Population pharmacokinetics of subcutaneous C1-inhibitor for prevention of attacks in patients with hereditary angioedema.

BackgroundLong-term prophylaxis with subcutaneous (SC) administration of a highly concentrated plasma-derived C1-esterase inhibitor (C1-INH) formulation was recently approved by the Food and Drug Administration for hereditary angioedema (HAE) attack prevention. ObjectiveTo characterize the population pharmacokinetics of C1-INH (SC) (HAEGARDA((R)); CSL Behring) in healthy volunteers and HAE patients, and assess the variability and influence of covariates on pharmacokinetics. MethodsC1-INH functional activity data obtained after administration of various C1-INH (intravenous; IV) and C1-INH (SC) doses from 1 study in healthy volunteers (n=16) and 2 studies in subjects with HAE (n=108) were pooled to develop a population pharmacokinetic model (NONMEM v7.2). Pharmacokinetic parameters derived from steady-state simulations based on the final model were also evaluated. ResultsC1-INH functional activity following C1-INH (SC) administration was described by a linear one-compartment model with first-order absorption and elimination, with inter-individual variability in all parameters tested. The mean population bioavailability of C1-INH (SC), and pharmacokinetic parameters for clearance (CL), volume of distribution, and absorption rate were estimated to be similar to 43%, 1.03mL/hour/kg, 0.05L/kg and 0.0146hour(-1), respectively. The effect of bodyweight on CL of C1-INH functional activity was included in the final model, estimated to be 0.74. Steady-state simulations of C1-INH functional activity vs time profiles in 1000 virtual HAE patients revealed higher minimum functional activity (C-trough) levels after twice-weekly dosing with 40IU/kg (similar to 40%) and 60IU/kg (similar to 48%) compared with 1000IU IV (similar to 30%). Based on the population pharmacokinetic model, the median time to peak concentration was similar to 59hours and the median apparent plasma half-life was similar to 69hours. Conclusions and Clinical RelevanceTwice-weekly bodyweight-adjusted dosing of C1-INH (SC) exhibits linear pharmacokinetics and dose-dependent increases in C-trough levels at each dosing interval. In this analysis, SC dosing led to maintenance of higher C-trough levels than IV dosing.