Pharmacogenomics Can Predict Patients’ Medication Responses

The enzyme 2C9 metabolizes more than 90% of active S-warfarin, Dr. Beier said, and testing for variation in metabolism is clinically relevant with about 2 million patients started on warfarin each year. Testing for 2C9 and other genetic variations can explain up to 40% of the difference in current warfarin dosing, she added.

Another discovery of impaired metabolism led the Food and Drug Administration to require a black box warning for the anticlotting agent clopidogrel (Plavix) in 2010. The agency announced a reduced effectiveness of clopidogrel in patients who are poor metabolizers. Clopidogrel is another prodrug that has to be metabolized before it is biologically active, this time through the 2C19 enzyme pathway.

Available tests for such genetic differences in drug metabolism can cost $300-$700 and often are paid for out of pocket by patients, according to the panel. Dr. Beier recommended www.23andme.com for information on less expensive genetic testing. "I love this site. For $199, you can get a genome analysis. You can have your whole family spit in a cup, just not the same cup." (According to the Web site, the price is now $99.).

Full genome sequencing costs approximately $10,000. "When it comes down to a couple thousand dollars, it will be more affordable," Dr. Winner said, "but what are you going to do with the information?"

Dr. Winner is medical director for a genetic testing firm but had no other relevant disclosures. Dr. Patel and Dr. Beier disclosed no conflict of interest.