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Cytochrome P450 2B6 (CYP2B6)

PG4KDS Implemented Genes

CYP2B6 is an enzyme that is responsible for breaking down (metabolizing) several medicines that are commonly used today. Medicines such as efavirenz and methadone are metabolized by CYP2B6 to forms that are not active and are more easily eliminated from the body. There are other medications that may be affected by CYP2B6.

Over 30 known differences exist in the gene for CYP2B6. These differences in the CYP2B6 gene result in an enzyme that ranges from completely inactive to overactive. A system designed to classify patients into metabolizer categories based on the ability of their CYP2B6 to break down medicines is used by doctors and pharmacists to help guide decisions about which medicines to use.

Priority CYP2B6 Phenotypes

  • Poor metabolizers – These patients have little or no working CYP2B6. About 10 percent of people are poor metabolizers.
    • Medicines that may need to be avoided or have their doses decreased:
      • Efavirenz. Blood levels of efavirenz are expected to be high in poor metabolizers of CYP2B6, and side effects may be more likely. If efavirenz is used in these patients, lower doses may be needed.
    • Medicines that may need close monitoring for side effects:
      • Methadone. There is a risk of methadone-induced QTc interval prolongation in these patients. If methadone is used in these patients, close cardiac monitoring may be needed.
    • Other medicines may be affected. The PG4KDS study will evaluate what should be done for the dosing of these other medicines.
  • Intermediate metabolizers – These patients metabolize drugs at a rate somewhere between poor and normal metabolizers. About 40 percent of people are intermediate metabolizers.
    • Medicines that may need to have their doses decreased:
      • Efavirenz. Blood levels of efavirenz are likely to be high in intermediate metabolizers of CYP2B6, and side effects may be more likely. If efavirenz is used in these patients, lower doses may be needed.
    • Other medicines may be affected. The PG4KDS study will evaluate what should be done for the dosing of these medicines.

Routine phenotypes

Most CYP2B6 medicines don’t need to be adjusted based on the following genotypes:

  • Ultra-rapid metabolizers – These patients have greater-than-normal CYP2B6 function. Less than 1 percent of people are ultra-rapid metabolizers of CYP2B6.
  • Rapid metabolizers – These patients have slightly higher CYP2B6 function compared to normal. About 7 percent of people are rapid metabolizers.
  • Normal metabolizer – These patients have normal CYP2B6 function. About 45 percent of people are normal metabolizers.

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.