What did we learn from new oral anticoagulant treatment?

Pharmacological Difference Between Platelet Aggregations in Cardioembolic Stroke Patients with Direct Oral Anticoagulants: A Pilot Study

Background Selecting the appropriate direct oral anticoagulants (DOACs) for embolic ischemic stroke patients, especially on concurrent antiplatelet therapy, is important. However, a limited number of studies have reported on the pharmacological differences in platelet aggregation of each DOAC. We aimed to evaluate the antiplatelet effects of selected DOACs, by comparing dabigatran (a direct oral thrombin inhibitor) and factor Xa (FXa) inhibitors (apixaban and rivaroxaban) in patients who had suffered a cardioembolic stroke. Methods We retrospectively evaluated 12 patients diagnosed with a cardioembolic stroke who took any DOAC without an antiplatelet drug and underwent platelet aggregation tests within 60 days from the onset of symptoms. The platelet aggregation tests were analyzed by both light transmission aggregometry and VerifyNow®. Results Six patients (50%) took dabigatran, while the other six (50%) took an FXa inhibitor (n = 4 for apixaban and n = 2 for rivaroxaban). From the light transmission aggregometry analysis, it was found that the maximal extent of aggregation for adenosine diphosphate (ADP) was significantly higher with dabigatran than with FXa inhibitors, and the ED₅₀ value of ADP on platelet aggregation was significantly lower with dabigatran than with FXa inhibitors. Moreover, the VerifyNow® analyses revealed that P2Y₁₂ reaction units were significantly higher with dabigatran than with FXa inhibitors. Conclusions Dabigatran had little impact on platelet aggregation compared to FXa inhibitors in patients who had suffered a cardioembolic stroke with atrial fibrillation, and who took DOACs for secondary prevention within 60 days from the onset.

Platelet activation and prothrombotic mediators at the nexus of inflammation and atherosclerosis: Potential role of antiplatelet agents

Platelets are central to inflammation-related manifestations of cardiovascular diseases (CVD) such as atherosclerosis. Platelet-activating factor (PAF), thrombin, thromboxane A₂ (TxA₂), and adenosine diphosphate (ADP) are some of the key agonists of platelet activation that are at the intersection between a plethora of inflammatory pathways that modulate pro-inflammatory and coagulation processes. The aim of this article is to review the role of platelets and the relationship between their structure, function, and the interactions of their constituents in systemic inflammation and atherosclerosis. Antiplatelet therapies are discussed with a view to primary prevention of CVD by the clinical reduction of platelet reactivity and inflammation. Current antiplatelet therapies are effective in reducing cardiovascular risk but increase bleeding risk. Novel therapeutic antiplatelet approaches beyond current pharmacological modalities that do not increase the risk of bleeding require further investigation. There is potential for specifically designed nutraceuticals that may become safer alternatives to pharmacological antiplatelet agents for the primary prevention of CVD but there is serious concern over their efficacy and regulation, which requires considerably more research.

Combination Antiplatelet and Oral Anticoagulant Therapy in Patients With Coronary and Peripheral Artery Disease

Antiplatelet therapy is the mainstay for the treatment of acute and chronic arterial disease involving the coronary and peripheral beds. However, questions remain about optimal antithrombotic therapy for long-term treatment of chronic vascular disease. The observation that dual antiplatelet therapy with acetylsalicylic acid and clopidogrel was associated with lower thrombotic event rates than acetylsalicylic acid monotherapy in patients with acute coronary syndromes and those undergoing percutaneous coronary intervention changed the treatment paradigm. Moreover, the demonstration that more pharmacodynamically potent P2Y₁₂ inhibitors than clopidogrel were associated with fewer thrombotic event occurrences further solidified the dual antiplatelet therapy approach. However, recurrent thrombotic events occur in ≈1 in 10 patients in the first year following an acute coronary syndrome event, despite treatment with the most potent P2Y₁₂ inhibitors, a limitation that has stimulated interest in exploring the efficacy and safety of approaches using anticoagulants on top of antiplatelet therapy. These investigations have included treatment with very-low-dose oral anticoagulation, and even its replacement of acetylsalicylic acid in the presence of a P2Y₁₂ inhibitor, in patients stabilized after an acute coronary syndrome event. Recent basic and translational studies have suggested noncanonical effects of coagulation factor inhibition that may further modulate clinical benefits. This in-depth review will discuss developments in our understanding of the roles that platelets and coagulation factors play in atherothrombosis and review the rationale and clinical evidence for combining antiplatelet and oral anticoagulant therapy in patients with coronary and peripheral artery disease.

