Skin testing and oral penicillin challenge in patients with a history of remote penicillin allergy

Background: Penicillin administration is usually contraindicated in penicillin-allergic patients with positive skin test results. Objective: To examine whether penicillin oral challenge for patients with a history of remote non-life-threatening allergic reaction to penicillin can be well tolerated irrespective of skin test results. Methods: In a prospective open-label trial, 8,702 individuals were screened between November 1998 and January 2000. Of 687 patients with a non-life-threatening allergic reaction to penicillin, occurring longer than 3 years earlier, 169 were enrolled. Regardless of the response to penicillin skin testing, patients received the usual 1-day dosage of penicillin and amoxicillin on 2 separate occasions. Two to 6 years later, a follow-up was conducted to assess the outcomes of further penicillin administration. Results: A total of 272 combined skin tests and oral challenges were performed on 169 patients. Among 137 challenges with a positive skin test result and 135 patients with a negative skin test result, 9 (6.6%) and 5 (3.7%) (P =.29), respectively, developed a mild rash to oral challenge. At follow-up, 2 to 6 years afterward, 3 of 55 patients (5.5%) who were given a full treatment course of penicillin developed a mild skin eruption. Conclusions: Positive penicillin skin test results for patients with a remote history of non-life-threatening allergic reaction to penicillin were not associated with a greater prevalence of adverse reactions to oral challenge with penicillin than negative results. Because skin testing is considered the gold standard and the safest method for predicting tolerance to penicillin administration, oral penicillin challenge may be used as a diagnostic method only in these specific patients when skin testing is not feasible.