Due to limited solubility and poor ionization of bilirubin and its glucuronide, the formation of estradiol 3-glucuronide was used as a surrogate to assess UGT1A1 activity, while the transport of pitavastatin, CDCF, and taurocholate were used as surrogate probe substrates to monitor the function of OATP1B1/OATP1B3, MRP2, and BSEP, respectively