Is cefazolin inferior to nafcillin for treatment of methicillin-susceptible Staphylococcus aureus bacteremia?

About 20% of methicillin-susceptible Staphylococcus aureus (MSSA) isolates have a substantial inoculum effect with cefazolin, suggesting that cefazolin treatment may be associated with clinical failure for serious MSSA infections. There are no well-matched controlled studies comparing cefazolin with nafcillin for the treatment of MSSA bacteremia. A retrospective propensity-score-matched case-control study was performed from 2004 to 2009 in a tertiary care hospital where nafcillin was unavailable from August 2004 to August 2006. The cefazolin group (n = 49) included MSSA-bacteremic patients treated with cefazolin during the period of nafcillin unavailability, while the nafcillin group (n = 84) comprised those treated with nafcillin. Treatment failure was defined as a composite outcome of a change of antibiotics due to clinical failure, relapse, and mortality. Of 133 patients, 41 patients from each group were matched by propensity scores. There were no significant differences in baseline characteristics between the matched groups. The treatment failure rates were not significantly different at 4 or 12 weeks (10% [4/41] versus 10% [4/41] at 4 weeks [P > 0.99] and 15% [6/41] versus 15% [6/41] at 12 weeks [P > 0.99]). Cefazolin treatment was interrupted less frequently than nafcillin treatment due to drug adverse events (0% versus 17%; P = 0.02). Cefazolin had clinical efficacy similar to that of nafcillin and was more tolerable than nafcillin for the treatment of MSSA bacteremia.