Marcus E. Carr

Exploratory study on the reversal of warfarin with rFVIIa in healthy subjects

The use of warfarin has a well-known bleeding risk. Recombinant activated factor VII (rFVIIa) is a non-plasma-derived, rapid-acting, and rapidly infused potential treatment. This randomized, single-center, placebo-controlled, double-blinded, dose-escalation, exploratory phase 1 trial assessed safety and effects of rFVIIa in reversing warfarin-induced changes in bleeding and coagulation parameters, using a punch biopsy-induced bleeding model in healthy subjects. The effects of warfarin (experiment 1) and rFVIIa (5-80 microg/kg; experiment 2) were evaluated. Outcomes were bleeding duration, blood loss, coagulation parameters, and safety. Warfarin treatment significantly increased bleeding duration and blood loss from pretreatment (experiment 1, 12 subjects). However, these parameters after rFVIIa treatment were not significantly different from placebo (experiment 2, 85 subjects). Mean activated partial thromboplastin time, prothrombin time, and international normalized ratio were reduced from warfarin-elevated levels. rFVIIa (80 microg/kg) significantly reversed warfarin effects on all thromboelastography parameters, compared with placebo (P < .05), and returned the thrombin generation speed to baseline. There were no thromboembolic or serious adverse events. In this exploratory trial, the reversal of warfarin effects was observed in the thromboelastography, thrombin generation, and clotting assays. However, this reversal did not translate to improvements in the bleeding model parameters evaluated in the punch biopsy model. Trial registration is exempt (phase 1).

Recombinant human factor VIIa (rFVIIa) cleared principally by antithrombin following IV administration in haemophilia patients.

Summary.u2002 Objective: The objective of the present study was to evaluate the pharmacokinetics and the clearance pathways of rFVIIa after intravenous administration to hemophilia patients. Methods: Ten severe hemophilia patients were included in the study; all patients were intravenously administered a clinically relevant dose of 90u2003μgu2003kg−1 (1.8u2003nmolu2003kg−1) rFVIIa. Blood samples were collected consecutively to describe the pharmacokinetics of rFVIIa. All samples were analyzed using three different assays: a clot assay to measure the activity (FVIIa:C), an enzyme immunoassay (EIA) to measure the antigen levels (FVII:Ag), and an EIA (FVIIa‐AT) to measure the FVIIa antithrombin III (AT) complex. Pharmacokinetic parameters were evaluated both by use of standard non‐compartmental methods and by use of mixed effects methods. A population pharmacokinetic model was used to simultaneously model all three datasets. The total body clearance of rFVIIa:C was estimated to be 38u2003mLu2003h−1u2003kg−1. The rFVII‐AT complex formation was responsible for 65% of the total rFVIIa:C clearance. The initial and the terminal half‐life of rFVIIa:C was estimated to be 0.6 and 2.6u2003h, respectively. The formation of rFVII‐AT complex was able to explain the difference observed between the rFVIIa:C and the rFVII:Ag concentration. The non‐compartmental analysis resulted in almost identical parameters.

Onset of force development as a marker of thrombin generation in whole blood: the thrombin generation time (TGT).

Summary.u2002 Prothrombin activation requires the direct interplay of activated platelets and plasma clotting factors. Once formed, thrombin causes profound, irreversible activation of platelets and reinforces the platelet plug via fibrin formation. Delayed or deficient thrombin production increases bleeding risk. Commonly employed coagulation assays, the prothrombin and partial thromboplastin times, use clot formation as a surrogate marker of thrombin generation. These assays routinely utilize platelet‐poor plasma and completely miss the effects of platelets. Other markers of thrombin generation, prothrombin fragment 1u2003+u20032 (F1u2003+u20032) and thrombin–antithrombin complex, are typically measured after the fact. We report a simple assay, which employs the onset of platelet contractile force (PCF) as a surrogate marker of thrombin generation. PCF generation occurs concomitant with the burst of F1u2003+u20032 release. The time between assay start and PCF onset is termed the thrombin generation time (TGT). TGT is prolonged in clotting factor deficiencies and in the presence of direct and indirect thrombin inhibitors. TGT shortens to normal with clotting factor replacement and shortens with administration of recombinant factor VIIa. TGT is short in thrombophilic states such as coronary artery disease, diabetes and thromboangiitis obliterans and prolongs toward normal with oral and intravenous anticoagulants.

