What is the treatment for Methicillin-sensitive Staphylococcus aureus (MSSA) bacteremia?

From the Guidelines

MSSA bacteremia should be treated with cefazolin or an anti-staphylococcal penicillin (ASP) as the first-line antibiotic therapy. The treatment of MSSA bacteremia requires prompt antibiotic treatment to reduce morbidity, mortality, and improve quality of life. According to the most recent and highest quality study 1, evidence-based and guideline-supported practices in the treatment of SAB include the use of cefazolin or an anti-staphylococcal penicillin (ASP) for MSSA.

Key Considerations

• The use of cefazolin or an anti-staphylococcal penicillin (ASP) is recommended for MSSA bacteremia 1
• Early source control is essential in the treatment of SAB, including the removal of infected devices and drainage of abscesses 1, 2
• Treatment duration should be at least 4-6 weeks for bacteremia with high-risk features, and blood cultures should be repeated daily until negative to ensure clearance of the infection 1
• Echocardiography is recommended to rule out endocarditis, particularly in patients with persistent fever, new heart murmurs, or risk factors for endocarditis 3

Antibiotic Therapy

• Cefazolin is an acceptable alternative to anti-staphylococcal penicillin (ASP) at a dose of 2 grams IV every 8 hours 1
• The treatment duration should be individualized based on the patient's clinical response and the presence of complications such as endocarditis or osteomyelitis 3
• Vancomycin or daptomycin may be considered for patients with methicillin-resistant S. aureus (MRSA) or in cases where ASP or cefazolin is not appropriate 1, 2

Source Control and Monitoring

• Source control is essential in the treatment of SAB, including the removal of infected devices and drainage of abscesses 1, 2
• Blood cultures should be repeated daily until negative to ensure clearance of the infection 1
• Echocardiography is recommended to rule out endocarditis, particularly in patients with persistent fever, new heart murmurs, or risk factors for endocarditis 3

From the FDA Drug Label

Nafcillin is indicated in the treatment of infections caused by penicillinase-producing staphylococci which have demonstrated susceptibility to the drug. The answer to MSSA bacteremia is that Nafcillin can be used for treatment, as MSSA (Methicillin-Susceptible Staphylococcus aureus) is a type of penicillinase-producing staphylococci.

• Key points: + Nafcillin is effective against penicillinase-producing staphylococci + MSSA is susceptible to nafcillin + Culture and susceptibility tests should be performed to confirm susceptibility 4

From the Research

MSSA Bacteremia Treatment

• MSSA bacteremia is a common cause of morbidity and mortality, and its treatment requires careful consideration of antibiotic options 5, 6, 7, 8, 9.
• Penicillinase-resistant penicillins, such as flucloxacillin and dicloxacillin, are considered the antibiotics of choice for the management of serious MSSA infections 5.
• First-generation cephalosporins, such as cefazolin, may be used as an alternative to antistaphylococcal penicillins for patients with non-severe penicillin allergies 6.
• Cefazolin has been shown to have similar clinical efficacy to antistaphylococcal penicillins, but with better tolerability and lower rates of discontinuation due to adverse drug reactions 6, 8.
• A meta-analysis of cefazolin versus antistaphylococcal penicillins found that cefazolin was associated with lower 90-day mortality and discontinuation due to adverse events 8.

Antibiotic Resistance

• MSSA isolates that are penicillin-resistant are more likely to also be resistant to other antibiotics, such as erythromycin 9.
• However, a significant proportion of MSSA isolates (28%) may still be susceptible to penicillin, which could offer pharmacokinetic advantages over other beta-lactam drugs and potentially improved outcomes 9.

Treatment Considerations

• The choice of antibiotic for MSSA bacteremia should be guided by the patient's allergy history, the severity of the infection, and the susceptibility pattern of the isolate 5, 6, 7, 8, 9.
• Once-daily treatment options, such as ceftriaxone and daptomycin, may be considered for therapy completion or in patients who cannot tolerate first-line therapy, but their role remains uncertain 7.