Background: Drug hypersensitivity reactions (DHRs) are among the most frequent reasons for consultation in allergy departments, and are becoming more common due to increasing prevalence and case complexity.

Objective: To study the clinical characteristics, drugs involved, diagnostic methods, and temporal variation of DHRs in a large series of patients over a 6-year period.

Methods: We included all patients attending our department between 2005 and 2010. The diagnosis was performed by in vivo and/or in vitro tests (basophil activation test and specific immunoglobulin [Ig] E in serum and drug provocation testing [DPT]) when indicated.

Results: We evaluated 4460 patients who reported 4994 episodes (mean [SD] of 1.13 [0.36] [range, 1-3] episodes per patient). Based on clinical history, 37% of the episodes were attributed to nonsteroidal anti-inflammatory drugs (NSAIDs), 29.4% to ß-lactam antibiotics (BLs), 15% to non-BLs, and 18.4% to other drugs. Analysis of the 1683 patients (37.45%) finally confirmed as allergic showed the most frequent diagnosis to be hypersensitivity to multiple NSAIDs (47.29%), followed by immediate reactions to BLs (18.12%). There was an increase in reactions to non-BLs (from 21.2% to 31.9%; P<.03) over the study period, mainly due to an increase in allergy to quinolones (from 0.5%
to 6.8%; P<.02); 44% of patients were diagnosed by clinical history, 14.6% by skin tests, 10.4% by in vitro tests, and 30.8% by DPT.

Conclusions: NSAIDs were the drugs most frequently involved in DHRs and the most common diagnosis was urticaria/angioedema with cross intolerance. Reactions to emerging drugs such as quinolone derivatives and radiocontrast media are becoming more common.

Key words: Drug hypersensitivity. Nonsteroidal anti-infl ammatory drugs. ß-Lactams. Epidemiology. Diagnosis.