Exposure misclassification as a result of free sample drug utilization in automated claims databases and its effect on a pharmacoepidemiology study of selective COX-2 inhibitors

Pharmacoepidemiology and Drug Safety
Susanna JacobusK Arnold Chan

Abstract

Free drug samples are widely used in clinical practice. We were concerned about free sample drug utilization as a source of misclassification in pharmacoepidemiology research using claims data that may result in biased effect estimates. We investigated the magnitude of potential bias with sensitivity analyses based on a published study that examined cardiovascular risk associated with selective cyclooxygenase 2 (COX-2) inhibitors. We derived an estimate of free sample drug utilization with market data for rofexcoxib and calculated sensitivity of the exposure ascertainment method using claims data. We corrected the incidence rate ratio assuming the observed unexposed incidence rate was actually a weighted average rate of the truly unexposed and free sample drug users. The impact of exposure misclassification measured as the percentage change from a corrected to the reported crude incidence rate ratio was examined under a range of free sample drug utilization proportions and unexposed cohort sizes. The proportion of free sample drug utilization of all rofecoxib use in our base case scenario was 15.48%, resulting in sensitivity of 84.52% for exposure ascertainment. The magnitude of bias was an underestimation of the unadjusted inc...Continue Reading

Citations

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