Optimizing clinical outcomes in patients with methicillin-sensitive Staphylococcus aureus bacteremia and reported penicillin allergy
Background: Methicillin-sensitive Staphylococcus aureus (MSSA) bacteremia is a morbid infection with 1st-line therapies including nafcillin, oxacillin and cefazolin. While these drugs are avoided in patients with true penicillin (PCN) allergy, most such patients are not allergic and could tolerate these medications. We used a decision tree to examine the optimal MSSA treatment strategy for patients with reported PCN allergy.
Methods: We developed a model comparing 3 treatment strategies for patients with MSSA bacteremia and reported PCN allergy: No allergy evaluation, give vancomycin (Vanc); Allergy history-guided treatment using cefazolin if reported PCN allergy excluded anaphylactic features (HX-Cefaz); and complete allergy evaluation with PCN skin testing, give cefazolin if negative (ST-Cefaz). Key literature-based input parameters included the 12-wk probability of MSSA recurrence and mortality associated with cefazolin (9.1%, 3.6%) and vancomycin (18.8%, 19.2%), penicillin and cefazolin cross reactivity (2.9%) and proportion of patients who react to cefazolin with a nonanaphylactic PCN allergy history (2.2%). 12-wk outcomes included MSSA cure and death; adverse drug reactions (ADRs, toxicity or intolerance); and allergic reactions including those potentially iatrogenic. In sensitivity analyses, we examined the impact of varying uncertain input parameters.
Results: Vanc resulted in the lowest cure and the highest mortality (Fig 1), and the highest ADRs and allergic reactions (Fig 2); most allergic reactions were not iatrogenic. Similar numbers of patients are cured with HX-Cefaz and ST-Cefaz, but ST-Cefaz resulted in fewer allergic reactions. HX-Cefaz would be preferred to ST-Cefaz, leading to the greatest proportion cured and the fewest allergic reactions if ˂1.6% of patients with a nonanaphylactic PCN allergy react to cefazolin.
Conclusion: Patients with MSSA bacteremia and a reported PCN allergy have improved outcomes when the allergy is addressed, either by history or skin testing, compared to vancomycin treatment without evaluation. Prospective data on cefazolin reactions in PCN-allergic patients are needed to confirm that full allergy evaluation is preferred over history alone.
E. S. Shenoy, None
R. Walensky, None