Bioavailability and pharmacokinetics of a new low molecular weight heparin (RO-11)--a three way cross-over study in healthy volunteers

Use of Real-World Data and Physiologically-Based Pharmacokinetic Modeling to Characterize Enoxaparin Disposition in Children With Obesity

Dosing guidance for children with obesity is often unknown despite the fact that nearly 20% of US children are classified as obese. Enoxaparin, a commonly prescribed low-molecular-weight heparin, is dosed based on body weight irrespective of obesity status to achieve maximum concentration within a narrow therapeutic or prophylactic target range. However, whether children with and without obesity experience equivalent enoxaparin exposure remains unclear. To address this clinical question, 2,825 anti-activated factor X (anti-Xa) surrogate concentrations were collected from the electronic health records of 596 children, including those with obesity. Using linear mixed-effects regression models, we observed that 4-hour anti-Xa concentrations were statistically significantly different in children with and without obesity, even for children with the same absolute dose (P = 0.004). To further mechanistically explore obesity-associated differences in anti-Xa concentration, a pediatric physiologically-based pharmacokinetic (PBPK) model was developed in adults, and then scaled to children with and without obesity. This PBPK model incorporated binding of enoxaparin to antithrombin to form anti-Xa and elimination via heparinase-mediated metabolism and glomerular filtration. Following scaling, the PBPK model predicted real-world pediatric concentrations well, with an average fold error (standard deviation of the fold error) of 0.82 (0.23) and 0.87 (0.26) in children with and without obesity, respectively. PBPK model simulations revealed that children with obesity have at most 20% higher 4-hour anti-Xa concentrations under recommended, total body weight-based dosing compared to children without obesity owing to reduced weight-normalized clearance. Enoxaparin exposure was better matched across age groups and obesity status using fat-free mass weight-based dosing.

Pharmacokinetic model of unfractionated heparin during and after cardiopulmonary bypass in cardiac surgery

Background

Unfractionated heparin (UFH) is widely used as a reversible anti-coagulant in cardiopulmonary bypass (CPB). However, the pharmacokinetic characteristics of UFH in CPB surgeries remain unknown because of the lack of means to directly determine plasma UFH concentrations. The aim of this study was to establish a pharmacokinetic model to predict plasma UFH concentrations at the end of CPB for optimal neutralization with protamine sulfate.

Methods

Forty-one patients undergoing CPB during cardiac surgery were enrolled in this observational clinical study of UFH pharmacokinetics. Patients received intravenous injections of UFH, and plasma anti-F_IIa activity was measured with commercial anti-F_IIa assay kits. A population pharmacokinetic model was established by using nonlinear mixed-effects modeling (NONMEM) software and validated by visual predictive check and Bootstrap analyses. Estimated parameters in the final model were used to simulate additional protamine administration after cardiac surgery in order to eliminate heparin rebound. Plans for postoperative protamine intravenous injections and infusions were quantitatively compared and evaluated during the simulation.

Results

A two-compartment pharmacokinetic model with first-order elimination provided the best fit. Subsequent simulation of postoperative protamine administration suggested that a lower-dose protamine infusion over 24 h may provide better elimination and prevent heparin rebound than bolus injection and other infusion regimens that have higher infusion rates and shorter duration.

Conclusion

A two-compartment model accurately reflects the pharmacokinetics of UFH in Chinese patients during CPB and can be used to explain postoperative heparin rebound after protamine neutralization. Simulations suggest a 24-h protamine infusion is more effective for heparin rebound prevention than a 6-h protamine infusion.

Pharmacodynamics assessment of Bemiparin after multiple prophylactic and single therapeutic doses in adult and elderly healthy volunteers and in subjects with varying degrees of renal impairment

INTRODUCTION

Aging and renal impairment may prolong the half-life and lead to accumulation of low molecular weight heparins. Correct dosing is critical to prevent bleeding or thrombosis.

MATERIALS AND METHODS

Open, parallel study. Healthy adult [n=13] and elderly (>65yrs) [n=12] volunteers; and subjects with mild (ClCr≥50 to ≤80mL/min, n=8), moderate (ClCr≥30 to <50mL/min, n=7), and severe (ClCr<30mL/min, n=8) renal impairment received four prophylactic doses (3,500IU/24h) and a single therapeutic dose (115IU/kg) of bemiparin with an interim washout period. Anti-FXa activity and the potential need for dose adjustment were evaluated.

