Procoagulant activities of skeletal and cardiac muscle myosin depend on contaminating phospholipid.

Recent reports indicate that suspended skeletal and cardiac myosin, such as might be released during injury, can act as procoagulants by providing membrane-like support for factors Xa and Va in the prothrombinase complex. Further, skeletal myosin provides membrane-like support for activated protein C. This raises the question of whether purified muscle myosins retain procoagulant phospholipid through purification. We found that lactadherin, a phosphatidyl-l-serine-binding protein, blocked >99% of prothrombinase activity supported by rabbit skeletal and by bovine cardiac myosin. Similarly, annexin A5 and phospholipase A2 blocked >95% of myosin-supported activity, confirming that contaminating phospholipid is required to support myosin-related prothrombinase activity. We asked whether contaminating phospholipid in myosin preparations may also contain tissue factor (TF). Skeletal myosin supported factor VIIa cleavage of factor X equivalent to contamination by ∼1:100 000 TF/myosin, whereas cardiac myosin had TF-like activity >10-fold higher. TF pathway inhibitor inhibited the TF-like activity similar to control TF. These results indicate that purified skeletal muscle and cardiac myosins support the prothrombinase complex indirectly through contaminating phospholipid and also support factor X activation through TF-like activity. Our findings suggest a previously unstudied affinity of skeletal and cardiac myosin for phospholipid membranes.

Novel factor Xa inhibitor, maslinic acid, with antiplatelet aggregation activity.

As antithrombotic effects of maslinic acid (MA) have not yet been studied, MA-mediated downregulation of coagulation factor Xa (FXa) and platelet aggregation was studied. We show that MA inhibited the enzymatic activity of FXa and platelet aggregation, induced by adenosine diphosphate (ADP) and a thromboxane A2 (TXA2 ) analog, U46619 with a similar antithrombotic efficacy to rivaroxaban, a direct FXa inhibitor used as a positive control. Mechanistically, MA suppressed U46619- or ADP-induced phosphorylation of myristoylated alanine-rich C kinase substrate, and the expression of P-selectin, and activated PAC-1 in platelets. MA increased generation of nitric oxide, but downregulated excessive secretion of endothelin-1 in ADP- or U46619-treated human umbilical vein endothelial cells. In arterial and pulmonary thrombosis mouse model, MA showed prominent anticoagulant and antithrombotic effects. Our data suggest MA as a candidate molecule for a new class of drugs targeting anti-FXa and antiplatelet.

Anticoagulation Management and Antithrombin Supplementation Practice during Veno-venous Extracorporeal Membrane Oxygenation: A Worldwide Survey.

BACKGROUND: There is a lack of consensus on how to manage anticoagulation during veno-venous extracorporeal membrane oxygenation, including antithrombin monitoring and supplementation. The authors' aim was to determine current practice in a large number of extracorporeal membrane oxygenation centers around the world. METHODS: This was an electronic survey disseminated in 2018 to directors and coordinators of extracorporeal membrane oxygenation centers as well as to extracorporeal membrane oxygenation experts. Participating centers were classified according to some covariates that may affect practice, including 2017 gross national income per capita, primary patient population, and annual extracorporeal membrane oxygenation patient volume. RESULTS: The authors analyzed 273 unique responses from 50 countries. Systemic anticoagulation was routinely prescribed in 264 (96.7%) centers, with unfractionated heparin being the drug of choice in 255 (96.6%) of them. The preferred method to monitor anticoagulation was activated partial thromboplastin time in 114 (41.8%) centers, activated clotting time in 82 (30.0%) centers, and anti-factor Xa activity in 62 (22.7%) centers. Circulating antithrombin activity was routinely monitored in 133 (48.7%) centers. Antithrombin supplementation was routinely prescribed in 104 (38.1%) centers. At multivariable analyzes, routine antithrombin supplementation was associated with national income, being less likely in lower- than in higher-income countries (odds ratio, 0.099 [95% CI, 0.022 to 0.45]; P = 0.003); with primary patient population being more frequent in mixed (odds ratio, 2.73 [1.23 to 6.0]; P = 0.013) and pediatric-only centers (odds ratio, 6.3 [2.98 to 13.2]; P < 0.001) than in adult-only centers; but not with annual volume of extracorporeal membrane oxygenation cases, being similarly common in smaller and larger centers (odds ratio, 1.00 [0.48 to 2.08]; P = 0.997). CONCLUSIONS: There is large practice variation among institutions regarding anticoagulation management and antithrombin supplementation during veno-venous extracorporeal membrane oxygenation. The paucity of prospective studies and differences across institutions based on national income and primary patient population may contribute to these findings.

