PEN-FAST-ED - Utilizing This Decision Tool to Guide Antibiotics Prescribing in the ED

Review Author: Ava Harrington, DO

PEN-FAST is a screening tool used to assess and potentially challenge penicillin allergies. This screening tool was developed to identify patients with low-risk penicillin allergies for beta-lactam rechallenge without formal skin testing. The PEN-FAST relies on four variables including five years or less since reaction, anaphylaxis or angioedema, severe cutaneous adverse rection, treatment requires for rection. Each yes counts as two points.

0	<1% (very low risk)
1-2	5% (low risk)
3	20% (moderate risk)
4-5	50% (high risk)

If scored as very low risk or low risk, the recommendation is to consider direct oral or graded challenge. Moderate to high risk should be referred to an allergist for a more detailed evaluation.

Background: This study “PEN-FAST decision tool to guide antibiotic prescribing in the emergency department” is aimed to test this decision tool in the setting of the ED. This was a single-center prospective operational cohort study with ED pharmacy available. Patents who needed antibiotics were flagged for screening. Of the patients that had a PEN-FAST score between 0-2, the ED pharmacist recommended rechallenging with penicillin or cephalosporin. With a score of 3, which is considered a moderate risk, the ED pharmacist recommended a patient specific assessment. Patients who scored 4-5 were considered high risk and a penicillin challenge was not recommended in the ED.

Results/Discussion: There were 61 patients who were considered low risk in this study, and they were all rechallenged, zero of them had any adverse effects within one hour. There were only 6 patients out of 30 in the moderate category who were rechallenged in the ED with beta-lactamase, zero of which had an adverse rection.

Challenges in This Study: This was a single center study with access to emergency department pharmacist 24/7. Another limitation of this study was the small sample size; there were only 362 patients screeded and 100 were included in the study. This data is promising but there is low power to the study to prove that every person with a low risk using the PEN-FAST score will have no adverse reaction.

References:

Tran K, Lund J, Sealy C, Langley D, Kisgen J. PEN-FAST-ED: Utilizing the PEN-FAST decision tool to guide antibiotic prescribing in the emergency department. Am J Emerg Med. 2025 Apr;90:124-128. doi: 10.1016/j.ajem.2025.01.039. Epub 2025 Jan 19. PMID: 39864256.

"Penicillin Allergy Decision Rule (PEN-FAST)" MDCalc. Dr. Jason A. Turbiano. Retrieved from: https://www.mdcalc.com/calc/10422/penicillin-allergy-decision-rule-pen-fast.