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Aims: Antithrombin is increasingly used in paediatric patients, yet there are few age-specific pharmacokinetic data to guide dosing. We aimed to describe the pharmacokinetic profile of human (plasma-derived) antithrombin concentrate in paediatric patients., Methods: A 5-year retrospective review was performed of patients <19 years of age admitted to our institution who received antithrombin concentrate, were not on mechanical circulatory support and had baseline (predose) and postdose plasma antithrombin activity levels available for analysis. Demographic and laboratory variables, antithrombin dosing information and data on the use of continuous infusion unfractionated heparin were collected. Population pharmacokinetic analysis was performed with bootstrap analysis. The model developed was tested against a validation dataset from a cohort of similar patients, and a predictive value was calculated., Results: A total 184 patients met the study criteria {46.7% male, median age [years] 0.35 [interquartile range (IQR) 0.07-3.9]}. A median of two antithrombin doses (IQR 1-4) were given to patients (at a dose of 46.3 ± 13.6 units kg -1 ), with median of three (IQR 2-7) postdose levels per patient. Continuous infusion unfractionated heparin was administered in 87.5% of patients, at a mean dose of 34.1 ± 22.7 units kg -1 h -1 . A one-compartment exponential error model best fit the data, and significant covariates included allometrically scaled weight on clearance and volume of distribution, unfractionated heparin dose on clearance, and baseline antithrombin activity level on volume of distribution. The model resulted in a median -1.75% prediction error (IQR -11.75% to 6.5%) when applied to the validation dataset (n = 30)., Conclusions: Antithrombin pharmacokinetics are significantly influenced by the concurrent use of unfractionated heparin and baseline antithrombin activity., (© 2017 The British Pharmacological Society.)

Herein, the synthesis and characterization of heparin-based nanocapsules (NCs) as potential drug delivery systems is described. For the synthesis of the heparin-based NCs, the versatile method of miniemulsion polymerization at the droplets interface was achieved resulting in narrowly distributed NCs with 180 nm in diameter. Scanning and transmission electron microscopy images showed clearly NC morphology. A highly negative charge density for the heparin-based NCs was determined by measuring the electro-kinetic potential. Measuring the activated clotting time demonstrated the biological intactness of the polymeric shell. The ability of heparin-based NCs to bind to antithrombin (AT III) was investigated using isothermal titration calorimetry and dynamic light scattering experiments. The chemical stability of the NCs was studied in physiological protein-containing solutions and also in medically interesting fluids such as sodium chloride 0.9%, Ringer's solution, and phosphate buffer saline using dynamic light scattering and measuring the fluorescence intensity. The impressive uptake of NCs in different cells was confirmed by fluorescence-activated cell sorting, confocal laser scanning microscopy, and transmission electron microscopy. The low toxicity of all types of NCs was demonstrated., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Acquired antithrombin (AT) deficiency has been associated with patients on extracorporeal membrane oxygenation (ECMO) as a result of hemodilution, blood coagulation activation, and the use of heparin. Replacement of AT has been typically utilized through the use of fresh-frozen plasma or AT concentrate. Antithrombin alfa (ATryn) is a recombinant form of AT (rAT) with an identical amino acid sequence as that of plasma-derived antithrombin. The primary objective of this study is to examine the relationship of rAT dose to measured plasma antithrombin activity in a small series of patients who received rAT while on ECMO. A retrospective chart review was performed of all patients at Medical City Children's Hospital who received ATryn while supported on ECMO between December 2011 and April 2012. Five patients were identified and the patients' weight, bolus dose of ATryn, drip rate of ATryn, and AT blood levels were collected for analysis. The median age of these patients was 1 month (range, 1 day to 3.75 years). Because no dosing guidelines exist for pediatric ECMO, a starting dose of ATryn was chosen based on the manufacturer's labeled indication (prevention of thromboembolic events in patients with AT hereditary deficiency). The median dose of rAT was 368 IU/kg/day (range, 104-520 IU/kg/day) to obtain AT activity level of 80-120%. The average time to reach the targeted AT activity level (80-120%) was 12.7 hours (range, 11-17 hours). Our findings suggest that the published ATryn dose may be inadequate to reach desired AT activity concentrations for pediatric patients on ECMO. Difference in patient population, use of extracorporeal circuits, and the use of heparin are likely explanations for this finding. We would also recommend frequent checking of AT levels while delivering this drug because making timely adjustments is necessary for achieving and maintaining the target AT activity level.

Background: Treatment with antithrombin (AT)-III is indicated for patients with sepsis or hereditary AT deficiency., Objective: The purpose of this study was to compare the pharmacokinetic and pharmacodynamic characteristics of 2 AT-III formulations in healthy Korean volunteers to satisfy the regulatory requirements for bioequivalence for marketing purposes., Methods: A single-center, single-dose, open-label, randomized, 2-period, 2-sequence crossover study was conducted in healthy Korean volunteers. Blood samples for the drug analysis were collected for up to 216 hours after drug administration. Participants received either the test or reference formulation of AT-III 100 U/kg IV for 20 minutes in the first period and the alternative formulation in the second period. Both the AT-III activity and antigen (Ag) were measured for the analysis of pharmacokinetic properties, and the prothrombin time and the activated partial thromboplastin time were assessed for the analysis of pharmacodynamic properties. Because AT-III is an endogenous compound, the analysis used data corrected from baseline values. The tolerability of the 2 formulations was also assessed based on physical examinations including vital sign measurements, laboratory tests, and 12-lead ECG., Results: Of the 20 subjects enrolled (mean [SD] age, height, and weight, 25.3 [2.3] years, 175.3 [4.5] cm, and 67.4 [6.3] kg, respectively), 19 completed both treatment periods; 1 subject withdrew consent for personal reasons. The observed mean (SD) Cmax, AUClast, and AUC0-∞ of AT-III activity were, respectively, 279.24% (35.92), 14,364.10 (2325.25) %·h, and 17,526.38 (3150.81) %·h with the test formulation and 249.75% (31.96), 12,962.95 (1897.52) %·h, and 15,957.67 (3189.21) %·h with the reference formulation. The observed mean (SD) Cmax, AUClast, and AUC0-∞ of AT-III Ag were 62.58 (5.66) mg/dL, 3051.94 (401.87) mg/dL·h, and 3639.80 (726.01) mg/dL·h, respectively, with the test formulation and 58.63 (5.27) mg/dL, 2805.08 (272.38) mg/dL·h, and 3340.00 (428.46) mg/dL·h with the reference formulation. The geometric mean ratios (90% CI) of the log-transformed data for AT-III activity between the 2 formulations were 1.11494 (1.08994-1.14053) for Cmax, 1.11305 (1.05435-1.17503) for AUClast, and 1.11527 (1.03754-1.19889) for AUC0-∞; corresponding values for AT-III Ag were 1.08802 (1.06258-1.11405), 1.10905 (1.05804-1.16242), and 1.11460 (1.02058-1.21726). During the study period, 8 adverse events were reported, and all were transient, mild, and resolved completely during the treatment period., Conclusion: The results of the present study showed that these 2 AT-III formulations met the regulatory criteria for pharmacokinetic bioequivalence with respect to AT-III activity and Ag in these healthy Korean subjects. ClinicalTrials.gov identifier: NCT00846274., (Copyright © 2013 Elsevier HS Journals, Inc. All rights reserved.)

