D1.30 - Allergy Care in Adult Cystic Fibrosis Patients with Drug Hypersensitivity: A Service Evaluation at St Bartholomew’s Hospital

Effective drug allergy management is a critical component of multidisciplinary cystic fibrosis (CF) care. CF patients are frequently exposed to repeated and prolonged antibiotic courses due to recurrent infections, increasing the risk of drug hypersensitivity reactions (DHRs). However, many patients carry long-standing but inaccurate drug allergy labels, which can significantly restrict therapeutic options, particularly in the context of multidrug-resistant pathogens. Drug challenge testing (DCT) is the gold standard for confirming or excluding DHRs and is central to de-labelling. Optimal use of DCT requires assessment by experts in drug allergy, including detailed clinical history, structured risk evaluation, and access to specialised techniques such as skin testing and in vitro assays when appropriate.

A retrospective longitudinal study included all CF patients aged ≥16 years referred for assessment of suspected DHRs between 2019 and 2024. Data were extracted from medical records and entered into a dedicated database. Variables included demographics, microbiology, Aspergillus sensitisation, characteristics and severity of reported reactions, diagnostic test results, and DCT routes and outcomes. We used EAACI/ENDA recommendations to classify the reactions, and to perform and interpret skin testing and DCT. 

Twenty-eight patients were included (71.4% female, mean age 29.5 years), with a mean of 2.6 drug allergy labels per patient. Of 23 culprit drug challenges, 30.4% corresponded to immediate reactions (all grade I–II), 43.5% to non-immediate reactions (90% mild, 10% moderate maculopapular exanthema), and 26.1% were non-specific. Twenty-one patients underwent skin testing and DCT (32 challenges: 68.8% intravenous, 28.1% oral). Skin tests were positive in 2/21 (9.5%). One patient who experienced non-specific rashes with several antibiotic showed both immediate and delayed positive intradermal tests to multiple beta-lactams (imipenem, piperacillin-tazobactam, cefoxitin, meropenem), which was considered atypical and we will revisit at a later date. Another patient who experienced a DRESS showed positive delayed intradermal testing and positive lymphocyte transformation test to piperacillin-tazobactam.

Among 19 patients with negative skin tests, only 2 (10.5%) had positive DCTs. One patient repeated a moderate delayed maculopapular exanthema to Kaftrio on DCT, and was sucessfully challenged with another alternative at a later date. Another patient, who had experienced previously anaphylaxis to piperacillin-tazobactam, experienced grade III anaphylaxis to ceftolozane-tazobactam on DCT, which confirmed an allergy to tazobactam; however, skin testing was negative for all these agents.

Drug allergy evaluation in adult CF patients was safe and effective, with a high proportion of negative DCTs supporting successful de-labelling. Personalised assessment by drug allergy specialists, integrating structured risk evaluation, skin and in vitro testing, and DCT, enabled most patients to remove inaccurate allergy labels and expand therapeutic options. Optimising allergy pathways can substantially improve antimicrobial management in this complex population.