Background: The importance of balance between controller and relieve medications in asthma is recognized. However, to what extent real-world practice has caught up with evidence-based guidelines is not studied.

Methods: This was a retrospective cohort study of individuals 15 to 67 years old who satisfied a validated definition of asthma in the administrative health data of British Columbia, Canada, between 2002 and 2013. Each patient-year was assessed for inappropriate and excessive prescription of SABAs and the balance between controller and reliever medications. Trends on three time axes were evaluated: calendar time, time course of asthma, and age. Poisson regression was used to test for linear trend.

Findings: 356,112 patients (56.5% female, mean age 30.5) contributed 2.6M patient-years. In 7.3% of patient-years SABAs were prescribed inappropriately. This proportion dropped by a relative rate of 5.3%/year (P<0.001). In the first year of asthma, 6.3% of patients had indicators of inappropriate SABA use which dropped within the first 3 years but increased thereafter. Excessive prescription of SABAs increased rapidly during the time course of asthma (change of 23.3%/year, P<0.001) and by age (change of 5.1%/year, P<0.001).

Conclusions: Despite overwhelming evidence on risks, inappropriate prescription for SABAs was prevalent. Excessive SABA use might explain high asthma mortality in older patients. Inappropriate prescriptions declined over the study period but increased over the course of asthma. These trends might have contributed to the declining asthma hospitalization rates in British Columbia, but there remain gaps in care and potentials for improvement in asthma outcomes.