Persistence, adherence, and effectiveness of combination therapy among adult patients with asthma

Background: Limited evidence exists on adherence and effectiveness of combination therapy (inhaled corticosteroids and long-acting beta(2)-agonists in the same inhaler) in asthma. Objective: To compare persistence, adherence, and effectiveness between patients with asthma 16 to 44 years old starting combination or concurrent therapies (inhaled corticosteroids and long-acting beta(2)-agonists in 2 different inhalers). Methods: This retrospective 1-to-1 matched cohort included newly treated asthmatics with either a combination or concurrent therapy selected from the Regie de l'assurance maladie du Quebec database between 1999 and 2002. Persistence was determined by Kaplan-Meier and Cox regression analyses. Adherence was estimated by the number of prescriptions filled during the first year and compared between the 2 drug regimens using a linear regression model. Treatment effectiveness to reduce the rate of moderate to severe asthma exacerbations was estimated with Poisson regression models. Results: Persistence fell to 10% and 5% after 12 months for combination and concurrent users, respectively. Combination users were found to be 17% less likely to stop their treatment (adjusted hazard ratio, 0.83; 95% CI, 0.78, 0.88) and filled on average 0.9 more prescription per year than concurrent users (P = .0001). Combination users were also found to be 17% less likely to have a moderate to severe asthma exacerbation (adjusted rate ratio, 0.83; 95% CI, 0.75, 0.91). Conclusion: The observed differences in treatment persistence and adherence were found to be associated with a reduction in the rate of moderate to severe asthma exacerbations among combination users. Clinical implications: Combination therapy might be preferred to concurrent therapy for patients with asthma with low adherence to controller therapies.