Drug utilization according to reason for prescribing: a pharmacoepidemiologic method based on an indication hierarchy

PURPOSE: To develop a pharmacoepidemiologic method for drug utilization analysis according to indication, gender, and age by means of register-based information. Statin utilization in 2005 was applied as an example. METHODS: Following the recommendations for statin therapy, we constructed an indication hierarchy with eight mutually exclusive levels of register markers of cardiovascular disease and diabetes. Danish residents, as of January 1, 1996, were followed at the individual level in nationwide registers with respect to dispensed prescriptions of cardiovascular drugs and antidiabetics (1996-2005) along with discharge diagnoses and surgical procedures (1977-2005). The highest current possible indication level was assigned to all cohort members. Stratified by indication, gender, and age, statin treatment prevalence and incidence were calculated. RESULTS: Statin treatment prevalence was highest among individuals with myocardial infarction and tended to be higher among men with indications in the upper part of the hierarchy, but it was higher among women (especially the elderly) in the lower part of the hierarchy. Treatment incidence rates followed roughly the same pattern. Women with no register marker or primary hypertension accounted for almost 50% of all incident female users; among men, the figure was 35%. The proportion of incident users with ischemic heart disease or myocardial infarction increased with age. CONCLUSION: The proposed indication hierarchy provided new insight into prescription patterns of statins. The method can be implemented for other drug categories and could be useful for studying trends in drug utilization, differential drug adherence, and cross-national comparisons.