First Bedside Gene Test Shows Promise
Study found it spotted which heart patients should not take blood thinner PlavixURL of this page: http://www.nlm.nih.gov/medlineplus/news/fullstory_123520.html
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Thursday, March 29, 2012
The test, which can be done by nurses and others, was able to identify patients in whom the blood thinner Plavix might be ineffective, putting the patients at risk for heart attacks or strokes.
"One of the shortcomings we have in medicine right now is that there isn't a quick and effective way of identifying these genetic variants," said lead researcher Dr. Derek So, from the University of Ottawa Heart Institute.
"We have created the world's first point-of-care genetic test," he said. "We now have the means of selecting the right drug for the right patient."
The report was published in the March 29 online edition of The Lancet.
To prove the test works, So's team randomly assigned 200 patients to either receive screening for a gene called CYP2C19*2 using the gene test, or to regular care.
All of the patients had undergone a procedure called angioplasty to open a blocked heart artery and had a stent placed there to keep the vessel open.
Standard care after the procedure is to give patients Plavix to prevent clotting. However, many patients have this gene mutation, which makes the drug ineffective and patients more likely to develop a clot that could result in a heart attack or stroke.
Among those with European ancestry, about 30 percent have this mutation, and among Asians it's as high as 50 percent, the researchers noted.
Normally, after starting a patient on Plavix, a platelet function blood test is done to see how the patient reacts to the drug.
In this study, those getting the gene test were given a low dose of Plavix and the others received a regular dose. Both groups were given the drug so the researchers could judge the accuracy of the rapid gene test using the platelet function test as confirmation.
The researchers found the gene test accurately identified all the patients with the gene mutation. Patients who had the mutation were switched to a newer drug called Effient, which is not affected by this mutation.
After one week, 30 percent of those in the standard group were identified by the platelet function test as having a raised risk for clotting, while none of those in the gene test group showed an increased risk for clotting, So said.
"This is the first step required for personalized medicine," So said. "Ours is a proof-of-concept study. Now that we have this tool we can apply this same technology to different groups of patients and alter patient's therapy. We have taken bench to bedside."
One expert, Dr. Kirk Garratt, the clinical director of interventional cardiovascular research at Lenox Hill Hospital in New York City, thinks more proof is needed of the benefits of this particular test, but its real value is its potential.
"Before anybody can get too worked up about the application of this technology in the clinic, we will have to see evidence that acting on the information provided actually yields benefit," Garratt said.
"There is one really dazzling benefit," he added. "These researchers have now shown that you can take a minimally trained allied health person and do accurate genotyping on patients in the clinic -- that is really big news."
The test is given by taking a swab from the patient's cheek, putting it in a machine and getting a result in about an hour. The test can be done by people who have never done genetic testing after just 30 minutes of training, So said.
Larger trials will be needed to see if the test makes a difference in patient outcomes, So noted. Spartan Biosciences, which makes the test used in the study, funded the trial.
In terms of cost, the machine goes for about $10,000 and each test kit is about $300, So said. That's relatively inexpensive if it prevents patients from getting the wrong drug.
One advantage is that the test can be given before patients receive their first dose of Plavix, So pointed out.
In addition, as Plavix (clopidogrel) becomes a generic drug -- as it is in Canada -- its cost goes down, while the newer drugs like Effient (prasugrel) and Brilinta (ticagrelor) are very expensive and are associated with an increased risk of bleeding, he noted.
Commenting on the study, Dr. Amber Beitelshees, an assistant professor of medicine at the University of Maryland School of Medicine in Baltimore and author of an accompanying journal editorial, said that "for the first time, a point-of-care genetic test has been developed which can be used to rapidly screen individuals who carry a particular gene and may benefit from an anti-platelet drug other than Plavix."
Beitelshees added that "this is important because rapid genotyping is necessary in order for genotype-guided therapy to be incorporated into clinical care of patients undergoing coronary interventions outside of clinical trials."
However, another expert thinks much more needs to be shown about the value of this test before it can start to be widely used.
Dr. Gregg Fonarow, director of the Ahmanson-UCLA Cardiomyopathy Center and co-director of the UCLA Preventative Cardiology Program in Los Angeles, said that "there has been great interest in using genetic testing information to guide selection of medications and dosing, yet to date there has been little evidence that this testing can improve clinical outcomes."
However, Fonarow continued, "as neither genetic testing for variant CYP2C19 or platelet-function testing has been demonstrated to improve clinical outcomes and routine use of these tests are not currently recommended, further studies demonstrating any clinical utility, if any, are needed."
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