Pharmacokinetic Evaluation of a Newly Introduced Von Willebrand Factor Concentrate At Two London Haemophilia Centres

Abstract 3384

Introducing new factor concentrates in VWD patients is complicated by VWD subtype and PK variability. Wilate, a VWF concentrate with a 1:1 VWF: FVIII ratio and has not yet been widely used in the UK. We conducted PK studies with Wilate, to determine its efficacy, peak VWF activity and FVIII levels, and clearance in patients with VWD. Where feasible, we compared the data with previously used concentrate (Haemate-P) handling. 17 VWD patients (4 type 1, 6 type 2, 7 type 3) from two London Haemophilia centres were evaluated. The median age was 36 yrs (range 12– 67 yrs); sex M:F 6:11; mean body weight 73 kg (range 39–122 kg). Seven were blood group O, 1 group AB, 4 group A and 4 group B. The mean dose of Wilate administered was 44 iu/kg VWF: RiCoF (range 17–61). VWF activity, VWF antigen and FVIII levels were measured pre- and post for up to 8 hrs. The mean dose of Wilate required to reach target VWF:RiCof activity level of >65 iu/dl in the type 3 VWD was 49.6 iu/kg, and 38.7 iu/kg in type 2 VWD. Of the type 1 patients mean dosing was 43.0 iu/kg. The median peak VWF:RiCoF activity was 82 iu/dl in type 3 and 115 iu/dl in type 2, and 92 iu/dl in type 1. VWF Antigen levels were 116 iu/dl in type 3, and 164 iu/dl in type 2 and 135 iu/dl in type 1. VWF handling in some individuals was suggestive of increased VWF clearance with a half-life below the suggested half-life of 12 hours. This observation indicates the importance of prolonged PK studies in individual cases. As expected, peak FVIII levels were generally higher with Wilate compared to previously used concentrate (94 iu/dl in type 3 and 82 iu/dl in type 2) but the PK profiles between the products were similar, with some inter-individual variability. In conclusion, Wilate achieves adequate VWF activity and FVIII levels and has similar PK properties to previously used concentrate. However, based on the results of this study prolonged PK assessment appears important in selected cases.