When you take a medicine (drug), your body has to have a way to handle the medicine. One way is for enzymes to metabolize (break down) the medicine. A family of enzymes called cytochrome P450s have the ability to break down certain medicines. By metabolizing a medicine, cytochrome P450 enzymes make the medicine either more or less active, depending upon the medicine. Cytochrome P450 3A5 (CYP3A5) is part of the cytochrome P450 family of proteins in the body. It is responsible for breaking down medicines, some of which are used after receiving a transplant.
DNA is like a set of instructions for your body that can help decide how well your enzymes will work. Each person differs from another at the DNA (gene) level. This means that each person has small differences in the genes that code for enzymes. The part of DNA that instructs how well CYP3A5 enzymes will work is called the CYP3A5 gene. The study of how genes like CYP3A5 affect the way you break down and respond to medicines is called pharmacogenetics (FAR mah coh je NEH tiks).
Differences in your DNA that make up the CYP3A5 gene can change how well you are able to remove certain medicines from your body. By testing your DNA (with a pharmacogenetic test), we may find differences that can allow us to predict how well your CYP3A5 enzyme will work. The results of this test will help your doctor choose the correct dose of medicine to give you.
The results of your CYP3A5 pharmacogenetic test will likely place you into one of three groups:
- High Risk CYP3A5 metabolizers: high risk means there is a recommended change to a medicine based upon the CYP3A5 gene.
- Normal metabolizer – This means there are two normal function copies of the CYP3A5 gene. People in this group have an active CYP3A5 enzyme. Your doctor may need to increase your dose of a medication if you are a CYP3A5 normal metabolizer. About 20 percent of African Americans are CYP3A5 normal metabolizers. Less than 1 percent of people of European descent are CYP3A5 normal metabolizers.
- Intermediate metabolizer – This means there is one normal function copy of the gene and one decreased function copy of the CYP3A5 gene. People in this group have working CYP3A5 enzymes, but they are less active than normal metabolizers. Your doctor may need to increase your dose of a medication if you are a CYP3A5 intermediate metabolizer. About 50 percent of African Americans are CYP3A5 intermediate metabolizers. Only 15 percent of people of European descent are CYP3A5 intermediate metabolizers.
- Low risk CYP3A5 metabolizer: low risk means there is no recommended change to a medicine based upon the CYP3A5 gene.
- Poor metabolizer – This means there are two copies of a decreased function CYP3A5 gene which results in poor CYP3A5 enzyme function. Medicines do not require a change in dose in patients who are poor metabolizers of CYP3A5, because most medicines were developed in CYP3A5 poor metabolizers. About 30 percent of African Americans are CYP3A5 poor metabolizers while 85 percent of people of European descent are CYP3A5 poor metabolizers.
Scientists continue to find new information about which medicines are affected by gene test results. For details about which medicines are broken down by CYP3A5, please go to www.stjude.org/pg4kds or www.pharmgkb.org.
If you have questions about pharmacogenetic testing at St. Jude, call one of the Pharmaceutical Sciences research nurses at 901-595-2482 or email firstname.lastname@example.org. If you are calling from outside of the Memphis area, dial toll free 1-866-2ST-JUDE (1-866-278-5833), then dial extension 2482.
This document is not intended to take the place of the care and attention of your personal physician or other professional medical services. Our aim is to promote active participation in your care and treatment by providing information and education. Questions about individual health concerns or specific treatment options should be discussed with your physician.
St. Jude complies with health care-related federal civil rights laws and does not discriminate on the basis of race, color, national origin, age, disability, or sex.
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