Precision medicine and how it relates to a patient’s medications
Medications are usually prescribed at a set standard dose based on the indication, sex, age and weight of a child. This is called the “one size fits all” model. However, some people respond differently to the same medication at the same dose. Precision medicine can be used to precisely (or specifically) tailor medication choice and dosing for people. This allows medications to be safer and more effective for patients.
An example of precision medicine is the use of pharmacogenetics (PGx) testing. PGx is the study of how differences (variants) in our genetic make-up affect our individual responses to certain medications. PGx can increase the chance of safely getting the benefits of a medication while lowering the risk of side effects.
It is common to carry genetic variants that affect our body’s response to a variety of medications. This information provides guidance on the best dosing strategy for an individual and caution about potential side effects. The goal of PGx testing is to try to find the most effective medication and tailor the optimal dose for each person.
Genes and PGx
Genes are the instructions that our bodies use to develop, grow and function throughout our lives. Humans have between 20,000 and 25,000 genes that make up their genetic blueprint. Everyone has a full set of genes in most cells of their body. The information or “sequence” that makes up our genes differs slightly from one person to the next. There can be many different versions of the same gene among the human population. When the sequence of a gene is changed, it is called a genetic variant. The presence of genetic variants explains why we are all genetically unique.
For example, some genes provide instructions for how the body breaks down (metabolizes), activates or responds to certain medications. PGx testing will look for genetic variants in these genes to try to prevent side effects and increase therapeutic success and the safety profile of medications.
A person’s genetic information remains mostly unchanged over time, but our understanding of genetics increases as we learn more. This means that as we learn more, PGx testing may be repeated to test for even more genes that can help further explain our response to medications.
Why is PGx testing helpful?
PGx testing can provide answers as to why a medication may or may not be working for someone. Some people’s PGx results may indicate that increased monitoring for side effects or specific dose adjustments may be needed for safer and more effective medication treatment. Sometimes, completely avoiding certain medications may be recommended. This is because some genetic variants can contribute to an increased risk of serious side effects or a failure of a medication to work. PGx testing is helpful because results can predict if a person will experience an unexpected reaction to a medication compared to the average population. Testing can also recommend other medications that may be predicted to work better. Additionally, PGx test results can help to reassure that changes to medication treatment may not be needed based on the genetic variants a person is carrying.
Check out this video to see how pharmacogenetic testing can be helpful to guide medication treatment based on a person’s test results.
Current limitations of PGx
While PGx testing is a useful tool, it is important to keep in mind that our genetics are just one factor influencing medication response. Our bodies and the medications we use are complex and interact in many ways. This means that other factors—for example, the environment, organ function, nutrition, interaction with other medications, and lifestyle choices—can also impact how a medication works. Keeping this in mind, PGx testing can be seen as one piece to the puzzle of predicting someone’s response to medication.
PGx is also a relatively new field in clinical practice; and because of this, it has not yet become a universal standard. As a result, its application and use remain limited, with only a select number of medications having established recommendations to incorporate PGx information to guide medication prescribing and treatment decisions.
Medications that may be impacted by PGx variants currently fall under the following health specialties:
- Autoimmune disorders (immunology)
- Blood clotting disorders (hematology)
- Cancer treatment (oncology)
- Digestive health (gastroenterology)
- Heart care (cardiology)
- Infectious diseases
- Mental health (psychiatry)
- Neurologic disorders (neurology)
- Pain management
How is the PGx test performed?
The inside of a person’s cheek is swabbed (buccal swab) or a blood sample is used to collect a sample of cells that contain DNA. This sample will be used to run the PGx test. The PGx test only looks at specific genetic variants that impact how a person processes certain medications.
To learn more about PGx at SickKids go the Pharmacogenetics page on SickKids.ca.