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Personalizing Your Medicine

Pharmacogenomics, also called pharmacogenetics, is the study of how genes affect each person’s response to medications. Based on the genes you have, doctors can predict what medication and dose will work best for you—and cause the fewest side effects. Previously, medications were administered with a one size fits all approach, meaning that each person received the same medication at common doses for a particular medical condition. Pharmacogenomic testing allows doctors to prescribe medications  and doses that offer the best chance of controlling or curing your medical condition.  

What are genes?
Your body has a set of instructions called DNA that tells it how to work to build protein molecules. Pharmacogenomics looks at variations in genes for proteins that influence medication responses. Every cell in your body has a DNA molecule, which is made up of genes. Your genes are different from everyone else’s genes.

What is pharmacogenomic testing?
Pharmacogenomic testing shows your unique genetic makeup. This allows doctors to select the best medication and dose based on your genetic information. Not all pharmacogenomic tests are covered yet by insurance so make sure you discuss the benefit and need with your physician.

One example of using pharmacogenomic testing involves people infected with HIV. Doctors routinely test HIV-infected patients for a variation of a gene that causes a bad reaction to the antiviral medication abacavir (Ziagen).

Another example of using pharmacogenomic testing is with the breast cancer medication trastuzumab (Herceptin). This medication works only in certain women whose tumors have a particular genetic profile.

Patients with acute lymphoblastic leukemia often undergo pharmacogenomics testing before receiving the chemotherapy medication mercaptopurine (Purinethol) Some people are unable to process the medication and this can lead to severe side effects. Pharmacogenomics testing allows doctors to adjust the standard dose of the medication so it won’t cause side effects.

How is pharmacogenomic testing done?
Pharmacogenomic testing can be done in several ways including a finger prick for a drop of blood or collecting saliva from your cheek. Some pharmacogenomic tests look for only one gene. This method is usually used when your doctor already knows that you may need a certain medicine that is influenced by a certain gene. Other pharmacogenomic tests look at how you may respond to several medications. If you ever need one of these medicines in the future, the results will be available ahead of time to help your doctors and pharmacists choose the best medicine or the best dose of a medicine for you.

How long do pharmacogenomic test results last?
Your genes do not change as you advance in age, which means that your pharmacogenomic test results will be applicable for life. It is important to save any pharmacogenomic test results that you have received, and share the results with your doctors and pharmacists.

By Cyrine-Eliana Haidar, Pharm.D., BCPS, BCOP, Clinical Pharmacogenetics Coordinator — St. Jude Children’s Research Hospital