Combination therapy does not decrease 30-day mortality but increases antibiotic consumption in methicillin-sensitive S. aureus bacteraemia.

PURPOSE: The study aimed to compare the impact of combination and monotherapy on mortality, antibiotic consumption using 'Days of Therapy (DOT)', and antibiotic-related adverse events in patients with methicillin-susceptible S. aureus (MSSA) bacteraemia.

METHODS

This retrospective study included all adult patients (>18 years) with MSSA bacteraemia who received either monotherapy (beta-lactam alone) or combination therapy (beta-lactam plus teicoplanin or daptomycin or linezolid) between 2018 and 2023. Mortality, antibiotic consumption, and factors predicting mortality were analysed. Groups were compared for 30-d mortality with survival analysis. Logistic regression models were used to identify risk factors for mortality. Antibiotic consumption was calculated by DOT.

RESULTS

Among 395 patients screened, 185 patients who had an MSSA bacteraemia received either monotherapy (n = 73, 39.5%) or combination therapy (n = 112, 60.5%). The 30-d mortality rate was similar between groups (%15.1 vs. 21.4, P = 0.280). Time to bacterial clearance was also similar (median (IQR): 4 (3-7) vs. 4 (3-7) d, P = 0.699). DOT per 1000 patient days was significantly higher in the combination therapy group than in the monotherapy group (median, IQR: 1420, 827-1836 vs. 933, 732-1000), P < 0.001). The 30-d mortality rate was 18.9% (n = 35/185), and the PITT bacteraemia score was the only independent predictor of mortality (median, IQR: 1506, 1.264-1.794, P < 0.001).

CONCLUSIONS

Our findings indicate that combination therapy does not confer a survival benefit over monotherapy in patients with MSSA bacteraemia. However, combination therapy was associated with a significant increase in antibiotic consumption. Therefore, our results do not support the routine use of combination therapy for MSSA bacteraemia in this patient population.