Anticoagulation by a standard dosage of an inhibitor of thrombin generation presupposes predictable pharmacokinetics and pharmacodynamics of the anticoagulant. We determined the inter-individual variation of the effect on thrombin generation of a fixed concentration of direct and antithrombin-mediated inhibitors of thrombin and factor Xa. Thrombin generation was determined by calibrated automated thrombinography in platelet-poor plasma from 44 apparently healthy subjects which was spiked with fixed concentrations of otamixaban, melagatran, unfractionated heparin, dermatan sulfate and pentasaccharide. The variability of the inhibitory effect of the different anticoagulants within the population was determined using the coefficient of variation, i.e. the standard deviation expressed as a percentage of the mean. The inter-individual coefficients of variation of the endogenous thrombin potential and peak height before inhibition were 18% and 16%, respectively and became 20%-24% and 24%-43% after inhibition. The average inhibition of endogenous thrombin potential and peak height (ETP, peak) brought about by the anticoagulants was respectively: otamixaban (27%, 83%), melagatran (56%, 63%), unfractionated heparin (43%, 58%), dermatan sulfate (68%, 57%) and pentasaccharide (25%, 67%). This study demonstrates that the addition of a fixed concentration of any type of anticoagulant tested causes an inhibition that is highly variable from one individual to another. In this respect there is no difference between direct inhibitors of thrombin and factor Xa and heparin(-like) inhibitors acting on the same factors.

Starting from a hit identified by focused screening, 3-aminopyrrolidine factor Xa inhibitors were designed. The binding mode as determined by X-ray structural analysis as well as the pharmacokinetic behaviour of selected compounds is discussed.

Aims: To investigate the safety, pharmacokinetics and pharmacodynamics of rivaroxaban, an oral, direct Factor Xa (FXa) inhibitor, in healthy, male Chinese subjects., Methods: Two randomized, single-blind, placebo-controlled, dose-escalation studies were conducted in healthy Chinese men aged 18-45 years. In the single-dose study, subjects received single, oral doses of rivaroxaban 2.5, 5, 10, 20 and 40 mg. In the multiple-dose study, oral rivaroxaban was administered in doses of 5, 10, 20 and 30 mg twice daily for 6 days., Results: Rivaroxaban, in single and multiple doses up to 60 mg, was well tolerated. Rapid absorption was observed in both studies (time to C(max) 1.25-2.5 h). In the multiple-dose study, rivaroxaban exposure increased dose-proportionally after the first dose and at steady state (for the 5-20-mg doses). The half-life of rivaroxaban was up to 7.9 h in the single-dose study. Maximal inhibition of FXa activity was achieved within 1-3 h of dosing in the single-dose study [at 20 mg FXa inhibition as a median percentage change from baseline, 45.92; 95% confidence interval (CI) 44.64, 50.70] and 2-3 h after administration at steady state in the multiple-dose study (at 20 mg median FXa inhibition as a median percentage change from baseline, 60.25; 95% CI 56.16, 63.05), in line with maximum rivaroxaban plasma concentrations., Conclusions: Rivaroxaban demonstrated predictable pharmacokinetics and pharmacodynamics in healthy Chinese subjects, in line with findings observed previously in White subjects. This suggests that fixed doses of rivaroxaban may be administered to all patients, regardless of their ethnic origin.

For the past five decades, there has been little progress in the development of oral anticoagulants, with the choices being limited to the vitamin K antagonists (VKAs). The situation is changing with the development of orally active small molecules that directly target thrombin or activated factor X (FXa). The two agents in the most advanced stages of development are dabigatran etexilate and rivaroxaban, which inhibit thrombin and FXa, respectively. Both are approved in the EU and Canada for venous thromboprophylaxis in patients undergoing elective hip- or knee-replacement surgery. Other agents in the early stages of development include several FXa inhibitors (apixaban, DU 176b, LY 517717, YM 150, betrixaban, eribaxaban [PD 0348292] and TAK 442) and one thrombin inhibitor (AZD 0837). With a predictable anticoagulant response and low potential for drug-drug interactions, these new agents can be given in fixed doses without coagulation monitoring. This renders them more convenient than VKAs. While the anticoagulant effect of the new thrombin and FXa inhibitors is similar, differences in the pharmacokinetic and pharmacodynamic parameters may influence their use in clinical practice. Here, we compare the pharmacokinetic and pharmacodynamic features of these new oral agents.

Purpose: The mechanism of action, pharmacodynamics, pharmacokinetics, efficacy in clinical trials, interactions, adverse effects and toxicity, and place in therapy of rivaroxaban are reviewed., Summary: Rivaroxaban, the first oral, direct factor Xa (FXa) inhibitor to reach Phase III trials, inhibits thrombin generation by both the intrinsic and the tissue factor pathways. It has shown predictable, reversible inhibition of FXa activity, and it may have the ability to inhibit clot-bound FXa. Rivaroxaban is being evaluated for prevention of venous thrombosis in patients undergoing hip or knee arthroplasty, treatment of venous thrombosis, long-term use for secondary prevention of venous thrombosis, and prevention of stroke in atrial fibrillation. To date, only short-term trials have been reported, but rivaroxaban's safety and efficacy appear to be at least equivalent to those of traditional anticoagulants. The results of four studies of primary prevention of venous thrombosis in patients undergoing orthopedic surgery suggest that rivaroxaban 10 mg daily is a promising alternative to low-molecular-weight heparins. Rivaroxaban appears to have a low potential for drug-drug or drug-food interactions. It offers the advantages of a fixed oral dose, rapid onset of action, and predictable and consistent anticoagulation effect, precluding the need for routine monitoring of anticoagulation., Conclusion: Rivaroxaban is a promising alternative to traditional anticoagulants for the prevention and treatment of venous thromboembolism and for stroke prevention in atrial fibrillation; it offers once-daily oral administration without the need for routine monitoring.

Introduction of the phenyl piperidinone and phenyl pyridinone P4 moieties in the anthranilamide scaffold led to potent, selective, and orally bioavailable inhibitors of factor Xa. Anthranilamide 28 displayed comparable efficacy to apixaban in the rabbit arteriovenous-shunt (AV) thrombosis model.

