Individualized drug utilization statistics. Analysing a population's drug use from the perspective of individual users.

The Danish retail pharmacies' drug subsidy system is completely computerized. The data are person-identifiable, making it possible to chart the population's drug use from the perspective of individual users. We decided to explore the potential of this data source and to analyse heavy drug users specifically. The analysis encompassed all 890,352 prescriptions presented by citizens of Odense in 1991. There was a total sales volume of 32 million defined daily doses consumed by 113,468 adult drug users, corresponding to 65.1% of the adult population. We found 2388 heavy drug users, defined by an annual purchase of more than 2000 defined daily doses. Heavy drug users accounted for 1.4% of the adult population and 22.9% of drug sales. They were remarkably well characterized by their main therapeutic class, which constituted a median of 47% of their drug use. A median of 97% of each heavy user's drugs were issued by one main prescriber. We conclude that heavy drug use can generally be ascribed to severe disease rather than to irresponsible prescribing. For the most important drug classes, we present various epidemiological measures of drug use, including 1-year prevalence, incidence, duration of therapy and some measures of skewness in utilization. If analysed regularly these measures can disclose subtle trends in clinical drug use that would not be evident from the wholesale figures.