Most of us are familiar with genetic testing through products like AncestryDNA and 23andMe to explore our family trees. Some may have already used it to uncover genetic markers for chronic or terminal illnesses. But with the growing trend of using genomic information to personalize care, is there a type of testing that can tell us whether medications we have been prescribed are actually working?
It is common for us to assume the medication we are taking will produce the intended beneficial effect. However, for some individuals, negative experiences arise when certain medications either fail to relieve symptoms as expected or, worse, cause life-threatening toxicity. This could sometimes simply be due to our genetic makeup.
This is where pharmacogenomic (PGx) testing comes in: A simple, one-time procedure that uses a cheek swab, blood test or saliva sample to analyze how individuals metabolize medications based on their genetic variations. PGx testing offers the potential to help find the most effective medication on the first try, reducing the trial-and-error process often involved in finding the right treatment.
Though Canada’s Drug Agency (CDA-AMC) included PGx testing on its 2023 Watch List as one of the top 10 precision medicine technologies that decision-makers should consider integrating into the health-care system, these testing options currently are not covered through publicly-funded health care.
The potential of precision medicine testing was shown in the largest PGx study to date. Conducted by the UK Biobank, nearly 24 per cent of participants were found to have been prescribed medications for which they were genetically predisposed to have an atypical response. For example, individuals with certain genetic variants may metabolize the common blood thinner clopidogrel poorly, reducing its effectiveness and increasing the risk of adverse cardiovascular events.
PGx testing holds particular promise in mental health. Estimates suggest that one in 10 Canadians will experience mental illness at some point in their lives, making it a major driver of health-care costs that exceed $50 billion annually. Reports indicate that more than 50 per cent of patients do not respond to the first psychiatric medication they are prescribed, and approximately 27 per cent experience adverse effects.
Furthermore, the Canadian Pharmacogenomics Network for Drug Safety (CPNDS) states that adverse drug reactions cost the Canadian health-care system more than $13 billion each year.
Adverse drug reactions cost the Canadian health-care system more than $13 billion each year.
The Canadian Medical Association Journal published a study in November 2023 examining the cost-effectiveness of PGx testing in British Columbia. The study used a simulation model to compare two care pathways over 20 years: one replicating the experiences of patients with depression treated through PGx-guided care, and the other representing patients receiving standard treatment without PGx testing.
The study found that implementing PGx testing could save the provincial public health system an estimated $956 million over the next 20 years. The added costs of PGx testing were offset by a reduction in the cost of refractory (treatment-resistant) care and higher remission rates. Other contributing factors include fewer hospitalizations and physician visits, and a decrease in direct costs, including medications and out-of-pocket expenses.
Despite these benefits, PGx testing still has hurdles to overcome.
When patients with lived experiences of mental illness were asked about PGx testing, many expressed hopes for its potential benefits but also voiced concerns about the possibility of discrimination based on the results, as well as risks to privacy and the safeguarding of confidential data. Some fear being stigmatized or facing barriers due to their ability to pay, or experiencing limitations in social opportunities based on their genetic profiles. Additionally, some experts warn that the reckless widespread implementation could exacerbate existing health disparities, particularly for racialized communities and Indigenous peoples, by widening gaps in research, systemic racism and access to care.
Health-care professionals have expressed a lack of confidence in their ability to accurately interpret PGx test results, highlighting the need for enhanced clinician training and education.
Incorporating PGx testing into clinical practice would require initial investments in technology-enabled clinical care, infrastructure, training and personnel. These costs would be offset over time by improved patient experiences, reduced healthcare costs (both direct and indirect), optimized workflows, and a more streamlined medication selection process. However, implementation is easier said than done and requires a clear roadmap and careful execution.
Successful PGx test development requires addressing biases and inequities in healthcare. Investing in the collection and creation of representative genomic databases is crucial for ensuring accurate and equitable outcomes.
As part of efforts to increase awareness, the B.C. government released guidance in June 2023 for both patients and health-care providers on how to utilize PGx testing in decision-making. Similar initiatives are underway in England, where the National Health Service (NHS) has invested in genomic medicine to streamline workflows and centralize laboratory services. In Ontario, Cancer Care Ontario and Ontario Health have identified opportunities to revise the scope of practice for health-care professionals in delivering genetic services, while also creating space to better utilize their expertise and training.
Surveys conducted in other jurisdictions, including Brazil and the United States, suggest that clinicians are eager to better understand how to incorporate PGx testing into psychiatric care in a meaningful way. As the demand for PGx knowledge increases, various genomic organizations in Canada are actively developing additional educational and training strategies to support the integration of pharmacogenomics into clinical practice.
If adoption is to increase in the next five years, equitable access will be crucial and will require collaboration and strong advocacy from health-care practitioners, policymakers, private partners and patients.
Consistent data from high-quality clinical studies will better inform clinical practices, guidelines and policy decisions, helping to shape the future role of pharmacogenomic testing in transforming health-care delivery and medication prescribing.
