Patient enrollment and study flow diagram. The diagram shows the flow and disposition of patients in the trial. Following screening, 63 subjects were enrolled in the study. All subjects who had not previously undergone PK analysis of rIX-FP in a previous study participated in PK evaluation of 25 IU/kg (n = 6) or 50 IU/kg rIX-FP (n = 46). A subset of subjects (n = 13) also participated in a PK evaluation of their previous FIX product (pdFIX or rFIX). A subset of subjects (n = 15) repeated PK analysis of 50 IU/kg rIX-FP at approximately week 26. Subjects were assigned either weekly prophylaxis (group 1) or on-demand treatment (group 2) with rIX-FP, based on their prior treatment regimen. Eight subjects discontinued from the study for the following reasons: AEs (n = 2), subject decision (n = 2), lost to follow-up (n = 3), and protocol violation (n = 1, unwillingness to switch to prophylaxis after on-demand treatment).