Background: Rivaroxaban (BAY 59-7939) is a novel, oral, direct Factor Xa inhibitor in advanced clinical development for the prevention and treatment of thromboembolic disorders. Unwanted pro-arrhythmic effects are a common reason for drugs failing to gain regulatory approval; these properties can be detected by assessing the effect of the drug on the QT interval., Objective: This study was performed, in accordance with International Conference on Harmonisation (ICH) E14 guidance, to assess whether rivaroxaban prolongs the QT interval., Study Design: This was a prospective, randomized, double-blind, double-dummy, four-way crossover study., Setting: The study was conducted at a clinical pharmacology research unit., Subjects: Healthy male and female subjects (n = 54) aged > or =50 years were enrolled and remained in the study unit for 3 days for each treatment. Of these, 50 patients were eligible for the QT analysis., Intervention: Subjects received single oral doses of rivaroxaban 45 mg or 15 mg, moxifloxacin 400 mg (positive control), or placebo., Outcome Measures: Multiple ECGs were taken at frequent intervals after drug administration, and the QT interval was measured manually under blinded conditions at a central laboratory. The Fridericia correction formula (QTcF) was used to correct the QT interval for heart rate. The primary outcome was the effect of rivaroxaban or moxifloxacin on the placebo-subtracted QTcF 3 hours after administration. The frequency of outlying QTcF values and the tolerability of the treatments were also assessed., Results: All treatments were well tolerated and had no effect on heart rate. Moxifloxacin established the required assay sensitivity; placebo-subtracted QTcF 3 hours after moxifloxacin administration was prolonged by 9.77 ms (95% CI 7.39, 12.15). Placebo-subtracted QTcF values 3 hours after rivaroxaban administration were -0.91 ms (95% CI -3.33, 1.52) and -1.83 ms (95% CI -4.19, 0.54) with rivaroxaban 45 mg and 15 mg, respectively. QTcF was not prolonged with rivaroxaban at any time, and the frequency of outlying results with rivaroxaban and placebo was similar., Conclusion: This thorough QT study, which was performed in accordance with ICH E14 guidelines, shows that rivaroxaban does not prolong the QTc interval. Therefore, the potential of rivaroxaban for the prevention and treatment of thromboembolic disorders, including chronic cardiovascular disorders, can be investigated in appropriate clinical studies without the need for intensive monitoring of the QTc interval.

A new series of pyrazole-based factor Xa inhibitors have been identified as part of our ongoing efforts to optimize previously reported clinical candidate razaxaban. Concern over the possible formation of primary aniline metabolites via amide hydrolysis led to the replacement of the primary amide linker between the pyrazole and phenyl moieties with secondary amides. This was accomplished by replacing the aniline with a variety of heterobicycles, of which indolines were the most potent. The indoline series demonstrated subnanomolar factor Xa binding K(i)s, modest to high selectivity versus other serine proteases, and good in vitro clotting activity. A small number of indoline fXa inhibitors were profiled in a dog pharmacokinetic model, one of which demonstrated pharmacokinetic parameters similar to that of clinical candidate razaxaban.

Pharmacokinetic (PK) data for antithrombin III (AT) are limited in the critical patients. We therefore performed PK analysis using a two-compartment model and also examined whether plasma AT activity would change depending on two administration methods, AT agent at 500 U/8 h (divided group) or 1,500 U/24 h (combined group) for 3 days, a regulated dosage for disseminated intravascular coagulation (DIC) treatment in Japan, in critical patients with DIC. Clinical prospective randomized study. A high care unit in a university hospital. Twenty-four consecutive critical patients with DIC. Ages ranged from 34 to 91 years. Acute physiology age and chronic health evaluation II scores were 25 to 35. Antithrombin III activities in the combined group caused remarkable transient increases but returned to near the preadministration level 24 h after the infusion. Antithrombin III level in the divided group showed small elevations on each session; therefore, steady increases were found after serial administrations of the agent. On the third day, AT trough activities in the divided group were significantly higher than those in the combined group (P = 0.005). However, peak AT activities in the combined group after AT administration were higher than those in the divided group throughout the study (P = 0.024). Aggravation of bleeding tendency occurred more frequently in the combined group (P = 0.03). Half-life times on the distribution phase in both groups were remarkably shorter than those of previously reported control in congenital AT deficiency. This suggests an increased vascular permeability in the critical patients in this study. Distribution volume in the patients here increased significantly as compared with the previous controls. This is the first PK report using a two-compartment model to demonstrate that remarkable increases in vascular permeability and distribution volume occur in critical patients with DIC, and if the same dose is administered intermittently in such PK situation, AT administration in divided manner can maintain plasma AT trough activity higher than that in the combined method.

Herein, we report the discovery of novel, proline-based factor Xa inhibitors containing a neutral P1 chlorophenyl pharmacophore. Through the additional incorporation of 1-(4-amino-3-fluoro-phenyl)-1H-pyridin-2-one 22, as a P4 pharmacophore, we discovered compound 7 (PD 0348292). This compound is a selective, orally bioavailable, efficacious FXa inhibitor that is currently in phase II clinical trials for the treatment and prevention of thrombotic disorders.

Background: Low-molecular-weight heparin (LMWH) has potential benefit in cats at risk for thromboembolic disease. However, LMWH pharmacokinetics has not been characterized in the cat. Drug effect with LMWH may be evaluated with analysis of factor Xa inhibition (anti-Xa) or thromboelastography (TEG)., Hypothesis: Administration of LMWH at previously recommended dosages and schedules to healthy cats will result in inhibition of factor Xa and hypocoagulable TEG., Animals: In vivo research with heparin was performed in 5 purpose-bred cats., Methods: In a prospective study with randomized crossover design, heparin or placebo was administered. Treatments were unfractionated heparin (UFH), 250 IU/kg q6h; dalteparin, 100 IU/kg q12h; enoxaparin, 1 mg/kg q12h; or 0.9% saline, 0.25 mL/kg q6h. Each drug was administered for 5 consecutive days followed by a minimum washout of 14 days. Baseline and post-treatment analyses included anti-Xa, TEG, and prothrombin time/activated partial thromboplastin time., Results: Mean anti-Xa activity 4 hours after enoxaparin (0.48 U/mL) approached the human therapeutic target (0.5-1.0 U/mL); however, mean trough anti-Xa activity was below detection limits. Mean anti-Xa activity 4 hours after dalteparin was lower, and only 1 cat attained therapeutic target at a single time point. Cats receiving UFH attained target anti-Xa activity and changes in TEG at trough and 4 hours., Conclusions: Cats have rapid absorption and elimination kinetics with LMWH therapy. On the basis of pharmacokinetic modeling, cats will require higher dosages and more frequent administration of LMWH to achieve human therapeutic anti-factor Xa activity of 0.5-1 U/mL. Peak anti-Xa activity is predicted at 2 hours after administration of LMWH.

