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.
bottles containing 250 IU, 500 IU and 1000 IU for reconstitution
Indication: haemophilia A
Haemophilia A is due to a deficiency or dysfunction of factor VIII. The patients are at risk of bleeding after minor injuries. If bleeding, e.g. into a joint, is suspected, the patient needs to be given factor VIII.
Although the safety of factor VIII products derived from human plasma has increased, there is still the potential for infection. Patients are also at risk of developing antibodies which inhibit factor VIII and so reduce the effectiveness of treatment. Although inhibitors can still occur, the risk of infection will be reduced by a recombinant factor VIII.
The factor VIII in this product is synthesised using Chinese hamster ovary cells. It has the same effects as human factor VIII, so it can be infused to prevent or treat bleeding.
The dose is determined by calculating how much factor VIII has to be given to raise its plasma concentration to a particular percentage of normal. While an early haemarthrosis may be stopped by raising the concentration to 20% of normal, severe bleeding may require the concentration to be raised to 100%. While the dose can be estimated using these calculations, the manufacturer recommends serial assays to ensure that adequate concentrations are reached. As the half life is 14 hours, the infusion should be repeated until the threat of bleeding has resolved.
Patients can develop inhibitors to recombinant factor VIII. If an inhibitor is present, bleeding might not be controlled as expected and additional factor VIII may be needed. Hypersensitivity is unusual, but patients should be informed of the possibility.
There have been shortages of plasma derived factor VIII in Australia, so this product will increase supply. The product is expensive and will probably only be available to patients registered at recognised treatment centres. Treatment may be reserved for children and new patients who are not 'virally compromised'.