Genetic Testing Can Aid Drug Prescriptions

Genetic Testing Can Aid Drug Prescriptions

There are few enduring dreams in medicine, and none is more potent than the promise of truly personalized care. Now, thanks to rapid advances in genetic testing and analysis, physicians are gradually unlocking the secrets to make the dream a reality. Tests now exist that can tell doctors who is at the greatest risk for developing various cancers, Alzheimer's disease and cystic fibrosis, among others. But the latest, and perhaps most important breakthroughs are happening in the field of pharmacogenomics - tests that reveal how different individuals metabolize various drugs.

Next month, the MedCan Clinic in Toronto will become the first clinic in Ontario offering clients the chance to take pharmacogenetic testing, in hopes of fine-tuning drug therapies, and eliminating the often-frustrating process of finding the right drug and right dose, without facing a host of side effects.

"We've known for a long time that people react differently to treatment, but what we've only learned in the past few years is that people metabolize medication differently," explains Dr. Lea Velsher, a clinical geneticist at Toronto's North York General Hospital, and a consultant to MedCan. "A lot of people are coming to us because they've been on various medications and have had trouble - either they've not worked or they've experienced really bad side effects. This [testing] gives them and their doctor one more tool to determine what drugs are likely to work best and at what dosage."

That promises to be especially important when it comes to prescribing antidepressants - a process that can be gruelling for people in mental distress, because it often takes weeks before doctor and patient know if a new drug is having any effect. Already many top U.S. hospitals, including the famed Mayo clinic in Minnesota, are using pharmacogenomic tests to custom tailor their treatment. And last month, the U.S. Food and Drug Administration began recommending genetic testing before doctors prescribe certain common blood thinners.

At MedCan, the testing comes down to a simple blood test, sent to a lab in Louisville, Ky., and the results are typically returned within five days. Doctors then interpret the data in light of family history, details about diet, other medications and a long list of other variables. The result is a detailed personal health profile that can help establish a treatment plan with the best chance of success.

If there is a danger in all this, it's that the flood of excitement over genetic testing leaves some patients with unrealistic expectations. And while MedCan is very circumspect about the promises it makes, many Internet clinics have popped up, cashing in on the hopes of patients desperate for quick relief. "A lot of the claims are outlandish. I've had patients go to the States and take these blood tests, come back with their results and say 'which drug should I take?' " says Dr. Anthony Levitt, psychiatrist-in-chief at Sunnybrook Health Sciences Centre in Toronto. "In this regard, there's still a little bit of art left in medicine. Yes, it's useful for us to know whether a person is going to be a slow metabolizer or a fast metabolizer. But it's a fraction of the picture."

Velsher agrees, and says it's important to bear in mind the limitations of the technology, as well as its advantages. "There may be this science fiction idea out there that people will get a printout that says 'take these drugs at this time, at this dosage, and your life will be perfect' - that's not going to happen, but it's still very useful," she says. "It's a tool for patients to help personalize the care they're getting, rather than relying on the 'off-the-rack' prescription approach."

Certainly, dispensing with that "off-the-rack" approach is the ultimate promise held in pharmacogenomics, and other genetic sciences. "When I started in med school we were always taught about the 70-kg, middle-aged man," Velsher explains. "Most medical practice is still based fundamentally on calculations based on that 70-kg man. The idea behind personalized medicine is really about taking every patient's individual characteristics into account. And pharmacogenetics is part of that - we are at the doorstep."

Already the tantalizing possibilities are coming into focus: tests that can predict the onset of disease, and can identify pinpoint treatments to snuff problems before they can take hold. Applied to clinical trials, genetic testing could one day answer the vexing questions of why certain experimental drugs work wonders for some, while triggering potentially fatal side effects in others.

Still, getting to that point will take time, and money. MedCan's genetic testing services start at about $1,000 and run as high as $2,000 depending on which genetic enzymes are being tested for, and they will only provide a fraction of the information a doctor needs to treat you. But as the science progresses, and the desire to tap into that wealth of knowledge spreads, you can bet that, for many of MedCan's patients, money will be no object.

See also GENETICS.

Maclean's October 1, 2007