Elevated thrombin-antithrombin complex (TAT) or decreased serum albumin levels suggest heightened vascular permeability in disseminated intravascular coagulation (DIC). In such a situation, plasma antithrombin III (AT-III) may decrease because of the leakage. We thus examined whether AT-III activity before and after administration of an AT-III agent changed depending on plasma TAT and/or serum albumin levels in 20 consecutive patients with DIC. We also analyzed the pharmacokinetics for AT-III using a two-compartment model. Serum albumin levels before AT-III administration correlated with preadministered and postadministered AT-III activity, but TAT levels did not. Regardless of TAT levels, AT-III trough activity on the third day increased significantly. In patients with albumin levels of 2.5 g/dL or less, AT-III trough levels on the third day were significantly lower than those with higher levels of albumin. The half-life of the distribution phase for AT-III agent in the patients was shortened to less than one third the value reported in congenital AT-III deficiency, suggesting increased vascular permeability in the acute state patients here. The distribution volume of the agent increased remarkably compared with the previous control. We report here for the first time that in critical patients with DIC, plasma AT-III levels before and after AT-III administration could be predicted by preadministered serum albumin levels, but not by TAT. These findings could be explained by the pharmacokinetic profile, increased vascular permeability and distribution volume, observed in critical patients.

Anticoagulants are often dose adjusted, or their use restricted, in patients with extremes of body weight. Rivaroxaban (BAY 59-7939) is a novel, oral, direct factor Xa inhibitor in clinical development. This was a randomized, single-blind, placebo-controlled, parallel-group study in healthy male and female subjects to assess the effect of extreme body weight (< or = 50 kg and >120 kg), and gender, on the safety, tolerability, pharmacokinetics, and pharmacodynamics of rivaroxaban 10 mg, compared with subjects of normal weight (70-80 kg). Rivaroxaban was well tolerated. Cmax of rivaroxaban was unaffected in subjects >120 kg but was increased by 24% in subjects weighing < or = 50 kg, resulting in a small (15%) increase in prolongation of prothrombin time, which was not considered clinically relevant. The area under the curve was unaffected by body weight or gender. No other clinically relevant differences were observed, suggesting that rivaroxaban is unlikely to require dose adjustment for body weight or gender.

Purpose: PD 0313052 is a potent, direct factor Xa (FXa) inhibitor (Ki = 0.33 nM) and its antithrombotic effect has been previously demonstrated in several animal models, via intravenous (IV) administration. In the present study, we evaluated four different subcutaneous (SC) formulations to test the feasibility of developing PD 0313052 as a subcutaneous agent., Methods: PD 0313052 was formulated in saline, methylcellulose (MC, 0.5% methylcellulose solution containing 1% Tween-80), sesame oil, and F127 (25% aqueous solution). Each formulation was injected subcutaneously into rabbits and the relative plasma exposure and the duration of action of PD 0313052 were assessed. Plasma concentration, FXa activity, and coagulation parameters were used to monitor the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of PD 0313052., Results: Regardless of formulation, there was a significant (p < 0.05) correlation between PD 0313052 plasma concentration and FXa activity (R2 = 0.90), prothrombin time (PT) (R2 = 0.86), and Heptest (R2 = 0.93). The saline and MC formulations had similar effects on FXa activity, coagulation parameters, and Heptest, peaking at 30 to 120 minutes after administration and decreasing rapidly thereafter. In contrast, formulations of F127 and sesame oil yielded lower maximal effects on PD markers but produced sustained PD effects over time., Conclusion: The data indicate that PD 0313052 is bioavailable after SC administration to rabbits and that there is a strong correlation between the PD parameters and plasma concentrations of PD 0313052. Modifications in the formulation of PD 0313052 produce marked differences in the PK and PD profiles of this agent after SC administration to rabbits. These results suggest that SC formulations can be optimized to improve the PK and PD profiles of PD 0313052, and that PD 0313052 is a viable candidate for development as a SC antithrombotic agent.

Objectives: There is a clinical need for safe new oral anticoagulants. The safety, tolerability, pharmacodynamics, and pharmacokinetics of BAY 59-7939--a novel, oral, direct Factor Xa (FXa) inhibitor--were investigated in this single-center, placebo-controlled, single-blind, parallel-group, multiple-dose escalation study., Methods: Healthy male subjects (aged 20-45 years, body mass index 18.6-31.4 kg/m(2)) received oral BAY 59-7939 (n=8 per dose regimen) or placebo (n=4 per dose regimen) on days 0 and 3-7. Dosing regimens were 5 mg once, twice (bid), or three times daily, and 10 mg, 20 mg, or 30 mg bid., Results: There were no clinically relevant changes in bleeding time or other safety variables across all doses and regimens. There was no dose-related increase in the frequency or severity of adverse events with BAY 59-7939. Maximum inhibition of FXa activity occurred after approximately 3 h, and inhibition was maintained for at least 12 h for all doses. Prothrombin time, activated partial thromboplastin time, and HepTest were prolonged to a similar extent to inhibition of FXa activity for all doses. Dose-proportional pharmacokinetics (AUC(tau, norm) and C(max, norm)) were observed at steady state (day 7). Maximum plasma concentrations were achieved after 3-4 h. The terminal half-life of BAY 59-7939 was 5.7-9.2 h at steady state. There was no relevant accumulation at any dose., Conclusions: BAY 59-7939 was safe and well tolerated across the wide dose range studied, with predictable, dose-proportional pharmacokinetics and pharmacodynamics and no relevant accumulation beyond steady state. These results support further investigation of BAY 59-7939 in phase II clinical trials.

In this work, we describe a method of constructing a film of linear poly(glycidyl methacrylate) (PGMA) polymer onto the surface of quartz crystal microbalance (QCM) electrode as a coating material that allows easy coupling of heparin molecules onto the electrode and facilitates the determination of the interaction between heparin and antithrombin III (AT III). The PGMA film was characterized with atomic force microscopy (AFM) and infra-red spectroscopy. The coupling of heparin was accomplished in one step solution reaction. A home-made quartz crystal microbalance-flow injection analysis (QCM-FIA) system with data analysis software developed in our laboratory was used to determine the interaction. The interactions between immobilized heparin and AT III were studied with various concentrations under various conditions. The obtained constants are kass=(1.49+/-0.12)x10(3)mol-1ls-1, kdiss=(3.94+/-0.63)x10(-2)s-1, KA=(3.82+/-0.33)x10(4)mol-1l.

