Older Adults at High Risk for Drug Interactions

At least one in 25 older adults, about 2.2 million people in the United States, takes multiple drugs in combinations that can produce harmful drug-drug interactions. Half of these interactions involve a non-prescription medication, researchers from the University of Chicago Medical Center report.

Although the number of people taking medications has remained stable for the last decade, the number of drugs taken by older people has significantly increased. This may be due to more intense therapy for chronic illness, improved access to medications due to Medicare Part D and the growth of the generic drug market. More than half of older adults now take five or more medications or supplements.

“Older adults are the largest consumer of prescription drugs,” Stacy Tessler Lindau, MD, assistant professor of obstetrics and gynecology and of medicine at the University of Chicago Medical Center and study author said. “We find that they commonly combine these prescription medications with over-the-counter medications and dietary supplements, which can increase their vulnerability to medication side-effects and drug-drug interactions.”

Patients using less common drugs and non-prescription medications could be more at risk for harmful interactions because health care providers may be less familiar with their safety profile.

The study also found ethnic and gender differences. Older Hispanics were more likely than other ethnic groups to be taking no medications. Older women were less likely than older men to take medicines to reduce cholesterol.

“In our study, men and women were equally likely to report a history of cardiovascular disease,” Dima M. Qato, PharmD, MPH, research associate in obstetrics and gynecology at the University and co-author said.

According to Qato, despite efforts to increase awareness in the medical community that older men and women are equally at risk for a cardiovascular event, disparities persist in the use of statin medications.

“Far fewer women than men were taking these effective cholesterol-lowering drugs,” she said.

The study used data collected for the National Social Life, Health and Aging Project, a nationally representative multi-purpose survey of adults aged 57 to 85 years old administered between July 2005 and March 2006. The survey team interviewed 3005 participants in their homes about the medications they used “on a regular schedule, every day or every week.” Of the 2,976 respondents, 99% completed the interview and medication log.

Of all respondents, 91% regularly used at least one medication, a percentage that increased with age. Of older adults, 29% took more than five prescription medications.

Of the adults who took prescription drugs, 68% also used over-the-counter medications or dietary supplements. Men were more likely to take over-the-counter medicines. Women were more likely to use supplements, such as vitamins or herbal remedies.

“Patients need to inform their providers about all medications they use, prescription and nonprescription. They should ask their physician or pharmacist about interactions any time they start a new drug on their own or following the doctor’s recommendation,” Lindau said.

Carrying a list of all medications in a wallet might be a good idea, the authors suggest. So is using the same pharmacy or chain for all medications, Qato suggested. The researchers also stressed that health professionals need to stay on top of drug-safety information and consider the evidence, where available, for safety in older adults.

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