Cytochrome P450 2C9 (CYP2C9)

PG4KDS Implemented Genes

CYP2C9 is an enzyme that is responsible for breaking down (metabolizing) several of the drugs that are commonly used today. Some medications, such as celecoxib, warfarin, and phenytoin require CYP2C9 in order for the medication to be metabolized to forms that are not active and are more easily eliminated from the body. There are other medications that may be affected by CYP2C9.

Many differences exist in the CYP2C9 gene. These differences in the CYP2C9 gene lead to the production of an enzyme with normal to no function. A system designed to classify patients into 3 metabolizer categories based on the ability of their CYP2C9 to break down drugs is used by clinicians to help guide drug therapy decisions.

Priority CYP2C9 genotypes

  • Poor metabolizers – These patients have little or no working CYP2C9. About 2 percent of people are poor metabolizers.
    • Drugs that may need to be avoided or have their doses decreased:
      • Celecoxib. Blood levels of celecoxib are expected to be high in poor metabolizers of CYP2C9, and side effects (such as gastrointestinal bleeding) may be more likely. If celecoxib is used in these patients, lower starting doses may be needed.
  • Other drugs may be affected, including warfarin and phenytoin.

Routine genotypes. Most CYP2C9 medicines don’t need to be adjusted based on the following genotypes:

  • Intermediate metabolizers – These patients metabolize drugs at a rate somewhere between the poor and normal metabolizers. About 25 percent of people are intermediate metabolizers.
  • Normal metabolizer – These patients have normal CYP2C9 function. About 73 percent of people are normal metabolizers.

More information for patients

More information for healthcare 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.