Decision Tool Hastens Delabeling of Erroneous Penicillin Allergy

The clinical decision support tool, PEN-FAST, introduced and validated in 2020 to facilitate identifying and "delabeling" erroneous penicillin allergy alerts, has recently undergone additional validation that affirms its potential to restore antibiotic treatment options that would otherwise be precluded.

"Our study showed PEN-FAST, a user-friendly tool that has been successfully validated, with an NPV (negative predictive value) of 100% in identifying patients with a low-risk penicillin allergy history who could safely proceed to DC (direct oral challenge) and ultimately penicillin allergy delabeling," wrote the developer of the tool, Jason Trubiano, MBBS, PhD, Centre for Antibiotic Allergy and Research, Department of Infectious Diseases, Austin Health, Heidelberg, Australia, and colleagues.

The tool was "urgently required," Trubiano and colleagues observed in 2020, to identify low risk allergies that do not require skin testing. In their current report, they tout the simplicity of the tool, which should facilitate its use beyond allergists "particularly in areas without easy access to allergists."

Trubiano and colleagues also contrast PEN-FAST to other tools to risk stratify patients with penicillin allergy. They point out that the results with some have not been easily generalized to different populations, and that others lack any external validation.

The PEN-FAST consists of 3 yes-no questions corresponding to the acronym, FAST:

• Five years or less since reaction[Yes scores 2 points}
• Anaphylaxis or angiodema (OR) Severe cutaneous adverse reaction [Yes to either scores 2 points]
• Treatment required for reaction[Yes scores 1 point]

The PEN-FAST Rule: 0 points <1% risk of positive penicillin allergy test; 1-2 points 5% risk; 3 points 20% risk; 4-5 points 50% risk.

In the current study, the investigators conducted a retrospective review of nonpregnant adult patients with reported penicillin allergies who underwent allergy testing in the period between October 2020 to July 2022, in allergy and immunology outpatient clinics of a large tertiary referral health care system in the US.

The cohort of 120 patients of median 54 years of age {37.3-67.0) included 95 females (79.2%). Allergy testing consisted of skin prick and intradermal testing followed by oral challenge, or oral challenge without skin testing. Direct oral challenge was performed in 16 patients (12.3%).

Trubiano and colleagues reported that patients who received DC had PEN-FAST scores of 0 (5 patients, 4.2%) or 1 (11 patients, 9.2%); and none had immune- or nonimmune-mediated reactions. PEN-FAST scores of 2 or less were obtained from 88 patients (73.3%), and all had negative allergic test results. Of four patients (3.4%) who tested positive for penicillin allergy: two had positive skin test results and PEN-FAST scores of 3; and two had negative skin test results but failed the oral challenge, with PEN-FAST scores, respectively of 3 and 5.

In predicting penicillin allergy, PEN-FAST scores of 2 or less were determined to have sensitivity, specificity, NPV and a positive likelihood ratio of, respectfully, 100% (95% CI 39.8-100), 75.9% (67.0-83.3), 100% (95.9-100%) and 4.14 (3.00-5.72).

"Penicillin allergy is a public health issue; however, less than 10% of reported penicillin allergy is confirmed by formal testing," Trubiano and colleagues observed."Clinical decision-making tools encourage the use of penicillin allergy evaluations and DC with greater frequency and accuracy."