ATLANTA — People taking warfarin, a leading blood thinner to prevent clots that cause heart attacks and strokes, soon may have a better way to get the tricky dose right.
A new formula that includes gene testing proved much better at setting the ideal dose than what doctors do now: Give a standard amount and adjust it by trial and error. The formula was tested in a large international study, which found the usual approach gets it wrong about half the time.
About 4 million Americans take warfarin, also known as Coumadin, the most-used blood thinner worldwide. It could be used even more if doctors didn’t have to worry about the all-too-common risks to patients if they get the dose wrong. Too little means a risk of stroke, and too much can mean fatal bleeding.
The new study is one of the first to show that genetic testing can be used to prevent dosing problems, experts said.
A new experiment will soon test the gene study’s results in a more rigorous way. Most patients will likely have to wait at least a few years before genetic testing becomes a common factor in warfarin dosing, some experts said.
In the most recent study, researchers in nine countries collected data on about 5,700 patients who — after some trial and error — were already on stable doses of the blood thinner. The scientists developed a dosing formula based on the gene test and other factors, including age and weight.
The formula using the gene test proved accurate in setting the dose in about 1 out of every 3 warfarin users — more accurate than a method based solely on age, weight and other characteristics.
Federal officials want to follow up the report by launching a large, three-year study of more than 1,200 patients beginning in April.
“People will go to their doctors and ask” about genetic tests, predicted Jeremy Berg, director of the National Institute of General Medical Sciences, one of the study’s funders.
But until the larger study is done, “it’s unlikely that very many places will offer this,” he said.
A few clinics are using these gene tests and others to estimate dosing, but some researchers have concluded that the method is not yet cost-effective for most patients.
Proper dose varies widely for patients
Warfarin patients generally are started on 5 milligrams a day, but that’s just a starting guess. The proper amount for one patient may be 10 times as much as what’s best for another.
Improper dosing leads to problems for thousands of patients each year and can even result in death, according to some estimates.
The Associated Press
