Cytochrome P450 3A5 (CYP3A5) and Medicines

What is CYP3A5?

When you take a medicine, your body needs a way to handle it. One way your body does this is by using enzymes to break down (metabolize) the medicine. A family of enzymes called cytochrome P450 breaks down certain medicines. Enzymes make a medicine more or less active, depending on the specific medicine.

Cytochrome P450 3A5 enzymes, known as CYP3A5, break down some medicines, such as tacrolimus (a medicine used after a bone marrow transplant or solid organ transplant).

How pharmacogenomic testing works

Each person differs from another at the DNA level. Genes are segments of DNA that act as a set of instructions and tell the body how to work. The CYP3A5 gene is a section of DNA that instructs how well CYP3A5 enzymes will work.

The study of how genes like CYP3A5 affect the way your body interacts with medicines is called pharmacogenomics. Differences in your DNA that make up the CYP3A5 gene can affect how well you are able to break down certain medicines.

If you break down a medicine too fast or too slow, the medicine may not work as well, or you may have more side effects. A pharmacogenomic test looks for differences that can help your medical team know how well your CYP3A5 enzyme will work. The test results can help your doctors and pharmacists choose the correct dose of medicine to give you. 

Please share your pharmacogenomic test results with all your new doctors and pharmacists.

After pharmacogenomic testing

The results of your CYP3A5 test will place you into 1 of 3 CYP3A5 gene groups:

• Normal metabolizer: People in this group have normal working CYP3A5 enzymes. People who are normal metabolizers have active enzymes and may need a higher dose of certain medicines. About 8% (8 in 100) of people are in this group.
• Intermediate metabolizer: People in this group have working CYP3A5 enzymes, but they are less active than normal metabolizers. They may need a higher dose of some medicines. About 25% (25 in 100) of people are in this group.
• Poor metabolizer: People in this group have little or no active CYP3A5 enzymes. In most cases, people who are poor metabolizers do not need a change in dose because most medicines were developed in people from this group. About 67% (67 in 100) of people are in this group.

Scientists continue to find new information about which medicines are affected by genes. Talk to your doctor or pharmacist if you have questions about your medicines, side effects, or pharmacogenomic testing.

Find more information about genes that are being used to make medication therapy decisions for patients at St. Jude.

If you have questions about pharmacogenomic testing done at St. Jude, you can email the Clinical Pharmacogenomics Program at pharmacogenomics@stjude.org.

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