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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. The enzymes make the medicine more or less active, depending on the specific medicine.

Cytochrome P450 3A5 enzymes, known as CYP3A5, break down some medicines, including medicines used after a bone marrow or solid organ transplant.

Pharmacogenomic testing

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.

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 doctor and pharmacist choose the correct dose of medicine to give you.

CYP3A5 gene groups

The results of your CYP3A5 test will place you into one of three 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 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 in 100 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 in 100 people are this group.

Scientists continue to find new information about which medicines are affected by gene test results. 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

Key points about CYP3A5

  • CYP3A5 is part of the cytochrome P450 family of enzymes that helps the body break down certain medicines.
  • A pharmacogenomic test can help your medical team know well your CYP3A5 enzyme will work.
  • Some people may need a change in medicine dose based on CYP3A5 enzyme activity.
  • Pharmacogenomic testing can help doctors and pharmacists know if you need a different dose or type of medicine.

Reviewed: September 2022