The criteria of the Italian Federation of Thrombosis Centres on DOACs: a "real world" application in nonvalvular atrial fibrillation patients already on vitamin K antagonist

The aim of this study was to evaluate the number of patients with nonvalvular atrial fibrillation (NVAF), anticoagulated with vitamin K antagonists (VKA), and monitored in our Thrombosis Centre, who could replace VKA with direct oral anticoagulants (DOACs) based on the Italian Federation of Thrombosis Centres (FCSA) consensus criteria. A total of 525 NVAF patients treated with VKA were studied. Therapeutic range (TTR) assessment and a capillary test for serum creatinine measure were carried out. The patients' preference was evaluated through the administration of a dedicated questionnaire. A history of intracranial bleeding was also taken into account. DOACs would cover 29 % of the patients considering a TTR <70 %; the percentage falls to 10 % if a TTR <55 % is considered. Only 20 % of the patients would move from VKA to DOACs because of the lack of an antidote and laboratory checks during DOACs therapy. Thirty-three percent of patients were worried that they would forget to take the tablets twice a day. About 2 % of patients could not use DOACs since their glomerular filtration rate was less than 30 ml/min, while in 23.6 %, a reduction in the daily dose of DOACs would have been required due to renal failure. TTR assessment, renal function and a previous history of intracranial bleeding would reduce the percentage of patients who could switch from VKA to DOACs, but it is the patients' preference that strongly influences the percentage of those who would benefit from DOACs treatment. However, if laboratory controls were available, it would rise considerably.

Direct thrombin inhibitors, but not the direct factor Xa inhibitor rivaroxaban, increase tissue factor-induced hypercoagulability in vitro and in vivo

BACKGROUND

Increased hypercoagulability has been reported with low doses of direct thrombin inhibitors but not with direct factor Xa inhibitors.

OBJECTIVES

To compare the effects of rivaroxaban with those of melagatran and dabigatran on thrombin generation (TG) and tissue factor-induced hypercoagulability and to explore the possible involvement of the thrombin-thrombomodulin/activated protein C system.

METHODS

In normal human plasma and in protein C-deficient plasma, TG was investigated in vitro in the presence and absence of recombinant human soluble thrombomodulin (rhs-TM). TG was determined by calibrated automated thrombography and an ELISA for prothrombin fragments 1+2 (F1+2 ). In an in vivo rat model, hypercoagulability was induced by tissue factor; levels of thrombin-antithrombin (TAT) and fibrinogen and the platelet count were determined.

RESULTS

Rivaroxaban inhibited TG in a concentration-dependent manner. In the absence of rhs-TM, melagatran and dabigatran also inhibited TG concentration dependently. However, in the presence of rhs-TM, lower concentrations of melagatran (119-474 nmol L(-1) ) and dabigatran (68-545 nmol L(-1) ) enhanced endogenous thrombin potential, peak TG, and F1+2 formation in normal plasma but not in protein C-deficient plasma. In vivo, rivaroxaban dose-dependently inhibited TAT generation, whereas melagatran showed a paradoxical effect, with an increase in TAT and a small decrease in fibrinogen and platelet count at lower doses.

CONCLUSION

Low concentrations of the direct thrombin inhibitors melagatran and dabigatran enhanced TG and hypercoagulability, possibly via inhibition of the protein C system. In contrast, rivaroxaban reduced TG and hypercoagulability under all conditions studied, suggesting that it does not suppress this negative-feedback system.

Advances in Oral Coagulants

This article reviews current and future treatment practices concerning oral anticoagulants. In the second decade of the 21st millennium clinicians can finally treat thrombotic disease with long-awaited new oral anticoagulant medications. In addition, improvements have been made in managing warfarin, the traditional but far from obsolete medication. The first part of this review will cover current advances with warfarin treatment. The second portion will discuss specific active coagulation factor inhibitors, the new oral anticoagulants.