Evaluation of the absolute bioavailability of pegylated interferon alfa-2a after subcutaneous administration to healthy male volunteers: an open-label, randomized, parallel-group study.

Background: Interferon (IFN)-based therapy is the recommended treatment for hepatitis C virus. Because pegylated IFN (PEG-IFN) alfa-2a is administered subcutaneously, it is of interest to determine the proportion of the dose that is absorbed from the subcutaneous (SC) tissue and ultimately reaches systemic circulation.

Objective: The goal of this study was to characterize the absolute bioavailability of PEG-IFN alfa-2a (40 kDa) after SC dosing (180 μg) and to evaluate the pharmacokinetics of PEG-IFN alfa-2a after intravenous (IV) and SC administration.

Methods: In this parallel-group study, 18 participants were given a single IV dose of PEG-IFN alfa-2a 90 μg and 18 participants received PEG-IFN alfa-2a 180 μg SC. Serum concentrations of PEG-IFN alfa-2a were measured predose and serially until 312 hours after the first dose. Pharmacokinetic parameters (CL/F, volume of distribution, C(max), and T(max)) were estimated using noncompartmental methods. Bioavailability was calculated by using the following formula: (AUC(SC)/AUC(IV)) · (dose(IV)/dose(SC)).

Results: Eighteen healthy males received IV PEG-IFN alfa-2a, and an additional 18 healthy males received SC PEG-IFN alfa-2a. Subjects in each group had comparable mean weight, height, and body mass index. After IV administration of PEG-IFN alfa-2a (90 μg), there was a slow decline in serum concentration, the mean rate of systemic clearance was low at 126 mL/h, and the estimated mean volume of distribution at steady state was 9 L. After SC administration of PEG-IFN alfa-2a 180 μg, absorption was sustained, with mean T(max) occurring 102 hours after administration. The mean absolute bioavailability was 84%. A higher rate of influenza-like symptoms was observed after IV administration, along with decreased neutrophil counts, compared with subjects who underwent SC dosing.

Conclusions: Approximately 84% of a SC-administered dose of PEG-IFN alfa-2a reached the systemic circulation in these male healthy volunteers. The slow absorption, restricted distribution, and slow elimination of PEG-IFN alfa-2a resulted in sustained serum levels throughout the 7-day dosing interval.