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Background: rVIII-SingleChain, a novel recombinant factor VIII (rFVIII), has been designed as a B-domain truncated construct with covalently bonded heavy and light chains, aiming to increase binding affinity to von Willebrand factor (VWF). Preclinical studies confirmed greater affinity for VWF, giving improved pharmacokinetic and pharmacodynamic properties compared with full-length rFVIII. Aim: To investigate the pharmacokinetics of rVIII-SingleChain and compare them against those of full-length rFVIII. Methods: This study enrolled 27 patients with severe haemophilia A in the AFFINITY clinical trial programme. After a 4-day washout period, all patients received a single infusion of 50 IU kg À1 octocog alfa (Advate â ); after a ≥4-day postinfusion washout period, they received a single infusion of 50 IU kg À1 rVIII-SingleChain. Blood samples for pharmacokinetic assessments of each product were collected before infusion (predose) and at 0.5, 1, 4, 8, 10, 24, 32, 48 and 72 h postinfusion for both products. Results: rVIII-SingleChain had a longer mean half-life (t 1/2 ) (14.5 vs. 13.3 h), lower mean clearance (CL) (2.64 vs. 3.68 mL h À1 kg À1), higher mean residence time (20.4 vs. 17.1 h) and larger mean AUC inf (2090 vs. 1550 IU·h dL À1 ) than octocog alfa, respectively. The mean AUC inf after rVIII-SingleChain infusion was~35% larger than after octocog alfa. A similar pattern was observed for AUC 0-last . No serious adverse events or inhibitors were reported. Conclusions: rVIII-SingleChain has a favourable pharmacokinetic profile compared with octocog alfa and was well tolerated. The prolonged t 1/2 , larger AUC and reduced CL of rVIII-SingleChain may permit longer dosing intervals, thereby improving patient adherence to prophylactic treatment.

Summary Background Immune tolerance induction (ITI) in patients with congenital hemophilia A is successful in up to 70%. Although there is growing understanding of predictors of response to ITI, the probability and predictors of inhibitor recurrence following successful ITI are not well understood. Objectives To determine the association of clinical characteristics, particularly adherence to FVIII prophylaxis following ITI, with inhibitor recurrence in patients with hemophilia A who were considered tolerant following ITI. Methods In this multicenter retrospective cohort study, 64 subjects with FVIII level <2% who were considered successfully tolerant following ITI were analyzed to estimate the cumulative probability of inhibitor recurrence using the Kaplan-Meier method. The association of clinical characteristics with inhibitor recurrence was assessed using logistic regression. Results A recurrent inhibitor titer ≥ 0.6 BU/ml occurred at least once in 19 (29.7%) and more than once in 12 (18.8%). The probability of any recurrent inhibitor at 1 and 5 years was 12.8% and 32.5% respectively. Having a recurrent inhibitor was associated with having received immune modulation during ITI (OR 3.8, 95% CI: 1.2-22.4) and FVIII recovery of <85% at the end of ITI (OR 2.6, 95% CI: 1.3-5.9), but was not associated with adherence to post-ITI prophylactic FVIII infusion (OR=0.5, 95% CI: 0.06-4.3). Conclusions The use of immune modulation therapy during ITI and lower FVIII recovery at the end of ITI appear to be associated with an increased risk of inhibitor recurrence following successful ITI. Adherence to post-ITI prophylactic FVIII infusions is not a major determinant of recurrence.

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