Beta-lactams are superior to vancomycin for definitive therapy, but not empiric treatment of methicillin-susceptible Staphylococcus aureus (MSSA) bloodstream infection, according to a large retrospective study.

Jennifer S. McDanel, PhD, from the University of Iowa in Iowa City and the Iowa City Veterans Affairs Health Care System, and colleagues published their findings online April 21 in Clinical Infectious Diseases.

Although prior research has linked vancomycin therapy to poor patient outcomes such as recurrence, treatment failure, and death, the validity of this construct with respect to empiric therapy has remained unclear.

“Vancomycin is often prescribed empirically for patients suspected of having S. aureus bloodstream infections since it has activity against both methicillin-resistant and methicillin susceptible strains,” the authors write.
“However, for a patient infected with [MSSA], organizations such as the Infectious Diseases Society of America…recommend switching therapy to a beta-lactam, such as cefazolin or an antistaphylococcal penicillin (nafcillin or oxacillin) once the isolate is known to be MSSA.”

Accordingly, the researchers analyzed data for MSSA culture-positive patients at 122 Veterans Affairs hospitals who received either a beta-lactam or vancomycin alone as empiric therapy (n = 2659 and 3125, respectively) or definitive treatment (n = 4698 and 935, respectively) during 2003 to 2010.

The researchers defined empiric therapy as treatment started 2 days before through 4 days after collection of the first culture positive for MSSA; definitive therapy started 4 to 14 days after collection of the first culture positive for MSSA.

Empiric use of beta-lactam monotherapy had no effect on 30-day mortality compared with vancomycin (hazard ratio [HR], 1.03; 95% confidence interval [CI], 0.89 – 1.20).

As expected, however, definitive therapy with a beta-lactam rather than vancomycin was associated with a significant 35% decrease in 30-day mortality (HR, 0.65; 95% CI, 0.52 – 0.80), with use of cefazolin or an antistaphylococcal penicillin yielding further benefit (HR, 0.57; 95% CI, 0.46 – 0.71).
Although the researchers made adjustments for variables such as age, dialysis/end-stage renal disease, Acute Physiology and Chronic Health Evaluation (APACHE) III score, and Charlson Comorbidity index, the authors note that the findings may be limited by the elderly nature of the study population, and some of the reported deaths may not have been attributable to MSSA. In addition, the researchers did not stratify the definitive therapy analysis by empiric therapy, and therefore did not account for potential switching-related survival benefits.

Beta-lactams are superior to vancomycin for definitive therapy, but not empiric treatment of methicillin-susceptible Staphylococcus aureus (MSSA) bloodstream infection, according to a large retrospective study.

Jennifer S. McDanel, PhD, from the University of Iowa in Iowa City and the Iowa City Veterans Affairs Health Care System, and colleagues published their findings online April 21 in Clinical Infectious Diseases.

Although prior research has linked vancomycin therapy to poor patient outcomes such as recurrence, treatment failure, and death, the validity of this construct with respect to empiric therapy has remained unclear.

“Vancomycin is often prescribed empirically for patients suspected of having S. aureus bloodstream infections since it has activity against both methicillin-resistant and methicillin susceptible strains,” the authors write.
“However, for a patient infected with [MSSA], organizations such as the Infectious Diseases Society of America…recommend switching therapy to a beta-lactam, such as cefazolin or an antistaphylococcal penicillin (nafcillin or oxacillin) once the isolate is known to be MSSA.”

Accordingly, the researchers analyzed data for MSSA culture-positive patients at 122 Veterans Affairs hospitals who received either a beta-lactam or vancomycin alone as empiric therapy (n = 2659 and 3125, respectively) or definitive treatment (n = 4698 and 935, respectively) during 2003 to 2010.

The researchers defined empiric therapy as treatment started 2 days before through 4 days after collection of the first culture positive for MSSA; definitive therapy started 4 to 14 days after collection of the first culture positive for MSSA.

Empiric use of beta-lactam monotherapy had no effect on 30-day mortality compared with vancomycin (hazard ratio [HR], 1.03; 95% confidence interval [CI], 0.89 – 1.20).

As expected, however, definitive therapy with a beta-lactam rather than vancomycin was associated with a significant 35% decrease in 30-day mortality (HR, 0.65; 95% CI, 0.52 – 0.80), with use of cefazolin or an antistaphylococcal penicillin yielding further benefit (HR, 0.57; 95% CI, 0.46 – 0.71).
Although the researchers made adjustments for variables such as age, dialysis/end-stage renal disease, Acute Physiology and Chronic Health Evaluation (APACHE) III score, and Charlson Comorbidity index, the authors note that the findings may be limited by the elderly nature of the study population, and some of the reported deaths may not have been attributable to MSSA. In addition, the researchers did not stratify the definitive therapy analysis by empiric therapy, and therefore did not account for potential switching-related survival benefits.