Tolerability of Cefazolin in Nafcillin-Intolerant Patients for the Treatment of Methicillin-Susceptible Staphylococcus aureus Infections.

Background: Non-immunoglobulin E (IgE)-mediated hypersensitivity reactions (HSRs) to nafcillin are commonly reported, but scarce data are available to guide appropriate antibiotic change following these reactions. Although cefazolin is an attractive therapeutic alternative in methicillin-susceptible Staphylococcus aureus (MSSA) infections when patients experience an HSR to nafcillin, more data are needed to evaluate the tolerability of cefazolin after switching from nafcillin. The purpose of this study was to describe the tolerability of cefazolin in patients who develop a suspected non-IgE-mediated HSR to nafcillin.

Methods: This was a retrospective, descriptive case series of patients who received nafcillin for an MSSA infection, experienced a suspected non-IgE-mediated HSR, and were switched to cefazolin between October 2015 and November 2019 at a single academic medical center. The primary objective was to identify the percentage of patients who completed cefazolin after experiencing a suspected non-IgE-mediated HSR to nafcillin.

Results: There were 80 patients with 87 prespecified non-IgE-mediated HSRs during the study period. Seventy-one (89%) patients completed cefazolin, with 53 (75%) of these patients completing at least 2 weeks of therapy. One patient was ultimately switched from cefazolin to daptomycin due to concern for treatment failure. Eight patients (10%) did not tolerate cefazolin after switching from nafcillin. Of these, 3 patients experienced an unrelated HSR, whereas 5 patients experienced the same non-IgE-mediated HSR that was attributed to nafcillin and discontinued cefazolin within 7 days. The most common HSR cited was immune-mediated nephritis; however, the majority were clinically presumed but did not meet objective diagnostic criteria.

Conclusions: Treatment with cefazolin after experiencing a suspected non-IgE-mediated HSR to nafcillin appears to be safe, even for patients requiring a prolonged duration of cefazolin.