Pharmacogenetic testing uses DNA to predict patients’ responses to medications

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Previously published with The Globe and Mail, October 25, 2021.

For many Canadians, finding the right medication is a long, and often frustrating, process of trial and error, especially for those dealing with chronic pain and mental-health issues. Time spent searching not only reduces quality of life for patients but wastes health-care dollars and resources, and can mean the difference between remaining actively employed or going on disability.

Fortunately, pharmacogenetic testing (PGx) may help people feel better sooner.

The test uses DNA to determine how an individual will metabolize more than 200 medications, from opiates to antidepressants like SSRIs (selective serotonin reuptake inhibitors), their optimal dosage and likelihood of effectiveness and adverse reactions.

Not to be confused with DNA tests that look at ancestry, ethnicity, or genetic markers for diseases like breast cancer, PGx testing reveals which genetic variants you have inherited (with nearly 100 per cent accuracy) and what that means in terms of your likely response to different drugs, according to Toronto-based company Inagene Diagnostics Inc.

It was a route that made the difference for Susan Fisher,* a 38-year-old mother of two from Alberta, who recently returned to work after struggling to manage her depression for more than 15 years.

Over that time, she was prescribed 10 different medications at varying doses – each one with side effects, including hand tremors, insomnia and severe headaches.

“My pharmacist suggested that I take a pharmacogenetic test in hopes of narrowing down the list of antidepressants that might work for me,” she recalls.

She used an at-home test kit (Personalized Insights™ from Inagene).

Available for purchase online (from $299) or through select pharmacies, the one-time test takes just five minutes and requires only a cheek swab.

Within a couple of weeks of deciding to take the test, Fisher received a detailed online report with her personalized results.

“What jumped out right away was that most SSRI drugs won’t work for me,” she says. “I was on four different SSRIs at escalating doses. The test showed I had a gene variant that caused major problems with this type of anti-depressants. My depression is essentially treatment-resistant to them. All of a sudden, everything started to make sense.”

She shared the results with her doctor who then prescribed a medication from a different class of drugs. For the first time in two years, her depression is lifting, and she has now been able to return to work.

“I wish I had this information long ago,” she adds. “It wouldn’t have lost normal, happy years with my kids. I wouldn’t have had the stress on my marriage. With this gene profile I now have, I feel I’m no longer grasping for straws.”

More pharmacists are recommending pharmacogenetic testing to patients. “It allows patients to get on the right drug quicker and help avoid adverse drug reactions, too,” explains John Papastergiou, a community pharmacist and an assistant professor at the Leslie Dan Faculty of Pharmacy and School of Pharmacy at University of Waterloo.

Each year, an estimated 200,000 Canadians will experience severe adverse drug reactions, causing death for 10,000 to 22,000 people, according to the non-profit group Adverse Drug Reaction Canada.

According to Inagene CEO Nancy White, up to 80 per cent of these incidents are preventable because they can be linked to genetics.

“Some people tend to metabolize drugs slower than others,” says Papastergiou. “With genetic testing, we’re able to predict whether someone is more susceptible to side effects. In that case, we can reduce the dose proactively or choose an entirely different medication.”

Results can be interpreted for patients by doctors or pharmacists who can intervene accordingly. Papastergiou hopes there will be more wide-scale adoption of pharmacogenetic tests in the future.

“There is a lot of value in the tests, especially for patients with certain conditions,” he says. “They do much better than those who don’t take tests. I think we’re going to become much more mainstream.”

In June, Inagene released results of a pilot project that evaluated the real-world value of PGx testing for optimizing treatments for chronic pain and mental-health conditions. The data indicates that, if used at the beginning of treatment, PGx tests would save patients more than $3,000 in wasted medications per person and 3.3 years of trial and error. With one out of every two Canadians having or having had a mental illness by age 40, the combined savings could total as much as $57-billion on average.

PGx tests have wide-reaching applications from easing the opioid crisis to enabling older Canadians to maintain their independence. White notes that PGx tests empower patients regardless of age or condition. “[A test] gives them invaluable information for their health-care decisions and it supports physicians to do their very best for the people they treat,” explains White.

White suggests not waiting to do PGx testing until you need to take medication. “Having the results before you ever take a medication will help you in the long run,” she says. “One day we’ll look back and it will seem barbaric to have put a drug in a person’s body without first knowing whether it is likely to be safe and effective. This requires a rethink among health-care providers and physicians. To be able to find the right medication through PGx testing is a real gamechanger.”

*Name has been changed.