Extended Half-Life Factor VIII and Factor IX Preparations.

In the last couple of years, several extended half-life factor VIII and factor IX preparations were intensively studied and gained approval. In order to extend half-lives, techniques like fusion to protein conjugates (Fc part of IgG1 or albumin), chemical modification (PEGylation), and protein sequence modification are implemented. With these techniques, it is possible to extend half-lives of factor IX products 4- to 6- fold, while half-life extension of factor VIII products is limited to 1.5- to 2-fold due to their interaction with von Willebrand factor. Nevertheless, both extended half-life factor VIII and IX products have improved and facilitated prophylactic factor replacement therapy in hemophilia A and B, respectively. Extended half-life factor concentrates pose challenges to coagulation laboratories because accurate therapy monitoring is not possible with all factor activity assays currently used.