Hypothesis: We hypothesize that warfarin dose requirement could be more accurately predicted using a simplified genotyping procedure requiring the identification of a single CYP2C9 allele and a single nucleotide polymorphism of VKORC1 to discern between the 2 major haplotypes H1 and H7.

Aims: The aim is to compare the clinical benefits of genetics-guided dosing versus traditional trial and error dosing with protocol guided-adjustments.

Two secondary objectives are (1) to prospectively evaluate a dosing algorithm built on demographics and genetic predictors; (2) to assess the feasibility of a simplified test for CYP2C9*3 and VKORC1 SNP in clinical practice.

Methodology: A randomized controlled trial targeted at accruing 100 patients with indication for wafarin therapy. The endpoint for comparing genetics-guided dosing against traditional dosing method at the anticoagulant clinic is the number of dosage titrations to achieve targeted International Normalized Ratio (INR) at 1, 2 and 3 months of initializing warfarin. Upon reaching steady-state, pharmacokinetics of warfarin R- and S-isomers will be assessed for correlation with dose requirements based. An assay for easy identification of genetic polymorphisms required in this dosing regimen in a clinic setting will also be validated.

Significance: This concerted, multi-disciplinary effort to bring pharmacogenetics-based therapy from bench to bedside has the potential to reduce the efforts incurred with multiple dose titrations of the most commonly prescribed oral anticoagulant. With the aid of mathematical modeling, a simplified and more cost-effective genotyping method could be implementation for the future treatment and prophylaxis of thromboembolic diseases.