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Linda Riches, shown in this handout image, tried at least 12 different antidepressants before one worked for her.HO/The Canadian Press

Loss. That’s the word that comes to mind when Linda Riches thinks of the debilitating depression that robbed her of the ability to fully care for her son, advance in her career and pursue her goal of a PhD in education.

Riches, 67, said she was prescribed at least a dozen antidepressants, starting in her 30s, but they failed to lift her mood while she missed a lot of days in her job as a high school teacher. When she would return to work, she felt isolated and alone among co-workers she believed would have responded differently if she’d had a physical illness.

“If you’ve been off because of a mental health issue, people just don’t want to talk about it. So they ignore it. Nobody wants to come and say, ‘Is there anything I can do to help you?’ " she said from her home near Prince George, B.C.

Years went by as she started to lose hope before one medication turned out to be the right fit.

Now, Riches says she hopes others can avoid a trial-and-error experience by having a genetic test to help predict which drugs would likely work best for them and cause fewer side-effects.

Known as pharmacogenomic testing, such personalized treatment is available for a fee. A lab examines DNA obtained from a sample such as from blood, saliva or a cheek swab to identify the genetic variants that affect how the patient would metabolize and respond to specific medications.

Riches is one of three patients who took part in a University of British Columbia study into the cost savings offered if pharmacogenomic testing were to be publicly funded.

A study published Tuesday in the Canadian Medical Association Journal suggests that providing the test as a standard part of care could save $956-million over 20 years for the health-care system in British Columbia alone. That excludes all the personal and economic savings from people returning to work, being able to afford child care and having a better quality of life.

Stirling Bryan, a senior author on the study, said more than 35 antidepressants are available in Canada but nearly half of patients do not respond to the first medication they are prescribed and about a quarter of those report intolerable side-effects.

Genes are responsible for about 42 per cent of the variation in how people respond to antidepressants, said Bryan, a professor at UBC’s school of population and public health and a senior scientist at Vancouver Coastal Health Research Institute.

Researchers accessed about 194,000 patients’ health data from 2015 to 2020. It included medications they were typically prescribed for major depression as well as clinical trial data linking genetic information to appropriate antidepressants. From that, they developed a simulation model for how people would fare over 20 years if they did not have pharmacogenomic testing compared with predictable outcomes with that testing.

Bryan said about 37 per cent of patients who don’t respond to various medications are deemed to have treatment-resistant depression, sometimes after they give up trying out of frustration, at which point they may need more doctors’ visits, including psychotherapy. They could also end up in hospital for electroconvulsive therapy (ECT) or other treatment, adding to health-care costs.

“One in 10 Canadians will experience major depression in their lifetime,” said Stirling, believing that widespread availability of pharmacogenomic testing could save billions of dollars throughout the country.

Beyond the financial savings, the study showed that an anticipated 1,869 lives would be saved over 20 years, Bryan said.

Few patients get a genetic test to determine which antidepressants could be best suited to them, but more people are choosing that option, usually by spitting into a tube they mail to a lab.

However, doctors may not know how to interpret someone’s genetic profile to help guide their prescribing decisions, said Bryan, urging more education on that through a program that would fund the testing.

Research on pharmacogenomic testing is also under way elsewhere in Canada.

Dr. Paul Arnold, a child and adolescent psychiatrist and director of the University of Calgary’s Mathison Centre for Mental Health Research and Education, is involved in a study for patients between ages six and 24 who are either starting on medication or about to switch to a different drug.

DNA samples have so far been collected from about 1,000 patients in Alberta, British Columbia, Saskatchewan and Alberta, but the goal is to recruit another 2,000 children and young adults, Arnold said.

The study initially included participants up to age 18 but expanded because most mental illnesses start before age 25.

The samples are being tested by a publicly funded lab but the hope is that costs could eventually be covered by the Alberta government depending on findings after researchers analyze prescribing patterns and changes in use of health-care services, Arnold said.

“The exciting thing about pharmacogenomic research is that you can see the immediate impact,” he said. “The goal is to catch (patients) early, before they go through that journey of having been on multiple medications without success.”

Dr. Jitender Sareen, a psychiatrist who is medical director of the mental health program for the Winnipeg Regional Health Authority, said plans are under way to launch a study that would determine the impact of pharmacogenomic testing for hospitalized adults, including seniors taking medications for multiple conditions.

“Our aim is to recruit all adults but we wanted to start on our inpatient units because there is mixed evidence about whether this kind of pharmacogenomic testing can actually reduce the length of hospitalization,” he said.

Pharmacogenomic testing currently costs between $200 and $400, but providing it to everyone who needs antidepressants would benefits the health-care system, care providers in the community as well as patients, Sareen said.

“People get tired of trying different medications and this could at least help guide treatment.”

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