What is the appropriate Intensive Care Unit (ICU) antibiotic regimen for a patient with Staphylococcus aureus (S. aureus) positive, Methicillin-resistant S. aureus (MRSA) negative pneumonia, currently treated with vancomycin, ceftriaxone, and azithromycin?

From the Guidelines

For a patient with Staphylococcus aureus pneumonia that is MRSA-negative in the ICU, the recommended antibiotic regimen would be to discontinue vancomycin and switch to an anti-staphylococcal beta-lactam antibiotic. Specifically, cefazolin (150 mg/kg/day every 8 hours) or semisynthetic penicillin, such as oxacillin (150–200 mg/kg/day every 6–8 hours), would be the preferred treatment, as indicated by the guidelines 1. The current azithromycin and ceftriaxone should be discontinued as they are not optimal for MSSA pneumonia. Treatment duration should typically be 7-14 days, depending on clinical response. If the patient has risk factors for Pseudomonas, consider adding an antipseudomonal agent like piperacillin-tazobactam until those cultures return negative. This recommendation is based on MSSA's susceptibility to beta-lactam antibiotics, which have better tissue penetration and clinical outcomes compared to vancomycin for MSSA infections, as supported by the guidelines 1. Vancomycin is primarily indicated for MRSA infections, and continuing it unnecessarily increases the risk of nephrotoxicity and contributes to antimicrobial resistance. Key considerations in this decision include:

• The patient's specific pathogen, Staphylococcus aureus, and its susceptibility pattern, MRSA-negative
• The current antibiotic regimen and its appropriateness for MSSA pneumonia
• The potential risks and benefits of continuing or discontinuing specific antibiotics, such as vancomycin
• The importance of tailoring treatment to the individual patient's needs and risk factors, such as the potential for Pseudomonas infection. Given the evidence from the guidelines 1, the most appropriate course of action is to switch to an anti-staphylococcal beta-lactam antibiotic, such as cefazolin or oxacillin, and discontinue vancomycin, azithromycin, and ceftriaxone.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Appropriate ICU Antibiotic Regimen for S. aureus Pneumonia

The patient has S. aureus positive, MRSA negative pneumonia and is currently treated with vancomycin, ceftriaxone, and azithromycin.

• The first-line therapy for CAP due to methicillin-susceptible S. aureus is usually cefazolin, oxacillin, or ceftaroline 2.
• Ceftriaxone represents a promising alternative for the treatment of MSSA bloodstream infections, with once daily dosing and a short infusion time 3.
• A systematic review and meta-analysis found that ceftriaxone could provide an alternative for the treatment of MSSA BSIs in acute care and OPAT settings, except in patients whose BSIs were due to infective endocarditis 4.
• Vancomycin has been the drug of choice for MRSA infections for many years, but linezolid may be superior to vancomycin in the treatment of MRSA nosocomial pneumonia 5.

Considerations for the Current Treatment Regimen

• The current treatment regimen includes vancomycin, which is effective against MRSA, but the patient's S. aureus is MRSA negative.
• Ceftriaxone is a potential alternative for the treatment of MSSA bloodstream infections, and its use in the current regimen may be justified 3, 4.
• Azithromycin is not typically used as a first-line treatment for S. aureus pneumonia, but its use in the current regimen may be intended to cover other potential pathogens.

Potential Adjustments to the Treatment Regimen

• Consider discontinuing vancomycin, as the patient's S. aureus is MRSA negative, and using an alternative antibiotic such as cefazolin, oxacillin, or ceftaroline 2.
• Continue ceftriaxone as part of the treatment regimen, as it may be effective against MSSA bloodstream infections 3, 4.
• Reevaluate the use of azithromycin in the treatment regimen, as it may not be necessary for the treatment of S. aureus pneumonia.