To the Editor, Quinolones are a family of antibiotics containing a bicyclic core structure related to the compound 4-quinolone and have presented an increased use because of their high potency, broad spectrum of activity, convenient formulations, as well as a comparatively low incidence of side effects.1-3 However, quinolones are the second most common antibiotic class associated with drug hypersensitivity reactions (DHR),3 being the fourth cause of consultations due to suspected drug allergy in Spain, and showing an increased incidence in the last years (4.3% of consultations in 2015 vs 1% in 1992).4 Allergic reactions to quinolones can be classified as IgE-mediated immediate reactions (IR) if they appear within 1 hour after drug intake, and T-cell-mediated nonimmediate reactions (NIR) if they appear more than 1 hour after drug intake.5,6 Current European guidelines5 for in vitro tests in the diagnosis of DHR indicate that the basophil activation test (BAT) can be recommended for diagnosing IgE-mediated allergy to fluoroquinolones although different studies have shown discordant results.6 A high rate of cross-reactivity among different quinolones has been described.6,7 We conducted a retrospective review of patient's clinical histories in a real-life setting, in whom BAT to quinolones was performed, from April 2015 to October 2018 at a tertiary hospital (La Paz University Hospital, Madrid, Spain). From the 10 patients with mild reactions (grade 1), three had presented a positive BAT result and one patient chose to not be studied with DPT. The allergy workup included compatible clinical history, skin testing (prick, intradermal, and/or epicutaneous tests), BAT, and, for some mild cases, drug provocation tests (DPT). [Extracted from the article]