Older Adults Face Increased Risk from Drug Interactions

A new study reports that at least one in 25 older adults takes multiple drugs in combinations that can produce a harmful interaction, and that half of these interactions involve a nonprescription medication.

Researchers at the University of Chicago Medical Center (UCMC, IL, USA) used data collected for the U.S. National Social Life, Health, and Aging Project, a multipurpose survey of adults aged 57 to 85 administered between July 2005 and March 2006. The survey team interviewed 3,005 participants in their homes about the medications they used regularly; of these 99% completed the interview and medication log. The study results showed that 91% of all respondents regularly used at least one medication, a percentage that increased with age; 29% of older adults took more than five prescription medications. Sixty-eight percent of the adults who took prescription drugs also used over-the-counter medications or dietary supplements. Men were more likely to take over-the-counter medicines, but women were more likely to use supplements, such as vitamins or herbal remedies. Older women were less likely than older men to take medicines to reduce cholesterol. The study also found ethnic differences; older Hispanics were more likely than other ethnic groups to be taking no medications.

The researchers found that nearly half of the drug interactions identified could cause bleeding problems. One of the most common was taking warfarin, a prescription drug designed to prevent blood clots, along with an over-the-counter drug such as aspirin, which also interferes with clotting. The most common potentially severe medication interactions included lisinopril-potassium, which causes elevated blood-potassium levels, disrupting heart rhythm; warfarin-simvastatin, warfarin-aspirin, and ginkgo-aspirin combinations, which can cause bleeding; and atorvastatin-naicin and simvastatin-niacin combinations, which cause muscle weakness and breakdown. The study was published in the December 31, 2008, issue of the Journal of the American Medical Association (JAMA).

"Physicians and pharmacists need to ask their patients about the use of nonprescription
medications,” said lead author Stacy Tessler Lindau, M.D., an assistant professor of obstetrics and gynecology, and of medicine at the UCMC. "Patients need to inform their providers about all medications they use--prescription and nonprescription--and should ask their physician or pharmacist about interactions any time they start a new drug, on their own or following the doctor's recommendation.”

Related Links:
University of Chicago Medical Center