GSTM1 and Decreased liver function: - Active bleeding/high risk of bleeding- eGFR <50 mL/min/1.73 m2 (12–18 years) or eGFR <80 mL/min/1.73 m2 (0–12 years) or dialysis- Liver dysfunction with active hepatitis A, B or C or ALT, AST or AP > 3 × ULN- Prosthetic heart valve (that requires AC)- Active infective endocarditis- Hb <8 g/dL or Plt <80 × 109/L- Use with P-glycoprotein inducers (e.g., rifampin)- Use with P-glycoprotein inhibitors (e.g., azole-antimycotics or HIV protease inhibitors) not studied