Chicago, IL - Roughly 4% of older adults are potentially at risk of major drug-drug interactions, with cardiovascular medications posing the bulk of the risk, new data show [1]. The figure comes from a nationwide US survey of 3005 men and women aged 57 through 85 that also speaks to the high proportion of nonprescription medications and supplements being taken by older adults, in combination with prescription drugs.

"In this sample of community-dwelling older adults in the United States, nearly one in 25 reported taking concurrent drugs with the potential for harm from serious drug-drug interactions," the authors, led by Dr Dima M Qato (University of Chicago, IL), write. "By establishing patterns of prescription and nonprescription medication use among older adults, these data may help support efforts to increase the safety and quality of pharmacotherapy for older adults."

But other experts who spoke with heartwire caution that Qato et al's data don't mean that medicine is being practiced inappropriately.

"We can't tell from this article whether these medicines or combinations were medically warranted or not. I have no doubt that there are physicians out there who are prescribing drugs in combinations when they shouldn't be, but many of these strike me as potential interactions that would be very common in any rational cardiovascular practice," Dr Dan Roden (Vanderbilt University Medical Center, Nashville, TN), who was not involved with the study, told heartwire. "What's missing in these data is how sick patients were who got these medications and whether there were any adverse health outcomes."

The report is published in the December 24/13, 2008 issue of the Journal of the American Medical Association.

Qato et al's data come from in-home interviews and medication logs conducted between June 2005 and March 2006. Participants were asked to keep track of their prescription drugs and also over-the-counter (OTC) medications and dietary supplements that they took on a regular basis.

The results point to a broad pattern of concurrent medication use, with cardiovascular drugs and supplements featuring prominently. More than four out of five adults took at least one prescription medication, two out of five took at least one OTC medication, and just under half took some kind of dietary supplement. The most commonly used prescription and OTC drugs were cardiovascular agents: antihypertensives, anticoagulants, and statins. For supplements, vitamins and minerals were the most common, but so were "alternative therapies" intended to improve cardiovascular health such as omega-3 fatty acids, garlic, and coenzyme Q10. Calcium, vitamin D, and glucosamine-chondroitin were the most common supplements among women, while niacin was more common among men.

More than half of the adults surveyed were taking five or more agents (prescription, OTC, and dietary supplements combined); the prevalence of taking five or more agents increased with age and was, overall, significantly higher among women. What's more, one out of every eight adults regularly took five or more dietary supplements alone.

Dr Harlan Krumholz (Yale University, New Haven CT), who also commented on the study for heartwire, said these numbers are in keeping with other reports. "The overall rate seems about right and is not surprising," he said.

When the data were used to look for potential drug-drug interactions, a total of 46 interactions were identified, of which 11 were classified as "potentially of major severity," and 28 were classified as "potentially of moderate severity," although no "absolutely contraindicated" interaction was seen across the entire sample. Overall, one out of every 25 older adults was at risk for a major potential drug-drug interaction, and more than half of these appeared to involve agents that would not require a prescription.

Increased risk of bleeding was one of the most common adverse effects when prescription drugs were taken in combination and when prescription drugs were taking in combination with OTC drugs, or OTC drugs were taken along with dietary supplements. Decreased drug effectiveness, hyperkalemia, myopathy, and rhabdomyolysis were also common.

The authors point out that older adults are the biggest consumers of OTC and prescription drugs as well as of nutritional supplements and alternative therapies. As such, they are the most vulnerable to adverse drug-drug interactions.

"Physicians are frequently unaware of their patients' nonprescription medication use because they do not ask patients, patients do not report use of nonprescription medications, or both," Qato et al write. "With as many as 4%, or 2.2 million, of older adults in the United States affected, the economic and health consequences of these potential interactions are considerable. . . . Our findings suggest that concurrent use of prescription and nonprescription medications in older adults remains a public-health problem and could be an important focal point for further improvements in drug safety for seniors."

But both Krumholz and Roden stressed to heartwire that the data speak to hypothetical risks but do not contain information on actual harm caused. "It's important to note that the drug interactions are potential problems—these are not combinations that are strictly contraindicated," 'Krumholz said. "Physicians may employ these combinations for a variety of reasons, and in many cases the use of the combination requires greater monitoring for potential adverse effects. . . . The real question is whether these patients' doctors were aware of these combinations and were appropriately monitoring the effects or if the use of combinations occurred inadvertently. That information is what would tell us if there is an opportunity for improvement in care."

As for the adverse interactions that arise when patients load up on supplements, Roden said cautiously that there is just not enough known about these interactions to understand how problematic—or unimportant—these might be. "We really don't know enough about the pharmacokinetics and pharmacodynamic consequences of the way those kinds of products interact with the medicines that we commonly use," he said.