Warfarin is a frequently prescribed anticoagulant in rehabilitation patients. 
Adverse drug reactions of warfarin were reported as bleeding and cutaneous 
microvascular thrombosis. Major bleeding, such as intracranial hemorrhage and 
psoas hematoma, in patients receiving anticoagulation therapy is a rare 
condition, but sometimes very serious complication that can even be fatal. 
Patient-specific factors (eg, age, body size, race, concurrent diseases, and 
medications) explain some of the individual variability in warfarin dose, but 
genetic factors, which influence warfarin response, explain a significantly 
higher proportion of the variability in the dose. There are two identified genes 
that are responsible for the main proportion of the genetic effect: CYP2C9, 
which codes for the enzyme cytochrome P450 2C9 that metabolizes S-warfarin, and 
VKORC1, which codes for warfarin's target, vitamin K epoxide reductase. We 
report a case of intolerance to warfarin dosing, due to impaired drug metabolism 
in a patient with CYP2C9(*)1/(*)3 and VKORC 1173TT. Fortunately, there are no 
severe complications.