Is pharmacogenetic testing the future of drug prescribing?

A growing number of companies are offering pharmacogenetic testing kits. Customers swab their cheek, mail the cells to a lab and receive a customized list of medications that will or will not work best for them, based on their genes.

Some say it’s the future of drug prescribing — a major improvement over the current one-size-fits-all, trial-and-error methods.

“We change your medications based on your weight or maybe the food you eat or how your liver works, but it turns out that genes also affect medication,” Dr. Lisa Guirguis told Global News.

“So you can have drug-drug interactions, but you can also have drug-gene interactions.”

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The pharmacist and University of Alberta associate professor is researching how to best implement pharmacogenetic testing in Alberta pharmacies. She feels it’s especially useful for choosing antidepressants.

“We know that half of all people do not get relief from their first antidepressant,” said Guirguis.

Patients need to be slowly weaned from the drug before they can try another. It can be a long, painful process.

“In the pharmacy, we see people coming in who are very discouraged,” Guirguis said.

“They’re facing depression and anxiety and they’re trying to get help and they’re waiting months, if not years.” .

READ MORE: DNA testing: How genetic testing could make prescription drugs safer 

Dr. Tony Kiang describes pharmacogenetic testing (or pharmacogenomics) as “personalized medicine” or “precision dosing”.

“Currently, drugs are prescribed empirically for most cases, which means that most people would get similar dosage,” said Kiang, an assistant professor of translational pharmacotherapy at the University of Alberta.

“(With pharmacogenetic testing), the doctor or the pharmacist can tailor the medication and the dosage to the patient, based on their genetic information,” he said.

Kiang is studying the use of pharmacogenomics for anti-rejection drugs after transplant surgery.

He explains genetic variations can affect how a person metabolizes medications. If someone processes or breaks down a drug quickly, it may not stay in their system long enough to have an effect. Those patients could need a higher dose.

On the other hand, if a person metabolizes a drug slowly, it can build up in their body and increase their risk of an adverse reaction. Severe reactions kill thousands of Canadians each year.

“One day, this type of testing is going to be completely mainstream,” Nancy White, CEO of Inagene Diagnostics, told Global News.

The Toronto company launched its pharmacogenetic test in December 2020. Clients’ results are colour-coded like a traffic light: green drugs can be used as directed, yellow should be used with caution and red are not recommended.

“If it’s red, it’s a ‘do not use’ medication. It means that there are genes in your system that will not make this medication work,” said White.

Debbie Roberge of Edmonton heard about Inagene from her doctor. She decided to pay for the testing to help find a new antidepressant, without having to try a few first.

“This brings a lot of hope to me… I wouldn’t do it any other way,” said Roberge.

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Her results coloured the antidepressant she is currently taking in red. She is now trying one that was yellow. Her list did not show any green antidepressants.

The licensed practical nurse sees the potential of pharmacogenomics for the mental health patients she cares for.

“If you have something like this where you have the profile and it says this person is a rapid metabolizer, and they have to have 25 to 50 per cent more of a dose for this medication to be effective, that would mean the world of difference for that patient,” said Roberge.

Both Guirguis and Kiang advise discussing pharmacogenetic testing results with a doctor or pharmacist. They also know most doctors and pharmacists are too busy to comb through lists of compatible drugs for their patients.

They say the key for the science to go mainstream is teaching it in medical and pharmacy schools. But Kiang adds it is already used in cancer and transplant therapy outside of Canada.

“There’s a lot of potential for more common indications such as cardiology, psychiatry and pain management,” said Kiang.