Apixaban exhibits anti-arthritic effects by inhibiting activated factor X-mediated JAK2/STAT3 and MAPK phosphorylation pathways.

Activated factor X (FXa) is strongly linked to various inflammatory events. This study aimed to investigate the effect of FXa on janus kinase2/signal transducers and activators of transcription3 (JAK2/STAT3) and mitogen-activated protein kinase (MAPK) phosphorylation in relation to rheumatoid arthritis (RA). It also extends its scope to explore the possible anti-arthritic effects of apixaban, a selective FXa inhibitor. Rats were allocated into normal control; complete Freund's adjuvant (CFA, 0.4 ml/4 days/12 days); FXa (120 µg/kg/day/3 days) and CFA + FXa groups as well as three treated groups including CFA + apixaban; FXa + apixaban and CFA + FXa + apixaban. Apixaban was administered at a dose of 10 mg/kg/12 h for15 days. By the end of the experimental period, tissue samples were collected for the assessment of phosphorylated (p)-JAK2, STAT3, MAPK, matrixmetalloprotein-1 (MMP-1) and protease-activated receptor 2. Furthermore, Serum interleukin-6 (IL-6), platelet-derived growth factor (PDGF), anti-citrullinated protein antibody (ACPA), 8-hydroxy-2'-deoxyguanosine (8-OHdG), plasma level of FXa and prothrombin time were evaluated. In support, histopathological and macroscopical examinations were performed. FXa activated JAK2, STAT3 and MAPK phosphorylation through activation of PAR 2, PDGF and IL-6 and concomitantly led to a significant elevation in ACPA, MMP-1 and 8-OHdG. Apixaban markedly amended FXa-induced changes. Conclusively, the current study revealed that FXa may have a drastic role in RA progression and pathogenesis at least through stimulation of JAK2/STAT3 and MAPK phosphorylation. Furthermore, apixaban exerted robust arthro-protective effects. These beneficial outcomes could be attributed to its ability to impede JAK2/STAT3 and MAPK activation, as well as to its antioxidant property.

Antiplatelet and anticoagulant activities of two phospholipase A2s purified from Cerastes cerastes venom: Structure-function relationship.

This study aimed to elucidate anticoagulant/antiplatelet mechanisms of two previously purified PLA2 s from Cerastes cerastes venom, here, termed Cc1 -PLA2 and Cc2 -PLA2 . Both PLA2 s present close molecular weights of 13,534 and 13,430 Da and Isoectric pH (pI) 7.38 and 7.86 respectively, for Cc1 -PLA2 and Cc2 -PLA2 . These Ca2+ -dependent enzymes showed a high catalytic activity upon phospholipids, inducing indirect hemolysis, since they conserve the catalytic domain of PLA2 s 26 CYCGWGGKG34 . They exhibited dual inhibition of platelet aggregation by targeting P2 Y12 and TPα receptors preventing Adenosine diphosphate/arachidonate binding and blood clotting. These effects are due to the interaction of Cc1 -PLA2 s/Cc2 -PLA2 s with factor FXa through a noncatalytic PL-independent mechanism leading to nonreleased thrombin. Both proteins consist of 120 amino acid residues and share similar three-dimensional structures close to other SV-PLA2 s. Structural data of PLA2 s allowed the relevant residues involved in binding to FXa and platelet receptors. These findings may lead to the design of novel noncompetitive FXa inhibitors.

