Pharmacogenomics testing aids in prescribing best meds

Q: I’ve been hearing a lot about lab tests that can look at my genetics to see how I metabolize medications. How does this work and why is it important for me to know how my body metabolizes medicine? A: Testing for how a person metabolizes medications is called pharmacogenomics testing, or PGx testing. This is a prime component of individualized medicine — selecting specific medications for each person based on personalized information.

Pharmacogenetic testing can help determine how a person metabolizes up to hundreds of common medications.

This testing can give pharmacists and health care providers insight into adverse drug reactions and interactions as they review the patient’s medications. These reviews identify potential and current medication-related problems, especially in patients who take multiple prescriptions and overthe-counter medications, along with herbal and dietary supplements.

Testing can guide therapy, optimizing medications to achieve the best outcomes. Your health care provider can use test results to guide medication selection and dosing. Pharmacogenetic labs also can help patients identify medications that they should never take to avoid serious, adverse drug reactions that could be fatal.

Testing is simple. A cheek swab is sent to a certified medical lab to be processed to determine how a patient metabolizes various medications. The process takes anywhere from two to five weeks.

Mayo Clinic routinely processes pharmacogenetic panels. Results from direct-to-consumer labs cannot be used for clinical decision-making, as the results may not have been reviewed by a licensed physician, so it is important to know the type of lab taking and processing the sample. At Mayo Clinic, a physician must order pharmacogenetic testing.

Pharmacogenetic testing results become a permanent part of a patient’s health record for future use by providers to guide medication therapy long term. When a provider inputs a future prescription, notices of drug-gene interactions pop up on the computer screen to indicate interactions that may result in an adverse drug reaction or ineffectiveness of therapy. Then, a health care provider can choose a more suitable medication therapy.

Another benefit of such testing is that it can influence future development and use of medications. One example of how pharmacogenetic testing has changed medication therapy is codeine use in young children. For codeine to relieve pain, it must be converted to morphine by an enzyme known as CYP2D6. This enzyme is commonly tested in pharmacogenetics panels.

People can metabolize

CYP2D6 enzyme medications at different speeds. It was determined that if children are ultrarapid metabolizers, they convert codeine to morphine too quickly, resulting in morphine overdose that can be fatal. As a result, federal guidelines were changed for the use of codeine in children under

12 and in certain adolescents 12 to 18 who have breathing problems.

One misconception is that pharmacogenetic testing is the same as allergy testing. Although there is some overlap, the body systems involved overall differ. Allergy testing looks at the immune system’s reaction to a foreign substance. It is important to speak to your health care provider about concerns if you believe you are allergic to a medication, but there still may be value in additional testing.

Speak with your health care provider or pharmacist to learn more. — Michael Schuh, Pharm.D., R.Ph., Pharmacy, Mayo Clinic, Jacksonville, Florida

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