For patients with hemophilia and high-titer inhibitors, a new era of treatment has begun with the development of improved variants of traditional bypassing agents and novel, nonfactor-based, prophylactic agents, say authors of a recent review article.
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“These new agents may transform the treatment of inhibitor patients and inhibitor-related bleeds, potentially decreasing morbidity and mortality and improving patients’ quality of life,” Amy D. Shapiro, MD, and coauthors wrote in the Journal of Thrombosis and Haemostasis.
Until recently, the only two bypassing agents available were activated prothrombin complex concentrates and recombinant factor VIIa, noted Dr. Shapiro, who is CEO and co-medical director of the Indiana Hemophilia and Thrombosis Center, Indianapolis, and her coauthors.
The first of the novel targeted agents, emicizumab, is a humanized, bispecific monoclonal antibody that was approved for prophylactic use in hemophilia A in the United States in November 2017.
Emicizumab could transform the treatment of patients with inhibitors, but it also requires reconsideration of how to treat breakthrough bleeds and eliminate the underlying inhibitor, the authors said.
In a phase 3 study, this biologic significantly decreased the annualized bleeding rate by 87% versus on-demand bypassing agent therapy, and by 79% versus a prophylactic bypassing agent regimen, they said, noting that 63% of patients had no bleeding events during the study.
Serious adverse events were seen in patients receiving emicizumab prophylaxis, including thrombosis in 2 out of 103 subjects and thrombotic microangiopathy in 3. In all cases, the patients were treating breakthrough bleeds with activated prothrombin complex concentrate, Dr. Shapiro and coauthors wrote.
Other novel agents in clinical development include fitusiran and tissue factor pathway inhibitors, which each target a different natural anticoagulant and could result in new prophylactic options, according to the study coauthors.
“The possibility of multiple therapeutic targets may allow for a highly personalized approach to prophylaxis therapy, with traditional bypassing agents providing options when breakthrough bleeds occur,” they wrote.
In the meantime, eptacog alfa is the “de facto standard” for recombinant factor VIIa, though a new variant under development, eptacog beta, has been accepted for regulatory review in the United States. In a phase 3 clinical trial, eptacog beta appeared to provide improved efficacy and decreased dosing requirements, possibly due to increased binding affinity to endothelial protein C receptor (EPCR), the authors said.
“The addition of improved rFVIIa variants with unique pharmacological and pharmacokinetic profiles will provide new tools to treat bleeding events in inhibitor patients,” Dr. Shapiro and her colleagues wrote.
The use of traditional bypassing agents is expected to decrease over time as new and improved therapeutics are developed. Traditional agents, however, will “remain a necessity” for breakthrough bleeds in hemophilia A patients with inhibitors, and until novel agents become available for hemophilia B, the authors said.
The review article was supported by an unrestricted educational grant from HEMA Biologics, LLC, which had no involvement or editorial control in research, writing or submission. Dr. Shapiro reported disclosures related to HEMA Biologics, Shire, Novo Nordisk, Kedrion Biopharma, Bioverativ, and Genentech.
SOURCE: Shapiro AD, et al. J Thromb Haemost. 2018 Sep 28.