Polypharmacy and the risk of drug-drug interactions among Danish elderly. A prescription database study.

OBJECTIVE

To analyze the use of all subsidized prescription drugs with special attention to the elderly (> or = 70 years of age), including their use of drug combination generally accepted as carrying a risk of severe interactions.

DESIGN

Descriptive prevalence study.

SETTING

Odense Pharmacoepidemiological Database, Denmark. The fourth quarter of 1994.

SUBJECTS

All inhabitants in the county of Funen, Denmark.

MAIN OUTCOME MEASURES

Prevalence of drug use for persons < 70 and > or = 70 years of age including number of drugs used and of drug combinations. Occurrence of 45 drug combinations generally accepted as carrying a risk of severe interactions.

RESULTS

Among persons less than 70 years, 67.9% used none, 16.5% used one drug and 15.6% used two or more prescription drugs. The corresponding prevalences for the elderly were 35.7%, 15.9% and 48.4%. The 26,337 elderly patients with at least two drugs used 21,293 different combinations. Of the elderly patients who had purchased > or = two drugs, 4.4% had combinations of drugs carrying a risk of severe interactions.

CONCLUSIONS

Most elderly use drugs and usually several drugs concomitantly. The elderly form a heterogeneous group of drug users. Drug combinations carrying a risk of severe interactions are relatively frequent.