Topical hemostatic agents have been used for more than 50 years. Currently, bovine thrombin is isolated from bovine plasma and has an inherent risk of transmitting blood-borne pathogens. Approximately 20% or more patients who receive various bovine thrombin preparations have been reported to develop antibodies to bovine thrombin product and impurities. In rare cases, these antibodies can cross-react with human endogenous coagulation proteins and may lead to alterations in coagulation laboratory parameters, hypersensitivity reactions, or severe bleeding or thrombosis. ZymoGenetics, Inc. has developed recombinant Thrombin (rThrombin) as an alternative to bovine and human plasma-derived thrombin preparations. The potential immunogenicity of rThrombin (n=198) and bThrombin (n=200) were compared in a well-controlled, randomized, double-blind Phase 3 study. Two enzyme-linked immunosorbent assays (ELISAs) were developed and validated under the principles of FDA Guidance Documents (FDA Guidance for Industry: BioAnalytical Method Validation, May 2001) to detect antibodies binding to either rThrombin or bThrombin product. A time-to-clot based assay was developed and validated to characterize whether antibodies to rThrombin had neutralizing activity for plasma-derived thrombin. Study results demonstrated rThrombin’s superior immunogenicity profile compared with bThrombin (1.5% versus 22%, respectively, p < 0.0001; antibodies developed to the products, as defined by seroconversion or significant change in titer units). Characterization of the binding antibodies demonstrated none of the anti-rThrombin antibodies neutralized human plasma thrombin. No subjects in either group had evidence of antibody-mediated coagulopathy. These results demonstrate that rThrombin has a superior immunogenicity profile when compared with bThrombin.
Disclosure: Employment: All authors are employees of ZymoGenetics, Inc. Ownership Interests:; Employees of ZymoGenetics, Inc. receive stock options in this publicly traded company.