‘Simple tool’ helps predict amoxicillin hypersensitivity

The PEN-FAST clinical decision tool can assist in efficient amoxicillin allergy assessment based on four recognizable features, according to a study published in Annals of Allergy, Asthma & Immunology.

PEN-FAST was designed to help physicians evaluate penicillin allergy risk and severity while identifying low-risk penicillin allergies that do not require formal allergy testing, according to Anays Piotin, MD, of Strasbourg University Hospital in Strasbourg, France, and colleagues.

“This simple tool is based on four features associated with a positive penicillin allergy test evaluation: penicillin allergy occurring 5 or fewer years ago, anaphylaxis or angioedema, severe cutaneous adverse reaction and treatment required for allergic reaction,” Piotin and colleagues wrote.

Researchers designed the current study to validate PEN-FAST in a population at high risk for immediate amoxicillin allergy and identify clinical factors that predict amoxicillin immediate hypersensitivity.

The retrospective cohort analysis involved an outpatient and inpatient population of 142 adults (median age, 52 years; 62% female) with a history of immediate hypersensitivity reaction to amoxicillin at Strasbourg University Hospital Allergy Unit between January 2015 and January 2020.

Researchers defined immediate reactions as those occurring within an hour after drug intake, including urticaria with or without angioedema and anaphylaxis. Researchers used the Ring classification to categorize hypersensitivity reactions into four grades of severity.

Clinicians evaluated each patient via PEN-FAST, for which two points were given each for patients who had experienced an allergy event within the previous 5 years or who had experienced anaphylaxis or angioedema. Patients who needed treatment after an allergy episode received one point. Patients totaling fewer than three points were considered low risk for amoxicillin allergy.

At least 4 weeks after the initial hypersensitivity reaction, trained staff performed skin prick tests (SPTs) followed by an intradermal test if the SPT was negative.

The researchers found that the PEN-FAST criteria agreed with the clinical characteristics of the reactions associated with positive immediate hypersensitivity diagnoses. According to the findings, 29 of the patients (20.4%) were classified at low risk for allergy, and only two of them (6.9%) had positive amoxicillin allergy test results.

Further, the researchers said the PEN-FAST score showed good discrimination during the study, with a 0.86 (95% CI, 0.79-0.92) area under the curve.

Also, sensitivity to identify amoxicillin allergy was 0.56 (95% CI, 0.41-0.71) and specificity was 0.98 (95% CI, 0.93-1). Researchers reported a negative predictive value of 0.93 (95% CI, 0.77-0.99), and a positive predictive value of 0.81 (95% CI, 0.73-0.88).

The researchers excluded reactions to other penicillins and delayed reactions, which, along with the fact the study was a retrospective analysis of a database, may have limited these findings.

“Our findings validate PEN-FAST in a large European cohort of adult patients reporting an immediate reaction to amoxicillin, notably including anaphylaxis,” the researchers wrote. “Our study suggests PEN-FAST is the only penicillin allergy clinical decision rule that has been widely validated internationally.”