Cytochrome P450 2C19 (CYP2C19) and Medicines

What is CYP2C19?

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 2C19 (known as CYP2C19) enzymes break down several commonly used medicines. These medicines include: 

• Clopidogrel (used to prevent blood clots)
• Voriconazole (used to treat or prevent fungal infections)
• Some medicines used for depression (such as amitriptyline, citalopram, escitalopram, imipramine, and sertraline)
• Some medicines used to treat stomach ulcers and reduce stomach acid (such as omeprazole, pantoprazole, and lansoprazole)

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 CYP2C19 gene is a section of DNA that instructs how well CYP2C19 enzymes will work.

The study of how genes like CYP2C19 affect the way your body interacts with medicines is called pharmacogenomics. Differences in your DNA that make up the CYP2C19 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 CYP2C19 enzyme will work. The test results can help your doctor and pharmacist choose the correct type or dose of medicine to give you.

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

After pharmacogenomic testing

Results of your CYP2C19 test will place you into 1 of 6 CYP2C19 gene groups:

• Ultra-rapid metabolizer: People in this group have very high activity of CYP2C19 enzymes. About 9% (9 in 100) of people are in this group.
• Rapid metabolizer: People in this group have a slightly higher activity of CYP2C19 enzymes. About 21% (21 in 100) of people are in this group.
• Normal metabolizer: People in this group have normal working CYP2C19 enzymes. About 38% (38 in 100) of people are in this group.
• Intermediate metabolizer: People in this group have lower than normal CYP2C19 enzyme function. They break down some medicines more slowly. About 27% (27 in 100) of people are in this group.
• Poor metabolizer: People in this group have little or no active CYP2C19 enzymes. People who are poor metabolizers break down some medicines slowly and are likely to need a different dose or different type of medicine. About 3% (3 in 100) of people are this group.
• Indeterminate phenotype: A small number of people will have unknown function of their CYP2C19 enzyme based on their test. About 2% (2 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 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.