β-Lactam allergy testing and delabeling-Experiences and lessons from Singapore.

Background: β-Lactam allergy is over-reported and this leads to greater healthcare costs. Allergy testing has inherent risks, yet patients who test negative may continue avoiding β-lactams.

Objective: To evaluate the safety and diagnostic value of β-lactams allergy testing locally and usage of antibiotics following negative testing.

Methods: We performed a retrospective medical record review and follow-up survey of patients who underwent β-lactam testing between 2010 and 2016 at the National Skin Centre, Singapore.

Results: We reviewed the records of 166 patients, with a total of 173 β-lactam allergy labels. Eighty (46.2%) labels were to penicillin, 75 (43.1%) to amoxicillin/amoxicillin-clavulanic acid, 11 (6.4%) to cephalexin, and 5 (2.9%) to others. Skin tests were performed in 142 patients and drug provocation tests (DPTs) in 141 patients. Eleven (6.6%) patients defaulted DPTs after skin testing. Out of 166 patients, 22 (13.3%) patients were proven allergic by either skin tests (16) or DPTs (6). Patients who tested positive had nonsevere reactions. Out of 155 patients who were conclusively evaluated, 133 (85.8%) were not allergic. Of these patients, 30 (22.6%) used the tested β-lactam subsequently, with one reporting a mild reaction. Fifty-one (38.3%) patients were uncontactable or uncertain if they consumed a β-lactam since testing negative. Fifty-two (39.1%) patients had no re-exposure (35 had no indication, 17 were fearful of reactions).

Conclusion: Drug allergy testing was safe and removed inappropriate labels.

Clinical Implication: Allergy testing is efficacious, but fears of subsequent rechallenge should be addressed to maximize the effectiveness of allergy delabeling.