Purpose:The purpose of this case report is to describe the successful application of a cefazolin desensitization protocol in a penicillin allergic patient and to discuss the potential advantages for the use of desensitization protocols in commonly encountered Staphylococcal infections. Summary: A 64 year old Caucasian man presented to the hospital with lower extremity pain and petechiae. Allergies documented in the medical chart at admission include amoxicillin and cefotetan. The patient was started on vancomycin 1 gram every 12 hours (14 mg/kg) empirically which was continued for 14 days. Two out of 2 blood cultures revealed MSSA. The patient's signs and symptoms improved and he was discharged on hospital day 16 after completing 14 days of vancomycin therapy for his MSSA bacteremia. Less than 72 hours after discharge, the patient presented again to the hospital with increasing lower extremity edema and fever. Infectious diseases consult on day 2 of hospitalization recommended continuing vancomycin due to abscess the documented reaction of severe itching with penicillin. On day 5, surgical debridement of the lower extremity abscesses was performed and the infectious diseases team recommended cefazolin desensitization followed by a 2-week course of cefazolin. The patient tolerated the desensitization protocol and was continued on cefazolin 1 gram every 8 hours for 14 days. The patient improved significantly and repeat blood cultures on day 18 of hospitalization were negative. Conclusion: For patients that have a true allergy to penicillin, desensitization should be a consideration to facilitate beta-lactam therapy in the management of patients with invasive MSSA infections. When performed appropriately, desensitization can be a safe alternative with minimal risk for serious adverse reactions.

Background Beta-lactams are the most commonly used antibiotics, although they are also associated with hypersensitivity reactions. Although approximately 10% of the population report an allergy to a beta-lactam, identifying erroneous beta-lactam allergies can lead to improved patient outcomes and lower rates of antimicrobial resistance. Methods This study was a single-center, retrospective review of a pharmacy resident driven beta-lactam allergy assessment. The allergy assessment consisted of a chart review and a 3-question interview. The primary outcome of this study was a composite of the following interventions: beta-lactam allergy delabeling, reaction specification, and/or identification of previously tolerated beta-lactams. Secondary outcomes included patients who were relabeled if delabeling occurred, patients who received beta-lactam therapy after changes occurred to their charted allergy, and impact on hospital utilization of beta-lactam alternative antibiotics. Results A total of 42 patients were interviewed between September 13, 2021, and December 17, 2021, with follow-up occurring 90 days after the initial interview. The most common beta-lactam allergy reported was penicillin (90.5%). Of the patients who were assessed, 95.2% met at least one of the components of the primary endpoint. Specifying the previous toleration of beta-lactam agents was the most common intervention, occurring after 78.6% of assessments. Complete delabeling of the patient's beta-lactam allergy occurred after 38.1% of the interviews conducted. Conclusions A pharmacy-resident driven beta-lactam allergy assessment was effective at clarifying beta-lactam allergies, including the complete delabeling of erroneous beta-lactam allergies.

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