Betrixaban: a direct oral inhibitor of activated factor X for the prophylaxis of venous thromboembolism in patients hospitalized for acute medical illness.

Venous thromboembolism (VTE), comprising deep vein thrombosis and pulmonary embolism, is a serious clinical and public health concern. Hospitalization is a major risk factor for developing VTE. Hospital-associated events account for more than 50% of all cases of VTE. Heparins have demonstrated to be efficacious in the prevention of VTE in medically ill patients. Despite the demonstrated efficacy and safety of the available direct oral anticoagulants in the prevention and treatment of different thromboembolic conditions, their net benefit in the prevention of VTE in hospitalized medically ill patients has not been fully confirmed. Betrixaban is an oral, specific and direct inhibitor of human coagulation factor Xa with demonstrated efficacy and safety for the prevention of VTE in patients undergoing total knee replacement and in patients with nonvalvular atrial fibrillation. Recent studies have successfully evaluated betrixaban 80 mg once daily in the prevention of VTE in acute medically ill patients in a large phase III trial. This review will address preclinical pharmacology and main aspects of the clinical development of betrixaban as an antithrombotic agent, with specific attention to recent studies on the prophylaxis of VTE in a specific population of patients hospitalized for acute medical illnesses.

Andexanet alfa: a recombinant mimetic of human factor Xa for the reversal of anticoagulant therapies.

Activated coagulation factor X (FXa) is a common target for classic and newer anticoagulants. Parenteral anticoagulants with an indirect inhibitory action on FXa (low-molecular-weight heparins) have a well-established clinical efficacy in the prophylaxis and therapy of thromboembolic conditions. More recently developed direct oral anticoagulants (DOACs) have emerged as a new class of antithrombotic drugs. Rivaroxaban, apixaban and edoxaban are direct inhibitors of FXa approved for the management of venous thromboembolism and stroke prevention in atrial fibrillation. Although these DOACs are associated with fewer hemorrhagic side effects than classic vitamin K antagonists, bleeding is still a main complication. FXa antagonists had no specific agents that could reverse their antihemostatic effects. Andexanet alfa is a modified, recombinant human FXa molecule with an enhanced ability to bind to both direct and indirect FXa inhibitors, but unable to contribute to blood coagulation mechanisms. Andexanet alfa is designed to reverse the anticoagulant effects of FXa inhibitors. This review will address the preclinical pharmacology and the main aspects of the clinical development of andexanet alfa for the reversal of anticoagulant therapies with an inhibitory action on FXa. It will also summarize additional completed or ongoing studies on andexanet alfa available to the scientific community until present.

Apixaban in the prevention of stroke and systemic embolism in nonvalvular atrial fibrillation.

Conventional anticoagulant therapies can significantly reduce the risk of stroke and related complications in patients with atrial fibrillation (AF). Classic oral anticoagulants based on vitamin K antagonism have shown effectiveness in the prevention of thromboembolic complications in this clinical setting. Unfortunately, vitamin K antagonists that have shown effectiveness in the prevention of thromboembolic complications in patients with nonvalvular AF hold inherent limitations including delayed onset of action, narrow therapeutic index, variability of their response, need for repeated control and numerous interactions with food and other drugs. Since the frequency of stroke related to AF increases with age, guidelines from different scientific societies advise that the risk of bleeding for a patient should be quantified before exposure to anticoagulation and balanced against the risk of stroke with and without anticoagulation. A consequence of assessing this risk/benefit balance is that not all patients with AF at thromboembolic risk receive adequate anticoagulant treatment. Apixaban is a new oral anticoagulant with a direct, specific and reversible inhibitory action on coagulation factor Xa and with demonstrated safety and efficacy in the prophylaxis and treatment of venous thromboembolism in several clinical studies involving thousands of patients subjected to major orthopedic surgery. Results of two large phase III trials have demonstrated the efficacy and safety of apixaban compared with aspirin or warfarin, in the prevention of stroke in patients with AF. Apixaban demonstrated superiority over classic vitamin K antagonists on the previously specified outcomes of stroke, systemic embolism, major bleeding and death. For those patients unsuitable for treatment with vitamin K antagonists because of an excessive bleeding risk, apixaban showed more efficacy than aspirin in stroke prevention with a not statistically significant modest increase of major bleeding.

Enoxaparin as bridging anticoagulant treatment in cardiac surgery.

