By Barbara Greenwood Dufour

A medication isn’t necessarily going to work for everyone. In fact, it may be effective in only 30 per cent to 60 per cent of patients. Each person’s genetic makeup will affect how they respond a medication. This is where pharmacogenomic (PGx) testing can help.

Pharmacogenomics is a rapidly expanding area of study into how our genetic differences make us respond differently to pharmaceutical treatments. PGx testing can help predict how well a drug will work for a patient and how likely they’ll have an adverse effect from it. So, it can help clinicians pick the right treatment without “experimenting” with medications until one works and without the additional health care interventions and hospital admissions caused by serious side effects.

What do patients and clinicians think of PGx testing? How could their experiences inform how pharmacogenomics is implemented into practice? To answer these questions, CADTH looked for published literature on PGx testing, specifically qualitative studies or studies on the perspectives and experiences of patients and health care providers. CADTH is an independent agency that finds, assesses, and summarizes the research on drugs, medical devices, tests, and procedures.

CADTH found 13 qualitative studies on PGx testing in a variety of health care settings. According to these studies, patients and health care providers do think that PGx testing is beneficial. To some, more information is always better, regardless of how it’s used. But, for many the value is specifically in avoiding the pain, suffering, and time lost trying medications that provide poor results. These studies, however, also shed light on related issues health care planners and providers should prepare for.

Make sure testing doesn’t limit choice.

Clinicians may approach PGx testing as just one tool for narrowing down potential treatments rather than determining a specific one. However, patients may need assurances that the tests will be used this way. Patients sometimes have unique perspectives or prior experiences with drug treatments that they would want clinicians to also consider. For example, the “best” medication according to a PGx test assumes the patient will accept an average level of risk to achieve a benefit. But individuals who have a higher-than-average tolerance for side effects might prefer a medication with more severe ones in order to get more clinical benefit. Patients also want to be assured that a medication ruled out by a PGx test taken today won’t be ruled out later on. This is of particular concern to people with chronic conditions who sometimes need to be treated with different medications over the course of their lives — in the future, they might benefit from a medication that was once rejected on the basis of a PGx test.

Make sure privacy is protected.

Concern about the confidentiality and privacy of personal health data isn’t unique to the field of pharmacogenomics. But it has been raised in the context of PGx test results. Some patients worry that the information could get in the hands of others and misused, for example by insurers to discriminate against them in terms of eligibility and coverage.

Provide guidance on when to test and how to use the results.

Some clinicians aren’t likely to order a PGx test because they aren’t sure how to interpret and use the results. But they may be more likely to use them if given educational materials to help guide them as they discuss test results with their patients. Even clinicians who are familiar with and comfortable using PGx tests may need guidance, such as clear direction on when to use the tests — at the beginning of treatment or after a patient isn’t responding well to a treatment.

Consider and plan for secondary findings.

It’s also important for clinicians to know how to address the ramifications of PGx test results for a patient’s family. If a test reveals that a patient has an increased risk of a disease, current and future family members could be at this increased risk as well. Guidance on if and how these findings should be communicated to patients, and who should do it (i.e., the clinician who ordered the test or a genetic counsellor), would be useful, especially when there’s no action that can be taken to reduce disease risk.

Most patients and clinicians acknowledge the potential of PGx testing to improve health care, helping patients access effective treatments more quickly and saving clinicians time and effort. Although PGx testing is not currently widely used, its use is expanding. Policies and resources will be needed to support the clinicians who order, interpret, and use PGx tests. And patients must be assured that PGx testing won’t restrict the medications offered to them and that their information is kept safe.

You can access the full report — Pharmacogenomic Testing for Medication Selection: A Rapid Qualitative Review — on the CADTH website. If you’d like to learn more about CADTH, visit cadth.ca, follow us on Twitter @CADTH_ACMTS, or speak to a Liaison Officer in your region: cadth.ca/Liaison-Officers.

Barbara Greenwood Dufour is a knowledge mobilization officer at CADTH.