The 100-mg cyclosporine dose and the 2-mg tacrolimus dose were chosen as they were well tolerated in healthy volunteers in previous studies.23, 24 The doses of cyclosporine and tacrolimus were lowered when coadministered with telaprevir because of the potential for marked increase in cyclosporine and tacrolimus exposure. Dose-normalized cyclosporine exposure increased significantly when coadministered with telaprevir compared to administration of cyclosporine alone: the dose-normalized Cmax increased by approximately 1.3- to 1.4-fold, dose-normalized AUC increased by approximately 4.1- to 4.6-fold, and mean t½ of cyclosporine

increased approximately 4-fold following coadministration

of cyclosporine with either a single dose or steady-state telaprevir. Cyclosporine exposure Acalabrutinib cell line was comparable when administered with either a single dose of telaprevir (day 1, period 2) or when telaprevir reached steady-state (day 8, period 2), suggesting an absence of time-dependent inhibition of cyclosporine metabolism by telaprevir. The effect of telaprevir coadministration was much greater with tacrolimus: the dose-normalized Cmax increased by approximately 9.3-fold, dose-normalized AUC increased by approximately 70-fold, and the mean t½ of tacrolimus increased approximately 5-fold. Because of the long t½ of tacrolimus and the long time it STA-9090 cell line would take to wash out any effect of telaprevir on its PK, the interaction with tacrolimus was only evaluated with steady-state telaprevir. It is unknown whether the magnitude of the effect of telaprevir on tacrolimus would be similar after the first dose of telaprevir, as seen with cyclosporine. These results are significant and ifenprodil indicate that without understanding the adjustments required for dose

and/or dosing frequency of cyclosporine and tacrolimus, telaprevir coadministration could lead to serious or life-threatening adverse events. The mechanism for the greater effect of telaprevir on the PK of tacrolimus compared to cyclosporine is unknown, but may be related to lower bioavailability of tacrolimus (≈18%) in healthy volunteers,19 making it more susceptible to CYP3A and/or P-gp inhibition in the gut and during first-pass metabolism. This is also suggested by the 9.3-fold increase in the tacrolimus Cmax and the sharp decrease in the mean (SD) apparent volume of distribution (Vz/F) of tacrolimus from 1,910 (859) L when administered alone to 106 (34) L (Table 2) in the presence of telaprevir (i.e., an increase in oral bioavailability, F, without a proportional change in volume of distribution, Vz, may decrease the ratio, Vz/F closer to the reported value of Vz, corrected for F, in healthy volunteers of 1.94 L/kg19).