Treatment of methicillin-susceptible S aureus (MSSA) bacteremia with a combination of β-lactam and daptomycin failed to reduce mortality compared with β-lactam monotherapy, according to study data published in Clinical Infectious Diseases.

In a retrospective cohort study the 7-, 30-, and 90- day mortality of 136 patients with MSSA bacteremia who were receiving β-lactam and daptomycin and 214 patients receiving β-lactam monotherapy was assessed. A 1:2 propensity score matching analysis was used and differences determined with Cox regression models.

Patients in the β-lactam and daptomycin group had higher Pitt scores and persistent bacteremia more often than the other group; however, in the raw analysis there were no differences in mortality rates between groups. After matching, there were no significant differences between the β-lactam and daptomycin group and the β-lactam monotherapy group for all-cause mortality rates at day 7 (8.18% vs 7.74%, respectively; P = 1.000), day 30 (17.3% vs 16.1%, respectively; P = .922), and day 90 (22.7% vs 23.2%, respectively; P = 1.000). Further, no differences were found in a subanalysis of patients with high-risk source of infection and a subgroup excluding catheter related bacteremia.

This was the largest cohort of patients treated with β-lactam and daptomycin to be analyzed to date, which the study investigators believe extended the external validity of the results beyond the single center where the study took place. However, despite the patients being followed prospectively by a specialist, the study’s main limitation was its retrospective design. Baseline characteristics of the groups were different and patients with suspected infective endocarditis or severe bacteremia more frequently received β-lactam and daptomycin, which is why propensity score matching was used to overcome this bias.

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In this study, β-lactam and daptomycin “failed to reduce mortality rates in patients with MSSA bacteremia.” The study authors concluded that treatment strategies for MSSA bacteremia that improve survival are urgently needed and randomized controlled trials testing different combination therapies are warranted.

Reference

Grillo S, Cuervo G, Carratalà J, et al. Impact of beta-lactam and daptomycin combination therapy on clinical outcomes in methicillin-susceptible Staphylococcus aureus bacteremia: A propensity score-matched analysis [published online January 7 2019]. Clin Infect Dis. doi: 10.1093/cid/ciz018