Table 6.

The CPIC Assignment of Likely CYP2C9 Phenotype Based on Genotype (2020)

CYP2C9 phenotypea,bActivity scoreGenotypeExamples of diplotypes
Normal metabolizer2An individual with 2 normal-function alleles*1/*1
Intermediate metabolizer1.5
1		An individual with one normal-function allele plus one decreased-function allele
OR one normal-function allele plus one no-function allele OR 2 decreased-function alleles		*1/*2
*1/*3
*2/*2
Poor metabolizer0.5
0		An individual with one no-function allele plus one decreased-function allele; OR
2 no-function alleles		*2/*3
*3/*3
a

Assignment of allele function and associated citations can be found at the CPIC website, also see (2).

b

See the CYP2C9 Frequency Table in refs. 3 and 4 from (2) for population-specific allele and phenotype frequencies.

Note: There are no known cases of CYP2C9 ultrarapid metabolizers

This CPIC table has been adapted from (2).

From: Phenytoin Therapy and HLA-B*15:02 and CYP2C9 Genotype

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