A study of Medicare patients concludes that the vast majority of adverse drug events experienced by elderly patients are caused by commonly prescribed medications, not those usually considered high-risk drugs. The highest percentage of adverse events was reported by patients using common cardiovascular, anti-inflammatory and cholesterol-lowering agents. The results are published in the March 2005 issue of The American Journal of Managed Care.
The study was conducted by Kimberly Rask, MD, PhD, associate professor of health policy and management, Emory University, Rollins School of Public Health, along with colleagues from the Emory Center on Health Outcomes and Quality, the University of South Florida (Tampa), Covance Clinical Development Services, (Princeton, New Jersey), and the Georgia Division of Public Health.
Using previous research that identified groups of medications that are potentially dangerous to the elderly, Dr. Rask and her team of researchers studied pharmacy claim data from managed care companies to identify patients at high risk for adverse drug events.
"Our hope was to identify the patients at risk so health plans could be better designed to potentially prevent the dangerous side effects," says Dr. Rask.
For the study, telephone surveys were conducted of random samples of both 211 community-dwelling Medicare managed care enrollees over age 65 who were taking a potentially contraindicated medication and a random sample of 195 similar enrollees identified as not taking a potentially contraindicated medication. Study participants were continuously enrolled in Medicare managed care from July 1999 through June 2000, and all participants were identified through pharmacy claim data.
Enrollee names and clinical and pharmacy information were obtained by the health insurer and the telephone interviews were performed by a contracted employee of the health insurance company. Participants were asked a series of questions related to their general health status, prescription drug usage, adherence to medical regimen and recent adverse drug events. All individual identifiers were stripped from the data and Emory researchers were provided only with blinded pharmacy and telephone data that could not be linked to any individual enrollee.
At the time of patient interviews, a total of 134 adverse drug events during the previous six months were reported by 24.4 percent of all respondents, and only 1.5 percent of the self-reported adverse drug events were attributed to a medication from the potentially contraindicated list.
While 31.9 percent of enrollees taking a potentially contraindicated medication reported an adverse drug event, 22.8 percent of enrollees not taking one of the potentially contraindicated medications reported an adverse drug event. Although not statistically significant, the higher rate of adverse drug events among those in the high-risk cohort may have been due to the concurrent use of multiple medications, rather than the specific use of the contraindicated medications, the study concludes.
Dr. Rask notes that patients should understand why they are taking each medicine, know what side effects might occur and what they should do if they experience a side effect. It is also the patient's responsibility, she says, to make sure their doctor is aware of all medications they are taking, including over-the-counter drugs.
"Patients, doctors and pharmacists will have to work together to prevent serious side effects," Dr. Rask says.
The research was supported by a grant from the Aetna Foundation and the Quality Care Research Fund.