Rivaroxaban Levels in Patients' Plasmas are Comparable by Using Two Different Anti Xa Assay/Coagulometer Systems Calibrated with Two Different Calibrators.

BACKGROUND: Rivaroxaban oral anticoagulant does not need laboratory monitoring, but in some situations plasma level measurement is useful. The objective of this paper was to verify analytical performance and compare two rivaroxaban calibrated anti Xa assays/coagulometer systems with specific or other branch calibrators. METHODS: In 59 samples drawn at trough or peak from patients taking rivaroxaban, plasma levels were measured by HemosIL Liquid anti Xa in ACLTOP 300/500, and STA liquid Anti Xa in TCoag Destiny Plus. HemosIL and STA rivaroxaban calibrators and controls were used. CLSI guideline procedures EP15A3 for precision and trueness, EP6 for linearity, and EP9 for methods comparison were used. RESULTS: Coefficient of variation within run and total precision (CVR and CVWL respectively) of plasmatic rivaroxaban were < 4.2 and < 4.85% and BIAS < 7.4 and < 6.5%, for HemosIL-ACL TOP and STA-Destiny systems, respectively. Linearity verification 8 - 525 ng/mL a Deming regression for methods comparison presented R 0.963, 0.968 and 0.982, with a mean CV 13.3% when using different systems and calibrations. CONCLUSIONS: The analytical performance of plasma rivaroxaban was acceptable in both systems, and results from reagent/coagulometer systems are comparable even when calibrating with different branch material.

Establishment of prophylactic enoxaparin dosing recommendations to achieve targeted anti-factor Xa concentrations in children with CHD.

BACKGROUND: Enoxaparin may be used to prevent central venous catheter-related thrombosis in patients with CHD. We aimed to determine whether current enoxaparin dosing regimens effectively achieve anti-factor Xa concentrations within prophylactic goal ranges in this patient population. METHODS: We implemented a formal protocol aimed at reducing central venous catheter-related thrombosis in children with CHD in January, 2016. Standard empiric prophylactic enoxaparin dosing regimens were used - for example, 0.75 mg/kg/dose every 12 hours for patients <2 months of age and 0.5 mg/kg/dose every 12 hours for patients ⩾2 months of age - with anti-factor Xa goal range of 0.25-0.49 IU/ml. Patients <2 years of age who received enoxaparin and had at least one valid steady-state anti-factor Xa measurement between 25 January, 2016 and 31 August, 2016 were retrospectively reviewed. RESULTS: During the study period, 47 patients had 186 anti-factor Xa concentrations measured, of which 20 (11%) were above and 112 (60%) were below the prophylactic goal range. Anti-factor Xa concentrations within the goal range were ultimately achieved in 31 patients. Median dose required to achieve anti-factor Xa concentrations within the prophylactic range was 0.89 mg/kg/dose (25, 75%: 0.75, 1.11) for patients <2 months (n=23 patients) and 0.79 mg/kg/dose (25, 75%: 0.62, 1.11) for patients ⩾2 months (n=8 patients). CONCLUSIONS: Enoxaparin doses required to achieve prophylactic anti-factor Xa concentrations in young children with CHD were consistently higher than the currently recommended prophylactic dosing regimens. Further study is needed to determine whether dose titration to achieve prophylactic anti-factor Xa concentrations is effective in preventing central venous catheter-related thrombosis.

Coagulation Factor Xa and Protease-Activated Receptor 2 as Novel Therapeutic Targets for Diabetic Nephropathy.

