Objectives: Inhaled corticosteroids (ICS) and inhaled short-acting β2-agonists (ISABA) are the most commonly used medications for management of asthma. Increased asthma morbidity and mortality have been reported with excess use of ISABA in several studies. In these studies, authors have used different indicators to control for the potential confounding by asthma severity. The objective of this study was to determine the effect of ICS use on the association between use of ISABA and first hospitalization for asthma after controlling for several indicators of asthma severity.
Design: An inceptional cohort study using Saskatchewan Health databases.
Setting: The Province of Saskatchewan, Canada.
Participants: A total of 29,957 persons aged 5 to 54 years who had at least five asthma-related visits to physicians between 1991 and 2000.
Results: Among the subjects with increased asthma severity, indicated by one or more average number of asthma-related physician visits per 3 months during the follow-up, high use of ISABA was a risk factor for hospitalization when no ICS were used (rate ratio [RR], 2.16; 95% confidence interval [CI], 1.51 to 2.95). There was a beneficial effect of ISABA when there was low use of ICS (RR, 0.65; 95% CI, 0.42 to 0.93) or high use of ICS (RR, 0.23; 95% CI, 0.12 to 0.41). Among the subjects with less severe asthma, indicated by less than one asthma-related physician visits per 3 months, on average, during the follow-up, the risk of hospitalization was even greater for high use of ISABA when no ICS were used (RR, 10.06; 95% CI, 6.99 to 14.47). This was reduced but not abolished when there was low use of ICS (RR, 3.24; 95% CI, 2.29 to 4.59) and negated altogether by high use of ICS (RR, 1.10; 95% CI, 0.39 to 3.12).
Conclusion: Among both severe and less severe asthma groups, high use of ISABA was associated with an increased risk of asthma hospitalization in the absence of any use of ICS, which was progressively reduced with low and high use of ICS. This finding was independent of asthma severity and could result from lack of control through over reliance on ISABA in asthma management.