PEN-FAST-ED: Utilizing the PEN-FAST decision tool to guide antibiotic prescribing in the emergency department

Patient-reported penicillin allergies are frequently encountered in the emergency department (ED), which often lead to non-beta-lactam antibiotic use despite beta-lactams' place as first-line therapy in most bacterial infections. The PEN-FAST clinical decision tool was developed and validated to identify patients with a low risk of true penicillin allergies that do not require formal skin testing for rechallenging. The tool consists of four questions that add up to a total score ranging from 0 to 5. Scores of 0-2 are associated with low risk of true penicillin allergy (<5% risk of true reaction); scores of 3 with moderate risk (<20% risk); and scores of 4-5 with high risk (50% risk). The purpose of our study was to determine the safety and efficacy of our facility's implementation of pharmacist utilization of the PEN-FAST screening tool to assess purported penicillin allergies and rechallenge low to moderate risk patients in the ED.

This was a single-center, prospective, observational cohort study conducted from October 2023 to March 2024. Adult ED patients with a documented penicillin allergy with an order for aztreonam, levofloxacin, clindamycin, or a consult for pharmacy to assist with antibiotic selection were included. Patients were excluded if the order or consult was placed by a non-ED physician, no penicillin allergy was documented, the patient had previously tolerated a penicillin or cephalosporin per chart review, was unable to participate in the interview, or the completion of the assessment would delay patient care. The primary outcome was the percent of patients with a PEN-FAST score of 0-2 who tolerated a beta-lactam antibiotic after pharmacist intervention. Secondary safety and logistical outcomes included the incidence of immune-mediated reactions within one hour of beta-lactam administration, timing of the assessment, and antibiotic selection in transitions of care.

Of the 361 patients screened, 100 patients were included. There were 61% of patients who had a PEN-FAST score of 0-2, 30% had a score of 3, and 9% had a score of 4-5. For the primary outcome, all 52 (100%) patients with a PEN-FAST score of 0-2 who were rechallenged tolerated a beta-lactam antibiotic in the ED. For secondary outcomes, 6 patients with PEN-FAST score of 3 were rechallenged and tolerated a beta-lactam. There were 0 incidences of any immune-mediated reactions within one hour of beta-lactam administration. The median time from initial order placement to change in therapy and to antibiotic administration was 17 min and 41 min, respectively. Of those rechallenged, 13 of 14 discharged (93%) and 39 of 44 admitted patients (89%) were continued on beta-lactam antibiotics.

In this prospective, observational study, administration of beta-lactam antibiotics to ED patients with previously reported penicillin allergies and a PEN-FAST score less than 3 did not result in any immune-mediated reactions. The PEN-FAST decision tool was able to safely identify and risk-stratify eligible patients for beta-lactam rechallenge in the ED.