[Polypharmacy estimated by means of a population-based prescription database]

The aim was to investigate estimators of polypharmacy (PP) from a population based prescription database. Data were retrieved from Odense Pharmacoepidemiological Database and contained a 10% random sample (n = 26,977) of drug users in 1994. PP was defined as simultaneous treatment with different drugs, and the duration of treatment was calculated from the date of purchase and the number of defined daily doses prescribed. This estimator was compared with an estimator based on the number of drugs purchased during a three month period. On an average day 8.7% were exposed to minor PP (two to four drugs) and 1.2% to major PP (five or more drugs). Purchase of five or more drugs during a three month period predicted episodes of major PP with a positive predictive value of 80%. Epidemiological measures of multiple drug use can be estimated from a prescription database. Conceptually, an estimator based on the number of simultaneously used drugs is preferable, but the number of drugs purchased during a three month period may be a useful alternative estimator.