Abstract

The utility of existing methods for the evaluation of hemostatic agents has been limited. The purpose of this study was to evaluate and optimize the use of a standardized punch biopsy to investigate the effects of hemostatic agents in healthy subjects. Recombinant FVIIa (rFVIIa) is licensed for the treatment of bleeding episodes in patients with hemophilia A or B with inhibitors. Recent reports (anecdotal and from randomized clinical trials) have described the successful use of rFVIIa in patients with liver disease, intracerebral hemorrhage, congenital and acquired coagulation factor deficiency, warfarin-induced bleeding, thrombocytopenia, traumatic brain injury, spinal cord surgery, and platelet disorders using a wide range of doses and dosing regimens. This variety of clinical situations, suggests a need to determine the optimal dose and dosing regime of rFVIIa for use in these potentially new therapeutic areas. A study was designed to evaluate the dose-response of rFVIIa in a controlled manner using a punch biopsy procedure in healthy volunteers that consented to participate in an IRB approved protocol. The study was designed as a three-part trial. Part A (6 subjects) optimized the size of the biopsy needed to create bleeding times and durations appropriate for study purposes. Part B (10 subjects) determined the feasibility of evaluating rFVIIa efficacy and safety in this bleeding model. Part C (48 subjects) examined, in an ascending dose escalation paradigm, the effect of a single dose of rFVIIa on bleeding time, blood loss volume, coagulation parameters and coagulation status in healthy volunteers. In Part C, all patients underwent three punch biopsies: the first (baseline biopsy) with no treatment, the second with either a low or high rFVIIa dose administered prior to biopsy, the third with either a low or high dose of rFVIIa administered prior to biopsy. The treatment pair sequences were placebo/10, 10/20, 20/40, 40/80, 80/120, and 120/160 μg/kg. Blood samples were drawn 15 minutes pre-, 15 minutes post-, and 1 hour post-biopsy to monitor coagulation and conduct ex-vivo assessments of hemostasis [Hemodyne Hemostasis Analyzer (HHA)]. Safety evaluations were conducted by an Independent Safety Officer after each dose tier, and subjects were permitted to enroll in the next higher dose tier only if no significant safety issues were observed. In healthy subjects with no pre-existing coagulopathies, regression analyses indicated that increasing doses of rFVIIa did not have a dose-related linear effect on blood loss volume or duration of bleeding. However, it is of interest that with HHA, a statistically significant impact was noted on the time to 20 mm clot strength, platelet contractile force, and clot elastic modulus, suggesting that rFVIIa does have a measureable and perhaps meaningful effect in individuals with normal coagulation systems. No safety issues were detected during this study. Thus in this model system, designed to evaluate hemostasis, interesting effects were seen with the HHA instrument which suggest that increasing doses of rFVIIa may impact clot stability, but these observations are limited by the significant hetereogeneity which may benefit from improved experimental controls.

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