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

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.

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

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.

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).

Drug allergy testing was safe and removed inappropriate labels.

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