Underestimation of unfractionated heparin therapy assessment due to platelet activation when using partial-draw (pediatric) citrate collection tubes

The “so-called” pediatric tubes are often used when collecting smaller blood volume is necessary, particularly in pediatric patients or in case of difficult/recurrent sampling. The aim of this multicenter study was to compare coagulation test results evaluated in evacuated polymer tubes containing 0.109 M citrate (1 vol./9 vol.) specifically designed to allow either a partial (2.0 mL,“pediatric”) or a total (3.5 mL) filling. No significantly relevant discrepancy was found between routine coagulation test results in both tubes collected from untreated patients and from patients on vitamin K antagonist or low molecular weight heparin. In contrast, aPTT was significantly shorter and anti-FXa activity was significantly lower in partial-draw than in full-draw tubes collected from 46 patients receiving unfractionated heparin (UFH). This discrepancy was likely related to increased platelet activation in partial-draw tubes, as suggested by higher platelet factor 4 plasma concentrations and platelet P-Selectin expression in partial-draw than in full-draw citrate tubes. To confirm this hypothesis, we then evaluated partial-draw tubes containing CTAD, a mixture of anticoagulant and antiplatelet agents. In 25 patients on UFH, aPTT and anti-FXa activity were not significantly different in partial-draw CTAD tubes and in full-draw citrate tubes. In conclusion, despite increased platelet activation, samples collected into partial-draw citrate tubes allow accurate routine coagulation testing in all patients but those requiring UFH assessment, in which their use could lead to significant underestimation of anticoagulation. In such cases, partial-draw tubes containing CTAD could be validly used to monitor heparin therapy as well as to perform routine coagulation testing.     

Comparison of antithrombotic and hemorrhagic effects of edoxaban,a novel factor Xa inhibitor,with unfractionated heparin,dalteparin, lepirudin and warfarin in rats

Background

Edoxaban is a novel, potent and orally active direct Factor Xa (FXa) inhibitor under development for prophylaxis and treatment of thromboembolic diseases. Properties of dose response and margin of safety of anticoagulants are the key factors for a positive risk/benefit of novel oral anticoagulants.

Objectives

To compare the dose response of antithrombotic effect and margin of safety between antithrombotic and hemorrhagic effects of edoxaban with conventional anticoagulants, unfractionated heparin (UFH), dalteparin (low molecular weight heparin), lepirudin, and warfarin in rat models of thrombosis and hemorrhage.

Methods

Rats were treated with edoxaban, UFH, dalteparin, and lepirudin by continuous intravenous (iv) infusion, or with oral warfarin for 4 days before inducing thrombosis or bleeding. Thrombosis was induced by inserting a platinum wire into the inferior vena cava for 60 minutes. Tail template bleeding time was measured after making an incision on the tail.

Results

In rats, iv infusion of edoxaban inhibited venous thrombosis in a dose-dependent manner. The other anticoagulants also exerted dose-dependent antithrombotic effects. The slopes of the dose–response curves of edoxaban were significantly shallower than the slopes of UFH, dalteparin, and warfarin. At supratherapeutic doses, edoxaban prolonged bleeding time in a rat tail bleeding model. To determine bleeding risk, the margins between antithrombotic and bleeding-time prolongation were compared. The margins of safety of edoxaban were wider than those of UFH, dalteparin, lepirudin, and warfarin.

Conclusions

These results suggest that edoxaban may be more easily controlled and has the potential for a more positive risk/benefit ratio compared to conventional anticoagulants.     

Safety assessment and pharmacodynamics of a novel ultra low molecular weight heparin (RO-14) in healthy volunteers--a first-time-in-human single ascending dose study

Introduction

RO-14 is a novel ultra low molecular heparin. The purpose of this study was to evaluate the safety and pharmacodynamic profile of RO-14 in healthy males.

Materials and methods

We conducted a two-stage, single-center, open-label, randomized study. Two cohorts of 6 volunteers were randomly assigned to 12 single, ascending subcutaneous doses (1750-19950 IU of anti-FXa activity) in an alternating crossover fashion. Safety was assessed by spontaneous/elicited adverse events, medical examination and laboratory tests. Anti-FXa activity and anti-FIIa activity were assessed throughout the 24 hours after dosing. Dose proportionality and linearity of the anti-FXa activity were evaluated.

Results

All doses were well tolerated and there were no bleeding events. At the lowest dose, anti-FXa activity A_max was 0.16 (± 0.02) IU/mL and AUC_0-24 was 1.11 (± 0.24) IU*h/mL, At the highest dose anti-FXa activity A_max was 1.67 (± 0.15) IU/mL; AUC_0-24 was 21.48 (± 4.46) IU*h/mL and t½ was 8.05 h. Mean T_max (all doses) was 2.86 (± 0.39) h. RO-14 showed proportional and linear pharmacodynamics [normalized A_max among doses (p = 0.594) and normalized AUC_0-24 (p = 0.092), correlations between A_max-dose (R² = 0.89, p < 0.001) and AUC_0-24-dose (R² = 0.86, p < 0.001)]. Anti-FIIa activity was below the detection limit (0.1 IU/ml) at all dose levels. No clinically significant changes were observed in the platelet count, APTT, PT, TT, fibrinogen and antithrombin.

Conclusions

In this phase I study, RO-14 exhibited a good safety profile, anti-FXa activity for either prophylaxis or treatment of venous thromboembolism, linear pharmacodynamics, a longer elimination half-life than currently marketed low molecular weight heparin and no anti-FIIa activity.