Genetic tests can predict who needs higher doses of Plavix
Genetic tests can now help predict which heart patients need higher doses of a common anti-clotting drug, shows a news study that is the latest example of "personalized medicine."
Doctors commonly prescribe the blood thinner Plavix to prevent blood clots in the hearts of people who've survived heart attacks.
Yet nearly one-third of heart patients have genes that can prevent them from properly processing the drug, says cardiologist Jessica Mega, author of the study presented today at the annual meeting of the American Heart Association in Orlando.
Genetic tests can now identify which patients have these mutations.
More importantly, Mega's study shows that tripling or quadrupling the typical dose of Plavix, 75 milligrams a day, helps most patients with these genes to process the drug normally.
"This is the most promising area for personalizing medicine in cardiology," says Christopher Cannon of Harvard Medical School, who wasn't involved in the new study.
Few hospitals today perform these genetic tests, says Mega, an associate physician at Brigham & Women's Hospital at Harvard Medical School, Boston. But doctors might be able to test patients' blood by sending it to a specialized lab.
The study's findings could help patients get the right dose of the most appropriate medication immediately, rather than after trying and failing a series of treatments, says Cam Patterson, chief of cardiology at the University of North Carolina-Chapel Hill. "You don't want to wait until after you have an event to say, 'Oh, this patient is Plavix-resistant,' " Patterson says. "That could have a big impact on how we treat patients."
Yet Mega notes her study had significant limitations. While it showed that higher Plavix doses made patients' platelets less likely to clot, researchers don't yet know whether those doses will reduce heart attack rates.
And high doses didn't work for everyone. While tripling or quadrupling doses helped those with one copy of the gene variation, high doses did little for those with two copies, the study shows.
The study didn't address whether higher doses actually reduce heart attack rates, Patterson says. Answering that question will require additional studies.
And Mega says heart patients still need to be closely monitored by their doctors. "You don't want patients to suddenly start taking three pills a day on their own," she says.
Still, Patterson says it's reassuring to see that increasing Plavix doses appears safe. Preventing blood clots in a stent — mesh scaffolds used to prop open clogged arteries — is "a life or death issue," Patterson says.
Plavix is the third best-selling drug in the country, with $6.1 billion in sales in 2010, according to IMS Health.
Plavix — also known as clopidogrel — will be available as a generic next year. So giving patients three or four pills may not be prohibitively expensive, Patterson says. Until now, patients who didn't respond to normal Plavix doses often have been prescribed brand-name alternatives — new drugs Effient and Brilinta, Patterson says.
Mega say the findings are encouraging, and point toward a day when doctors no longer have to give "one size fits all" medicine. Cancer specialists have had tools to personalize therapy for years, she notes. For example, doctors can use genetic profiles to predict which early-stage breast cancer patients need chemotherapy and which can safely avoid it. Cardiologists have far fewer genetic tests.
But heart doctors are pursuing one uniquely personalized approach: heart stem cells.
Research presented Monday showed that heart stem cells — taken from patients during surgery, then injected back into their bodies four months later — appear to help the heart muscle repair itself, if only modestly. Researchers caution that the study was very small and preliminary, with just 23 patients, only 14 of whom received the stem cells. Doctors still need to perform long-term follow-up of the patients, who suffered from heart failure, a condition in which the heart can no longer pump enough blood to the rest of the body. Yet another study of stem cells derived from bone marrow cells was disappointing. These cells, while safe, had no benefit for heart failure patients, a presentation showed.
Still, Mega says she hopes her findings will translate into better care for patients.
"Ten years ago, when the human genome was sequenced, there was so much enthusiasm about personalizing care," Mega says. "Now, we're starting to get there."