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Methods: We conducted a retrospective study evaluating a total of 108 pediatric patients (age ≤18y) with history of penicillin allergy who after negative PST either underwent formal oral challenges in our clinic or informal oral challenges. The latter was defined as a full dose oral penicillin given after negative PST as clinically indicated by their primary care doctor. PST was performed using standard methods utilizing benzylpenicilloyl-polysine, penicillin G, benzlpenicilloate, negative control, and histamine control. This study was IRB approved and charts were reviewed for demographics, formal oral challenge results, and subsequent penicillin or aminopenicillin exposures.
Results: Thirty patients (median age at reaction 2.25 years, range 0.33-10) underwent formal penicillin oral challenges, and seventy-eight patients (median age at reaction 2 years; range 0.25-12) underwent informal oral challenges. Patients who underwent formal oral challenges were more likely to have a reaction compared to those who underwent informal oral challenges (p= 0.0199). Compared to the informal challenge group, patients who had formal challenges were more likely to have immediate type reactions (onset <1 hour) (6/30 vs. 1/77; p=0.0017) and had a shorter interval from skin testing to challenge (74.9 vs. 547 days; p=0.0001).
Conclusions: Immediate type reactions along with a shortened time interval between reaction and oral challenge were associated with a higher likelihood of having a reaction on oral challenge despite negative PST.