Background: Tissue factor (TF), a membrane-bound glycoprotein that initiates blood coagulation by allosteric activation of factor (f) VII, is regulated predominantly by tissue factor pathway inhibitor (TFPI). Because vascular endothelial cells synthesize and constitutively secrete TFPI and fXa may directly influence its cellular clearance, we sought to determine the effects of DX-9065a, a direct and selective fXa inhibitor, on TFPI kinetics in culture., Methods/results: Human umbilical vein endothelial cells were grown to confluence and incubated with unfractionated heparin (1.0 U/mL), enoxaparin (1.5 U/mL), or DX-9065a at low (10 ng/ml), moderate (30 ng/ml), or high (90 ng/ml) concentrations. Compared to control, increases in TFPI were seen with both unfractionated heparin (182% higher, p < 0.001) and enoxaparin (194% higher, p < 0.001). Low concentration DX-9065a did not increase TFPI levels above control (0.8% higher, p = 0.91). In contrast, moderate and high concentrations produced 124% higher (p < 0.001) and 198% higher (p < 0.001) TFPI concentrations than control, respectively., Conclusions: DX-9065a increases vascular endothelial cell TFPI concentrations in human tissue culture. Although the mechanism has yet to be established, decreased fXa availability may limit fXa-TFPI complex formation and its subsequent cellular uptake. Whether increased surface TFPI contributes to the overall anticoagulant profile of DX-9065a will require further investigation.

GTC Biotherapeutics (formerly Genzyme Transgenics Corporation) is developing a transgenic form of antithrombin III known as recombinant human antithrombin III [rhATIII]. It is produced by inserting human DNA into the cells of goats so that the targeted protein is excreted in the milk of the female offspring. The transgenic goats have been cloned in collaboration with the Louisiana State University Agriculture Center. GTC Biotherapeutics is conducting clinical trials of rhATIII in coagulation disorders. rhATIII is believed to be both safer and more cost-effective than the currently available plasma-derived product. rhATIII is also being investigated in cancer and acute lung injury. Genzyme Transgenics Corporation, originally a subsidiary of Genzyme Corporation, changed its name to GTC Biotherapeutics in June 2002; it is no longer a subsidiary of Genzyme Corporation. GTC Biotherapeutics is seeking partners for the commercialisation of rhATIII. Restructuring of GTC Biotherapeutics to support its commercialisation programmes was announced in February 2004. Genzyme Transgenics Corporation was developing rhATIII in association with Genzyme General (Genzyme Corporation) in the ATIII LLC joint venture, but in November 2000 a letter of intent was signed for the reacquisition of the rights by Genzyme Transgenics Corporation. It was announced in February 2001 that this reacquisition was not going to be completed and that the development of rhATIII was to continue with ATIII LLC. However, in July 2001, Genzyme Transgenics Corporation reacquired all the rights in the transgenic antithrombin III programme. SMI Genzyme Ltd, a joint venture between Sumitomo Metal Industries, Japan, and Genzyme Transgenics Corporation, USA, was set up to fund development of transgenic antithrombin III in Asia. However, in October 2000, Genzyme Transgenics Corporation reacquired, from Sumitomo Metal Industries, the rights to its technology for production of medicines from milk in 18 Asian countries, including Japan. The 10-year-old joint venture, SMI Genzyme Ltd, was dissolved. In June 2002, GTC Biotherapeutics estimated the current market size for plasma ATIII products to be approximately $US250 million - of which sales in Europe amounted to $US110 million, Japan $US130 million and the US $US10 million.

Fondaparinux is the first synthetic selective factor-Xa inhibitor. It is indicated for prophylaxis of deep vein thrombosis in patients undergoing hip fracture, hip replacement, and knee replacement surgeries. In these patients, fondaparinux appears to be more efficacious than enoxaparin. It is a safe and effective, but expensive, alternative to the available antithrombotic agents. Its long half-life allows for once-daily dosing, yet a truly viable antidote is not available in the event of overanticoagulation. Trials are currently underway to determine its efficacy and safety for the treatment of deep vein thrombosis, unstable angina, and acute myocardial infarction, as well as its role in coronary angioplasty.

To overcome the low bioavailability of our substituted acrylamide P1 benzamidine factor Xa inhibitors reported previously, neutral and less basic groups were used to replace the benzamidine. As a result, a series of P1 aminoisoquinoline substituted acrylamide Xa inhibitors was identified to be potent, selective, and orally bioavailable. Modification of P4 moiety of these compounds further improved their pharmacokinetic properties.

DPC-423 is a biphenylamine-containing amide which is under development by Bristol-Myers Squibb (formerly DuPont Pharmaceuticals) as a Factor Xa inhibitor for the potential treatment of thrombotic disorders [372092]. As of August 2000, DPC-423 was in phase I trials [380880]. DPC-423 was discovered as a result of SAR modifications of DuPont's SN-429, including replacement of the benzamidine moiety with a less basic benzylamine [398701]. Its 2-aminomethylphenyl analog DPC-602 is also under investigation for thrombotic disorders [402714].

Recently, N2-aroylanthranilamides have been reported as novel series of possible anticoagulant drug candidates and the two aryl rings (A and B) have been suggested to interact with S1 and S4 regions, respectively, of human factor Xa (hfXa). In the present effort, quantitative structure-activity relationship (QSAR) of the hfXa binding affinity of 32 N2-aroylanthranilamides have been attempted, in continuation of our previous report on the QSAR analysis of the data set using linear free energy related (LFER) model, with electrotopological state atom (ETSA) index (Kier and Hall, 1991, Adv. Drug Design., 22, 1-38), to explore the atoms/regions of the compounds that modulate the activity comparatively to the greater extent. The univariate and bivariate relations involving the ETSA values of different common atoms of the compounds show importance of the atom nos. 12, 3 and 17 (arbitrary numbering): B ring carbon bearing meta R2 substituents, C ring carbon bearing R4 substituent, and carbonyl oxygen of A ring amide linkage. The importance of atom 12 is suggested to be due to detrimental effects of meta R2 substituents (B ring) on the hfXa binding affinity, which may be owing to interference in the attainment of the proper orientation of the phenyl ring in the S4 site. Atom 3 signifies the impact of R4 substituents (central C ring) on the binding affinity. Again, atom 17 (carbonyl oxygen of A ring amide linkage) has been suggested to form hydrogen bonding with the NH group of the other amide linkage, producing a pseudo ring and thus stabilizing the structure. The relations were improved further using indicator and physicochemical variables and the present results are in good agreement with the previous findings of the Hansch analysis.

black triangle Fondaparinux sodium, a selective factor Xa inhibitor, is the first in a new class of antithrombotics. It binds selectively with high affinity to antithrombin III and specifically catalyses the inactivation of factor Xa. The elimination half-life of fondaparinux sodium permits once daily treatment. black triangle A randomised, double-blind, parallel-group, dose-ranging, multicentre phase IIb study in 933 eligible patients established that a subcutaneous dose of between 1.5 and 3mg of fondaparinux sodium has the optimum efficacy and safety profile for prophylaxis of venous thromboembolism in patients undergoing major orthopaedic surgery. black triangle Fondaparinux sodium, given to more than 3600 patients undergoing major orthopaedic surgery who participated in prospective, randomised, double-blind, multicentre phase III clinical trials, significantly reduced the incidence of venous thromboembolism, with an overall risk reduction of 55.2% compared with enoxaparin. black triangle Fondaparinux sodium was well tolerated by patients undergoing major orthopaedic surgery, and at the recommended clinical dose of 2.5mg has a similar tolerability profile, including bleeding events, to standard enoxaparin regimens. Fondaparinux sodium has not been reported to cause antibody-induced thrombocytopenia.

