Prevalence and predictors of adherence to controller therapy in adult patients with severe/difficult-to-treat asthma: a systematic review and meta-analysis.

Objective: Nonadherence to prescribed treatment is an important cause for poor asthma control. This systematic review aimed to determine the prevalence and determinants of nonadherence in adult patients with severe asthma.Data sources: Embase and Pubmed were searched for publications in English studying adult patients and containing the keywords "severe asthma", "adherence", and "compliance".Study selection: Only studies utilizing objective methods for monitoring adherence and clear definition of the level of asthma severity were included. Predominantly pediatric studies or studies of less severe asthma were excluded.Results: The search returned 488 reports, of which 14 reports (of 2297 patients) were included. The weighted mean age of patients was 44 years and 64% were females. In studies using a cutoff of acquiring 50% or less of the medication, an overall rate of nonadherence was 42.9%. For studies reporting nonadherence of a continuous scale, the weighted mean nonadherence was 42.9% (95% CI 28.2-49.5). Meta-analysis of adherence predictors showed that male sex was associated with adherence with an odds ratio of 2.25 and higher asthma quality of life questionnaire (AQLQ) scores with a mean difference 0.47 points in adherent patients. Other predictors were reported to have significant association with adherence (e.g. older age, more knowledge about asthma, simpler medication schedules) but these were from single studies.Conclusion: Nonadherence to therapy is a common problem in the management of patients with severe asthma. More robust and objective methods are needed to homogenize and improve the accuracy of assessment methods. More studies are needed from developing countries. Systematic review registration number: CRD42018114669.