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CYP2C19 is one of the metabolizing enzymes involved in the metabolism of both R- and S-warfarin. The aim of this study was to investigate the association of CYP2C19 polymorphisms on the variability of stable warfarin doses in Thai patients. A total of 254 Thai patients with stable warfarin doses were enrolled in the study. Demographics and clinical data e.g. age, body mass index, and concomitant medications, were recorded. The single nucleotide polymorphisms in the CYP2C19*2 and CYP2C19*3 were detected from gDNA using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), while CYP2C19*17 was detected by using TaqManÒ allelic discrimination assay. The results showed that there were no significant differences in the mean stable warfarin doses after adjustment for confounding factors among those of four CYP2C19 metabolizer statuses including the extensive metabolizers (CYP2C19*1/*1 or CYP2C19*2/*17 or CYP2C19*3/*17), and the intermediate metabolizers (CYP2C19*1/*2 or CYP2C19*1/*3 genotypes), the poor metabolizers (CYP2C19*2/*2 or CYP2C19*2/*3 genotypes), and the rapid metabolizers (CYP2C19 *1/*17 genotype) (p > 0.05). In conclusion, the genetic polymorphisms of drug metabolizing enzyme CYP2C19 were not associated with the stable warfarin doses in Thai patients. In addition, CYP2C19 genotypes may not be a useful predictor of warfarin dose adjustments in clinical practice.
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