A phase I pharmacokinetics trial comparing PF-05280586 (a potential biosimilar) and rituximab in patients with active rheumatoid arthritis

Aims: Pharmacokinetic (PK) similarity was assessed among PF‐05280586 (a proposed biosimilar) vs. rituximab sourced from the European Union (rituximab‐EU) and the United States (rituximab‐US). Pharmacodynamics (PD), overall safety and immunogenicity were also evaluated. Methods: Patients with active rheumatoid arthritis on a background of methotrexate and inadequate response to one or more tumour necrosis factor antagonist therapies were randomized to intravenous PF‐05280586, rituximab‐EU or rituximab‐US 1000 mg doses on study days 1 and 15. Results: A total of 220 patients were randomized to receive study treatment as assigned. Of these, 198 met per‐protocol population criteria for inclusion in the PK data analysis. PF‐05280586, rituximab‐EU and rituximab‐US exhibited similar PK profiles following administration of assigned study drug on days 1 and 15. The 90% confidence intervals of test‐to‐reference ratios for Cmax, AUCT, AUC0–∞ and AUC2‐week were within the bioequivalence margin of 80.00–125.00% for comparisons of PF‐05280586 with rituximab‐EU, PF‐05280586 with rituximab‐US, and rituximab‐EU with rituximab‐US. All treatments resulted in a rapid and profound reduction in CD19+ B cells and sustained profound B cell suppression up to week 25. The incidence of antidrug antibody (ADA) response (n = 7, 10 and 9 for PF‐05280586, rituximab‐EU and rituximab‐US, respectively), time to ADA emergence and ADA titres were similar across treatments. None of the ADA‐positive samples was positive for neutralizing activity. No clinically meaningful differences in adverse events were identified. Conclusions: The study demonstrated PK similarity among PF‐05280586, rituximab‐EU and rituximab‐US. In addition, all treatments showed comparable CD19+ B cell depletion PD responses, as well as safety and immunogenicity profiles