Think PEN-FAST: Evaluation of implementing PEN-FAST into pharmacist-led medication reconciliation

PURPOSE: Approximately 10% of US patients report a penicillin allergy, yet fewer than 1% have a true immunoglobulin E-mediated reaction. Mislabeled allergies contribute to unnecessary use of broad-spectrum antibiotics, increasing healthcare costs, hospital stays, antimicrobial resistance, and mortality. Despite guideline recommendations for risk stratification and allergy delabeling, implementation remains limited. PEN-FAST is a validated clinical tool used to facilitate delabeling without resource-intensive skin testing. This study aimed to determine the prevalence of low-risk penicillin allergy among adult patients using the PEN-FAST tool within a pharmacist-led medication reconciliation process. METHODS: A multicenter, retrospective prevalence study was conducted at 2 community hospitals. Patients admitted or seen in the emergency department from September 16 through December 16, 2024, with a documented penicillin allergy who underwent a pharmacist-performed PEN-FAST assessment were included. The primary outcome was the proportion of patients classified as having low-risk penicillin allergy (PEN-FAST score of <3). Secondary outcomes included allergy delabeling rates and the frequency of direct oral penicillin challenges. Descriptive analysis was used to evaluate the results. RESULTS: Of 95 patients assessed, 74% (n = 70) were classified as low risk. Among these low-risk patients, 10% (n = 7) had their allergy label removed and 3% (n = 2) underwent a direct oral penicillin challenge, with both tolerating penicillin without adverse reactions. CONCLUSION: These findings suggest that pharmacist-led PEN-FAST implementation is a feasible strategy to identify low-risk penicillin allergies, but allergy delabeling and oral challenge rates remain low. Further efforts are needed to integrate PEN-FAST into clinical workflows and enhance antimicrobial stewardship.