The pharmacist considered the possibility that the decrease in vitamin K intake due to anorexia for 1 week and the change from bosentan to macitentan may have resulted in prolongation of PT-INR, because bosentan discontinuation cancels CYP2C9 and CYP3A4 enzyme induction, and requested the physician to measure the patient’s PT-INR. The gene discussed is CYP3A4; the disease is Anorexia.