Breakthrough: Should you customize your drugs to your DNA?

Here's a shocker: Due to differences in DNA, up to 60% of the most common drugs are associated with adverse reactions. This includes medication used to treat common conditions like hypertension, heart failure, depression, high cholesterol, and asthma.

Hence the hope being pinned on "pharmacogenetics," a field of medicine that promises to improve health care by allowing doctors to customize medical treatment to suit a person's unique genetic signature. Though experts predict that it could be decades before personalized medicine becomes the norm, research is moving ahead: Last fall, for instance, researchers at Duke University reported that people with a specific genetic variant saw less reduction in LDL, or "bad" cholesterol, when taking statins.

But for some drugs, the future is now. A genetic test recently approved by the FDA should help doctors determine the optimal dose of warfarin (sold as Coumadin), a blood thinner used by 1 million Americans. Determining the right dose is crucial: Too much may result in an increased risk of excessive bleeding, while too little may cause a potentially fatal blood clot. By one estimate, using DNA analysis to prescribe warfarin would prevent about 17,000 strokes and 85,000 serious bleeding incidents.

A small but growing number of doctors and hospitals are also using genetic testing to tailor treatment for these medicines:

• Tamoxifen DNA testing identifies the 8% of women with genetic variants that keep them from metabolizing the breast cancer drug, rendering it ineffective.
  
• Painkillers like codeine Up to 8% of whites and 2% of Asians and African Americans are poor metabolizers of these drugs and won't get relief from them; for the 1% of "ultrarapid metabolizers," risks include respiratory problems.
  
• Antidepressants and antipsychotics Some of these drugs are metabolized by the CYP2D6 and CYP2C19 genes. In 2005, the FDA approved a test that looks for these gene variations, and now companies sell consumer versions. But experts advise against using the at-home tests without having your doctor interpret the results, notes Julie Johnson, PharmD, professor of pharmacy and medicine at the University of Florida. The reason: These genes are involved in the metabolization of 25% of all prescription drugs, including several where they're very important. If you misinterpret the results of an at-home test (and mistakenly think you don't have the gene), you might avoid taking one or more drugs you really need.