Inappropriate medication use as a risk factor for self-reported adverse drug effects in older adults.

OBJECTIVES To determine the association between inappropriate medication use and self-reported adverse drug effects (ADEs). DESIGN Prospective cohort study with three annual mailed surveys. SETTING Population-based sample of Iowa Medicare beneficiaries. PARTICIPANTS Cohort members (n5626) with established mobility disability and complete pharmacy dispensing records, continuous Medicare eligibility, and survey data. MEASUREMENTS The number of unique drug ingredients dispensed and inappropriate use were assessed for the year before the ADE survey. Inappropriate medication use was defined according to published criteria: contraindicated drugs for elderly people, drug-disease interactions (constructed from linked Medicare claims), drug-drug interactions, and therapeutic duplications. An ADE was defined from the following question: "In the past 12 months, have you experienced an unwanted effect or side effect of a medication?" RESULTS Of respondents to the ADE survey, 22.0% reported having experienced an ADE in the past year, and 322 (51.4%) received at least one potential inappropriate medication. Factors associated univariately with ADE self-report were number of medications, number of mobility limitations, any inappropriate medication use, and each of the individual domain appropriateness indicators, as well as number of different domains of inappropriate use. The adjusted odds ratio for developing an ADE was 2.14 (95% confidence interval=1.26-3.65) for those with inappropriate use versus no inappropriate use. CONCLUSION Efforts to reduce ADEs by reducing medication inappropriateness should be encouraged as a complement to efforts focused on reducing the number of medications prescribed.