OBJECTIVE: To assess enoxaparin as bridging anticoagulant treatment in cardiac surgery. METHODS: Prospective registry of those patients who underwent cardiac surgery in our centre between December 2003 and June 2004 and required long-term anticoagulation. Subcutaneous enoxaparin was used as bridging anticoagulant treatment according to a pre-established protocol. The global thromboembolic risk was carefully assessed in all patients. All patients were followed up for 3 months. RESULTS: Of 140 patients who were included (mean (SD) age 66 (11); 49% female), 51 were already receiving long-term acenocumarol treatment before the index intervention. 50% of the patients were at high or very high risk for thromboembolic events in the postoperative period. The mean (SD) number of days between surgery and the first dose of anticoagulant was 2.01 (7) for acenocumarol and 1 (1.01) for enoxaparin. The mean (SD) daily dose of enoxaparin was 1.1 (0.27) mg/kg. Six thromboembolic events (4.3%; 95% CI 1.6 to 9.1) occurred, but only four of them were plausibly related to enoxaparin (2.9%; 95% CI 0.8 to 7.1). Six major haemorrhagic events (4.3%; 95% CI 1.6 to 9.1) occurred, but only three were plausibly related to enoxaparin (2.1%; 95% CI 0.4 to 6.1). CONCLUSIONS: These findings show a reasonable rate of adverse events using enoxaparin as bridging anticoagulant treatment in cardiac surgery. Randomised studies are necessary to evaluate the real efficacy and safety of enoxaparin as bridging anticoagulant treatment in cardiac surgery.

Essential thrombocythemia in young individuals: frequency and risk factors for vascular events and evolution to myelofibrosis in 126 patients.

The frequency of vascular events and evolution to myelofibrosis (MF) in young individuals with essential thrombocythemia (ET) is not well known. The incidence and predisposing factors to such complications was studied in 126 subjects diagnosed with ET at a median age of 31 years (range: 5-40). Overall survival and probability of survival free of thrombosis, bleeding and MF were analyzed by the Kaplan-Meier method and the presence of the Janus Kinase 2 (JAK2) V617F mutation correlated with the appearance of such complications. The JAK2 mutation (present in 43% of patients) was associated with higher hemoglobin (Hb) (P<0.001) and lower platelets at diagnosis. With a median follow-up of 10 years (range: 4-25), 31 thrombotic events were registered (incidence rate: 2.2 thromboses/100 patients/year). When compared with the general population, young ET patients showed a significant increase in stroke (odds ratio 50, 95% CI: 21.5-115) and venous thromboses (odds ratio 5.3, 95% CI: 3.9-10.6). Thrombosis-free survival was 84% at 10 years, with tobacco use being associated with higher risk of thrombosis. Actuarial freedom from evolution to MF was 97% at 10 years. In conclusion, young ET patients have thrombotic events, especially stroke and venous thrombosis, more frequently than generally considered, whereas they rarely transform to MF.

Frequency and risk factors for thrombosis in idiopathic myelofibrosis: analysis in a series of 155 patients from a single institution.

Thrombosis is a frequent complication of polycythemia vera and essential thrombocythemia, but its incidence and predisposing factors in idiopathic myelofibrosis (IM) are unknown. In 18 (11.6%) of 155 patients diagnosed with IM in a single institution, 31 thrombotic events (19 arterial, 12 venous) were registered after a mean follow-up of 4.2 (s.d.: 4.5) years. In six patients, the thrombosis was simultaneous to or appeared a few months before IM diagnosis and 14 had one or more thrombotic episodes. When compared with the general population, a significant increase was observed in the incidence of venous thrombosis (odds ratio 17.5, 95% confidence interval: 10.3-31.4). At multivariate analysis, the initial variables associated with an increased risk of thrombosis were thrombocytosis (platelets >450 x 10(9)/l, P=0.001), presence of one cardiovascular risk factor (arterial hypertension, smoking, hypercholesterolemia, or diabetes, P=0.003), cellular phase of myelofibrosis (P=0.005), and Hb >11 g/dl (P=0.02). Considering post-diagnosis events, the 5-year thrombosis-free survival probability was 90.4% in the series, 80.6% for patients with platelets >450 x 10(9)/l, 82.6% for patients with one cardiovascular risk factor, and 85.1% for those in cellular phase. These results indicate an increased thrombotic risk for IM patients with hyperproliferative features and/or coexistent cardiovascular risk factors.

Successful treatment by selective arterial embolization of severe retroperitoneal hemorrhage secondary to bone marrow biopsy in post-polycythemic myelofibrosis.

Severe retroperitoneal hemorrhage represents an infrequent and serious complication of bone marrow biopsy. A 53-year-old man, diagnosed with polycythemia vera 12 years earlier, was submitted to a bone marrow biopsy due to the appearance of anemia with clinical and hematological features suggesting myelofibrotic transformation, a diagnosis that was confirmed by the marrow study. At 2 h of a right anterior iliac bone marrow trephine biopsy, the patient suddenly developed severe pain in the area of the biopsy, with antialgic flexion of the right leg. Computed tomographic (CT) scan of the abdomen showed a 5 x 9.5 cm hematoma in the right iliac and psoas muscles. The patient was initially managed with analgesics and transfusional support, but the pain persisted and a continuous fall in the hematocrit was observed in the following days. Angiographic examination of the right external iliac artery showed contrast extravasation arising from the circumflex iliac branch, which was embolized using polivinyl alcohol particles and one coil. Following such procedure, the patient recovered uneventfully and was discharged in good condition a few days later. This case illustrates the effectiveness of an endovascular approach in providing a fast and minimally invasive treatment for this life-threatening complication of bone marrow trephine biopsy.