Case report on Pharmacogenetic guided warfarin dosing in a postoperative valve replacement patient

Patient underwent mitral valve replacement with mechanical valve and was initiated on oral anticoagulation with standard dose of warfarin. She developed supra therapeutic INR levels. Genotyping of CYP2C9 and VKORC1 encoding genes revealed homozygous variation of CYP2C9*3*3 and heterozygous variation of VKORC1 G>A making her hypersensitive to warfarin. Based on this study result and Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline, a low dose of warfarin (0.5mg per day) was prescribed, to achieve a therapeutic INR of 2.5 to 3.5 and adverse drug effects were avoided.