Potential drug, dietary supplement interactions often overlooked

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Nearly half of older adults take herbal and dietary supplements, but many forget to mention this to their health care providers – increasing their risk for dangerous drug interactions.

Researchers from Intermountain Medical Center Heart Institute and Utah State University, both in Salt Lake City, interviewed 100 patients with atrial fibrillation to determine how well they understood potential interactions between supplements such as vitamins and fish oil, and medications, including the blood thinner warfarin. 

Patients taking blood thinners are at particular risk for drug interactions because dietary supplements can compete with these medications in the liver, thereby intensifying or reducing the effect of active blood thinner ingredients.

Although events such as this can lead to an increased risk for either bleeding or stroke, 54% of the 35 patients that reported using warfarin along with another supplement were unaware of these outcomes.

Vitamins (92%), glucosamine/chondroitin (28%), fish oil (26%) and coenzyme Q10 (6%), were the most popular supplements that patients used. Furthermore, data indicated that of the 100-most common supplements, 69% interfere with warfarin's effectiveness.

“We need to do a better job of teaching our patients about the dangers of mixing warfarin with these products,” study researcher and heart rhythm specialist T. Jared Bunch, MD, said in a press release.

Study findings indicated that the patients who took herbal and dietary supplements (HDS) experienced worse outcomes that were potentially attributable to drug interactions, such as higher rates of unexplained bleeding (23% vs. 17%) and a greater need for blood transfusion (14% vs. 10%). Additionally, patients who reported taking supplements were more likely to skip or double up doses of warfarin (34% to 17%).

“We have also learned that – for whatever reason – patients don't want to tell their doctors that they are taking HDS,” Bunch said, noting that only 47% of those surveyed considered HDS drugs, and 63% did not consult with a health care provider before taking such supplements.

Clinicians are failing to do their part, too, data indicated – 63% of participants reported that health care providers did not ask about HDS as part of the medication history, and 73% did not have supplement use documented in medical records.

“As more patients present with prescribed medications and self-prescribed HDS, physicians must bridge the communication gab with proactive inquiry, investigation and guidance on appropriate HDS use,” the researchers wrote.

These data were first presented at the 2010 American Heart Association Scientific Sessions in Chicago (Abstract #17248).

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