No abstract

2317 Introduction: Heparin and low molecular weight heparins such as enoxaparin and dlateparin are widely used in the management of thrombosis and cardiovascular disorders. However these anticoagulants are capable of producing the generation of HIT antibodies and their use is not recommended in patients with previous history of HIT. More recently several new oral anticoagulants have been approved around the world. These include the oral anti-Xa agents namely, Apixaban (Bristol-Myers Squibb), Rivaroxaban(Bayer Healthcare) and anti-IIa agents, dabigatran (Boehringer-Ingelheim). All of these represent synthetic low molecular weight compounds. Apixaban and Rivaroxaban are active agents where as Dabigatran requires endogenous activation. The purpose of this investigation was to determine the relative effects of the newer anticoagulants and enoxaparin on HIT antibody mediated platelet aggregation and other interactions with platelets. Materials: Rivaroxaban was obtained in powdered form from Bayer Healthcare (Wuppertal, Germany) Apixaban and Dabigatran were of synthetic origin. Enoxaparin was obtained from Sanofi-Aventis (paris, France). All drugs were dissolved in appropriate solutions and a working solution of 100 ug/ml was prepared in buffered saline. Pooled HIT sera was prepared by pooling clinically symptomatic HIT patients with high titers of anti-heparin platelet factor 4 antibodies. Method: Whole blood samples drawn from normal healthy volunteers were supplemented with each of these agents at a graded concentration of 0–100 ug/ml for 60 minutes to determine the relative release of platelet factor 4. To test the interaction of HIT antibody with each of these agents 50 ul of PRP samples were mixed with 150 ul HIT positive heat inactivated sera/plasma or plasmapheresis fliud (collected from symptomatic HIT patients). Graded amounts of each of these new anticoagulants at 0.1, 1.0 and 10 ug/ml were added to test the platelet aggregation response at a period of 60 minutes. Results: In contrast to enoxaparin which produced an increase in the platelet factor 4 release upon 60 minute incubation 25.6+3.1 ng/ml), none of the new oral anticoagulants produced an increase in the PF4 <15.0 ng/ml. Enoxaparin also produced a strong HIT antibody mediated response, whereas none of these newer oral agents produced any aggregation responses. Conclusion: These studies demonstrate that –enoxaparin the newer oral anticoagulant drugs do not interact with HIT antibody to mediate plarelet aggregation responses. Moreover, these newer agents do not promote platelet factor 4 release. Thus, these agents can be used in the long term anticoagulant management of heparin compromised patients. Disclosures: No relevant conflicts of interest to declare.

The newer oral anticoagulants include Dabigatran, Apixiban and Rivaroxiban. These drugs are developed for the DVT and stroke prevention in atrial fibrillation. These drugs are useful as alternate anticoagulants for heparin compromised patients. The purpose of this investigation was to study their effects on agonist induced platelet aggregation. Such agonist as epinephrine, collagen, arachidonic acis, ADP and thrombin were used in whole blood (multiplate) and citrated PRP systems (PAP8). In addition the interaction of these agents with heparin induced thrombocytopenia associated antibodies were also studied. Each of these agents were supplemented in citrated whole blood at a concentration range of 0–10ug/ml, agonists were added and the aggregation profile was recorded in both the whole blood and PRP. Serum from patients with HIT syndrome was also used to compare the aggregation profile of these agents with heparin. None of these newer oral anticoagulants produced any alterations of the aggregation profile in both the whole blood and platelet rich plasma (20–30;p=<0.05) with all of the agonists except thrombin. Dabigatran supplemented systems showed inhibition wheras Apixiban and Rvaroxiban did not produce inhibition of thrombin aggregation. These results suggest that newer oral anticoagulants do not impair the agonist induced platelet aggregation and will be useful in heparin compromised patients.

Careful adjustment of the dosages of anticoagulant drugs may be necessary to avoid bleeding or thrombosis.

5131 Argatroban represents a parentral antithrombin agent which is used in the management of anticoagulation in heparin compromised patients. Its main mechanism of action is mediated via inhibition of thrombin and its generation. While its effect on platelet activation inhibition by thrombin have been reported, very little information on the effects of this drug on thromboxane formation and Arachidonic Acid mediated activation of platelets is available. Argatroban and its generic versions namely Slovastan, Argaron and Gartban, may modulate Arachidonic Acid mediated platelet aggregation and release processes. To test this hypothesis a branded version of Argatroban (Mitsubishi – Tanade, Tokyo, Japan) and three generic versions of Argatroban namely Slovastan, Gartban, and Slovastan were compared for their effects on Arachidonic Acid mediated aggregation of platelets in normal healthy male and female volunteers (and n = 4). Other agonists such as Epinephrine, Collagen, and ADP were also used. The effect of Arachidonic Acid on serotonin release was also measured using an Elisa technique for the measurement of serotonin. All of the generic and branded versions of Argatroban produce varying levels of the inhibition of the Arachidonic Acid mediated aggregation of platelets, ranging from the 24 to 36 percent in comparison to the control at a concentration of 1 mg/ mL (p value < 0.05). Interestingly all of the Argatrobans produced a relatively weaker inhibition of the Arachidonic Acid mediated aggregation of platelets 24–26 percent inhibition versus 36 percent at the final concentration of 1 mg/mL. No differences were noted in the aggregation profile of ADP, Collagen, and Epinephrine between the control and the Argatrboban at a final concentration of 1 mg /mL. No differences were noted between the generic and branded Argatroban on all of the other agonists induced aggregation. In the serotonin release assays, all of the generic and branded Argatroban produced a concentration dependent inhibition of serotonin release which was stronger with the branded version of Argatroban. These results indicate that besides the inhibition of thrombin Argatroban is capable of inhibiting platelet activation via other mechanisms. Moreover, the generic versions of Argatroban exhibit a weaker inhibition of Arachidonic Acid mediated platelet aggregation and release. These studies suggest that beside thrombin mediated aggregation Argatroban and its generic versions can modulate platelet activation and release reactions. Furthermore a difference is observed between the generic and branded product which may impact the safety inefficacy profile in these agents. Argatroban is used commonly in the management of patients with heparin induced thrombocytopenia where multiple mechanisms of platelet activation are contributory to the pathogenesis of this syndrome. Modulation of thrombanxane formation and platelet release mechanism by Argatroban may represent an additional mechanism of the clinical effects of this parentral antithrombin agent. Disclosures: No relevant conflicts of interest to declare.