Recombinant factor IX

Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.

Benefix (Wyeth)
vials containing 250 IU, 500 IU and 1000 IU as lyophilised powder
Approved indication: haemophilia B
Australian Medicines Handbook Section 7.4

Factor IX is part of the intrinsic pathway of coagulation. Approximately one boy in 100 000 is born with a deficiency or dysfunction of factor IX (haemophilia B).

If someone with a factor IX deficiency develops bleeding, they can be treated with plasma concentrates derived from blood donations. There is always a small risk of a blood-borne infection being transmitted in these products. In addition some of the concentrates are enriched with prothrombin and can cause thromboembolism. A recombinant factor IX should avoid these problems.

Patients switched to the recombinant factor IX may need to be given a higher dose than would be needed with a plasma-derived product. An assay should be used to ensure the correct level of factor IX activity is reached.

As haemophilia B is a rare disease clinical trials have only included 108patients. In addition to the treatment of bleeding, recombinant factor IX has also been used successfully to prevent bleeding during surgery.

In the clinical trials the slow injection of factor IX could cause headache, fevers, chills, nausea and vomiting. Prescribers must be ready to deal with acute hypersensitivity reactions. Allergic reactions may be more frequent inpatients who have developed inhibitors (neutralising antibodies) to factor IX products.