Effect of recombinant factor VIIa variant (NN1731) on platelet function, clot structure and force onset time in whole blood from healthy volunteers and haemophilia patients

Summary.u2002 NN1731 is a novel variant of recombinant factor VIIa (rFVIIa) that binds to activated platelets, but has greater enzymatic activity than rFVIIa in generating FXa and thrombin. The effect of NN1731 on clot structure and platelet function was characterized ex vivo in whole blood from healthy volunteers and haemophilic patients. Blood samples from six healthy volunteers, nine haemophilia A patients with and without inhibitors and one acquired haemophilia A patient, were spiked with increasing concentrations (0.32, 0.64 and 1.28u2003μgu2003mL−1) of rFVIIa and NN1731. Platelet contractile force (PCF) or platelet function, clot elastic modulus (CEM) or clot structure, and force onset time (FOT) or the thrombin generation time (TGT) were determined using the Hemodyne Hemostasis Analysis System (HAS™). Baseline PCF, CEM and FOT values in patients were abnormal compared to healthy volunteers’ baseline values. Overall, haemophilia blood samples with or without inhibitors spiked with NN1731 had significantly greater PCF, CEM and shorter FOT values relative to samples spiked with corresponding doses of rFVIIa. The variability in response to treatment between patients was greater with rFVIIa compared to NN1731. At 1.28 μgu2003mL−1 (90u2003μgu2003kg−1), NN1731 normalized PCF, CEM and FOT in nine of 10 patients, while rFVIIa normalized these parameters in four of 10 patients. Increasing in vitro concentrations of NN1731 normalized platelet function, clot structure and thrombin generation consistently in haemophilia blood with or without inhibitors. NN1731 may be a promising haemostatic agent for patients with bleeding disorders. These results should be confirmed in an in vivo study.

Reversal of Clopidogrel-Induced Bleeding with rFVIIa in Healthy Subjects: A Randomized, Placebo-Controlled, Double-Blind, Exploratory Study

BACKGROUND:Clopidogrel (Plavix®) therapy, although effective for minimizing risk of thrombotic events, is also associated with potential bleeding risk. Recombinant activated FVII (rFVIIa, NovoSeven®) induces hemostasis in hemophilia patients with inhibitors (alloantibodies) and has been proposed as potential treatment for mitigating clopidogrel therapy–mediated bleeding. METHODS:In this single-center, randomized, placebo-controlled, double-blind, dose-escalation, exploratory phase I trial, we assessed the safety and effects of rFVIIa in reversing clopidogrel-enhanced bleeding in an experimentally induced punch biopsy in healthy subjects. Efficacy assessments included the reversal of bleeding characteristics (bleed duration [BD], the primary end point and blood loss volume [BV] induced by punch biopsy, and thromboelastograph [TEG®] parameters) with rFVIIa or placebo after clopidogrel treatment. RESULTS:A significant number of subjects (56%) had limited response to clopidogrel (defined as ⩽30% platelet aggregation inhibition) and were discontinued from study. The remaining subjects continued and had 4 biopsies. Of 40 subjects randomized, 37 were evaluated for efficacy. Clopidogrel treatment increased BD and BV compared with the baseline biopsy. Recombinant FVIIa (10 and 20 &mgr;g/kg) significantly mitigated the clopidogrel-induced effects on BV (P = 0.007 and P = 0.001, respectively). Early trial termination limited the evaluation of effects of higher rFVIIa doses. Subgroup analyses of subjects biopsied by the same physician demonstrated significant reduction of clopidogrel-induced BD with 20 &mgr;g/kg rFVIIa (P = 0.048). Ex vivo analysis of rFVIIa demonstrated clotting dynamics presented by parameters time to clot onset (TEG®-R) and clot angle (TEG®-A) (P < 0.005). CONCLUSIONS:In this clinical study, rFVIIa (10 and 20 &mgr;g/kg) reversed the effect of clopidogrel on blood loss.