OBJECTIVE: The role of hypercoagulability in the pathogenesis of diabetic nephropathy (DN) remains elusive. We recently reported the increased infiltration of macrophages expressing tissue factor in diabetic kidney glomeruli; tissue factor activates coagulation factor X (FX) to FXa, which in turn stimulates protease-activated receptor 2 (PAR2) and causes inflammation. APPROACH AND RESULTS: Here, we demonstrated that diabetes mellitus increased renal FX mRNA, urinary FXa activity, and FX expression in glomerular macrophages. Administration of an oral FXa inhibitor, edoxaban, ameliorated DN with concomitant reductions in the expression of PARs (Par1 and Par2) and of proinflammatory and profibrotic genes. Diabetes mellitus induced PAR2, and lack of Par2 ameliorated DN. FXa or PAR2 agonist increased inflammatory cytokines in endothelial cells and podocytes in vitro. CONCLUSIONS: We conclude that enhanced FXa and PAR2 exacerbate DN and that both are promising targets for preventing DN. Alleviating inflammation is probably more important than inhibiting coagulation per se when treating kidney diseases using anticoagulants.

Edoxaban vs warfarin in patients with nonvalvular atrial fibrillation in the US Food and Drug Administration approval population: An analysis from the Effective Anticoagulation with Factor Xa Next Generation in Atrial Fibrillation-Thrombolysis in Myocardial Infarction 48 (ENGAGE AF-TIMI 48) trial.

BACKGROUND: Edoxaban is a specific anti-Xa inhibitor that, in comparison to warfarin, has been found to be noninferior for the prevention of stroke or systemic embolism (SSE) and to reduce bleeding significantly in patients with nonvalvular atrial fibrillation (AF). The US Food and Drug Administration (FDA) approved the higher-dose edoxaban regimen (60/30 mg) in patients with AF and a creatinine clearance of ≤95 mL/min. We report for the first time the clinical characteristics, efficacy, and safety of the FDA-approved population in the ENGAGE AF--TIMI 48 trial. METHODS: The patients included had been treated with either warfarin or edoxaban 60/30 mg and had a creatinine clearance of ≤95 mL/min. The primary efficacy was SSE, and the principal safety end point was major bleeding (International Society on Thrombosis and Haemostasis classification). Median follow-up was 2.8 years. RESULTS: Patients in the FDA-approved cohort were older, were more likely female, and had higher CHADS2 and HAS-BLED scores, as compared with patients not included in the FDA label. The primary end point occurred in 1.63%/y with edoxaban vs 2.02%/y with warfarin (hazard ratio [HR] 0.81, 95% CI 0.67-0.97, P = .023). Edoxaban significantly reduced the rate of hemorrhagic stroke (HR 0.47, 95% CI 0.31-0.72, P < .001) and cardiovascular death (HR 0.84, 95% CI 0.73-0.97, P = .015). Ischemic stroke rates were similar between the treatment groups (1.31%/y vs 1.39%/y, P = .97). Major bleeding was significantly lower with edoxaban (3.16%/y vs 3.77%/y; HR 0.84, 95% CI 0.72-0.98, P = .023). CONCLUSION: In the FDA-approved cohort of the ENGAGE AF--TIMI 48 trial, treatment with edoxaban 60/30 mg was superior to warfarin in the prevention of SSE and significantly reduced cardiovascular death and bleeding, especially fatal bleeding and hemorrhagic stroke.

Anti-Factor Xa Activity of Prophylactic Enoxaparin Regimens in Critically Ill Patients.

