Comparison of measures of medication persistency using a prescription drug database
Purpose
Studies of medication persistency using drug databases use different definitions of persistency, making it difficult to compare the results from separate studies. We undertook a study of persistency to statins using various definitions to compare the results obtained with the different definitions.
Methods
All patients with an acute myocardial infarction in the province of Quebec between April 1999 and March 2004 who filled a prescription for a statin within 30 days of discharge were identified. The main outcomes were the 1-year rates of persistency defined as (1) the proportion of individuals with a medication possession ratio ≥80%, (2) the proportion of individuals having filled a prescription in the last 60 days of the year, and (3) the proportion of individuals with continuous exposure after the initial prescription, using a grace period of 7 days or 25% of the duration of the previous prescription between successive prescriptions. Kaplan-Meier analysis was also performed to assess continuous persistency over time using a 7-day grace period.
Results
Of the 20
239 patients identified, 1 year persistency to statins ranged from 41% to 90%, depending on the definition used: 85% had a medication possession ratio for statins ≥80%, 90% filled a prescription in the last 60 days of the year, 41% to 44% had continuous persistency, and, in survival analysis, the probability of continuous persistency was 41%.
Conclusions
Measures of medication persistency yield different results, depending on the definition used to define persistency. Results of studies of persistency should thus be interpreted with caution.
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Drs Hudson and Pilote are funded by the Canadian Institutes of Health Research. Dr Pilote is a William Dawson Professor of Medicine at McGill University, Montreal, Quebec, Canada. This study was supported in part by a grant from the Canadian Institutes of Health Research (#ATF 6669).
Dr Hudson was responsible for the conception of the study. Dr Pilote was responsible for acquisition of the data. Mr Richard was responsible for the data programming. All authors were responsible for the design of the study, data analysis, and interpretation. Dr Hudson was responsible for drafting the manuscript. All other authors were responsible for revising the manuscript critically for important intellectual content. All authors have seen and approved the final version of the manuscript.
None of the authors have any conflicts of interests to disclose.
The funding agency had no role in the design of the study; in the collection, analysis, and interpretation of the data; in the writing of the manuscript; and in the decision to submit the article for publication.
PII: S0002-8703(06)00930-6
doi:10.1016/j.ahj.2006.10.018
© 2007 Mosby, Inc. All rights reserved.