Monitoring rFVIIa 90 μg kg−1 dosing in haemophiliacs: comparing laboratory response using various whole blood assays over 6 h

Summary.u2002 Recombinant FVIIa is a haemostatic agent administered to patients with severe FVIII or FIX deficiency with inhibitors. Although rFVIIa is effective at stopping bleeding, a reliable assay to monitor its effect is lacking. To characterize the pharmacokinetics and global coagulation effects of rFVIIa for 6u2003h following a IV dose of 90u2003μgu2003kg−1. Ten non‐bleeding subjects with severe FVIII or FIX deficiency were infused with a single‐dose of rFVIIa 90u2003μgu2003kg−1 body weight and blood was collected before and at 0.5, 1, 2, 4 and 6u2003h postdose. Global haemostasis was characterized throughout the study utilizing whole blood analyses (Hemodyne HAS, TEG, ROTEM). The clearance and half‐life of factor FVII:C was estimated as 39.0u2003±u20038.8u2003mLu2003h−1u2003kg−1 and 2.1u2003±u20030.2u2003h respectively. There was good inter‐assay agreement with respect to clot initiation parameters (R, CT and FOT) and these parameters all fell to a mean of approximately 9u2003min following rFVIIa dosing. The platelet contractile force (PCF) and clot elastic modulus (CEM) were positively correlated to FVII:C (Pu2003< 0.0001), and these parameters were dynamic throughout the 6‐h period. The MA and MCF did not correlate to FVII:C nor did they significantly change during the study. Prothrombin F1u2003+u20032 significantly increased following rFVIIa dosing (Pu2003<u20030.001), but remained steady throughout the study. There was no change in D‐dimer concentrations over time. The FOT, R and CT characterized clot initiation following rFVIIa dosing. The PCF and CEM were correlated to FVII:C and characterized the dynamics of platelet function and clot strength over the rFVIIa dosing interval. The clinical significance of these findings needs additional study.

Re: Discordant pair analysis of rFVIIa and pd-aPCC response

arthropathy than the children, which may be another reason for their lower response. The bleeding response was rated as good in 71% of patients with mild bleeds and in 42% of those with moderate bleeds. Overall, in 97% of bleeding episodes the event stopped with only two doses of rFVIIa (average 1.5 doses). In the 29 joint bleeds, pain and tenderness disappeared and joint mobility improved after the first dose of rFVIIa in 18 cases (62%). The remaining haemarthroses responded to a second dose. In all three reported haematomas, the pain disappeared and haematoma size diminished after two doses of rFVIIa. It was noted that the response to rFVIIa varied in the three patients with oral bleeding. In one case, arrest of bleeding was achieved with the first dose of rFVIIa, whereas a second dose of rFVIIa was required for the second case, and the remaining patient started to re-bleed within 24 h, despite attaining full haemostasis initially. No adverse events were reported during the administration of rFVIIa in this patient cohort. The recent literature contains a number of reports of the use of a higher and single dose of rFVIIa to achieve bleeding control in haemophilia patients with inhibitors. Overall, these studies demonstrate that a single dose of rFVIIa 270 lg kg optimizes on-demand treatment by offering the same level of efficacy and safety as dosing schedules of rFVIIa 90 lg kg given every 2–3 h [4,5]. The results of this study support the view that a single high dose of rFVIIa offers a viable and effective alternative to standard dosing without altering the safety profile. Although this was a small study which used single doses of rFVIIa that are lower than those recently shown to be both effective and well tolerated by adults and children with haemophilia with inhibitors, it highlights the importance of optimizing the dose regimen according to local resources and patient characteristics, such as age, with the possibility of reducing the cost of the treatment.