BACKGROUND: Enoxaparin is frequently used as prophylaxis for deep venous thrombosis in critically ill patients. OBJECTIVES: To evaluate three enoxaparin prophylactic regimens in critical care patients with and without administration of a vasopressor. METHODS: Patients admitted to intensive care units (general and post-cardiothoracic surgery) without renal failure received, once daily, a subcutaneous fixed dose of 40 mg enoxaparin, a subcutaneous dose of 0.5 mg/kg enoxaparin, or an intravenous dose of 0.5 mg/kg enoxaparin. Over 5 days anti-activated factor X levels were collected before the daily administration and 4 hours after the injection. RESULTS: Overall, 16 patients received the subcutaneous fixed dose, 15 received the subcutaneous weight-based dosage, and 8 received the dose intravenously. Around two-fifths (38%) of the patients received vasopressors. There was no difference between anti-activated factor X levels regarding vasopressor administration. However, in all three groups the levels were outside the recommended range of 0.1 IU/ml and 0.3 IU/ml. CONCLUSIONS: Although not influenced by vasopressor administration, the enoxaparin regimens resulted in blood activity levels outside the recommended range.

[Evaluation of oral anticoagulation with rivaroxaban, in patients with new onset non valvular atrial fibrillation]. / Evaluación de la anticoagulación con rivaroxaban, en pacientes con fibrilación auricular no valvular de reciente diagnóstico.

BACKGROUND: Atrial fibrillation (AF) generates a hypercoagulable state with an increased thrombin generation and raised levels of thrombin-antithrombin complexes, which results in a high risk of stroke and thromboembolism. AIM: To evaluate the anticoagulant effect of rivaroxaban by anti-Xa factor activity and its correlation with thrombin-antithrombin complexes, thrombin generation and prothrombin time in patients newly diagnosed with non-valvular AF. PATIENTS AND METHODS: Prospective study in patients with indication of anticoagulation. Demographic variables, cardiovascular risk factors, CHA2DS2-VASc and HAS-BLED scores were recorded. Blood samples were taken at baseline, at 3 and 24 hours after the administration of the drug and at 30 days. Rivaroxaban levels, anti-Xa activity, prothrombin time, thrombin generation and plasma levels of thrombin-antithrombin complexes were determined. RESULTS: We studied 20 patients aged 76.3 ± 8.0 years (60% female) with a CHA2DS2-VASc score > 2 points. The anti-Xa factor activity correlated with rivaroxaban plasma levels at 3 hours (r = 0.61, p < 0.01), at 24 hours (r = 0.85, p < 0.01) and at 30 days (r = 0.99, p < 0.01), with prothrombin time at 3 hours (r = -0.86, p = 0.019) and at 30 days (r = -0.63, p = 0.02) and with a sustained decrease in thrombin generation at 30 days of follow-up (r = -0.74, p < 0.01). There was no correlation with thrombin-antithrombin complexes (r = -0.02, p = 0.83). CONCLUSIONS: Rivaroxaban consistently inhibited the mild pro-coagulant state found in newly diagnosed non-valvular AF patients through the first 24 hours and this effect was maintained at 30 days. Plasma levels of the drug correlated with anti-Xa factor activity, thrombin generation and prothrombin time.

Three new compounds isolated from the seeds of Vaccaria segetalis.

Two new capsaicin analogs, N-(3-methoxy-4-hydroxyphenethyl)-tetracosanamide (1) and N-(3,4-dihydroxyphenethyl)-tetracosanamide (2), along with one new flavonoidal glycoside pinnatifin E (3) were isolated from the ethanolic extract of the seeds of Vaccaria segetalis. Their structures were elucidated on the basis of spectroscopic methods including 1D, 2D NMR, MS, and other spectroscopic techniques, as well as by comparison with the relevant literatures. All compounds were evaluated for their coagulation Factor Xa inhibition activities.

Emicizumab promotes factor Xa generation on endothelial cells.