Antithrombin III (CAS 52014-67-2) is produced from plasma of healthy donors and is purified from any detectable agent of transmissible infection. This drug is used in therapy by i.v. route to manage acute thrombotic episodes and to treat patients suffering from its deficiency. The present trial was conducted with the aim to evaluate the pharmacokinetics and the safety of a new preparation of antithrombin III, which in the purification procedure has included a nanofiltration step to increase the safety against the transmission of any agent of infection. The trial was conducted in twelve healthy volunteers of either sex. All the ethics procedures were fully respected, namely the approval from Ethics Committee, the notification to the central regulatory authority, the approval of consent form in writing. Volunteers were hospitalized about 36 h before drug treatment. The baseline situation was investigated throughout the day before the treatment (day-1). On day 1, the drug was infused i.v. for 20 min. Twenty blood samples were drawn from each volunteer, in baseline situation, during and after the infusion. Functional antithrombin III, antithrombin III antigen, prothrombin time, partial thromboplastin time were evaluated in all plasma samples. Both functional antithrombin III and antithrombin III antigen produced well defined plasma concentration-time profiles after the infusion, which allowed net values of these two analytes to be obtained subtracting baseline from post-infusion concentrations. Net pharmacokinetic parameters of functional antithrombin III and antithrombin III antigen proved to be almost superimposable. A comparison of data obtained in this trial on healthy volunteers with those previously obtained by other authors on target population demonstrates similar and fully comparable results. The authors conclude that the nanofiltration step neither affects at all the pharmacokinetics/pharmacodynamics nor the safety of the formulation investigated.

Quantitative structure-activity relationship (QSAR) study of human factor Xa inhibitor N2-aroylanthranilamides, recently reported by Yee et al. (J. Med. Chem., 43, 873-882), has been performed using principal component factor analysis as the preprocessing step. The study reveals that presence of electron-donating R2 substituent at the para position (with respect to the amide linkage) is conducive to the binding affinity, whereas a meta R2 substituent decreases the affinity. Again, electron-donating R1 substituents with less bulk and optimum hydrophilic-lipophilic balance (particularly, methyl and methoxy groups) favor the activity. The study further suggests that electron-withdrawing R3 substituents are detrimental for the activity, whereas bulkier R4 substituents (particularly NHSO2Me group) increase the activity.

Objectives: To evaluate the safety, pharmacokinetics, and the practicability of two different antithrombin III (AT III) high-dose regimens in patients with severe sepsis., Design: Prospective, open, randomized, 2 parallel groups, multinational clinical trial., Setting: Eleven academic medical center intensive care units (ICU) in Austria, Belgium, Denmark, Germany, Norway and Sweden., Patients: Thirty-three patients with severe sepsis who received standard supportive care and antimicrobial therapy, in addition to the administration of AT III., Interventions: Patients received an intravenous loading dose of 6,000 IU AT III followed by either intermittent bolus infusions of 1,000 IU AT III every 4 h or a continuous infusion of 250 IU AT III/h for 4 days, resulting in a total dose for both dosage regimens of 30,000 IU AT III., Measurements: All patients were evaluated for safety and all but one for pharmacokinetics., Results and Conclusions: The administration of AT III was safe and well tolerated. The overall 28-day all-cause mortality was 30% (43% intermittent bolus infusions; 21% continuous infusion). The mean probability of dying according to the SAPS II was 48%. The difference in mortality between both groups was within the range of chance. AT III plasma levels were elevated from low baseline levels to above 120% soon after onset of AT III therapy and remained at these levels for the treatment phase of 4 days. Functional and immunologic levels of AT III corresponded very well. With an overall median volume of distribution of 4.5 l (range: 2.4-6.5 l), AT III only moderately extended beyond plasma. The overall median elimination half-life was 18.6 h (range: 5.1-37.4). Overall, median response was 1.75% per IU/kg (range: 1.14-2.8). The variability of elimination parameters was quite noteworthy (CV = 41-59%), whereas distribution-related parameters showed a moderate variability (CV = 24%). In spite of this variability, both high-dose IV regimens reliably provided AT III levels above 120% for all but one patient. An increased mortality was observed for patients with a distribution volume exceeding 4.5 l (or a response < 1.7% per IU/kg). AT III distribution volumes above 4.5 l might indicate a capillary leak phenomenon. The continuous infusion regimen was slightly preferred by the investigators with regard to practicability.

Inhibition of factor Xa (FXa) may interrupt thrombus progression. This study compared the antithrombotic activity of a novel FXa inhibitor, ZK-807834 [MW, 527 D; Ki (human FXa), 0.11 nM], with recombinant tick anticoagulant peptide [rTAP; MW, 6,685 D; Ki, (human FXa) = 0.28 nM], and DX-9065a [MW 445 D, Ki (human FXa), 40 nM] in rabbits with arterial thrombosis induced by electrical vascular injury. ZK-807834 also was compared with low molecular weight heparin (LMWH; MW, 5,500 D) during venous thrombosis induced by placing a copper wire and threads in the vena cava. Inhibitors were administered as an i.v. bolus and 2-h infusion. Total dosages of ZK-807834, > or =0.7 micromol/kg (n = 18); rTAP, > or =1 micromol/kg (n = 18); or DX-9065a, > or =11 micromol/kg (n = 18) decreased the incidence of arterial thrombotic occlusion compared with control animals (p < 0.05). However, five of six animals given the lowest effective dosage of rTAP and four of six animals given DX-9065a bled from a surgical incision >5 min, but only two of six animals given ZK-807834 bled >5 min. Venous clot weights were reduced compared with controls for dosages of ZK-807834 > or =0.007 micromol/kg (n = 36) or LMWH > or =0.2 micromol/kg (n = 18). Prothrombin time (PT) and activated partial thromboplastin time (aPTT) were unchanged from baseline at the minimally effective dose of ZK-807834, whereas aPTT was increased twofold at the effective dose of LMWH. Thus ZK-807834 may be useful to attenuate thrombosis at lower dosages and with less perturbation of systemic hemostasis compared with available agents.

