Investigating Subtherapeutic & Supratherapeutic INR

•  Full history regarding 

• Compliance
• Drugs
• Diet
• Associated medical conditions 

•  Plasma levels of Warfarin 

• Therapeutic levels 
• At specific intervals after administration 

• FII & FX assays 

• Pharmacogenetic analysis 

• P450 CYP2C9*2 and CYP2C9*3 polymorphism →↑ INR
• Missense mutations of VKORC1 gene CYP 2D6 & CYP2A6 →↓ INR
• Polymorphism in VKORC1 gene → Variable INR