St. Jude Research
PG4KDS Implemented Genes

Cytochrome P450 3A5 (CYP3A5)

CYP3A5 is an enzyme that helps to break down (metabolize) some medications in the body. Tacrolimus is a common immunosuppressive medication used to prevent rejection in patients who have received a transplant. Tacrolimus is broken down by CYP3A5 and other enzymes in the body. Differences in the CYP3A5 enzyme function, caused by differences in the CYP3A5 gene, can mean that one person can remove tacrolimus from their body faster than another person.

At least nine differences in the CYP3A5 gene have been identified that can result in an enzyme with normal to no function. Patients who are tested for CYP3A5 can be classified into groups of enzyme function. Knowing the CYP3A5 enzyme function that an individual has can help clinicians make drug therapy decisions to attempt to decrease side effects and improve how well the medication will work. Clinicians will still need to monitor tacrolimus levels in the blood even if the CYP3A5 enzyme function is known.  

Priority CYP3A5 genotypes

Normal metabolizers - These patients have normal CYP3A5 enzyme function. Approximately 20% of African Americans are CYP3A5 normal metabolizers while less than 1% of individuals of European descent are CYP3A5 normal metabolizers.

  • Drugs that need a dose adjustment:
    • Tacrolimus. Blood levels of tacrolimus are expected to be lower in individuals with normal CYP3A5 enzyme function because more of the enzyme is available to break down the drug. This means you may need a higher dose of tacrolimus.

Intermediate metabolizers - These patients have more CYP3A5 enzyme function than poor metabolizers, but less CYP3A5 enzyme function than normal metabolizers. Approximately 50% of African Americans are CYP3A5 intermediate metabolizers while only 15% of individuals of European descent are CYP3A5 intermediate metabolizers.

  • Drugs that need a dose adjustment:
    • Tacrolimus. Blood levels of tacrolimus may also be lower in individuals with intermediate CYP3A5 enzyme function.  This means you may need a higher dose of tacrolimus.

Routine genotypes

Most CYP3A5 medicines do not need to be adjusted based on the following genotypes:

Poor metabolizers - These patients have little to no CYP3A5 enzyme function. Approximately 30% of African Americans are CYP3A5 poor metabolizers while 85% of individuals of European descent are CYP3A5 poor metabolizers.

  • No changes in the dose of tacrolimus are recommended based upon this enzyme function  

More information

For patients

If you have questions or concerns about pharmacogenomic testing done at St. Jude, you can email the Clinical Pharmacogenomics Program at pharmacogenomics@stjude.org, or call one of the Pharmaceutical Sciences Research Nurses at 901-595-2482. 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.

For health care professionals

Legal Disclaimer: This page is intended to provide implementers with guidance on establishing a clinical pharmacogenetic program at their institution. Information contained on this page is for information and educational purposes only. Although reasonable efforts have been made to ensure that the information provided on this page is current, complete and, where appropriate, based on scientific evidence, St. Jude Children's Research Hospital makes no assurances as to whether the provided information will at all times be current or complete. St. Jude Children's Research Hospital, in offering this document, is not providing medical advice or offering a consultative opinion, and is not establishing a treatment relationship with any given individual. You, therefore, should not substitute information contained herein for your own professional judgment, nor should you rely on information provided herein in rendering a diagnosis or choosing a course of treatment for a particular individual.