A prospective surveillance study of inhibitor development in haemophilia A patients following a population switch to a third-generation B-domain-deleted recombinant factor VIII.

INTRODUCTION: Following a provincial tender, most subjects with haemophilia A in Quebec switched their treatment to a third-generation recombinant B-domain-deleted factor VIII (FVIII).

AIM: Our objective was to evaluate the incidence of inhibitor development and FVIII recovery in patients following the switch of factor replacement therapy.

METHODS: One hundred and thirty-five subjects were enrolled and tested for FVIII activity and inhibitors every 6 months during 1 year. Subjects with mild haemophilia A or current inhibitors were excluded. Data on demographics, bleeds and FVIII usage were collected.

RESULTS: A total of 125 switchers and 10 non-switchers were enrolled. Most subjects had severe haemophilia A (95.6%) and were on prophylaxis (89.6%). Mean FVIII recovery was similar at 0, 6 and 12 months postswitch. Two switchers developed de novo inhibitors in the 6 months postswitch, one of which was transient. No recurrent inhibitor was observed. A small but significant increase in FVIII usage was observed for adult switchers and the whole cohort of switchers and non-switchers. There was an increase in the annualized bleeding rate (ABR) for non-joint bleeds for the whole cohort of switchers. However, no significant differences were observed in ABR for joint bleeds.

CONCLUSION: Our surveillance study shows comparable inhibitor development to similar published studies. A significant increase in FVIII utilization was noted for the whole cohort, switchers and non-switchers. Lastly, no clinically significant changes were observed in ABR for joint bleeds, but a difference for non-joint bleed ABRs was observed in switchers.