An antithrombin (AT) deficiency develops in patients with thermal injuries as a result of the subclinical disseminated intravascular coagulation. We conducted a pilot study to assess AT(Human [H]) concentrate infusions for safety and efficacy in thermal injury. Nine patients with burns who received Thrombate (Bayer Corporation, Berkeley, Calif) AT(H) concentrate infusions every 8 hours to raise the plasma level to 175% in the first 72 hours after injury were compared with 9 control patients with burns. Admission AT plasma levels were 45%+/-10% in patients treated with AT(H) versus 49%+/-18% in control patients (normal, 100%+/-20%). Day-2 to day-4 levels were 120%+/-25% in patients treated with AT(H) patients versus 50%+/-12% in the control patients (P < .002). In the group treated with AT(H), the time to wound healing was shorter for all body regions and was significantly shorter for the hand (P < .02). Compared with control patients, patients treated with AT(H) had similar blood loss per grafted area. A trend toward fewer autografting procedures, a shorter meshed autograft healing time, and a decreased hospital stay was found for the patients treated with AT(H). AT(H) concentrate infusions are safe with thermal injury and are a viable option to shorten the length of hospitalization and to promote graft viability and survival. Clinical trials to confirm the benefit of this medication in the acute phase of thermal injury would be worthwhile.

Procoagulant activities associated with human clots may contribute to thrombus extension. We investigate the inhibition of clot-associated factor Xa and thrombin activities by purified human antithrombin either alone or as combination with a low molecular weight heparin (enoxaparin) as compared with unfractionated heparin (UFH). The standard clots were prepared by recalcification of frozen platelet-poor human plasma. Clot-associated thrombin was measured on the clot after clot incubation in recalcified buffer or recalcified prothrombin solution. The enzymatic reaction was measured using a specific substrate for thrombin (CBS 3447). The thrombin concentration was determined both on the clots and in the reaction mixtures. In parallel, prothrombin fragment 1.2 and thrombin-antithrombin complexes (TAT) were measured using enzyme-linked immunosorbent assay methods. We demonstrated that in the presence of purified human prothrombin and antithrombin (AT), a partial inhibition of clot associated thrombin activity correlated with an increase of TAT complexes. However, antithrombin was unable to inhibit thrombin generation induced by the clot-associated factor Xa. Enoxaparin (low molecular weight heparin) and UFH did not enhance clot-bound thrombin inhibition induced by AT. We conclude that clot-bound thrombin is accessible to human antithrombin alone. AT is also able to inhibit thrombin generated by factor Xa-associated clot. However, neither a low molecular weight heparin or UFH enhanced the effect of AT alone.

Thrombin is inhibited by its cognate plasma inhibitor antithrombin, through the formation of covalent thrombin-antithrombin (TAT) complexes that are found as ternary complexes with vitronectin (VN-TAT). To determine whether the metabolism of VN-TAT ternary complexes is different from that previously reported for binary TAT complexes, plasma clearance studies were done in rabbits using human VN-TAT. 125I-VN-TAT was shown to be cleared rapidly from the circulation (t1/2alpha = 3.8 min) in a biphasic manner mainly by the liver. 125I-TAT had a similar initial clearance (t1/2alpha = 5.3 min) but had a significantly faster beta-phase clearance (t1/2beta = 42.8 min versus 85.4 min for VN-TAT; p = 0.005). Protamine sulfate and heparin abolished the rapid initial alpha-phase of 125I-VN-TAT clearance and reduced its liver-specific association and in vivo degradation. Heparin also reduced the alpha-phase clearance of 125I-TAT and was associated with the appearance of high molecular weight complexes, suggesting enhanced complex formation between VN and TAT. 125I-VN-TAT binding to HepG2 cells was reduced by competition with VN-TAT or heparin but to a much lesser extent in the presence of TAT. The binding of VN-TAT to HepG2 cells was not inhibited by competition with the low density lipoprotein receptor-related protein ligand, methylamine-alpha2-macroglobulin. 125I-VN-TAT binding was also inhibited by treating HepG2 cells with heparinase or by growing the cells in the presence of beta-D-xyloside. Finally, both heparin and chloroquine, but not methylamine-alpha2-macroglobulin, reduced the internalization and degradation of VN-TAT by HepG2 cells. Taken together, these data indicate the importance of VN in TAT metabolism and demonstrate that VN-TAT binds to liver-associated heparan sulfate proteoglycans, which mediate its internalization and subsequent intracellular degradation.

YM-60828 was found to potently inhibit human factor Xa following oral administration. YM-60828 showed high affinity for factor Xa (Ki = 1.3 nM), but did not affect thrombin (Ki > 100 microM). YM-60828 doubled factor Xa clotting time, prothrombin time (PT) and activated partial thromboplastin time (APTT) at 0.10, 0.21, 0.24 microM, respectively. Importantly, it did not prolong thrombin time at 100 microM. YM-60828 also inhibited factor Xa in the prothrombinase complex with an IC50 value of 7.7 nM. In addition to its anticoagulant activity, YM-60828 inhibited platelet aggregation induced by various agonists (IC50 = 3 to 23 microM). Squirrel monkeys were used to study the ex vivo anticoagulant activity and pharmacokinetic properties of YM-60828. One hour after oral administration at 3 mg/kg, YM-60828 strongly prolonged PT and APTT by 4.8- and 1.9-fold, respectively, and plasma concentration reached 788 +/- 167 ng/ml. Bioavailability was calculated to be 20.3%. These results strongly suggest that YM-60828 will be a valuable orally active and potent anticoagulant agent showing potential antithrombotic activity.

Although heparin has been used clinically for prophylaxis and treatment of thrombosis, it has suffered from problems such as short duration within compartments in vivo that require long term anticoagulation. A covalent antithrombin-heparin complex has been produced with high anticoagulant activity and a long half-life relative to heparin. The product had high anti-factor Xa and antithrombin activities compared with noncovalent mixtures of antithrombin and heparin (861 and 753 units/mg versus 209 and 198 units/mg, respectively). Reaction with thrombin was rapid with bimolecular and second order rate constants of 1.3 x 10(9) M-1 s-1 and 3.1 x 10(9) M-1 s-1, respectively. The intravenous half-life of the complex in rabbits was 2.6 h as compared with 0.32 h for similar loads of heparin. Subcutaneous injection of antithrombin-heparin resulted in plasma levels (peaking at 24-30 h) that were still detectable 96 h post-injection. Given the increased lifetime in these vascular and intravascular spaces, use of the covalent complex in the lung was investigated. Activity of antithrombin-heparin instilled into rabbit lungs remained for 48 h with no detection of any complex systemically. Thus, this highly active agent has features required for pulmonary sequestration as a possible treatment for thrombotic diseases such as respiratory distress syndrome.

The metabolic characteristics of two rabbit plasma thrombin inhibitors, heparin cofactor II (HCII) and antithrombin (AT), have been compared in healthy young rabbits. Purified HCII and AT-alpha were differentially radiolabeled (125I, 131I) and injected intravenously; blood samples were taken at prescribed intervals over 7 days. From the plasma clearance curves of protein-bound radioactivities, fractional catabolic rates and compartmental distributions were calculated using a three-compartment model. The whole body fractional catabolic rate for HCII (jt, 0.43/day, equivalent to t1/2 = 1.61 days) was significantly faster than for AT (jt, 0.37/day; t1/2 = 1.89 days; P < 0.005). The fractional distribution of HCII in the intravascular compartment (Ap, 0.20) and in the extravascular compartment (Ac, 0.63) differed significantly from AT (Ap, 0.30; Ac, 0.56). From the catabolic data and blood concentrations, absolute quantities of HCII and AT catabolized by a 3-kg rabbit amounted to 12.8 and 19.9 mg/day, respectively, equivalent to a molar ratio, AT/HCII, of 1.7. The catabolic molar ratio was compared with the relative release rates of HCII and AT from perfused rabbit livers. Both proteins were released from the liver, the molar ratio in the perfusate rising to approximately 1.4 at 2.5 h. This report increases our understanding of the in vivo dynamics of these two proteins.

