In the case of [ 18 F]1c, the pre-injection of highly plasma protein-bound suvorexant may have led to an increase in the free fraction of [ 18 F]1c in the blood, so that the observed increased initial brain uptake of [ 18 F]1c could be explained. This was not the case for However, cyclosporine A is metabolized by CYP3A4 , which is also the most important enzyme for the metabolism of suvorexant , thereby most likely influencing the plasma levels of [ 18 F]1c and [ 18 F]1f to increase apparent brain uptake.