Abstract
BackgroundTo determine the suitability of using the self-controlled case series design to assess improvements in health outcomes using the effectiveness of beta blockers for heart failure in reducing hospitalisations as the example.MethodsThe Australian Government Department of Veterans' Affairs administrative claims database was used to undertake a self-controlled case-series in elderly patients aged 65 years or over to compare the risk of a heart failure hospitalisation during periods of being exposed and unexposed to a beta blocker. Two studies, the first using a one year period and the second using a four year period were undertaken to determine if the estimates varied due to changes in severity of heart failure over time.ResultsIn the one year period, 3,450 patients and in the four year period, 12, 682 patients had at least one hospitalisation for heart failure. The one year period showed a non-significant decrease in hospitalisations for heart failure 4-8 months after starting beta-blockers, (RR, 0.76; 95% CI (0.57-1.02)) and a significant decrease in the 8-12 months post-initiation of a beta blocker for heart failure (RR, 0.62; 95% CI (0.39, 0.99)). For the four year study there was an increased risk of hospitalisation less than eight months post-initiation and significant but smaller decrease in the 8-12 month window (RR, 0.90; 95% CI (0.82, 0.98)).ConclusionsThe results of the one year observation period are similar to those observed in randomised clinical trials indicating that the self-controlled case-series method can be successfully applied to assess health outcomes. However, the result appears sensitive to the study periods used and further research to understand the appropriate applications of this method in pharmacoepidemiology is still required. The results also illustrate the benefits of extending beta blocker utilisation to the older age group of heart failure patients in which their use is common but the evidence is sparse.
Highlights
To determine the suitability of using the self-controlled case series design to assess improvements in health outcomes using the effectiveness of beta blockers for heart failure in reducing hospitalisations as the example
Department of Veterans’ Affairs (DVA) claims data contain records of prescription medicines dispensed under the Repatriation Pharmaceutical Benefits Scheme, medical and allied health services and hospital admissions provided to veterans for whom DVA pays a subsidy
The results from the one year study period are comparable with those seen in a meta-analysis[15] which found a reduction in hospital admissions for heart failure for patients randomised to receive beta blockers compared to controls (OR, 0.63; 95% CI (0.56, 0.71) P < 0.0001)[15]
Summary
To determine the suitability of using the self-controlled case series design to assess improvements in health outcomes using the effectiveness of beta blockers for heart failure in reducing hospitalisations as the example. Research to assess the practical viability of study designs using administrative data in a variety of contexts is imperative so that policy makers and health professionals can be more confident in the conclusions that are made using these data sources. The self controlled case series design includes only those individuals who have had an outcome of interest. Confounding by indication can be assessed and controlled for in this method through the use of pre-exposure risk periods. Confounding by indication is present if patient characteristics alter the likelihood of being prescribed a medicine and are at the same time related to the probability of an outcome[7]
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