The Right Drugs for Your DNA
By: Source: AARP Bulletin Today Date Posted: 2005-03-09 18:58:39
Is the medication your doctor prescribed really going to work? Often it doesn’t, and sometimes it even does more harm than good, in the form of adverse side effects. Because people metabolize drugs at different rates, medicines don’t work quite as intended in 25 to 60 percent of patients. But a newly approved genetic test may soon eliminate the guesswork in prescribing many drugs.
The AmpliChip CYP450, cleared for use by the U.S. Food and Drug Administration in December and expected to be available by June, is the first test that will allow doctors to tailor medication doses to a patient’s genetic makeup. The matchbox-size device, developed by Roche Molecular Systems, a division of Swiss pharmaceutical giant F. Hoffmann-La Roche, employs microassay technology developed by Affymetrix Inc. of Santa Clara, Calif. At the heart of the system is a DNA chip, which is like a computer chip. Instead of circuits, it contains millions of DNA molecules, which it uses to analyze genetic material from a patient’s blood.
Doctors will be able to send a standard blood sample to a laboratory, where the patient’s DNA is extracted and applied to the chip. A computer scans the chip and generates a detailed report.
"It’s a huge breakthrough," says Peter J. Wedlund, an associate professor at the University of Kentucky’s College of Pharmacy. "Rather than just knowing that there may be genetic variability in how some patients respond to drugs, we’ll have a tool for identifying when it’s happening."
The AmpliChip CYP450 zeroes in on two genes, 2D6 and 2C19, that regulate the enzymes the liver produces to metabolize certain drugs, including antiseizure medications, beta-blockers for hypertension, codeine, the breast cancer drug tamoxifen, several antidepressants and even over-the-counter heartburn medications.
"This new test can identify people who clear certain drugs from their systems at an abnormal rate, either too fast or too slow," says James W. Cooper Jr., a professor at the University of Georgia’s College of Pharmacy. "Fast metabolizers end up with too little medicine in their bodies to do any good, while slow metabolizers can build up dangerous levels of a drug."
If the AmpliChip can make dosages more precise, it may especially benefit older patients. "Many older people have multiple health problems and already are taking several medications," Wedlund says. "That may reduce their ability to deal with a drug that’s out of whack." He expects future versions of the test to look at additional genes that affect other medications.
Indeed, doctors may someday be able to predict with pinpoint precision who will do better on a specific drug—and why. "The genomic prediction of drug response," Cooper says, "is just beginning to be appreciated."
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