BACKGROUND: Until recently, the treatment of hemophilia A relied on factor (F)VIII replacement. However, up to one-third of patients with severe hemophilia A develop neutralizing alloantibodies that render replacement therapies ineffective. The development of emicizumab, a bispecific antibody that partially mimics FVIIIa, has revolutionized the treatment of these patients. However, the use of an activated prothrombin complex concentrate [FEIBA (Takeda)] to treat breakthrough bleeding in patients on emicizumab has been associated with thrombotic complications including a unique microangiopathy. OBJECTIVES: We hypothesized that the thrombotic complications observed with the combination of emicizumab and FEIBA might be due to excessive expression of procoagulant activity on the surface of endothelial cells. METHODS: We examined the ability of emicizumab to promote FX activation on endothelial cells using 2 cell culture models. RESULTS: We found that endothelial cells readily support emicizumab-mediated activation of FX by FIXa. The level of FXa generation depends on the concentration of available FIXa. The addition of FEIBA to emicizumab increased FXa generation in a dose-dependent manner on endothelial cells in both models. The rate of FXa generation was further enhanced by endothelial cell activation. However, unlike emicizumab, we found limited FXa generation in the presence of FVIII(a), which followed a significant lag time and was not dependent on FIXa concentration under these conditions. CONCLUSION: Emicizumab promotes FXa generation on the surface of endothelial cells, which is markedly enhanced in the presence of FEIBA. These findings demonstrate a potential mechanism for the thrombotic complications seen with the combined use of emicizumab and FEIBA.

Rivaroxaban delivery and reversal at a venous flow rate.

OBJECTIVE: Rivaroxaban is an oral anticoagulant that directly targets both free factor Xa and factor Xa in complex with its protein cofactor, factor Va, in the prothrombinase complex. It is approved in the United States for the prophylaxis of deep vein thrombosis and stroke in patients with atrial fibrillation; however, it also carries a black box warning regarding the risk of thrombosis after discontinuation of treatment. The purpose of this study was to determine the degree to which rivaroxaban, over a range of physiologically relevant free plasma concentrations, inhibits preassembled prothrombinase at a typical venous shear rate (100 s(-1)) and to determine the dynamics of rivaroxaban washout. METHODS AND RESULTS: Prothrombinase was assembled on phospholipid-coated glass capillaries. Its activity was characterized with respect to the activation of prothrombin (mean plasma concentration, 1.4 µmol/L) in the absence and presence of rivaroxaban (2, 5, and 10 nmol/L). The degree of inactivation of preassembled prothrombinase is sensitive to the solution-phase rivaroxaban concentration; however, prothrombinase unmasking upon removal of rivaroxaban is concentration independent. CONCLUSIONS: The model system presented suggests that when rivaroxaban plasma concentrations decrease after cessation of therapy, there will be an unmasking of thrombus-associated prothrombinase that may be related to the reported rebound phenomena.

Enoxaparin dose adjustment is associated with low incidence of venous thromboembolic events in acute burn patients.

BACKGROUND: Inadequate antifactor Xa levels have been documented in critically ill patients given prophylactic enoxaparin and may result in increased risk of venous thromboembolic (VTE) events. The objective of this study was to examine the impact of dose adjustment of enoxaparin and associated incidence of VTE in acute burn patients. METHODS: All acute burn patients who were treated with prophylactic enoxaparin on a burn/trauma intensive care unit were prospectively followed. Patients with subtherapeutic antifactor Xa levels had enoxaparin doses increased as per unit protocol with the goal of obtaining a therapeutic antifactor Xa level. RESULTS: Eighty-four acute burn patients who were treated with enoxaparin had at least one appropriately obtained antifactor Xa level between June 2009 and October 2010. Initial antifactor Xa levels in 64 patients (76.2%) were below 0.2 U/mL, resulting in increased enoxaparin dose. Fifteen patients never achieved the target antifactor Xa level before enoxaparin was discontinued. Median final enoxaparin dose required to achieve therapeutic antifactor Xa levels was 40 mg every 12 hours (range, 20-70 mg). Using linear regression, final enoxaparin dose correlated with burn size (%total body surface area) and weight. No episodes of hemorrhage, thrombocytopenia, or heparin sensitivity were documented. Two patients (2.4%) had VTE complications despite adequate prophylaxis. CONCLUSIONS: Frequent occurrence of low antifactor Xa levels observed in this study demonstrated the inadequacy of standard dosing of enoxaparin for VTE prophylaxis in many patients with acute burns. Enoxaparin dose adjustment was associated with a low incidence of VTE events and no bleeding complications.

