Exposure to potential drug interactions in primary health care.

OBJECTIVE

To analyse the prevalence of potential drug interactions, and to identify patients particularly prone to drug interaction.

DESIGN

Database study (Odense University Pharmacoepidemiologic Database).

SETTING

Individuals exposed to polypharmacy in 1999 were examined for potential drug interactions.

SUBJECTS

Inhabitants of the County of Funen (n = 471 732).

MAIN OUTCOME MEASURES

Prevalence of potential drug interactions.

RESULTS

One-third of the population were exposed to polypharmacy and among these 15% were exposed to drugs carrying a risk of harmful interaction. Among the elderly with polypharmacy, 25% aged 60-79 years and 36% over 80 years received drugs carrying the risk of interaction. Among individuals exposed to potential drug interaction, 62% were exposed only to one drug interaction and 38% to two or more different drug interactions. The drugs accounting for the highest number of potential interactions were diuretics, NSAIDs, ACE-inhibitors, digoxin, oral antidiabetics, calcium channel blockers, anticoagulants and beta-blockers. When focusing only on major drug interactions, potassium-sparing diuretics and oral anticoagulants were the most frequently involved drugs.

CONCLUSION

Elderly patients exposed to polypharmacy should be kept under intensified monitoring as they are at increased risk of clinically significant drug interactions.