Pharmacokinetics of regadenoson infused for 12 hours during stage 1. Plasma concentrations of regadenoson were measured at 0, 1, 6, 12, and 18 hours. Dose level 0 was 0.24 μg/kg/h (white boxes), dose level 1 was 0.60 μg/kg/h (hatched boxes), and dose level 2 was 1.44 μg/kg/h (dark gray boxes).