Methods: 42 patients with suspected beta-lactam hypersensitivity reactions were evaluated at a drug allergy clinic at a tertially allergy center. Skin prick tests (SPT) with major determinants (PPL), minor determinants (MDM), penicillin G, ampicillin, amoxicillin, intradermal tests (ID) and specific IgE determination were done. If all tests were negative, a drug challenge was performed.
Results: 42 patients were enrolled (mean age 39 years, 71.4% female and 28.6% males). History of atopy was present in 59.5%. The offending antibiotics were amoxicillin and amoxicillin/clavulanic acid in 28 (66.6%), penicillin in 10 (23.8%), and ampicillin in 4 (9.5%). Specific IgE to penicillin was negative in almost all patients with history of penicillin allergy (41 patients, 97.6%). SPT and ID tests were positive in 11 patients (26.1%) as follows: 3 patients (7.1%) had positive SPT to PPL, 1 patient (2.4%) SPT to MDM, 2 patients (4.8%) SPT to Penicillin G, 1 patient (2.4%) SPT to Ampicillin, 1 patient (2.4%) SPT to Amoxicillin, 8 patients (19%) ID to PPL, 3 patients (7.1%) ID to Penicillin G, 3 patients (7.1%) ID to Ampicillin. Only 1 patient had both positive specific IgE and skin tests. The remaining 31 patients (73.8%) underwent a drug challenge with the culprit antibiotic with no reported reactions.
Conclusions: One fourth of patients with history of beta-lactam hypersensitivity reactions were confirmed after testing. A combination of skin testing, specific IgE and drug challenge is necessary since none has sufficient sensitivity to be used alone