Objective : To examine past trend and present status of polypharmacy, multiple drug therapy, which can be a cause of serious adverse events induced by drug interactions.
Design : Drug utilization survey using a database of the Kagoshima University Hospital Information System.
Methods : Data of the prescriptions issued during every May between 1985 and 1994 were extracted from the database. Monthly prescriptions were classified by the number of drugs they included.Furthermore, the data were sorted by patients' ID to obtain the age distribution of patients observed in each year and the distribution of the number of drugs per prescription was analyzed in each age group.
Results : The average number of medicines per prescription was increased from 3.07±2.16 (average±S.D.) in 1985 to 3.46±2.61 in 1994. During 10 years between 1985 and 1994, the proportion of patients receiving ten drugs or more also increased from 1.50%to 3.90%. There was a clear tendency that a large number of drugs were given to old patients and comparatively few drugs to young patients.Proportion of the old patients over 59 years of age increased linearly from 25.71%in 1985 to 35.37% in 1994.
Conclusion : The average number of medicines per prescription was increased during 10 years. This trend is considered to be attributable in part to the increase in the proportion of the old patients. The concomitant use of so many drugs is a problem and a rule for diminishing returns recently adopted as a reimbursement policy of health insurance system has been applied to prescriptions with ten drugs or more. Further studies are needed to examine possible adverse outcomes and other characteristic features of multiple therapy.