Background Spacers may be compatible but unlicensed for an inhaler device. A prior study showed that co-prescription of unlicensed spacers with non-extrafine (non-EF) beclometasone dipropionate (BDP) asthma therapy was common.1 This study aimed to compare the occurrence of patient-reported inhaled corticosteroid (ICS)-related adverse events (AEs) in patients with asthma co-prescribed the licensed Volumatic or unlicensed Aerochamber spacer with their non-EF BDP therapy.Method A cross-sectional study using completed questionnaires and data extracted from the Optimum Patient Care Research Database including patients with asthma, aged =2 prescriptions for non-EF BDP and co-prescription of either a Volumatic or Aerochamber spacer. Patient characterisation was performed for the year prior to receipt of the completed questionnaire. AEs captured via questionnaire included continual sore mouth/throat, oral thrush, hoarse voice, bruising, weight gain and cough. The primary outcome was non-inferiority of the proportion of patient-reported oral candidiasis (reported as oral thrush/hoarse voice). The two spacer groups were compared using logistic regression, adjusted for gender, ICS average dose and smoking status. Non-inferiority was claimed if the upper 95% confidence interval (CI) of the marginal effect estimate was lt;0.13. Comparisons by age (lt;16, 16textendash65,>=65 years) and ICS dose (lt;1000 textmug,>=1000 textmug) were additionally performed.Results Of the patients co-prescribed the licensed Volumatic spacer (n=155), 29.9% reported oral candidiasis, compared to 27.7% of patients co-prescribed the unlicensed Aerochamber device (n=385, p=0.622). The marginal effect estimate was -0.043 (95%CI -0.133, 0.047) and the Aerochamber was determined to be non-inferior to the Volumatic spacer. In terms of the total number of reported AEs, there were no significant differences for the main population (=65 years (p=0.425), high dose (p=0.084) and low dose (p=0.443) groups between those co-prescribed a Volumatic or an Aerochamber spacer.Conclusion Co-prescription of the unlicensed Aerochamber spacer with non-EF BDP asthma therapy, in recommended patient groups, does not increase the risk of developing oral candidiasis or other ICS-related AEs, as compared to co-prescription of the licensed, Volumatic device.ReferenceICARUS study submitted to PCRS2017.