Source and purity of factor VIII products as risk factors for inhibitor development in patients with hemophilia A.

Background: Inhibitor development is influenced by several factors and the type of factor VIII (FVIII) products may play a role.
Objectives: In order to explore such a role, we designed a cohort study whose novelty resides in the classification of products not only according to the source of FVIII (plasmatic, pd, or recombinant, r) but also to their degree of purity (expressed as specific activity).
Patients/methods: Treatment data up to inhibitor development or 150 exposure days were collected in 377 patients with hemophilia A.
Results: Inhibitors developed in 111 patients (29%; 96 high-responders, 25%). The cumulative incidence was progressively higher from patients treated with low/intermediate-purity pdFVIII compared with those treated with high-purity pd and rFVIII. The adjusted hazard ratio of inhibitor development was 4.9 with rFVIII and 2.0 with high-purity pdFVIII (95% CI, 2.9-8.3 and 1.1-4.0), taking as reference low/intermediate-purity pdFVIII. There was no difference in the frequency of inhibitor testing between treatment groups. Sensitivity analyses (in patients who never switched product type, previously untreated patients, those treated on-demand and those with high-risk F8 mutations) confirmed an increased inhibitor risk with rFVIII and high-purity pdFVIII.
Conclusions: This study shows that the degree of purity of FVIII products influences inhibitor development independently from other risk factors, and emphasizes that differences exist within pdFVIII products.
(© 2012 International Society on Thrombosis and Haemostasis.)