Comparative Effectiveness of Cloxacillin/ versus Empiric Therapy for -susceptible (MSSA) Bacteremia Davie Wong MD1, Titus Wong MD2, Marc Romney MD2, Victor Leung MD2 1. Infectious Diseases Residency Training Program PGY-5, University of British Columbia, Vancouver, Canada. 2. Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, Canada.

INTRODUCTION RESULTS RESULTS

Staphylococcus aureus is the leading cause of bacteremia and Table 1: Baseline characteristics and clinical outcomes of patients with methicillin-susceptible S. aureus bacteremia. carries a mortality of 20-30% [1]. Empiric vancomycin is Patient characteristics β-lactam (n=131) Vancomycin (n=124) P-value commonly prescribed for patients with S. aureus bacteremia Age (years) 53.2 ± 16.5 59.4 ± 18.3 0.005 (SAB) to cover methicillin-resistant S. aureus (MRSA) as up to Community-onset 108 (82.4) 88 (71.0) 0.03 50-60% of bloodstream isolates are methicillin-resistant at some centres [2,3]. Charlson comorbidity index 3 (1.0-6.0) 4 (1.0-7.0) 0.001 Infectious diseases consultation 98 (74.8) 80 (64.5) 0.07 However, vancomycin is inferior to semi-synthetic anti- Infective endocarditis 24 (18.3) 12 (9.7) 0.05 Staphylococcal and first generation for the treatment of methicillin-susceptible Staphylococcus aureus Surgical source control 33 (25.2) 19 (15.3) 0.05 (MSSA) bacteremia [4]. Vancomycin is associated with higher Empiric antimicrobials rates of infection-related mortality, re-infection and bacteriologic Vancomycin 88 (67.2) 123 (99.2) <0.001 failure compared to cloxacillin or cefazolin in the definitive Cloxacillin or cefazolin 131 (100.0) 0 (0.0) <0.001 treatment of MSSA bacteremia [4,5]. 3rd generation 40 (30.5) 0 (0.0) <0.001 Early studies suggested that empiric vancomycin may be inferior - 33 (25.2) 0 (0.0) <0.001 to empiric β-lactam [2,6,7]. Although controversial, some experts Other 47 (35.9) 66 (53.2) 0.01 recommend empiric combination therapy with vancomycin plus Duration of empiric therapy (hours) 54 (42.0-69.0) 48 (29.6-75.8) 0.28 Figure 1: Patient enrollment process. Abbreviations: MSSA, cloxacillin or cefazolin for patients at the highest risk of Duration of definitive therapy (days) 31.5 (13.0-42.0) 28 (10.0-42.0) 0.17 methicillin-susceptible S. aureus; BSI, bloodstream infection. morbidity and mortality from SAB [8]. However, no studies have Time to receipt of empiric therapy (hours) 2 (0-7) 20.9 (4.2-28.3) <0.001 directly compared cloxacillin or cefazolin to vancomycin as CONCLUSIONS empiric therapy for patients with MSSA bacteremia who are Time to receipt of β-lactam (hours) 3.00 (0.2-16.3) 68.2 (51.5-95.4) <0.001 transitioned to cloxacillin or cefazolin as definitive therapy. We Time to receipt of cloxacillin or cefazolin (hours) 21.0 (4.4-31.2) 68.3 (51.6-95.4) <0.001 Empiric therapy with cloxacillin or cefazolin was associated with assessed if empiric cloxacillin or cefazolin compared to earlier clearance of bacteremia by a median of 1 day compared to vancomycin was associated with differences in survival and Primary outcome vancomycin, but was not associated with a difference in all-cause microbiological cure in this patient population. 28-day mortality 7 (5.3) 11 (8.9) 0.27 mortality in patients with MSSA bacteremia. Vancomycin Secondary outcomes monotherapy for the empirical treatment of MSSA bacteremia 90-day mortality 14 (10.7) 22 (17.7) 0.11 may be appropriate if definitive therapy with cloxacillin or MATERIALS & METHODS cefazolin can be initiated within 3 days. Duration of bacteremia (hours) 70.7 (46.9-119) 97.1 (61.6-148) 0.007 We performed a retrospective cohort study of adult inpatients ≥ 3 days 58 (50) 72 (63.2) 0.047 REFERENCES with their first episode of MSSA bacteremia at two tertiary care Hospital length of stay (days) 19 (12-41) 22.5 (13-46.5) 0.16 hospitals in Vancouver, Canada, between January 2007 and 1. Thwaites GE, Edgeworth JD, Gkrania-Klotsas E et al. Clinical management of December 2014, inclusive. Consecutive patients were included if Staphylococcus aureus bacteraemia. Lancet Infect Dis 2011; 11: 208-222. Table 2: Outcome analysis comparing β-lactam versus vancomycin group, adjusted for predefined confounding variables. Abbreviations: they received cloxacillin or cefazolin for definitive therapy. 