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.