Background: Current asthma guidelines recommend a stepwise approach to asthma treatment. Patients should be evaluated for adherence to inhaled corticosteroid (ICS) prior to escalation.

Aim: To explore and describe adherence to ICS treatment of patients with asthma, prior to treatment escalation.

Methods: A retrospective, longitudinal study of patients diagnosed with asthma, ?18 years, registered in the Swedish National Airway Register (SNAR). Data from SNAR was linked to the Swedish Prescribed Drug Register to obtain a complete dataset of drug treatment for a period of 24 months pre-index date and 12 months post-index date. Patients were categorized based on GINA-defined treatment steps. Adherence was based on ?defined daily dosages? of dispensed ICS packages and Medication Possession Ratio (MPR). Adherence to ICS therapy was calculated for the period 12 months pre-index date. MPR<80% was considered poor adherence. Analysis covered SNAR data from 01 July 2017 and 28 Feb 2019.

Results: Data from 30,880 patients was included in the study; with 3%, 24%, 29%, 34% and 3% categorized into Steps 1, 2, 3, 4, and 5 respectively. Remaining 7% was identified as ?no inhalation treatment? or ?other? (e.g. LABA only). Totally, 1681, 2108 and 477 patients escalated to treatment step 3, 4 and 5 respectively; of those on ICS therapy in the preceding year, 79%, 55% and 57% had poor adherence to ICS, respectively. Of the new patients on biologics (n=58), 36% were previously non-adherent to ICS therapy.

Conclusions: A large proportion of patients are non-adherent to their ICS therapy, therefore evaluation of adherence needs to be prioritized prior to treatment escalation.