Are all beta-lactams similarly effective in the treatment of methicillin-sensitive Staphylococcus aureus bacteraemia?

Methicillin-sensitive Staphylococcus aureus (MSSA) is susceptible to many beta-lactams. We compared cloxacillin and cefazolin, the first-line recommended antibiotics, and other beta-lactams in the treatment of MSSA bacteraemia. This was a retrospective cohort study. Included were adult patients with clinically-significant MSSA bacteraemia treated with a beta-lactam that was started within 48 h after blood cultures were taken. We separated between empirical treatment administered to the patient before receipt of final blood culture results and definitive treatment administered thereafter. Univariate and multivariable analyses for 30-day (empirical treatment) and 90-day (definitive treatment) mortality were conducted, including the type of beta-lactam administered to the patient. Five-hundred and forty-one patients were included for the analysis of empirical treatment and 498 patients alive at 7 days were evaluable for definitive treatment. Empirical treatment with cloxacillin or cefazolin (n = 131) was associated with lower 30-day mortality as compared with cefuroxime (n = 98, p 0.058), ceftriaxone or cefotaxime (n = 194, p 0.008) and beta-lactam-beta-lactamase combinations (n = 61, p 0.013), with adjusted odds ratios (OR) for death ranging from 1.98 to 2.68. Definitive treatment with cefazolin (n = 72) was not significantly different from cloxacillin (n = 281); adjusted OR for 90-day mortality 0.91 (95% confidence interval 0.47-1.77). Treatment with cefazolin both in the empirical and definitive periods was not significantly different from cloxacillin; adjusted OR 0.81 (95% confidence interval 0.18-3.62). Treatment of MSSA bacteraemia with cefazolin is not significantly different from treatment with cloxacillin, while treatment with other beta-lactams, including second and third generation cephalosporins, might be associated with higher mortality.