March 2006

Getting Personal about Drugs

Genetic testing is poised to revolutionize prescription writing, says one of its leading proponents.

By Erika Jonietz

The age of "personalized medi­cine" has arrived, but chances are your doctor doesn't know it yet. Existing tests can analyze patients' genetic makeup to provide guidance on whether certain drugs--such as codeine, antidepressants, and even some cancer medications--will help them, harm them, or do nothing. And a host of even newer "pharmacogenetic" tests are now in the R&D pipeline.

But the existing tests aren't widely ordered by doctors, a fact that bothers David Flockhart, chief of clinical pharmacology at the Indiana University School of Medicine. Flockhart, who has developed genetic tests to help guide the prescription of diabetes and high-blood-pressure drugs, says doctors are generally uneducated about the availability of such tests. But he predicts that that will change if the U.S. Food and Drug Administration recommends that doctors test two specific genes in all patients prescribed a widely used anticoagulant.

Technology Review:In November, an FDA advisory subcommittee you sit on recommended genetic testing for patients being prescribed warfarin, a drug used to treat blood clotting and stroke. Why did you make this recommendation?

David Flockhart: If the FDA accepts the recommendation, this will mean that it suggests everyone prescribed this valuable medication receive a genetic test at the start of warfarin treatment in order to ensure less costly and medically simpler treatment courses in which patients have fewer bad bleeding episodes and reach a stable, effective dose more quickly. It will bring pharmacogenetics for the first time to thousands of general practitioners and family practitioners.

TR: But the FDA has already approved a number of genetic tests to guide prescriptions. Aren't doctors using them?

DF: No. The big, big market is going to be in doctors' offices and hospitals, but it's really only now starting there. A major problem is going to be educating physicians who are, as yet, relatively uneducated about the availa­bility of genetic tests to guide some of their prescribing decisions.

TR: How long will that take?

DF: Every one of the large clinical-­testing labs is jockeying for position to try to exploit the large, anticipated growth in this kind of testing. The movement of these tests into the clinic will happen gradually with fits and starts....Demand will kick in within a year or two, as patients realize the power of these tests. That will be the biggest driver.

TR: Are some diseases or drugs receiving more emphasis?

DF: All branches of medicine and all the big, important diseases are under study. The size of the current effort to exploit the human genome sequence and bring that to the clinic is truly massive. The National Institutes of Health have made cardiovascular disease a priority, but it is clear that the psychiatric utility and tests used in oncology will also be important. The FDA recently approved a test to guide the use of irinotecan to treat colon cancer. A new test that will predict the effectiveness of tamoxifen for breast cancer patients is coming. Patients may first encounter these tests in the offices of psychiatrists and in hospital oncology practices.