Does the beta-lactam matter? Nafcillin versus cefazolin for methicillin-susceptible staphylococcus aureus bloodstream infections

Background: Antistaphylococcal penicillins have historically been regarded as the drugs of choice for methicillin-susceptible Staphylococcus aureus (MSSA) bloodstream infections (BSI). However, recent outcomes data compared to cefazolin treatment are conflicting. Objective: This study compared treatment failure and adverse effects associated with nafcillin and cefazolin for MSSA BSI. Methods: Adult inpatients with MSSA BSI between January 1, 2009 and August 31, 2015 were included in this retrospective cohort study if they received ?72 h of nafcillin or cefazolin as directed therapy after no more than 72 h of any empiric therapy. The primary composite endpoint was treatment failure defined by clinician documentation, 30-day recurrence of infection, allcause 30-day in-hospital mortality, or loss to follow-up. Secondary outcomes included antibiotic-related acute kidney injury (AKI), acute interstitial nephritis (AIN), hepatotoxicity, and rash. Results: Among 157 patients, 116 (73.9%) received nafcillin and 41 (26.1%) received cefazolin. The baseline characteristics were similar except cefazolin-Treated patients had higher APACHE II scores and more frequent renal dysfunction. No difference in the composite treatment failure outcome (28.4 vs. 31.7%; p = 0.69) was detected between the nafcillin and cefazolin groups, respectively. In a sensitivity analysis excluding patients without known follow-up, there was no significant difference of treatment failure. AKI, AIN, hepatotoxicity, and rash were all numerically more frequent among nafcillin-Treated patients. Conclusions: Among nafcillin-or cefazolin-Treated patients with MSSA BSI, there was no significant difference in treatment failure. Observing more frequent presumptive adverse effects associated with nafcillin receipt, future prospective studies evaluating cefazolin appear warranted.