However, the bioavailability of cyclosporine varies considerably depending on patient population this website (ranging from <10% in liver transplant patients to 89% in some kidney transplant patients).18 Therefore, the effect of telaprevir on cyclosporine concentrations in liver transplant patients may differ from that observed in this healthy volunteer study, and close monitoring of cyclosporine concentrations to guide individual dose adaptations would be necessary

during coadministration. The decrease in hepatic clearance and increase in t½ of both cyclosporine and tacrolimus upon telaprevir coadministration suggests that systemic clearance of these immunosuppressants was also reduced by telaprevir. The effect of telaprevir on hepatic transporters that could have contributed to lower clearance or enhanced absorption is unknown. Notably, in this study the effect of steady-state telaprevir on the PK of cyclosporine or tacrolimus was evaluated only at single doses of these immunosuppressants.

Because the elimination half-lives increased significantly for both cyclosporine and tacrolimus when telaprevir was coadministered, without proper adjustment of dose and dosing interval of these immunosuppressants, further increases in blood exposure may occur when multiple doses of these drugs are coadministered with telaprevir. However, studies of telaprevir with multiple doses of cyclosporine and tacrolimus have not been performed. The effects of

telaprevir on cyclosporine and tacrolimus C59 wnt exposure were similar to that reported for human immunodeficiency virus (HIV) protease inhibitors known to be potent CYP3A inhibitors, where significant reductions in dose and/or dosing interval of immunosuppressants were needed to achieve the desired range of trough concentrations, based on frequent monitoring of trough concentrations of the immunosuppressants.25 For example, addition of lopinavir/ritonavir (n = 7 patients) reduced tacrolimus Non-specific serine/threonine protein kinase dose by 99% to maintain tacrolimus concentrations within the therapeutic range.26 Similarly, during coadministration of Highly Active Antiretroviral Therapy (HAART) regimens with ritonavir-boosted HIV protease inhibitors, daily cyclosporine doses were reduced by 80%-95% to maintain cyclosporine exposure at pre-HAART levels. Because of the flat absorption/elimination profiles of cyclosporine during combination with ritonavir-boosted HAART therapy, cyclosporine exposure could be reliably monitored long-term by measuring cyclosporine trough concentrations.27 Treatment of posttransplant patients coinfected with HIV/HCV with antiretrovirals and telaprevir could be even more challenging, depending on the drugs involved. Telaprevir levels are not significantly affected by ritonavir28; however, whether the net effect of antiretroviral drugs on cyclosporine and tacrolimus PK would be similar or different is hard to predict, as these drugs may have their own effects.