This thesis relates to the study of drug effectiveness using observational designs. First, we investigate the ability of inhaled corticosteroids, an anti-asthma medication, in preventing hospitalization for asthma. We then address methodological issues related to temporal dimensions of drug exposure and to the estimation of time-dependent rate ratios in case-control studies. To examine these questions, a cohort of 19,168 newly treated asthmatics was selected from the computerized databases of Saskatchewan Health. / Using a sub-cohort of 2,059 patients hospitalized for asthma, we found that regular users of inhaled corticosteroids were about 40 percent less likely to be readmitted to hospital for asthma than nonusers of these medications, and this after only 15 days of therapy. The beneficial effects lasted up to six months and waned thereafter. Using a case-control sample from the entire cohort, we found that therapy with inhaled corticosteroids, initiated early after the onset of symptoms of asthma, was more effective than theophylline in preventing the first hospitalization for asthma. When compared with anti-allergic agents, early treatment with inhaled corticosteroids was not found to significantly reduce the risk of asthma hospitalization, however. / Finally, we showed that the common use of exposure time-windows defined solely in terms of the outcome produces biased estimates of rate ratios that vary over time. Application of principles based on time-related dimensions of exposure provides, however, valid case-control estimates of time-dependent rate ratios. / In conclusion, we were able to show that regular use of inhaled corticosteroids is highly effective in preventing asthma hospitalizations. We also showed the importance of defining the exposure in terms of both the onset of therapy and the time of the outcome for the valid estimation of time-dependent rate ratios in case-control studies.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34505 |
| Date | January 1997 |
| Creators | Blais, Lucie. |
| Contributors | Suissa, Samy (advisor), Ernst, Pierre (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Epidemiology and Biostatistics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001601357, proquestno: NQ36957, Theses scanned by UMI/ProQuest. |
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