 9.
Comparative Effectiveness of Antibiotics
- A study comparing the effectiveness of cefazolin versus nafcillin or oxacillin for the treatment of MSSA infections complicated by bacteremia found that patients who received cefazolin had a lower risk of mortality and similar odds of recurrent infections compared to those who received nafcillin or oxacillin 8.
- Another study found that patients who received nafcillin or cefazolin had a 79% lower mortality hazard compared to those who received vancomycin alone, and that switching from vancomycin to nafcillin or cefazolin was associated with a 69% lower mortality hazard 9.
Management of Persistent MSSA Bacteremia
- There is limited guidance on the best approach to managing patients with persistent MSSA bacteremia, and treatment often involves modification of antimicrobial therapy, source control, and infectious diseases consultation 10.
- Dual beta-lactam regimens have been used in some cases of persistent MSSA bacteremia, but more data are needed to determine the effectiveness of this approach 10.