Impact of CYP2C9 genetic polymorphism on warfarin dose requirements in Pakistani population.

Variations of cytochrome-P450 enzyme system (CYP2CP) are associated with impaired metabolism of warfarin. The objective of our study was to estimate the frequency of genetic and allelic variants of CYP2C9 in Punjabi population of Pakistan and their effects on warfarin dose requirement. One hundred and twenty unrelated Pakistani subjects belong to Punjab province, were randomly included from the registry of National Institute of Heart Disease Rawalpindi, Pakistan. The patients had stable international normalized ratio (INR) of 2 to 3 for last 3 months with warfarin therapy after heart valves replacement. The detection of CYP2C9 variant was done on polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay. Total 120 patients (73 males; 47 females) of mean age of 37 years participated in the study. Nine patients had mutant allele CYP2C9*3 (7.5%), one CYP2C9*2 (0.8%) and 110 patients exhibited wild type CYP2C9*1 (91.7%). The frequency of CYP2C9 genotype was *1/*1 (0.858) ; *1/*3 (0.117) ; 2/*20 (0.08 ) and *3/*3 (0.017) in our study population. A high dose of warfarin (42.2+9.56) mg/week is required for patients with *1/*1 genotype as compared to patients with *2/*2 (17.5+1.9) and *1/*3 (16.6+2.3) allele (p<0.001). Individuals with CYP2C9*3/3* need lowest (8.75±1.76 mg/week) daily warfarin dose. In conclusion, the genetic variations in the CYP2C9 occur in 14% of Punjabi ethnic group in Pakistan. Presence of CYP2C9*2 or *3 variants is an independent predictor of low warfarin dose requirement in our patients. CYP2C9 variants assay may be used in high risk groups for appropriate dose adjustment to avoid complications on long term basis.