Medicine made just for you

But the case of Aczone illustrates a barrier to this new era. Pharmaceutical companies fear that if testing for such genetic markers is required, that will discourage doctors from prescribing a drug or limit sales to a subset of patients.

Upon learning of the testing requirement for Aczone, Astellas, one of its developers, abandoned the drug. The other developer, QLT, is planning another clinical trial hoping to have the testing requirement lifted. It argues that in a previous clinical trial, only 1.4 per cent of patients had the enzyme deficiency, and none developed anemia.

Tailoring drugs to patients can introduce problems for doctors and drugmakers. Transfused blood is an example. Many transfusion centers would love to have a single type of blood suitable for everyone, rather than stocking different types and worrying that severe problems may occur if the wrong type is transfused. Still, many physicians, regulators, market analysts and pharmaceutical executives agree that despite the obstacles, personalised medicine is inevitable. About 40 of the 50 psychiatrists at the Mayo Clinic use genetic tests to help choose drugs to prescribe, said Dr David A Mrazek, chairman of psychiatry at Mayo. And some companies are offering tests directly to consumers.

Mary Jane Q. Cross, an artist in Newport, New Hampshire, developed a permanent tremor on her right side after taking antidepressant Prozac 14 years ago. She now paints with her fingers as she cannot hold a brush. A year ago, she paid about $600 to Genelex, a company in Seattle, for genetic tests that showed she would have trouble tolerating certain drugs, possibly Prozac too. ‘‘Had I known that 14 years ago, I would not have used the drug,’’ Cross said.

Recently, when she had an emergency appendectomy, she advised the doctors to use a low dose of anesthesia based on her genetic test results. ‘‘My husband had to go home in the middle of the night to get the material, and make it clear to them that this was an important issue,’’ she said.

Scientists are finding numerous examples of variations in genes that help predict who will respond to a drug or who will suffer side effects. Most drug companies now routinely collect DNA samples from patients in clinical trials to look for such markers. In March, the FDA issued guidelines to encourage drug companies to pursue personalised medicine, and the agency is adding information about genetic tests to the labels of a few drugs.

Since June, the label for Camptosar, a Pfizer drug for colon cancer, has advised doctors that a lower starting dose may be appropriate for the 10 per cent of people who have a particular version of a gene called UGT1A1. The variant makes them more prone to a side effect: a serious decline in white blood cells.

But many more years of work will be required before combinations of drugs and tests, sometimes called theranostics, can reach the market. ‘‘I don’t see any drug hitting markets in the next five years that will have a DNA-targeted market,’’ said Dr Gualberto Ruano, president of Genomas, a company working on genetic tests for drug use.

New York Times