Treatment of Methicillin-Sensitive Staphylococcus aureus (MSSA) Bacteremia

First-Line Treatment Options for MSSA Bacteremia

The European Society of Cardiology recommends antistaphylococcal beta-lactams, such as cloxacillin, oxacillin, and nafcillin, as the preferred agents for MSSA bacteremia due to their superior efficacy compared to vancomycin 1
For MSSA bacteremia, cloxacillin should be administered at 12 g/day intravenously in 4-6 doses for 4-6 weeks depending on the severity and presence of complications 2, 3

Cefazolin (1-2g IV every 8 hours) is an acceptable alternative to cloxacillin for MSSA bacteremia with similar efficacy 1
For patients with confirmed severe beta-lactam allergy, daptomycin should be chosen where available, given in combination with another effective antistaphylococcal drug 4, 3
Vancomycin is inferior to beta-lactams for MSSA bacteremia and should only be used when beta-lactams cannot be administered 4, 1

For uncomplicated right-sided native valve MSSA infective endocarditis, short-term (2-week) treatments have been proposed, but these regimens cannot be applied to left-sided IE 4, 2, 3
For patients with penicillin allergy, penicillin desensitization can be attempted in stable patients since vancomycin is inferior to beta-lactams 4, 3

Follow-up blood cultures should be obtained 2-4 days after initial positive cultures to document clearance of bacteremia 1
Echocardiography is recommended for all adult patients with S. aureus bacteremia to rule out endocarditis 1

The European Society of Cardiology recommends that the addition of aminoglycosides in staphylococcal native valve IE is no longer recommended due to increased renal toxicity without improved outcomes 4, 2, 3

The Infectious Diseases Society of America recommends completing an MRI urgently to identify deep-seated infection in patients with persistent MSSA bacteremia, as inadequate source control is a common cause of treatment failure 5
Aggressive surgical debridement of the foot wound is critical in patients with deep infection, as source control is essential for effective treatment 5, 6
The American Heart Association suggests that patients with S. aureus bacteremia should undergo transthoracic echo at minimum, with transesophageal echo indicated for persistent bacteremia, persistent fever, or metastatic infection 6

The European Society of Cardiology endorses cefazolin as an acceptable first-line agent for proven MSSA infections, with equivalent efficacy to antistaphylococcal penicillins 6
Cefazolin should be continued for a minimum of 2-3 weeks for uncomplicated bacteremia with prompt clearance and no endocarditis, and at least 4-6 weeks for complicated infections including osteomyelitis, endocarditis, or metastatic foci 5, 6

Switching from cefazolin to alternative antibiotics such as daptomycin should only be considered in cases of documented treatment failure after adequate source control has been achieved 7, 8
The use of vancomycin is explicitly inferior to beta-lactams for MSSA and should only be used when beta-lactams cannot be administered, and aminoglycosides are not recommended due to increased renal toxicity without improved outcomes 6

The Infectious Diseases Society of America recommends performing transesophageal echocardiography (TEE) immediately to detect vegetations, intracardiac abscesses, and valvular complications in patients with persistent MSSA bacteremia, as TEE is superior to transthoracic echo 9, 10
Obtain repeat blood cultures every 48-72 hours until clearance is documented, as prolonged bacteremia ≥48 hours is associated with 39% 90-day mortality, according to the Clinical Infectious Diseases guidelines 9, 10

The Infectious Diseases Society of America advises against adding gentamicin or rifampin to beta-lactam therapy, as these combinations do not improve outcomes and increase toxicity 9, 10

For uncomplicated bacteremia, the Infectious Diseases Society of America recommends a minimum of 2 weeks of IV therapy, as defined by exclusion of endocarditis, no implanted prostheses, blood cultures negative by days 2-4, defervescence within 72 hours, and no metastatic infection 9, 10
For complicated bacteremia, the Infectious Diseases Society of America recommends 4-6 weeks of IV therapy, as persistent bacteremia, delayed clearance, or any concern for deep-seated infection requires extended treatment 9, 10
If endocarditis is identified, the Infectious Diseases Society of America recommends 6 weeks of IV therapy from the date of first negative blood culture 9, 10

The American Heart Association recommends using TEE instead of transthoracic echo alone in persistent bacteremia, as TEE is required to adequately exclude endocarditis 9