A Population Pharmacokinetic/Pharmacodynamic Analysis of Regadenoson, an Adenosine A_2A-Receptor Agonist, in Healthy Male Volunteers

Results: Adverse events were more prevalent at regadenoson doses above 3 μg/kg, and the increase in the occurrence of adverse events was dose-related. Most of the adverse events were related to vasodilation and an increase in heart rate and were generally of mild to moderate severity. Based on the severity and frequency of adverse events, the maximum tolerated doses of regadenoson were deemed to be 10 μg/kg in the standing position and 20 μg/kg in the supine position. The pharmacokinetics of regadenoson were successfully described by a three-compartment model with linear clearance. Following intravenous bolus dose administration, regadenoson was rapidly distributed throughout the body, followed by relatively slower elimination (terminal elimination half-life of approximately 2 hours). The clearance was estimated to be 37.8 L/h, with renal excretion accounting for approximately 58% of the total elimination. The volume of distribution of the central compartment and the volume of distribution at steady state were estimated to be 11.5L and 78.7L, respectively. Individual pharmacokinetic parameter estimates were fixed in the pharmacodynamic model, where changes in heart rate were related to plasma drug concentrations using a Michaelis-Menten model. The maximum heart rate increase (E_max) and plasma regadenoson concentration causing a 50% increase in the maximum heart rate (EC50) were estimated to be 76 beats per minute and 12.3 ng/mL, respectively. None of the tested covariates was found to be correlated with any of the pharmacokinetic model parameters.