Researchers from Emory University in Atlanta, GA, along with technical assistance from the Centers for Disease Control and Prevention (CDC), have been studying the rate of inhibitor development among hemophilia A patients. Inhibitors, a serious complication for individuals with hemophilia, occur when antibodies are produced by the body in response to infused factor VIII or IX, further preventing proper clot formation. Although the complication appears in both types of hemophilia, it is more common in people with type A.
One challenge facing hematologists is the difficulty they have anticipating the likelihood of the development of an inhibitor when prescribing a new factor product for their patients. Study authors say another problem is that the rate of inhibitor development in previously treated patients (PTPs) is not well defined. This study was an attempt to further clarify why and under what conditions certain patients with hemophilia develop inhibitors.
“Understanding the baseline rate of inhibitor development in the population of PTPs is important when evaluating the effect of exposure to new factor replacement products on inhibitor formation,” explained Dr. Christine Kempton, lead author and assistant professor of pediatrics at Aflac Cancer Center and Blood Disorders Services of Children’s Healthcare of Atlanta at Emory University.
A total of 838 PTPs were included in the study. Data on the patients was drawn from the CDC’s Universal Data Collection Project (UDC).
The selected patients, all males with type A hemophilia, had UDC data collected on four or more occasions, prior to March 30, 2003. None of the patients had previously experienced an inhibitor prior to the start of the study. Based on calculations that incorporated the number of verified incident inhibitor cases during the study period, investigators found that the overall incidence rate was 2.14 cases per 1,000 person years.
“Given the low rate of inhibitor development in PTPs with hemophilia A, small, non-randomized studies are inadequate to determine the rate of inhibitor development after exposure to novel products. Ongoing, standardized, postmarketing surveillance is needed to determine if novel factor products pose an increased risk of inhibitor development,” concluded Kempton.
The report, “Incidence of Inhibitors in a Cohort of 838 Males with Hemophilia A Previously Treated with Factor VIII Concentrates,” was published in the December 2006 issue of the Journal of Thrombosis and Haemostasis.
Source: Hematology Week, January 8, 2007