Many of the serious, potentially fatal complications of hematopoietic stem cell transplantation have similarities to the multiple organ dysfunction syndrome (MODS) in critically ill nontransplant patients. One of these similarities is the alteration in the hemostatic system in such a way as to lower the levels of the naturally occurring anticoagulant proteins, especially antithrombin III. As in MODS, the outcome of transplant patients with these complications correlates with the degree of change in antithrombin III levels. Preliminary studies suggest that antithrombin III concentrate in pharmacologic doses along with intensive supportive care efforts can improve the clinical outcome of patients with these transplant-related complications. Further work to confirm these findings and, it is hoped, provide insight into the mechanism of action of antithrombin III in this setting is obviously warranted. Until such studies are completed, however, the preponderance of evidence suggests that when subjected to a risk-benefit analysis, patients in the early stages of transplant-related complications would be better off receiving antithrombin III supplementation than not.

Treatment with AT III concentrates is a good example for the discrepancy between the optimistic expectations based on theoretical considerations or animal experiments and the result of clinical studies. 15 years after the introduction into clinical practice, a benefit for patients treated with AT III concentrates has not been proven. In hereditary antithrombin III deficiency, randomized clinical trials are completely lacking and only few and small sized randomized studies were performed in patients with acquired AT III deficiency. In none of these trials, a significant clinical benefit with regard to reduction of morbidity or mortality was detectable. Based on the published data, one can state that AT III concentrates may be beneficial in some special clinical situations in patients with hereditary antithrombin III deficiency (such as delivery, acute serious thromboembolic complications and postoperative thromboprophylaxis). In acquired AT III deficiency, there is no proven indication for the use of AT III concentrates.

The general characteristics of antithrombin III (AT III) concentrates available in the United States are described in this article. The effectiveness of AT III concentrates in the prevention and treatment of thrombotic episodes in patients with hereditary AT III deficiency are summarized, and the use of this product in various conditions with acquired AT III deficiency are reported.

The efficacy of different mechanical prophylaxes against venous thromboembolism, such as aggressive early mobilization, elastic stockings, continuous passive motion, and external pneumatic compression, is discussed and placed in perspective. The published literature regarding dextran, hydroxychloroquine, and antithrombin III is reviewed and critically assessed in terms of efficacy and safety.

The distribution and behavior of the rabbit plasma proteins albumin, fibrinogen, and antithrombin III (ATIII) (isoforms alpha and beta), have been examined in groups of alloxan-induced diabetic rabbits and control rabbits. By injecting radiolabeled preparations intravenously, measurements of plasma clearance, rates of catabolism, and compartmental distribution were made for each protein. In addition, after allowing the radiolabeled proteins to circulate for 12 hours, we excised aortas after exsanguination and determined the content of these proteins in the endothelium and subendothelium. The respective fractional catabolic rates of ATIII-alpha and ATIII-beta were similar in the diabetic and control rabbits, but fibrinogen and albumin were catabolized more slowly in the diabetic rabbit than in the control rabbit. The distributions of albumin and the ATIII isoforms between the intravascular, noncirculating vascular, and extravascular compartments in the diabetic rabbit were similar to the respective proteins in the control rabbit, but a smaller proportion of fibrinogen was associated with the vascular compartment of the diabetic rabbit when compared with that in the control rabbit. At 12 hours after injection, the quantities of fibrinogen and albumin associated with the diabetic aorta endothelium and particularly the subendothelium were increased, whereas ATIII-alpha and ATIII-beta were decreased relative to the control aorta. The fibrinogen-to-ATIII ratio in the diabetic aorta was increased twofold to threefold when compared with that in the control aorta. We conclude that the increased ratio of fibrinogen to ATIII in the aorta wall of the diabetic rabbit may be characteristic of the prothrombotic state that is conspicuous in insulin-dependent diabetes.

Background and Methods: Seventeen adult patients with acute lymphoblastic leukemia (ALL) treated with L-asparaginase (20,000 IU/m2 on six alternate days) were infused with antithrombin III (AT III) concentrates (Kybernin P, Behring). Substitution therapy was aimed at increasing the reduced AT III concentration usually found in these patients, since AT III deficiency is thought to be associated with an increased risk of thrombosis. Two schedules of AT III administration, different in dosage, timing and duration were evaluated. The first 7 patients (group A) received a fixed dose of 2,000 U every day for 6 times, starting with the second L-asparaginase (L-ase) infusion, independently of their plasma AT III levels. In the following 10 patients (group B), 20-25 U/Kg b.w. were administered daily for 7 times only when the plasma AT III level was lower than 60% with plasma fibrinogen higher than 100 mg/dl and platelet count higher than 50 x 10(9)/l, or when AT III was below 40%. Thirteen patients who received L-ase without AT III substitution served as controls., Results and Conclusions: Both substitution regimens resulted in mean plasma AT III nadir values significantly (p less than 00.1) higher than in the controls. Our data suggest that, in ALL patients receiving L-ase according to the L20 protocol, satisfactory plasma AT III levels may be assured with infusions of 20-25 U/Kg b.w./day for 7-10 days, starting by day 2 of L-ase treatment.

The activity elimination half-life of heat-treated antithrombin III (AT III) concentrate was studied in 5 healthy pregnant and 5 preeclamptic women with a documented AT III deficiency. Healthy pregnant women received 1500 units over 20 minutes. Serial blood specimens were obtained over the next 12 hours. The mean (+/- SEM) activity elimination half-life of AT III was 29.4h +/- 3.4h. Preeclamptic subjects had a mean baseline AT III activity of 70.5 +/- 2% (range 61 to 75%). Their activity eliminator half-life after 3000 units of AT III concentrate was 8.5 +/- 1.2h. There was a direct relationship between the pre-concentrate AT III activity level and the AT III activity elimination half-life (r = 0.79, p = 0.01) for all subjects. Based upon parameters calculated from the first infusion, the AT III activity of preeclamptic subjects was maintained by a constant infusion at approximately 100% for 96h. At the conclusion of the infusion, the activity elimination half-life was again measured. A dramatic increase in the activity elimination half-life was demonstrated (433.6h). We conclude that the activity elimination half-life of AT III concentrate is increased during normal pregnancy and further increased in preeclamptic women with an acquired deficiency.