Cytochrome P450 2B6 (CYP2B6) and Medicines

What is CYP2B6?

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 2B6 enzymes, known as CYP2B6, break down several commonly used medicines. These medicines include efavirenz (used for certain infections) and methadone (used for pain management).

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 CYP2B6 gene is a section of DNA that instructs how well CYP2B6 enzymes will work.

The study of how genes like CYP2B6 affect the way your body interacts with medicines is called pharmacogenomics. Differences in your DNA that make up the CYP2B6 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 CYP2B6 enzyme will work. The test results can help your doctor and pharmacist choose the correct type or dose of medicine to give you.

CYP2B6 gene groups

The results of your CYP2B6 test will place you into one of five groups:

• Ultra-rapid metabolizer – People in this group have very high activity of CYP2B6 enzymes. About 1 in 1000 people are in this group.
• Rapid metabolizer – People in this group have high activity of CYP2B6 enzymes. About 4 in 100 people are in this group.
• Normal metabolizer – People in this group have normal working CYP2B6 enzymes. About 44 in 100 people are in this group.
• Intermediate metabolizer – People in this group have lower than normal CYP2B6 enzyme function. They break down some medicines more slowly. About 40 in 100 people are in this group.
• Poor metabolizer – People in this group have little or no active CYP2B6 enzyme. People who are poor metabolizers break down some medicines slowly and are likely to need a different dose or different type of medicine. About 10 in 100 people are this group.
• Indeterminate – A small number of people will have unknown function of their CYP2D6 enzyme based on their test. About 3 in 100 people are in 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 pharmacogenomics@stjude.org.