Comparison of different methods to estimate prevalence of drug use by using pharmacy records

Several methods to estimate prevalence of drug use are available, which may complicate a valid comparison of these estimates. Standardization may cont ribute to more valid comparisons. We compared different methods to estimate prevalence of drug use by using pharmacy records. Data were obtained from the Dutch population-based PHARMO-database comprising medication histories of 300,000 subjects. Five point prevalences and a 1-year prevalence of chol esterol-lowering drug use were estimated in 1995. Four point prevalences di ffered in data handling before estimating prevalence (e.g., correction for irregular drug use or construction of episodes of drug use). The numerator of the fifth point prevalence estimate represented the number of defined da ily doses (DDDs) instead of the number of patients filling a prescription. The first four point prevalences ranged from 11.0-12.1 parts per thousand. Prevalence ratio (male:female) was 1.2 for these methods. The fifth method resulted in an estimate similar to the other point prevalences (11.9 DDDs/1 000 inhabitants). However, the prevalence ratio was 1.4 due to larger avera ge number of DDDs prescribed to men. One year-prevalence was 4-5 parts per thousand higher than point prevalences. The comparison of these methods ind icated that the choice of prevalence measure (point versus period prevalenc e) substantially influenced the prevalence estimate, whereas the influence of data handling was negligible. For standardization purposes in drug utili zation research, we recommend estimating point prevalence instead of period prevalence. The various methods of data handling before estimating point p revalence yielded similar results and therefore we cannot recommend one spe cific method. However, defined daily doses should not be used to estimate ( point) prevalences of drug use because this measure is significantly influe nced by prescribed dosage regimens. (C) 2001 Elsevier Science Inc. All righ ts reserved.