Table 1. The predicted CYP2C19 metabolic status (genotype) vs actual CYP2C19 activity (phenotype) in cancer patients.

Genotype		Phenotype
Alleles	Predicted metaboliser status	Extensive metaboliser (log OMP HI<1)	Poor metaboliser (log OMP HI>1)
wt/wt or wt/var	Extensive metaboliser	19	11
var/var	Poor metaboliser	0	1

There was a significant discordance between CYP2C19 genotype and phenotype (McNemar's test P<0.0005).

Two patients with wt/wt genotype had no detectable drug or metabolite in plasma and hence could not be phenotyped and were not included in this comparison.