Multiple Medication Use Increase as a Function of Age and Antidepressant Use,studies show
Feb 6, 2005 - 11:56:38 AM

Two new studies show that combinations of medications taken by patients vary widely, making it extremely difficult to monitor or predict drug-drug interactions.The articles published in the January 2005 issue of the Journal of Psychiatric Practice found that virtually no two patients on more than one drug were taking the same combination of medications,which highlights the difficulty of monitoring for and predicting potentially dangerous drug-drug interactions.

The articles present the results of two studies of multiple medication use(MMU)in outpatients in the Veterans Affairs (VA) Healthcare System. MMU was found to increase as a function of both age and whether the patient was taking an antidepressant,with over a third of older patients on antidepressants taking eight or more medications.

The number of patients taking unique combinations of drugs (a combination different from any other patient in the sample) ranged from 70% in younger patients not taking antidepressants to 96% in older patients taking antidepressants.

These figures mean that no single prescriber can have extensive clinical experience with the combined effects of all of the medications his or her patients are taking, setting the stage for potentially adverse drug-drug interactions.

"The frequency and complexity of multiple medication use was surprising and troubling,"said Sheldon Preskorn,MD, principal investigator on the studies."It underscores the importance and the difficulty of avoiding complex and potentially dangerous drug-drug interactions."

The study results reinforce and extend the message of the recent Health, United States 2004 report from the Centers for Disease Control.The CDC reported that almost half of all Americans are taking at least one prescription drug, while, among those 65 years of age and older, five out of six are taking at least one medication and almost half are taking three or more.The CDC study also found that antidepressant use has almost tripled over the last decade, with 10% of adult women and 4% of men now taking antidepressants.

These results are also relevant to the issue of potentially dangerous drug-drug interactions--a problem that has been receiving increasing attention in recent years as highlighted by the withdrawal of drugs such as Vioxx and Seldane from the U.S. market.

The first study,Complexity of Medication Use in the Veterans Affairs Healthcare System: Part I.Outpatient Use in Relation to Age and Number of Prescribers,examined levels of medication use and complexity of drug regimens in a sample of 7,000 outpatients in Veterans Integrated Service Network 15 in the U.S. midwest.The investigators wanted to determine how use of multiple medications related to age and number of prescribers and if it was possible to identify frequently used medication combinations,in order to better predict and prevent adverse drug interactions.

The investigators found that,of the 5003 patients currently taking prescriptions medications,38% were receiving five or more drugs and 14% were taking eight or more.It was also not possible to identify commonly used medication combinations in this population.Almost three quarters of the patients were receiving a unique combination of drugs different from any other patient in the sample, and there was no single combination that occurred in even 1% of the patients.

The second study, Complexity of Medication Use in the Veterans Affairs Healthcare System: Part I.Antidepressant Use Among Younger and Older Outpatients,compared medication use in patients receiving antidepressant medications with patients not receiving antidepressants.The investigators found that patients receiving antidepressants were likely to be receiving significantly higher numbers of other medications than patients not taking antidepressants, with 24% of younger patients and 38% of older patients on antidepressants receiving eight or more medications (compared to 6% and 13% in those not receiving antidepressants).Again no single combination of medications occurred in even 1% of patients.

The large number of unique drug combinations involving antidepressants is especially troubling,since some antidepressants have significant potential to cause serious drug interactions.

The investigators strongly recommended more education for prescribers,pharmacists,healthcare organizations and patients about the complexity of drug prescribing and how it limits our ability to detect and prevent potential adverse drug interactions.They also advocated increased research to identify common medication combinations and evaluate their potential for adverse interactions as well as improved drug alert systems that are more capable of identifying potential problems involving multiple medications.

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