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As targeted medicine moves to the clinical setting, nurses will need to learn the language of genetics and to think at a molecular level in order to explain new therapies to patients, families and communities. Nurse practitioners who prescribe drugs will need a basic understanding of genetics and research to keep up with the latest findings.

As individual genetic information and what it means becomes increasingly available, nurses will be able to use it as another tool to help their patients better understand their illnesses and responses to treatments. But they also will have to deal with new implications of old ethical issues, including privacy, access and distribution of new therapies.

"It's analogous to the discovery of penicillin," said Agnes Masny, MSN, MPH, NP, RN, a nurse practitioner specializing in cancer risk assessment at the Family Risk Assessments Program at the Fox Chase Cancer Center in Philadelphia. "The genomics era is going to change the way we practice medicine and nursing."

Informed choice. Of all the medical breakthroughs promised by the rapidly moving field of genetics, targeted medicine-also known as personalized medicine or pharmacogenomics-is the one most likely to be used soonest on a large scale, leaders in the field of medical genetics agree. Constantly emerging discoveries linking genetic variations to physiological reactions and increasingly powerful and sophisticated computers that can analyze and categorize this information have opened up a new universe to drug researchers.

Almost all pharmaceutical companies have some form of pharmacogenomic research department. Some targeted therapies-especially in oncology-already are being used and more are expected soon to treat diseases like hypertension, diabetes and mental illness.

Today, much conventional drug therapy is hit-or-miss educated guessing. Physicians assault a tumor with an arsenal of chemotherapy and hope the barrage wipes it out without destroying too many healthy cells. Or they give a standard dose of anti-depressants that probably will need to be adjusted based on patient response.

"There are so many drug choices for hypertension," said Mary Engler, Ph.D., MS, RN, professor and director of the cardiovascular and genomics graduate programs in the department of physiological nursing at the University of California, San Francisco.

These include various diuretics, calcium channel antagonists, beta-blockers, ACE inhibitors, alpha-adrenergic blockers and angiotensin II receptor antagonists, she said. Some drugs may not work or may work only in higher doses. Some patients may not metabolize the drug well and be at risk for its toxicity. Some may have an inherited defect that can alter normal response to medication.

"How are [the proper drugs] selected?" Engler asked. "There are certainly guidelines; however, selecting optimal medications and dosages can be trial and error at best."

Targeted medicine takes a more evidence-based approach, although in its present state, it is still far from a sure bet. A classic example is Herceptin (trastuzumab), a drug that targets a protein involved in a certain type of breast cancer. Herceptin blocks the growth of tumor cells spurred by overabundance of a gene called Her2. About 30 percent of breast cancer patients have this condition. Herceptin seems to help about half the patients who take it.

In combination with other therapies, tests show Herceptin keeps tumors under control for up to 17 months. But, perhaps most important, because the drug targets only cancerous cells, it has considerably fewer side effects than traditional chemotherapy. Patients do not experience nausea, hair loss, exhaustion or other symptoms that can make the cure seem worse than the disease.

Besides providing clues to choose the best drug to fight a particular disease, genetic markers also can predict how various people respond to various drugs-how the drugs are absorbed, metabolized, distributed and eliminated. Researchers are looking closely at the anticlotting drug warfarin, used to treat heart patients. They have found genetic differences to account for the way various patients respond to the drug and why some experience dangerous bleeding at what seems a normal dose.

The Swiss-based pharmaceutical company Roche announced in May that it planned to launch a genetic test that would determine a patient's metabolic status as a guide to prescribing drugs and doses, Reuter's News Service reported. Roche's division head, Heino von Prondzynski, told Reuter's the test eventually could be used to screen all newborns to show whether there were certain drugs they should never be given.

"The escalating numbers of serious adverse drug reactions and drug-related morbidity and mortality, as well as the associated costs, are accelerating the progress of pharmacogenomics," Engler said. Depending on how the statistics were interpreted, adverse reactions to drugs were the fourth or sixth leading cause of death in the United States in 1998.