2. Khatib R, Saeed S, Sharma M et al. Impact of initial choice and OR, odds ratio; CI, confidence interval. delayed appropriate treatment on the outcome of Staphylococcus aureus bacteremia. Patients were excluded if there was missing data for 28-day Eur J Clin Microbiol Infect Dis 2006; 25: 181-185. Outcomes Crude OR (95% CI) P-value Adjusted OR (95% CI) P-value mortality, no empiric therapy was administered, death occurred 3. David MZ, Daum RS. Community-Associated Methicillin-Resistant within 24 hours following diagnosis of bacteremia, or 28-day mortality 0.58 (0.22-1.55) 0.28 1.03 (0.29-3.63) 0.96 Staphylococcus aureus: Epidemiology and Clinical Consequences of an Emerging polymicrobial bacteremia. 90-day mortality 0.56 (0.27-1.14) 0.11 1.02 (0.40-2.60) 0.97 Epidemic. Clin Microbiol Rev 2010; 23: 616-687. 4. Kim SH, Kim KH, Kim HB et al. Outcome of Vancomycin Treatment in Patients The primary outcome was 28-day mortality. Secondary outcomes Ratio of Mean (95% CI) P-value Adjusted Ratio of Mean (95% CI) P-value with Methicillin-Susceptible Staphylococcus aureus Bacteremia. Antimicrob Agents were 90-day mortality, duration of bacteremia and hospital Duration of bacteremia 0.77 (0.64-0.93) 0.01 0.78 (0.63-0.97) 0.02 Chemother 2008; 52: 192-197. length-of-stay. Hospital length-of-stay 0.85 (0.68-1.07) 0.16 0.86 (0.68-1.08) 0.20 5. 15. McDanel JS, Perencevich EN, Diekema DJ et al. Comparative Effectiveness of Beta-lactams versus Vancomycin for Treatment of Methicillin-Susceptible Logistic regression methods were used to model the odds ratio of Staphylococcus aureus Bloodstream Infections among 122 Hospitals. Clin Infect death in the β-lactam compared to vancomycin group. Linear RESULTS Dis 2015; 61: 361-367 6. Schweizer ML, Furuno JP, Harris AD et al. Comparative effectiveness of regression model was conducted for hospital length-of-stay and or cefazolin versus vancomycin in methicillin-susceptible Staphylococcus aureus duration of bacteremia. All models were adjusted for pre- The most common sources of bacteremia were unknown (27.1%), Rifampin and aminoglycosides were added for synergy in patients bacteremia. BMC Infect Dis 2011; 11: 279. specified confounding variables including age, sex, age-adjusted skin and soft tissue infections (18.4%), peripheral or central venous with prosthetic valve infective endocarditis or prosthetic joint 7. Lodise TP Jr., McKinnon PS, Levine DP, Rybak MJ. Impact of Empirical- Charlson-comorbidity index, Pitt bacteremia score, infectious catheters (16.5%) and injection drug use (15.7%). The prevalence infections. Fluoroquinolones, macrolides, trimethoprim- Therapy Selection on Outcomes of Intravenous Drug Users with Infective of infective endocarditis (IE) was 14.1%. Among patients with IE, sulfamethoxazole, and clindamycin were used for either treatment Endocarditis Caused by MSSA. Antimicrob Agents Chemother 2007; 51: 3731- diseases consultation, infective endocarditis and time to receipt 3733. 28-day and 90-day mortality was 2 (1.53%) and 3 (2.29%) in the β- of non-bacteremic co-infections or prophylaxis for other medical of empiric . 8. McConeghy KW, Bleasdale SC, Rodvold KA. The Empirical Combination of lactam group and 0 and 1 (0.81%) in the vancomycin group. conditions. Vancomycin and a β-Lactam for Staphylococcal Bacteremia. Clin Infect Dis 2013; 57: 1760-1765.

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