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Pharmacogenomics Offers Pluses for Patients, Pharmacists

Kate Traynor

As pharmacogenomics—the study of genetic variations that influence the response to drug therapy—moves from the research laboratory to the clinic, this emerging science should produce new opportunities to improve patients' pharmaceutical care.

William E. Evans, Pharm.D., chairman of pharmaceutical sciences at St. Jude Children's Research Hospital in Memphis, Tenn., said the public is becoming increasingly aware that genetic testing can yield information to help guide drug therapy. Patients, he added, "are relying more on their pharmacist and their physician to understand this and bring it to their treatment."

But patients are not the only group that can benefit from advances in pharmacogenomics. Larissa Humma, Pharm.D., BCPS, assistant professor of pharmacy practice at the University of Illinois at Chicago, predicted that the advent of clinical pharmacogenomics means "pharmacists are going to have a really big role in helping to manage therapy."

Humma and a colleague published an article in the July 1 issue of AJHP describing genetic variations that affect patients' responses to cardiovascular drugs. Among the issues discussed in the article was the growing body of evidence showing that polymorphisms in the gene encoding cytochrome P-450 (CYP) isoenzyme 2C9 affect the way patients respond to warfarin therapy.

If the connection between CYP 2C9 polymorphisms and patients' warfarin-therapy response bears out and a test for detecting the genetic variants becomes commercially available, Humma said the product could be "very useful in managing warfarin therapy—particularly in initiating warfarin therapy."

"You could individualize the dosing and start lower doses in patients who have a variant allele," she said. "You might be able to reduce the time for them to achieve a stable dose, possibly decrease the length of hospitalization if they're hospitalized during warfarin initiation, maybe decrease the risk of bleeding."

But Humma cautioned that much of the data on the CYP 2C9 allele and its effect on patients' response to warfarin come from retrospective studies. "We're going to have to first study [the relationship] prospectively" before the testing enters clinical practice, she said.

Evans said he is aware of only a small number of prospective clinical studies that examine how genotypes influence drug responses. But he believes this situation will change soon.

"I think what's going to happen, based on the way a number of clinical trials are being conducted in the pharmaceutical industry, [is that] they're doing genotyping at the same time that they test their drug in Phase II/III trials," he said. Researchers at that stage in the drug development process, he said, should be able to detect whether genetic differences influence how some patients respond to the pharmaceutical agent.

But before the results of pharmacogenomic studies can be translated into clinical practice, he noted, laboratories must offer standardized genotyping services that adhere to Clinical Laboratory Improvement Amendments (CLIA) conditions. Evans is on the scientific advisory board of Gentris Corp., a Morrisville, N.C., company that is developing diagnostic genotyping kits for commercial use.

"Diagnostic tests for genotyping...are still largely in research laboratories," Evans noted, with some tests advancing to CLIA-certified laboratories.

Also lacking today, Evans said, is a consensus on how to interpret complex information about multiple genes.

"You get all of these genotypes. Then, how do you put it together to 'What do I do for my patient with this mixture of genotypes?'" he asked. "Right now, [such decisions are] having to be made sort of gene-by-gene, drug-by drug" on the basis of the available scientific literature.

Despite these hurdles, Evans predicted that, within 10 years, genetic data from patients will guide drug-therapy decisions in the way that serum creatinine concentrations and other laboratory test results do today. "It's really going to be driven by the fact that some people with some genotypes will not respond to drug they will with drug B." In the future, he said, the best way to identify which patients will respond favorably to a certain drug will be to examine their genotypes for DNA sequences encoding specific polymorphisms.

Evans said pharmacists are well positioned to take advantage of opportunities in the field of pharmacogenomics.

"I think this is an area where pharmacists see it as a science that's directly related to medications and how they should be individualized in their patients," he said. "That's basically what pharmacists have been what we call clinical pharmacy."