Risk factors for self-reported adverse drug events among Medicare enrollees

Adverse drug events (ADEs) occur in older adults. ADEs occur in up to 6.5% of all hospitalized patients and outpatients, and about 28% of these events are preventable. The proportion of outpatients with an ADE ranges from 5% to 35%, depending on the exact definition used. There is a critical need to examine the risk factors associated with having an ADE to increase awareness about medication safety among older adults.

To quantify the association between risk factors such as the number of pharmacies used by patients and their concern and necessity beliefs about medicines, and self-reported ADEs.

A cross-sectional Internet survey was administered by Harris Interactive. Harris Interactive asked individuals from their online panel who were 65 years of age or older, US residents, and enrolled in Medicare to complete the survey. A convenience sample of 1220 anonymous surveys was obtained. Multiple logistic regression analysis was performed. The dependent variable was self-reported ADEs, defined as the patient's visiting a physician to report an unwanted reaction or medicine problem in the past year. Independent variables included sociodemographics, self-rated health, number of medications, sum of symptoms experienced, concern and necessity beliefs about medicines, number of pharmacies, and whether subjects skipped doses of their medications to save money or stopped taking the drugs due to cost.

Eighteen percent of respondents reported an ADE. ADEs were related to being female (OR 1.56; 95% CI 1.05 to 2.33), number of pharmacies (OR 3.40; 95% CI 1.56 to 7.41), number of symptoms experienced (OR 3.39; 95% CI 1.87 to 6.14), concern beliefs about medicines (OR 1.14; 95% CI 1.08 to 1.20), and having a graduate academic degree (OR 2.17; 95% CI 1.41 to 3.36).

The number of pharmacies, concern beliefs about medicines, and number of symptoms experienced in the past month were associated with self-reported ADEs. Discussing patients' beliefs about their drug therapy with them is likely to affect their expectations and interpretation of symptoms, as well as future attributions regarding drug therapy.