Tailor-made drugs step closer to reality

Main Category: Public Health
Article Date: 04 Nov 2003 - 0:00 PDT

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Some people's genes make them uniquely susceptible to a drug's side effects or immune to its benefits. Now the U.S. government wants to see more of drug companies' research into this new science, a small step toward one day customizing medication.

Even the best medicines do not help everyone. Drugs are sold after they prove an effect on the average disease sufferer, not every individual. So there is little way to know in advance which is the best option, and at what dose, for each patient.

A new science called pharmacogenomics aims one day to replace some of today's one-dose-fits-all culture with gene tests to help tailor prescriptions to each patient's DNA.

Many of the tests remain experimental; pharmacogenomics is a developing field.

But the Food and Drug Administration was issuing draft guidelines on Monday that urge drug companies to share with the government more of the pharmacogenomic data they have begun gathering when studying new medicines.

Some data will be required when companies seek approval of a new medicine, and some will be voluntary and used by the FDA merely to keep up with the new field, the agency's drug chief, Dr. Janet Woodcock, said in an interview.

Still, it is an important step toward 'turning the explosion of information on pharmacogenomics into real knowledge,' FDA Commissioner Mark McClellan said in a speech last week.

How does pharmacogenomics work? Consider p450, a family of drug-metabolizing enzymes. An estimated 7 percent of Americans lack certain p450 enzymes, allowing some drugs to climb to toxic levels in their bodies. Other people have p450 enzymes that work so fast that a drug clears their bloodstream before it can fight their disease.

If doctors could test p450 easily, they could predict a person's susceptibility to a drug before prescribing it. Research to develop such tests is under way.

The FDA occasionally has used early pharmacogenomics information on a drug's label. For example, the drug Straterra, for attention deficit and hyperactivity disorder, contains information that people with a variation of the 2D6 drug-metabolizing enzyme process the drug more slowly and thus are more prone to side effects, Woodcock said.

Also, some leukemia specialists test child patients for another enzyme deficiency that makes the standard dose of a therapy called mercaptopurine far too high for their bodies. The FDA's scientific advisers recently recommended adding that information to the drug's label, too.

'The community's starting to come to grips with how to handle this new genomic information,' Woodcock said.

Under the new guidelines, companies would have to submit some pharmacogenomic data to FDA: If they use a well-known and validated genomic marker to determine how quickly patients will metabolize the drug; use genomics to choose which patients to target or to make the case that, say, a side effect seen in early animal studies isn't likely to occur in people.

Data on newer, less understood genomic markers or merely screening medicine users to check for any patterns of side effects, for example, would not be required, Woodcock said.

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