Longer lasting concentrates are now available. These new factor concentrates use various methods to ensure that the product lasts for longer in the circulation. The latest clinical trial results from many of these products are very encouraging. Longer acting recombinant factor VIII products in clinical trials show a half life extended from 12 hours up to 19 hours for one product and a 1.5 to 1.7 fold increase in half life for a second product. The normal half life for factor IX is approximately 18 hours. In late stage clinical trial results with three products, this half life has been extended to 64 hours, 93 hours and 94 hours respectively, up to a 5 fold increase in half life.
It is none the less extremely encouraging that these results are now available. The availability of longer acting factor concentrates could mean that infusions could be taken less frequently. For factor VIII deficiency this could mean a change from prophylaxis three times per week to twice per week or even once per week.
For factor IX deficiency this could mean a change to prophylaxis from twice per week to once per week or once every two weeks. This will of course be of major benefit not only in terms of convenience, but also will be of major benefit to people who have difficult venous access and may also reduce the requirement for dependence on central venous access devices, such as port-a-caths, in children in the future.
However, the potential advantages of these products go well beyond the possibility of less frequent infusions. Longer acting concentrates may allow for higher trough levels and therefore better clinical management of bleeding and less bleeding episodes. The current objective of prophylaxis in haemophilia care is to maintain the trough levels (lowest factor level) at above 1% at all times. A level maintained above 1% should prevent the majority of spontaneous bleeds, but does not prevent all bleeding episodes or joint damage. With the availability of these new concentrates in the future there is a possibility of increasing this trough level for example to 3% or 5% and therefore allowing better clinical management for bleeds. In the recently published phase 3 trial results of one of the longer acting factor VIII concentrates where treatment was given prophylactically every 3 to 5 days, the annualised bleeding rate was reduced to 1.6 bleeds per annum.
Availability of these new concentrates in the future will also hasten the requirement for an individualised approach to therapy.
For Haemophilia A patients with an Inhibitor Roche’s Emicizumab is being included in the UK early access medicines scheme. It is a weekly subcutaneous injection.
There have been encouraging results with Gene Therapy trials. 13 Haemophilia A patients were injected with a copy of the Factor 8 gene and are still producing normal levels of factor 8 over a year later.