Herbal and Nonherbal Supplements a Danger for Warfarin Patients

May 18, 2010

May 18, 2010 (Denver, Colorado) — The safety of warfarin use can be compromised by many popular herbal and nonherbal supplements taken by individuals, with eight of the 10 most widely used supplements interacting with warfarin, and many of these associated with significant changes in the international normalized ratio (INR) [1].

Of these, cranberry, garlic, ginkgo, and saw palmetto have been linked to increased rates of bleeding, whereas others have been shown to cause changes in prothrombin times, which would result in a need to alter warfarin doses, according to investigators.

"The internet has changed a lot of things, and that's why herbal supplements are such a problem," said lead investigator Dr Jennifer Strohecker (Intermountain Medical Center, Salt Lake City, UT). "Patients are educated, often before they even go see their doctors. They read something on the internet, choose what they want, and they trust what they read."

Communication Gap

Speaking with heartwire , however, she stressed that the delivery of medical information is also very different these days and that having more knowledge can empower patients to take care of themselves and to really understand when something is awry. Working in an ambulatory-care clinic last year, Strohecker noticed a "communication gap" when educating patients about warfarin; many would return to the clinic with problems, often loaded with "pages and pages" of information on the herbal and nonherbal supplements they were taking.

The internet has changed a lot of things, and that's why herbal supplements are such a problem.

"It was very, very difficult to decipher what was happening to some of these patients, and there was also a lot of antagonism to even listening to what I had to say," she added. "They trusted their health-food store source, their chiropractor, or whoever referred them to the product, more than they trusted me."

In this small study, Strohecker and colleagues began looking at the most commonly used herbal and nonherbal supplements used in the US. Approximately 20% of the population takes some form of supplement, but many do not disclose this information to their doctor, she added. The researchers assessed the top 20 herbal and top 20 nonherbal supplements based on 2008 sales data and reviewed their potential to interact with warfarin. They searched numerous databases for relevant case reports and clinical trials documenting supplement-drug interaction, including changes in INR, bleeding risks, and thromboembolic events.

Of the 40 most commonly used herbal and nonherbal supplements, more than 50% have a direct or indirect interaction with warfarin. Among the 10 most popular supplements, 80% are known to interact with warfarin. Of the 40 herbal and nonherbals, 35% can significantly change the INR, with nine supplements known to increase the risk of bleeding and five known to decrease the effectiveness of warfarin. Glucosamine, essential fatty acids, multiherb products, and primrose oil can increase prothrombin times, while coenzyme Q10, soy, melatonin, ginseng, and St John's wort can decrease prothrombin times.

Most Patients Don't See Herbs as Drugs

In addition to these data, Strohecker and colleagues followed up in 100 warfarin-treated patients, asking how many used herbal supplements, whether doctors asked about supplement use, and whether or not they disclosed this information to their clinician. To heartwire , Strohecker said that most patients are taking a multivitamin or individual vitamins. Among these, vitamin K can alter the efficacy of warfarin, although most clinicians account for its consumption when dosing warfarin. Many patients are also taking high-dose antioxidants, which can have an antiplatelet effect.

"Based on that survey, we found that doctors are truly not talking to their patients about supplements," said Strohecker. "When we actually compared what the patients were taking with what was in their profile, we found that many of these herbs, most of the time, were not listed. I think this is because most patients don't see herbs as drugs, and healthcare providers aren't specifically asking if they're using any herbal supplements or over-the-counter medications. 'What drugs are you on?' is usually what gets asked."

With these findings, Strohecker is now working on the development of an interactive learning program that outlines these data and encourages doctors and clinical staff to ask questions about supplements. The program is also designed for patients, educating them about herbal supplements and interactions. This program is expected to be used later in the year at the Intermountain Medical Center in Salt Lake City, UT.

"With my students in the clinic, we're working on learning how to really communicate with the patient and to engage with them," said Strohecker. "It's important for the patient to have this knowledge. I have times when they look perfect, but if they go out to celebrate the Super Bowl and have five beers to drink and then start to bleed, they need to know what to do. They need to be able to put two and two together and say, Oh, okay, I did something wrong here."