Analysis of individual drug use as a time-varying determinant of exposure in prospective population-based cohort studies

B. H. Ch. Stricker (1, 2, 3) , T. Stijnen (4)

1 Department of Epidemiology
2 Department of Internal Medicine
3 Department of Medical Informatics
4 Department of Biostatistics

In pharmaco-epidemiology, the use of drugs is the determinant of interest when studying exposure-outcome associations. The increased availability of computerized information about drug use on an individual basis has greatly facilitated analyses of drug effects on a population-based scale. It seems likely that many negative findings in the early days of pharmaco-epidemiology can be explained by non-differential misclassification because of too simple (yes/no) exposure measures. In this paper, the authors discuss the importance of an adequate definition of drug exposure in pharmaco-epidemiological research and how this time-varying determinant can be analyzed in cohort studies. To reduce the risk of non-differential misclassification, a precise definition of exposure is mandatory and it is important to distinguish the complete follow-up period of a population into mutually exclusive episodes of non-use, past use and current use for each individual. By analyzing exposure to drugs as a time-dependent variable in a Cox regression model, cohort studies with complete coverage of all filled prescriptions can provide us with valid and precise risk estimates of drug-outcome associations. However, such estimates may be biased in the presence of time-dependent confounders which are themselves affected by prior exposure.

Mots clés: Pharmaco-epidemiology; Drug exposure analysis; Cohort studies; Cox regression models for time-varying determinants

B. H. Ch. Stricker, T. Stijnen. Analysis of individual drug use as a time-varying determinant of exposure in prospective population-based cohort studies. European Journal of Epidemiology, 2010, 25 (4), pp.245-251. ⟨10.1007/s10654-010-9451-7⟩. ⟨hal-00582189⟩