The reason for the dose reduction to 75 mg twice daily varied from case to case; however, almost all of the patients on the very low-dose in this study were older than 70 years except for 3 patients, and some of them had aPTT prolongation, minor bleeding such as anemia or bloody stool, or renal dysfunction, or were on the combination of dabigatran and an antiplatelet drug or a P-glycoprotein inhibitor. Here, ABCB1 is linked to anemia.