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Senior Citizen Health & Medicine
Coumadin Label Update Ushers in Genetic Prescribing
to Make Drugs Safer, More Effective
FDA advises doctors to watch for two genes in
prescribing warfarin
 Aug. 16, 2007 – A major step toward making
medicines safer and more effective was taken today by the Food and Drug
Administration with the approval of updated labeling for the widely used
blood-thinning drug, Coumadin. The change will advise doctors that
people’s genetic makeup may influence how they respond to the drug. This
is the first time genetic considerations have been used on a drug label
and FDA says this is the beginning of its "personalized medicine"
initiative making use of pharmacogenomics.
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The labeling change highlights the opportunity for
healthcare providers to use genetic tests to improve their initial
estimate of what is a reasonable warfarin dose for individual patients.
Testing may help optimize the use of warfarin and lower the risk of
bleeding complications from the drug.
“Warfarin may cause severe bleeding that can be
life-threatening and even cause death,” according to information
provided by the National Institutes of Health at MedlinePlus.
“Bleeding is more likely during warfarin treatment
for people over 65 years of age, and it is also more likely during the
first few weeks of warfarin treatment,” adds the NIH information.
These labeling updates are based on an analysis of
recent studies that found people respond to the drug differently based,
in part, on whether they have variations of certain genes.
FDA estimates that 2 million persons start taking
warfarin in the United States every year to prevent blood clots, heart
attacks and stroke. Warfarin is a difficult drug to use because the
optimal dose varies and depends on many risk factors including a
patient's diet, age, and the use of other medications.
Patients who take a dose larger than they can
tolerate are at risk of life-threatening bleeding. Those who receive too
low a dose are at risk of equally dangerous blood clots. Dosing is
particularly important at the beginning of therapy, when problems in
adjusting the dose can lead to complications such as bleeding.
Warfarin is the second most common drug – after
insulin –implicated in emergency room visits for adverse drug events.
Physicians and other health care professionals who
prescribe warfarin regularly check to see if the drug is working
properly by ordering a test called the PT or prothrombin time that
evaluates the blood's ability to clot properly. The results are measured
in seconds and compared with the expected value in healthy people, known
as the International Normalized Ratio or INR.
"Today's approved labeling change is one step in
our commitment to personalized medicine. By using modern science to get
the right drug in the right dose for the right patient, FDA will further
enhance the safety and effectiveness of the medicines Americans depend
on," said Commissioner of Food and Drugs Andrew C. von Eschenbach, M.D.
The FDA's "personalized medicine" initiative makes
use of pharmacogenomics—the science that predicts a response to drugs
based upon a person's genetic makeup. This effort supports the
personalized health program spearheaded by Health and Human Services
Secretary Mike Leavitt.
A person's genes "encode" enzymes and differences
in the sequence of a gene can cause differences in enzyme activity or
sensitivity. That is why different people process the same drug
differently.
One-third of patients receiving warfarin metabolize
it quite differently than expected. Research has shown that some of the
unexpected response to warfarin depends on a patient's variants of the
genes CYP2C9 and VKORC1.
"Although genetic testing can currently identify
who has these genetic variants, more studies are needed to explore the
precise starting dose for these patients," said Larry Lesko, Ph.D.,
director of the FDA's Office of Clinical Pharmacology. "FDA has been
working with other government agencies and organizations to develop such
studies under the auspices of our three-year-old Critical Path
Initiative, which addresses the challenges of moving promising medical
products from discovery to patient use."
FDA's
Critical Path Initiative has funded a research project with the
University of Utah and the Critical Path Institute of Tucson, Ariz., to
develop genetically based instructions for warfarin dosing. The
Initiative has also facilitated meetings and planning with the National
Heart, Lung and Blood Institute for a clinical trial that will study
warfarin dosing based on genetic test information and is helping to pay
for another clinical study being conducted by Harvard Partners that will
derive personalized warfarin dosing algorithms for patients new to the
drug.
The dosage and administration of warfarin must be
individualized for each patient according to the particular patient's
PT/INR response to the drug. The specific dose recommendations are
described in the warfarin product labeling, along with the new
information regarding the impact of genetic information upon the initial
dose and the response to warfarin. Ongoing warfarin therapy should be
guided by continued INR monitoring.
Bristol-Myers Squibb Co. of Princeton, N.J., is the
manufacturer of Coumadin Manufacturers and will add information to their
products' labeling, the FDA said.
For more information see
New Labeling Information for Warfarin.
More important information about Warfarin at
MedlinePlus, the information site for senior citizens by the National
Institutes of Health –
CLICK HERE.
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