Prevalence, incidence and persistence of antipsychotic drug prescribing in the Italian general population: retrospective database analysis, 1999-2002.

PURPOSE: To investigate the prevalence, incidence and persistence with antipsychotic drug therapy in a large and geographically defined catchment area of Italian general population.

METHODS: All antipsychotic drug prescriptions dispensed during 1999, 2000, 2001 and 2002 were extracted from an administrative prescription database covering a population of 2 640 379 individuals. Antipsychotic drug users were defined as patients who had at least one recorded prescription in the current year. New users were defined as patients receiving a first prescription without any recorded antipsychotic drug treatment in the previous 12 months. Prevalence data were calculated by dividing users by the total number of male and female residents in each age group. Incidence data were calculated as the number of new users divided by the person-time free from antipsychotic drugs in the current year. The cumulative persistence of each medication was calculated by dividing the total prescribed amount of antipsychotic drug by the recommended daily dose, according to each agent's defined daily dose (DDD).

RESULTS: A progressive rise in prevalence and incidence rates was observed during the 4-year period. In each census year, the prevalence and incidence of prescribing was higher in females than males, and progressively rose with age, with the highest rates in old and very old subjects. The analysis of persistence with therapy revealed that 3176 individuals (78.5%) were occasional antipsychotic drug users, and that occasional use was more frequent among individuals receiving conventional antipsychotic drugs than among individuals receiving novel antipsychotic drugs. This difference was not explained by differences in the occurrence of neurologic adverse reactions, as shown by the concurrent prescribing of anticholinergic drugs, which was fairly similar between the two groups of new drug users. Additionally, we found that conventioal antipsychotic drugs were more often used in older individuals, where occasional use is very frequent, while novel antipsychotic drugs were more often prescribed in young and adult individuals, where regular use is more frequent.

CONCLUSIONS: An epidemiologically relevant proportion of everyday individuals is annually exposed to antipsychotic drugs. The distribution of prevalence and incidence rates by age highlighted an emerging public health issue related to the adverse and beneficial consequences of antipsychotic drug exposure in the elderly. The finding that persistence with therapy was longer in new users of novel antipsychotic drugs compared with new users of conventional agents might be explained by the different demographic and clinical characteristics of individuals receiving these two drug classes and not by the different tolerability profile of these two drug classes.