Limited evidence exists on adherence and effectiveness of combination therapy (inhaled corticosteroids and long-acting β₂-agonists in the same inhaler) in asthma.

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 β₂-agonists in 2 different inhalers).

This retrospective 1-to-1 matched cohort included newly treated asthmatics with either a combination or concurrent therapy selected from the Régie de l’assurance maladie du Québec 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.

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).

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.

Combination therapy might be preferred to concurrent therapy for patients with asthma with low adherence to controller therapies.