ABCG2 and atrial fibrillation: On the one hand, studies by Ueshima S. et al. (2017, 2018) demonstrated a positive association of ABCG2 rs2231142 and CYP3A5*3 rs776746, in combination with renal function, with the concentration-to-dose ratio of apixaban in Japanese patients with atrial fibrillation [10,11].