Genetic Testing Can Help People Get the Right Medicine

April 12, 2000 (Atlanta) -- Wouldn't it be great if the next time you went to the doctor, you could walk away with a prescription you knew was going to work because your doctor had tailored the dose and the drug type to your own body chemistry? That day may not be far off. In fact, the technology is already being used in some countries for certain illnesses.

An article in this week's British Medical Journal outlines how pharmacogenetics -- the study of genetic factors that can affect a person's reaction to a drug -- is being used today, and where the fast-growing field is headed.

"[Pharmacogenetics] is using genetics to get a dose of medicine right," author Robert L. Smith, DSc, PhD, tells WebMD. "Drugs will be developed and targeted in relationship to [patients'] specific genes. It will make the use of medications both safer and more effective, and also increase cost-effectiveness from the point of view of avoiding adverse drug reactions, or side effects."

Such bad reactions, Smith says, injure millions of people a year and kill hundreds of thousands. "Over the course of 20 years, I have seen people badly harmed and, in fact, I have seen people killed because of the mismatch of medications and [a patient's] genetic status. We need to do a better job and we can do it; we've got the tools to do a better job now."

Researchers say pharmacogenetic research is moving in two main directions: identifying gene variations that influence the way the body responds to drugs and identifying genes associated with various diseases, which can be targeted with new drugs.

"Firstly, genes determine how quickly you destroy [metabolize] drugs in the body. Some people destroy drugs very quickly, and some people very slowly," Smith says. "Clearly, if you are destroying a drug more slowly, you are more likely to receive an overdose of that drug even though it is a so-called "normal dose" of that medicine. Whereas if you are a rapid destroyer of the medicine, then you are quite likely receiving doses that are not appropriate."

Further, he says, some drugs are only effective when the patient has certain genes that produce specific receptors. "Receptors are the place where drugs act. And some people have the appropriate receptors [for certain drugs] and others don't." Genetic testing can determine whether a patient has the proper receptors and if he or she metabolizes a certain drug quickly, slowly, normally, or not at all.

Ira Herskowitz, PhD, says researchers also want to tailor drugs to fit specific diseases.

"For example, breast cancer: Knowing the kind of cancer one has is tremendously valuable for treatment," Herskowitz says. Women whose cancer is due to their body's overproduction of a protein called HER-2 can be treated with certain drugs that affect this process, he says. Herskowitz is a professor of genetics at the School of Medicine at the University of California in San Francisco.

Herskowitz adds that pharmacogenetics will also help reduce serious interactions between drugs in the future.

Right now, the use of pharmacogenetics is limited. The most advanced uses are in Scandinavian countries, to treat psychiatric illnesses, but the technology is slowly moving into other areas.

"I think in psychiatry, for the treatment of mood disorders, is where you will see this type of genetic information applied; it is being applied now," says Smith. "I think we occasionally see this type of application in the area of cancer treatment ... and maybe also in the treatment of [heart] disease -- for example, blood-pressure medicine."

The future of pharmacogenetics appears to be wide open, Smith says. He foresees cards encoded with genetic information that patients will take to their doctors to help them make treatment decisions.

"I think certain kinds of information will be made available on a sort of 'smart card,' which will tell the physician how a person responds [to certain medication] and what sort of dosage changes may be needed," Smith says. "I think it is almost here now."

Herskowitz says he believes those smart cards will be in use in five years -- maybe not for every patient, but for some.

"This is not information that needs to be highly confidential, etc. It is about a patient's ability to handle drugs," Smith says. "This is information, too, that I think ethically should be available to the patient [so they can] protect themselves from the adverse effects of medicines."