Allergological work-up in the suspicion of drug hypersensitivity in patients undergoing allergen-specific immunotherapy

Background: Poorly documented self-reported drug allergy (DA) is a frequent problem in daily clinical practice and has a considerable impact on prescription choices. Atopy has been described as a risk factor for drug hypersensitivity (DH). The aim of this study was to better investigate the cases of suspicion of DH reported by patients undergoing subcutaneous allergen-specific immunotherapy (SCIT).

Methods: In this prospective study conducted since 2013, we firstly evaluated the self-reported cases of DH in patients undergoing SCIT in the Allergy Department of our Hospital. The SCIT has been indicated to atopic patients based on the dust mite in vivo or in vitro specific-IgE (D.pteronyssinus and/or B.tropicalis) and clinical relevance of these allergens. We excluded cases with unrelated history of DH. For the evaluation of suspected DH, we used the European Network for Drug Allergy(ENDA) questionnaire and the DA work-up followed the ENDA recommendations.

Results: Of all 1400 patients undergoing SCIT evaluated on May/2013, 691(49,3%) replied the first questionnaire, 133(19%) of those self-reported having drug allergies. Forty-five (34%) indicated hypersensitivity to antibiotics(ATB), 46(35%) to non-steroidal anti-inflammatory drugs (NSAIDs), 5(4%) to both ATB and NSAIDs, 31(23%) to other drugs and 6(4%) didn’t remember the medication involved. Of the 133 reports, 65(49%) were evaluated by ENDA questionnaire and 68(51%) refused to go through the drug-allergy evaluation. Of those 65 evaluated cases, forty-two (65%) were women and the mean age was 28 (4 to 70 years). Thirty (46%) cases had history of immediate reaction and the mean time between the reaction and the evaluation was 10 years. Eleven (17%) cases were excluded and the DH investigation has been offered to 54(83%) patients, from whom 38(58%) had possible/probable clinical history of DH. Twenty-five (38%) cases refused or were not interested in undergoing the investigation and 11(17%) are still under investigation. Of 18(28%) who completed the investigation, 11 were with NSAIDs and 7 with antibiotics, all negative.

Conclusions: The major result of this study confirmed that DH reactions occurred in less than one quarter of patients with a history suggesting possible DA. Negative results on DA work-up may have occurred due to the loss of sensitization and cofactors not included in the diagnostic procedure. Diagnostics tests in individuals with self-reported DA can exclude these conditions.