Abstract

Background: Inhaled corticosteroids are effective at preventing asthma morbidity and mortality. Most studies, however, have focused on short term effects, raising uncertainty about their effectiveness in the long term.

Methods: The Saskatchewan Health databases were used to form two population based cohorts of asthma patients aged 5–44 between 1975 and 1991. The first cohort included all subjects from the start of asthma treatment, while the second included subjects hospitalised for asthma from the date of discharge. Subjects were followed up, starting 1 year after cohort entry and continuing until 1997, 54 years of age, or death. The outcome was the first asthma hospital admission and readmission, respectively, to occur during follow up. A nested case-control design was used by which all cases were matched on calendar time and several markers of asthma severity to all available controls within the cohort.

Results: The full cohort included 30 569 asthmatic subjects of which 3894 were admitted to hospital for asthma and 1886 were readmitted. The overall rate of asthma hospitalisation was 42.4 per 1000 asthma patients per year. Regular use of inhaled corticosteroids was associated with reductions of 31% in the rate of hospital admissions for asthma (95% confidence interval (CI) 17 to 43) and 39% in the rate of readmission (95% CI 25 to 50). The rate reduction found during the first 4 years of follow up was sustained over the longer term. Regular use of inhaled corticosteroids can potentially prevent between five hospital admissions and 27 readmissions per 1000 asthma patients per year.

Conclusion: Regular use of low dose inhaled corticosteroids prevents a large proportion of hospital admissions with asthma, both early and later on in the course of the disease.