Precision medicine and how it relates to a patient’s medications
Medications are usually prescribed at a set standard dose based on the indication, 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.
We all carry genetic variants that affect our body’s response to a variety of medications. More than 400 medications now include PGx information on their labels. This information gives guidance about precision dosing and caution about potential side effects. The goal with PGx testing is to try to find the most effective medication and tailor the optimal dose for each person.
PGx and the science behind precision medication dosing
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 every cell 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.
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 from happening and to increase therapeutic success.
A person’s genetic information does not change over time but our understanding of genetics does as we learn more. This means 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 unusual 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.
How is the PGx test performed?
The inside of a person’s cheek is swabbed (buccal swab) to collect a sample of cells that contain DNA. A blood sample is only collected when several buccal swab attempts are unsuccessful and if your health-care team thinks it is necessary. 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.
The difference between pre-emptive and reactive PGx testing
Pre-emptive testing is done before a doctor prescribes a medication. The doctor then has the patient’s PGx information available when they are prescribing a medication before an unexplained side effect occurs. Pre-emptive testing tries to tailor medications for a patient before they need medication therapy. This means the patient will have better medication choices and prevention of specific side effects.
Reactive PGx testing is done to understand why certain medications have not been effective or why a side effect may have occurred. It is also done to prevent a treatment failure from happening again.
To learn more about PGx at SickKids go the Pharmacogenetics page on SickKids.ca.