Warfarin

Pharmacogenomic Information in the Context of the FDA-Approved Drug Label*

The FDA recommends genetic testing prior to initiating treatment with warfarin.

Excerpt from the warfarin drug label:

The patient's CYP2C9 and VKORC1 genotype information, when available, can assist in selection of the starting dose. Table 5 describes the range of stable maintenance doses observed in multiple patients having different combinations of CYP2C9 and VKORC1 gene variants. Consider these ranges in choosing the initial dose.

The VKORC1:G-1639A polymorphism is associated with lower dose requirements for warfarin in Caucasian and Asian patients. Increased bleeding risk and lower initial warfarin dose requirements have been associated with the CYP2C9*2 and CYP2C9*3 alleles. Approximately 30% of the variance in warfarin dose could be attributed to genetic variation in VKORC1, and about 40% of dose variance could be explained taking into consideration both VKORC1 and CYP2C9 genetic polymorphisms. Accounting for genetic variation in both VKORC1 and CYP2C9, age, height, body weight, interacting drugs, and indication for warfarin therapy explained about 55% of the variability in warfarin dose.

See the Warfarin drug label PDF for the complete drug label text with sections containing pharmacogenetic information highlighted. Pharmacogenomics-related dosing information is found in Table 5 on page 27.

Pharmacogenomic Diagnostic Testing

The information below is provided for educational purposes only and does not constitute an endorsement of any listed test or manufacturer.

¹ Entries in this column link to test manufacturer's website.
² Information in this column was found using searches of the entire FDA website (http://www.fda.gov/search.html), searches of the FDA CDRH CLIA database (http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfClia/Search.cfm), or searches of the FDA CDRH Premarket Approval Database (http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfPMA/pma.cfm).

Table updated 4/15/2009.

Related PharmGKB Resources