Gene Test Pinpoints Heart Drug Dosage

Wednesday, 17 Mar 2010 07:32 AM

 

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A simple genetic test can help pinpoint the precise dose of a potentially life-saving medication taken by millions to ward off blood clotting after heart surgery, a study published Tuesday found.

The clinical study led by two leading medical researchers — Medco Research Institute specializing in pharmacy care, and the Mayo Clinic in Rochester, Minnesota — found that hospital stays can be reduced by one-third by undertaking genetic testing to determine the sensitivity of patients to the widely used drug warfarin.

Warfarin is the world's most widely prescribed blood thinner. It has been in use for half a century to reduce the risk of heart attack or stroke after a patient has had a heart attack.

It also is used to prevent blood clots, pulmonary embolism, and other complications following atrial fibrillation or heart valve replacement surgery. About two million people begin warfarin therapy every year in the United States.

But there are significant risks associated with the use of the drug if the proper dose is not determined.

Warfarin therapy requires doctors to closely monitor patients because the dose needed to obtain a therapeutic effect is very close to the dose that can cause negative medical reactions.

Some 20 percent or more of patients are hospitalized for bleeding within six months of the drug, and warfarin is the leading cause of drug-related emergency room visits among the elderly.

Doctors say it can take weeks or even months of repeated blood tests and dose adjustments to determine the right dose for each patient.

During that time, patients run an increased risk of thrombosis, a potentially serious condition brought about by the formation of a blood clot in a vein if too little warfarin is administered. But if given too much warfarin, patients face a risk of hemorrhaging.

Researchers in the study presented at the 59th annual conference of the American College of Cardiology in Atlanta, Georgia, said genetic testing offers a better way to help clinicians determine the optimum dose of the drug for each individual patient.

"Genetic testing is a tool clinicians can use to more accurately predict the best warfarin doses early on," said Dr Robert Epstein, chief medical officer and president of the Medco Research Institute.

With the benefit of genetic testing "patients may get to a stable dose more quickly and therefore have a lower risk of negative outcomes," he said.

The study presented Tuesday, the first to be conducted at a national level, involved 896 patients in 49 states. It compared the hospitalization rates of patients who were given the genetic test early in their warfarin therapy against a control group of 2,688 patients who were taking warfarin but had not received a genetic test.

The researchers found that hospitalization rates for heart patients taking warfarin dropped by approximately 30 percent when genetic information was available to doctors prescribing the drug.

Doctors said that with the aid of genetic testing and with far less guesswork, individuals with low sensitivity to warfarin can be given a higher dose to reduce the risk of stroke, while a patient who is highly sensitive to the drug can be given a lower dose to avoid internal bleeding.

Given the high price of hospital rooms in the United States, "if we reduce just two hospitalizations per 100 patients tested, that more than compensates for the cost of genotyping," Epstein said.

Copyright AFP





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