The pharmacokinetics and safety profiles of belimumab after single subcutaneous and intravenous doses in healthy Japanese volunteers

What is Known and Objectives Belimumab is a recombinant human monoclonal antibody that binds and antagonizes the biological activity of soluble B-lymphocyte stimulator (BLyS) protein. BLyS appears to play a role in the pathogenesis of systemic lupus erythematosus, and the biological profile of belimumab suggests that it may have a therapeutic benefit in the treatment for the disease. In this healthy Japanese subjects study, we investigated the pharmacokinetics and safety of a single subcutaneous and intravenous injection of belimumab administered as a 200 mg/mL liquid formulation. Methods This was an open-label, randomized, parallel-group, single-dose study in healthy Japanese subjects. Each subject received a single intravenous infusion or a subcutaneous injection of 200 mg belimumab. The pharmacokinetic parameters and safety parameters including local tolerance (injection site), biomarkers, immunogenicity and adverse events were evaluated up to 70 days post-dosing. Results After a single intravenous or a subcutaneous administration of 200 mg belimumab, all 16 subjects completed the study. There were no serious adverse events or adverse events related to injection site reactions. All seven adverse events were considered mild or moderate in intensity and deemed unrelated to belimumab except for cellulitis following intravenous administration. The bioavailability of the single subcutaneous dose of 200 mg belimumab in the subjects was estimated to be 77·5%. Time to the maximum serum concentration after subcutaneous injection was 6·5 days (median). The geometric mean terminal half-life was comparable between the two administration routes (17·7 days intravenous and 15·9 days subcutaneous). Serum immunoglobulin G level decreased slightly after each treatment. No subjects were found to produce antibelimumab antibodies. What is New and Conclusions A favourable absolute bioavailability in healthy Japanese subjects was seen following a subcutaneous injection of 200 mg belimumab. Considering the intersubject variability, exposures were consistent with those previously observed in healthy non-Japanese subjects. Safety and biomarker data were also consistent with previous non-Japanese clinical studies.