Specific antidotes against direct oral anticoagulants: A comprehensive review of clinical trials data

Use of novel oral anticoagulant agents in venous thromboembolism

New oral anticoagulants (NOAC) serve as alternatives for patients currently using warfarin for the prevention and treatment of venous thromboembolic (VTE) disease. This article provides a brief summary of the clinical use of these drugs as well as a review of the landmark clinical trials which evaluated described their safety and efficacy. As more data becomes available, a fundamental understanding of these medications will be vital to cardiovascular practitioners managing patients with VTE.

Stroke prevention

Patients who have had a stroke are at high risk for recurrent stroke, myocardial infarction, and vascular death. Prevention of these events should be initiated promptly after stroke, because many recurrent events occur early, and should be tailored to the precise cause of stroke, which may require specific treatment. Lifestyle advice including abstinence from smoking, regular exercise, Mediterranean-style diet, and reduction of salt intake and alcohol consumption are recommended for all patients with stroke. For most patients with ischemic stroke or TIA, control of risk factors, including lowering blood pressure under 140/90mmHg and LDL cholesterol under 1g/L, together with antiplatelet or oral anticoagulant therapy, depending on the cause of stroke, have been shown to decrease the risk of recurrent stroke and cardiovascular events. Aspirin, clopidogrel, or the combination of aspirin and dipyridamole, are all acceptable options for secondary prevention in patients with ischemic stroke or TIA of arterial origin. Dual therapy with aspirin and clopidogrel might be considered for 3 weeks after a minor ischemic stroke or TIA and for 3 months in patients with stroke due to severe intracranial stenosis. Oral anticoagulants are very effective to prevent cardioembolic stroke. Non-VKA oral anticoagulants have a favorable risk-benefit profile compared with VKAs, with significant reductions in stroke, intracranial hemorrhage, mortality, with similar major bleeding, but increased gastrointestinal bleeding. Carotid endarterectomy reduces the risk of ipsilateral stroke in patients with recent (<6 months) non disabling ischemic stroke or TIA in the territory and severe carotid artery stenosis. Carotid stenting is a potential alternative to surgery in patients younger than ≈70 years or patients with greater risk of surgery due to anatomic or medical conditions or specific circumstances such as radiation-induced stenosis or restenosis after surgery. For patients with hemorrhagic stroke due to hypertension-associated small vessel disease or cerebral amyloid angiopathy, strict control of blood pressure is essential. Restarting oral anticoagulants in patients after intracranial hemorrhage is a difficult decision that should weigh the risks of recurrent ischemic and hemorrhage stroke with and without oral anticoagulants. Several areas of uncertainty persist including the optimal target of blood pressure in patients with cerebrovascular disease, the benefit of PFO closure in patients with PFO-associated stroke, of stenting procedures in patients with atherosclerotic intracranial artery or extracranial vertebral artery stenosis, and of interventional procedures in patients with brain arteriovenous or cavernous malformations.

New Oral Anticoagulants and Their Reversal Agents

OPINION STATEMENT

Direct oral anticoagulants (DOAC) are an attractive therapeutic option for anticoagulant treatment in the setting of venous thromboembolism or non-valvular atrial fibrillation. These drugs overall appear to have a lower risk of life-threatening hemorrhage than the vitamin K antagonists. In addition, they demonstrate more predictable and stable pharmacokinetics. Measurement of the degree of anticoagulation is desirable in patients with DOAC-associated hemorrhage, but commonly available coagulation assays show poor sensitivity for degree of DOAC effect. DOAC-specific tests are time consuming and not widely available. All coagulation tests should be interpreted considering the timing of last intake and renal function. When life-threatening bleeding occurs, hemostasis should be restored as rapidly as possible. Non-specific prohemostatic drugs may have a role in DOAC reversal, and specific antidotes are at different stages of development. In this review, we provide a summary of DOAC characteristics and an overview of the different therapeutic options available for DOAC reversal.

Intravenous thrombolysis in acute ischemic stroke after dabigatran reversal with idarucizumab - a case report

Much excitement has been generated with the approval of idarucizumab, a humanized monoclonal antigen‐binding antibody fragment that is capable of reversing the anticoagulant activity of dabigatran. Here, we describe our initial experience of using tissue plasminogen activator (tPA) in an acute posterior circulation ischemic stroke after dabigatran reversal with idarucizumab. Both treatments were well tolerated and no hemorrhagic or procoagulatory complications were observed. We propose that the option of dabigatran reversal needs to be considered for contemporary treatment concepts of acute ischemic stroke.

Exactin: A specific inhibitor of Factor X activation by extrinsic tenase complex from the venom of Hemachatus haemachatus

Unwanted clots lead to heart attack and stroke that result in a large number of deaths. Currently available anticoagulants have some drawbacks including their non-specific actions. Therefore novel anticoagulants that target specific steps in the coagulation pathway are being sought. Here we describe the identification and characterization of a novel anticoagulant protein from the venom of Hemachatus haemachatus (African Ringhals cobra) that specifically inhibits factor X (FX) activation by the extrinsic tenase complex (ETC) and thus named as exactin. Exactin belongs to the three-finger toxin (3FTx) family, with high sequence identity to neurotoxins and low identity to the well-characterized 3FTx anticoagulants-hemextin and naniproin. It is a mixed-type inhibitor of ETC with the kinetic constants, Ki’ and Ki determined as 30.62 ± 7.73 nM and 153.75 ± 17.96 nM, respectively. Exactin does not bind to the active site of factor VIIa and factor Xa based on its weak inhibition (IC₅₀ ≫ 300 μM) to the amidolytic activities of these proteases. Exactin shows exquisite macromolecular specificity to FX activation as compared to factor IX activation by ETC. Exactin thus displays a distinct mechanism when compared to other anticoagulants targeting ETC, with its selective preference to ETC-FX [ES] complex.