Combination of Recombinant Factor VIIa and Fibrinogen Corrects Clot Formation in Primary Immune Thrombocytopenia At Very Low Platelet Counts

Primary immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a low platelet count and an increased risk of bleeding. Hemostatic treatment modalities, bypassing the need for platelet transfusion, would be desirable for control of serious acute bleeds in patients with ITP. This study aimed at (i) performing a thorough characterization of the coagulopathy of ITP, (ii) investigate new ways to obtain acute correction of the coagulopathy performing in vitro experiments with recombinant factor VIIa (rFVIIa, NovoSeven®), fibrinogen (RiaSTAP®), and the combination of rFVIIa and fibrinogen, and finally (iii) investigate the correlation of the hemostatic response to the baseline platelet counts of the ITP patients. We challenged the hypothesis that rFVIIa combined with fibrinogen concentrate can correct whole blood (WB) clot formation in patients suffering from ITP even at very low platelet counts.

Blood from 12 ITP patients and 15 healthy controls was drawn into 3.2% citrate containing corn trypsin inhibitor 18.3μg mL⁻¹ to inhibit artificial contact activation. The WB (mean platelet count 22 × 10⁹L⁻¹ (range 0–42)) was spiked in vitro with buffer (control), fresh donor platelets (+40×10⁹ L⁻¹), rFVIIa (1 or 4μg mL⁻¹), or fibrinogen (1 or 3mg mL⁻¹) as well as the combination of rFVIIa and fibrinogen. Dynamic WB coagulation profiles were recorded by ROTEM® Thromboelastometry using activation with tissue factor (0.03pM) and re-calcification. Parameters of clot initiation (clotting time, CT), clot propagation (maximum velocity, MaxVel) as well as clot termination (maximum clot firmness, MCF) were evaluated. Thrombin generation in “platelet-rich” ITP plasma was evaluated using calibrated automated thrombography. Overall differences between groups were evaluated by paired and unpaired t-tests as appropriate. Simple linear regression analyses were performed using the differences observed after addition of the various interventions (intervention – baseline) as the dependent variable (y) and the platelet count as the independent variable (x). The slope was used to evaluate dependency of the hemostatic response on the platelet count, whereas the intercept was used to evaluate the hemostatic response at very low platelet counts. A p-value less than 0.05 was considered statistically significant.

Compared with healthy controls the WB coagulation profiles of the ITP patients were characterized by a prolonged CT (mean: 1490 vs. 941s, p<0.001) as well as a markedly reduced MaxVel (3.4 vs. 9.7mm×100s⁻¹, p<0.001) and MCF (38.2 vs. 49.4mm, p=0.01). Fibrinogen showed no positive hemostatic effect. Recombinant FVIIa reduced the CT (744s, p<0.001) and increased the MaxVel (6.28mm×100s⁻¹, p<0.001) whereas no change was observed in the MCF. Thrombin generation in “platelet-rich” plasma supported the findings in WB. The improvement in CT following addition of rFVIIa was independent of the platelet count (p-values > 0.45) and the intercept showed a significant improvement at very low platelet counts (1μg mL⁻¹: −643s, p<0.001; 4μg mL⁻¹: −811s, p<0.001). In contrast, the increase in MaxVel after addition of rFVIIa was highly dependent on the platelet count (1μg mL⁻¹: R² = 0.81, p < 0.001; 4μg mL⁻¹: R² = 0.86, p < 0.001) and the intercept was not significant (1μg mL⁻¹: 0.05mm×100s⁻¹ p=0.87; 4μg mL⁻¹: 0.54 mm×100s⁻¹ p=0.15). The combination of fibrinogen and rFVIIa revealed a synergistic effect also showing an increased MCF (50.7mm) in addition to a reduced CT (794s) and improved MaxVel (7.9 mm×100s⁻¹) displaying larger effects than following fresh donor platelet substitution (CT 1164s; MaxVel 6.96mm×100s⁻¹; MCF 49.6mm). Furthermore, rFVIIa together with fibrinogen also showed a significant response at very low platelet counts in all parameters (Intercept: CT −788s, MaxVel 3.3mm×100s⁻¹, MCF 13.9mm, p-values<0.004)

Data suggest that rFVIIa combined with fibrinogen can correct the coagulopathy of ITP even at very low platelet counts, and may be an alternative to platelet transfusion. Clinical trials are needed to further investigate if this new treatment modality holds the potential to serve as an effective acute treatment option in ITP.

Off Label Use: Recombinant activated factor VII (NovoSeven) and fibrinogen concentrate (RiaSTAP). In vitro data suggesting a haemostatic effect in primary immune thrombocytopenia will be presented. S∅rensen:Novo Nordisk: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Baxter: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; CSL Behring: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bayer: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; SOBI: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pentapharm: Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau; Grifols: Research Funding; LFB: Research Funding; Octapharma: Research Funding.