Impact of adherence to treatment with inhaled corticosteroids/long-acting β-agonists on asthma outcomes in the United States

Background: Suboptimal adherence to maintenance medication has been associated with poor outcomes in asthma. This study examined single-inhaler inhaled corticosteroid (ICS)/long-acting β2 agonist (LABA) adherence and asthma-related outcomes.

Methods: This retrospective observational study of patients with asthma initiating ICS/LABA used data from IQVIA PharMetrics Plus (1 January 2014-31 March 2019). Patients included were ⩾18 years old and had ⩾12 months continuous eligibility before, and ⩾180 days follow-up after, the index date. Adherence was measured as proportion of days covered ([PDC] adherent ⩾ 0.8; non-adherent <0.8) each quarter, with outcomes measured each subsequent quarter. Endpoints were asthma-related overall and severe (inpatient/emergency department [ED] visit) exacerbations, rescue medication use, and asthma-related healthcare resource utilization and costs. Regression models evaluated associations between adherence and outcomes, controlling for repeated measures and differences in baseline characteristics.

Results: Overall, 50,037 patients were included (mean age 45.3 years; mean follow-up 23.3 months). Adherent patients were less likely to experience asthma-related overall (adjusted odds ratio [aOR] 95% confidence interval [CI]: 0.942 [0.890, 0.998]; p = 0.041), or severe exacerbations (aOR [95% CI]: 0.778 [0.691, 0.877]; p < 0.001) per quarter versus non-adherent patients. Adherent patients had lower severe exacerbation rates (adjusted rate ratio [aRR] [95% CI]: 0.792 [0.702, 0.893]; p < 0.001) but similar overall exacerbation rates (aRR [95% CI]: 0.993 [0.945, 1.044]; p = 0.783) versus non-adherent patients. The odds of rescue medication use were lower per 20% PDC increase (aOR [95% CI] short-acting β2 agonist: 0.991 [0.985, 0.996]; p = 0.001; oral corticosteroid: 0.988 [0.982, 0.995]; p < 0.001). Adherent patients were less likely to visit EDs per quarter (aOR [95% CI]: 0.775 [0.680, 0.883]; p < 0.001) and odds of hospitalization were lower per 20% PDC increase (aOR [95% CI]: 0.930 [0.881, 0.982]; p = 0.009). Across most measures, adherent patients incurred lower costs.

Conclusion: This real-world study highlights the short-term clinical and economic benefits of ICS/LABA adherence in asthma, particularly in reducing severe exacerbations.