Retrospective Comparison of Andexanet Alfa and 4-Factor Prothrombin Complex for Reversal of Factor Xa-Inhibitor Related Bleeding.

The aim of this retrospective study was to compare andexanet alfa and 4-factor prothrombin complex (4F-PCC) for reversal of factor Xa (FXa)-inhibitor bleeding. Patients that received andexanet alfa for reversal were included. An equivalent number of patients administered 4F-PCC for FXa-inhibitor bleeding were randomly selected as historical controls. The primary outcome was effective hemostasis achievement within 12 h, defined using ANNEXA-4 criteria. Thromboembolic events and mortality within 30 days were also evaluated. A total of 32 patients were included. Baseline characteristics were not statistically different between andexanet alfa (n = 16) and 4F-PCC (n = 16). Intracranial bleeding was the primary reversal indication in 43.8% versus 62.5% of patients, respectively. Effective hemostasis was reached in 75.0% of andexanet alfa patients compared to 62.5% of 4F-PCC patients (P = .70). Thromboembolic events occurred in 4 (25.0%) patients and 3 (18.8%) patients, respectively (P = .99). Mortality incidence was 12.5% and 31.3%, respectively (P = .39). Andexanet alfa and 4F-PCC attained hemostasis in a majority of patients. A high, but a similar rate of thromboembolic events was seen with both treatments. Prospective studies are needed to elucidate comparative risks and benefits of the 2 agents.

Study on the Relationship between Rivaroxaban and Factor Xa Activity in Blood Based on HPLC-MS/MS.

OBJECTIVE: The aim of the study was to investigate a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for the determination of rivaroxaban and evaluate the correlation between plasma concentration and anti-Xa activity in patients using oral rivaroxaban. METHODS: In this study, the plasma concentration of rivaroxaban and anti-Xa factor activities was determined in 125 patients, and the relationship between the two variables was analysed by SPSS 21.0 software. RESULTS: The results showed that the plasma concentrations of oral rivaroxaban patients were significantly correlated with the activity of the anti-Xa factor (Spearman's r = 0.990, P < 0.05). CONCLUSION: The plasma concentrations of rivaroxaban are a potentially useful monitoring indicator to assess the patient's bleeding risk if testing for plasma anti-Xa activity is not available.

Adequate thromboprophylaxis in critically ill patients.

Venous thromboembolism is a relatively frequently occurring complication in critically ill patients admitted to the ICU despite prophylactic treatment with subcutaneous low molecular weight heparin. Several studies show that critically ill patients have significantly lower plasma anti-factor-Xa activity levels compared to control patients after administration of subcutaneous heparin. Robinson and colleagues show in this issue of Critical Care dose-dependent but relatively low levels of anti-factor Xa activity at increasing doses of enoxaparin. Anti-factor Xa levels thought to be required for adequate thromboprophylaxis are observed only at doses of enoxaparin that are one and a half times higher than the conventional dose (40 mg).

Treatment of pulmonary embolism in an extremely obese patient.

Low-molecular-weight heparins are effective as initial therapy for pulmonary embolism (PE) in a weight-based dosing regimen up to known body weights of 160 kg. The present case reports an extremely obese man of 252 kg (body mass index (BMI) 74 kg/m2) with PE who was treated with tinzaparin, dosed on a body weight of 160 kg. Morbid obesity defined as a BMI higher than 40 kg/m2 is becoming more common in general practice, but there are no evidence-based drug dosing strategies for these patients. This case demonstrates the successful use of a maximum dose of 28,000 anti-Xa international units of tinzaparin for an extremely obese patient with proven PE, instead of the accepted doses of 175 IU/kg, as bridge therapy to a coumarin.