Exposure to potential drug interactions in primary health care

Abstract

Harmful drug interactions may occur if one drug alters the effect of another drug. During the course of one year, about one-third of the population are exposed to the concurrent use of two or more drugs (polypharmacy). On average, 15% of individuals with polypharmacy are exposed to drugs carrying a risk of potential interactions. Elderly patients exposed to polypharmacy are at highest risk and should therefore be kept under intensified monitoring. 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 t 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.