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PEN-FAST – Penicillin Allergy Risk Tool

April 30, 2020

Written by Vivian Lei

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Using the PEN-FAST rule, patients with low-risk penicillin allergies can be identified without need for formal allergy testing.

Why does this matter?
Many patients self-report penicillin allergies, but most are not truly penicillin allergic. This unnecessarily eliminates this drug class, leaving less effective, broader spectrum alternatives. But formal testing is both resource and labor-intensive. This study derives and validates a clinical decision rule to risk stratify patients claiming to have penicillin allergies based on historical features and to identify those who may safely use this family of drugs without need for confirmatory allergy testing. 

Life in the PEN-FAST lane
To develop the decision rule, 622 patients reporting a penicillin allergy prospectively underwent allergy testing via skin prick, intradermal, or patch testing and/or oral challenge. The clinical variables associated with positive penicillin allergy test results were distilled into a mnemonic, PEN-FAST. Calculate by QxMD has a new calculator.

  • For patients reporting a PENicillin allergy:

  • Five years or less since reaction (2 points)

  • Anaphylaxis or angioedema OR

  • Severe cutaneous adverse reaction (2 points)

  • Treatment required for reaction (1 point)

0 points = Very low risk of positive penicillin allergy test <1%
1-2 points = Low risk of positive penicillin allergy test 5%
3 points = Moderate risk of positive penicillin allergy test 20%
4 points = High risk of positive penicillin allergy test 50%

In the low risk group (scores <3), which comprised 74% of the cohort, only 17 of 460 patients had a positive test result (3.7%). The negative predictive value was 96.3%. External validation of the PEN-FAST decision aid remained clinically relevant in a retrospective cohort of 945 patients from 3 centers in Sydney and Perth, Australia and Nashville, TN. This study supports identifying patients with low risk for true penicillin allergy and safe use of this drug class, perhaps through an observed oral challenge in a primary care setting.

Development and Validation of a Penicillin Allergy Clinical Decision Rule.  JAMA Intern Med. 2020 Mar 16. doi: 10.1001/jamainternmed.2020.0403. [Epub ahead of print]

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