METHODS: Prospective single-blind, placebo-controlled clinical trial of patients ≥ 7 years old with historical non-life-threatening reactions to penicillin. Patients were challenged with placebo followed by a 2-step graded challenge to amoxicillin. The HSR rate was compared to the rate of HSR observed in our previous study with antecedent skin testing and to the currently reported penicillin allergy prevalence in the US population.
RESULTS: 119 patients underwent amoxicillin challenges. Patients were predominantly women (75.6%) with a median age of 54 years (range 7-90) and were Latino (36.1%), White (30.3%), and Black (25.2%). Only four patients experienced HSRs (3 nonimmediate rashes, 1 intractable pruritus). This observed 3.4% rate was not significantly different than the 2.4% HSR rate we observed previously among patients who underwent skin testing prior to challenges (p=0.5) and was significantly less than the 10% reported penicillin allergy prevalence in the US population (p=0.02). The rate of subjective reactions after amoxicillin (14/119, 11.8%) was not significantly different than that observed after placebo (16/119, 13.4%, p=0.6). Reactions to amoxicillin that were subjective and resolved spontaneously were deemed not to be allergic with no restrictions on future penicillin use.
CONCLUSIONS: Graded amoxicillin challenges without prior skin testing in this patient population with non-life-threatening historical reactions to penicillin were observed to be safe. The drug HSR rate we observed is similar to recent studies in patients who underwent skin tests prior to challenges.