Real World Use of Extended Half-Life Products and the Impact on Bleeding Events and Joint Health in the United States

Background: The hemophilia treatment landscape has evolved substantially in the last several years with the approval of extended half-life (EHL) products which reduce the burden of prophylaxis. Data reported from the American Thrombosis and Hemostasis Network (ATHN) as of June 2017 indicate that 21% of patients with moderate or severe hemophilia A, and 42% of patients with moderate or severe hemophilia B, receive prophylaxis utilizing an EHL. As new treatments become available and are adopted into practice, it is important to recognize the need for evaluation of efficacy, safety, and economic impact of their use outside of the clinical trial setting. We aimed to characterize the real world impact of EHL products by collecting detailed information on bleeding rates, joint health and quality of life amongst patients cared for at ATHN-affiliated Hemophilia Treatment Centers. We hypothesized that use of EHL products were utilized in at least 30% of patients and would lead to decreased ABRs and improved joint health. To date 67 of a planned 135 subjects have been enrolled, constituting this interim analysis.

Methods:Subjects were recruited from seven U.S. Hemophilia Treatment Centers. Subjects with severe hemophilia A or B ≤ 30 years of age on prophylaxis or demand therapy were eligible for enrollment. Subjects excluded from study were those with a recent joint bleed (within the last 2 weeks) or those unwilling to complete all elements of the study. Data were collected during a one-time encounter concurrent with an appointment for clinical evaluation, including demographic information, treatment regimen, product type, frequency, location and severity of all bleeds, Hemophilia Joint Health Scores (HJHS), and Quality of life (QoL).

Bleeding rates in subjects receiving prophylaxis were compared with those receiving on demand therapy by type treatment, EHL vs standard half-life (SHL), and by hemophilia type. Severity of bleeding events (mild, moderate, or severe) and HJHS were compared by prophylaxis groups.

Results: A total of 67 patients were enrolled and eligible for analysis. This included 58 subjects with severe hemophilia A, and 9 subjects with severe hemophilia B. The mean age of the cohort was 15 years (median 12 years, IQR 8 - 21 years). For these patients whose race information was known, 89.1% were Caucasian, 3.3% African-American, 3.3% Asian, and 4.7% were of mixed or 'other' race. Eleven out of 61 (18.0%) subjects with known ethnicity were Hispanic. Among 59 patients whose treatment type were available, the majority were on prophylaxis (n=53; 89.8%) as compared to on demand therapy (n=6; 10.2%).

The average annualized bleeding rate (ABR) was 2.8 amongst all individuals. As expected, the ABR was substantially lower in those receiving prophylaxis (ABR=1.0) as compared to on demand therapy (ABR=18.6) (p<0.001). Additionally, HJHS in those receiving prophylaxis was lower (mean HJHS= 3.9), meaning less evidence of joint damage, than in those receiving demand therapy (mean HJHS= 8.8) (p=0.162).

For patients with severe hemophilia A, the ABR was lower in those individuals receiving EHL (ABR= 0.5) versus SHL (ABR= 1.5), although this did not reach statistical significance (p=0.136). All subjects with severe hemophilia B enrolled to date receive EHL products (n=9) therefore no comparison of ABR could be made between EHL and SHL products; the ABR in this group was 0.9. In patients with severe hemophilia A, there was a higher HJHS for those receiving EHL (mean HJHS= 7.0) versus those receiving SHL (mean HJHS = 2.1) (p=0.053). For patients with severe hemophilia B, all of whom received EHL, the mean HJHS was lower than in the hemophilia A cohort (mean HJHS=1.2).

Conclusions: We report real-world bleeding events and joint health in patients with severe hemophilia A and B utilizing EHL and SHL products across a wide U.S. geographic distribution. As anticipated, there is substantial bleed reduction with prophylaxis versus on demand therapy. In our severe hemophilia A cohort, the ABR for patients receiving EHL products was similar to ABRs reported in clinical trials, suggesting clinical trial data may be reflective of real world use. Patients with severe hemophilia A receiving EHL for prophylaxis had a lower ABR than those receiving SHL, although the early impact is not reflected in the HJHS score. Longer follow-up will be necessary to determine the impact of EHL on HJHS.