What antibiotic should a patient with suspected endocarditis and positive blood cultures for Staphylococcus aureus (S. aureus) receive?

From the Guidelines

For a patient with suspected endocarditis and positive blood cultures for Staphylococcus aureus, the recommended initial antibiotic therapy is intravenous nafcillin or oxacillin (2 grams every 4 hours) if the S. aureus is methicillin-sensitive (MSSA), as stated in the 2015 update from the American Heart Association 1.

Key Considerations

• If the patient has a penicillin allergy, cefazolin (2 grams every 8 hours) can be used as an alternative.
• However, if methicillin-resistant S. aureus (MRSA) is suspected or confirmed, intravenous vancomycin (15-20 mg/kg every 8-12 hours, adjusted based on levels and renal function) should be administered, as recommended by the Infectious Diseases Society of America in 2011 1.
• In some cases, combination therapy with gentamicin (3 mg/kg/day divided every 8 hours) for the first 3-5 days may be considered to enhance bactericidal activity, although this is based on extrapolation from experimental models and may increase the risk of renal and otic toxicity 1.

Treatment Duration and Monitoring

• Treatment duration typically ranges from 4-6 weeks, depending on complications and clinical response.
• Blood cultures should be repeated to confirm clearance of bacteremia.
• The choice between anti-MSSA and anti-MRSA therapy should be guided by local resistance patterns and adjusted once susceptibility results become available.

Important Notes

• Patients with S. aureus endocarditis should be cared for in a medical facility with cardiothoracic surgery capabilities and infectious diseases consultation 1.
• Decisions concerning outpatient therapy may be considered and individualized based on clinical impression of symptomatic recovery, cardiovascular stability, and availability of infrastructure for outpatient monitoring 1.

From the FDA Drug Label

5.9 Persisting or Relapsing S. aureus Bacteremia/Endocarditis Patients with persisting or relapsing S. aureus bacteremia/endocarditis or poor clinical response should have repeat blood cultures. The patient with suspected endocarditis and positive blood cultures for Staphylococcus aureus (S. aureus) should receive daptomycin (IV), and the following should be considered:

• Repeat blood cultures
• Minimum inhibitory concentration (MIC) susceptibility testing of the isolate
• Diagnostic evaluation to rule out sequestered foci of infection
• Appropriate surgical intervention and/or consideration of a change in antibacterial regimen may be required 2

From the Research

Antibiotic Treatment for Suspected Endocarditis with Positive Blood Cultures for Staphylococcus aureus

• The choice of antibiotic for a patient with suspected endocarditis and positive blood cultures for Staphylococcus aureus (S. aureus) depends on various factors, including the susceptibility of the isolate and the severity of the infection.
• According to studies 3, 4, 5, 6, vancomycin remains a primary treatment option for methicillin-resistant Staphylococcus aureus (MRSA) infections, including endocarditis.
• Vancomycin is effective against MRSA isolates with a minimum inhibitory concentration (MIC) ≤2 μg/mL 4.
• Alternative treatment options for MRSA endocarditis include daptomycin, which has shown noninferiority to vancomycin in the treatment of MRSA bacteremia 5.
• Ceftaroline is also a promising option for the treatment of MRSA infections, including endocarditis 4.
• The treatment of MRSA endocarditis should be individualized based on the patient's clinical condition, the susceptibility of the isolate, and the potential for resistance 5, 6.

Considerations for Antibiotic Treatment

• The emergence of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) may affect patient outcomes, and the use of vancomycin population susceptibility analysis profile (PAP) can help predict treatment failure 6.
• The role of population MIC analysis in predicting outcome with MRSA infections warrants further investigation 6.
• Repeating blood cultures until they become negative may not be necessary, as persistent bacteremia and fever may be present in the first 3 days of endocarditis despite treatment 7.
• The timing of valve culture negativization and the claim for prolongation of antibiotic therapy starting from negative blood cultures should be critically appraised 7.