RESULTS

There were statistically significant differences in the severe renal impairment group vs. adult volunteers in all anti-FXa related parameters, but no significant differences in any of the anti-FXa related parameters between the adult and the elderly. Anti-FXa simulations after 10 prophylactic doses predicted mean Amax=0.59IU/mL in subjects with severe renal impairment and 0.33-0.39IU/mL in the rest. Simulations in the severe renal impairment group with dose adjustment (2,500IU/24h) predicted all individual Amax<0.60IU/mL (mean Amax=0.42IU/ml). Simulations after 10 therapeutic doses predicted mean Amax=1.22IU/mL in severe renal impairment group and 0.89-0.98IU/mL in the rest. Simulations in the severe renal impairment group with 75% dose adjustment predicted individual Amax≤1.60IU/mL (mean Amax=0.91IU/mL).

CONCLUSIONS

No dose adjustments are required in elderly with preserved renal function. A dose adjustment of bemiparin is only advisable in patients with severe renal impairment when using prophylactic or therapeutic doses.

Anticoagulants in the treatment of deep vein thrombosis

Intravenous (IV) infusion of unfractionated heparin (UFH) followed by oral administration of warfarin remains the cornerstone of clinical treatment of deep vein thrombosis (DVT). Results from numerous clinical trials demonstrate that subcutaneously administered low-molecular-weight heparin (LMWH) is at least as effective and as safe as IV UFH. Treatment with LMWH has several clinical advantages over treatment with UFH, including less-frequent dosing and elimination of the need for monitoring. The introduction of LMWHs has made it possible for physicians to offer outpatient treatment of DVT, with the associated advantage of reduced costs due to shortened hospital stays. However, the optimal duration of anticoagulant therapy after DVT is still debated, as it depends on an individual patient's potential risk for recurrence or treatment-associated complications. Patients are usually risk stratified on the basis of multiple clinical characteristics, including the location of thromboemboli, the presence or absence of cancer, the assumed etiology or cause of DVT (idiopathic vs. due to a transient risk factor), and the presence of certain thrombophilic conditions. High-risk patients often receive inpatient treatment with UFH or LMWH and are candidates for long-term (> or = 6 months) oral anticoagulation, whereas short-term anticoagulation (3 to 6 months) is usually indicated for patients who are at lower risk of recurrence or therapeutic complications and who can be treated with LMWH on an outpatient basis. The introduction of LMWHs has resulted in significant clinical progress for the treatment of DVT.

Efficacy and safety of bemiparin compared with enoxaparin in the prevention of venous thromboembolism after total knee arthroplasty: a randomized, double-blind clinical trial

In this randomized, multicenter, controlled, double-blind, sequential trial, 381 patients undergoing primary total knee replacement were randomly assigned to receive subcutaneous injections of either 3500 IU anti-factor Xa of bemiparin sodium, first dose 6 h after surgery, or 40 mg of enoxaparin, first dose 12 h before surgery, followed by daily doses for 10 +/- 2 days, for the prophylaxis of venous thromboembolism. The primary efficacy endpoint was venous thromboembolism up to postoperative day 10 +/- 2, defined as deep vein thrombosis detected by mandatory bilateral venography, documented symptomatic deep vein thrombosis and/or documented symptomatic pulmonary embolism. The primary safety endpoint was major bleeding. Eighty-seven percent of all randomized patients (333 of 381 patients) were evaluable for efficacy. The incidence of venous thromboembolism was 32.1% (53 of 165 patients) in the bemiparin group and 36.9% (62 of 168 patients) in the enoxaparin group. The absolute risk difference was 4.8% in favor of bemiparin [95% confidence interval (CI), -15.1% to 5.6%; non-inferiority P-value: 0.02; superiority P-value: 0.36]. The incidence of proximal deep vein thrombosis was 1.8% (three of 165 patients) in the bemiparin group and 4.2% (seven of 168 patients) in the enoxaparin group. Major bleeding occurred in six patients (three in each group). There were no deaths during the study. This trial shows that bemiparin started postoperatively is as effective and safe as enoxaparin started preoperatively in the prevention of venous thromboembolism in patients undergoing total knee replacement.

Comparative study of the pharmacokinetic profiles of two LMWHs--bemiparin (3500 IU, anti-Xa) and tinzaparin (4500 IU, anti-Xa)--administered subcutaneously to healthy male volunteers

Pharmacokinetic profiles of bemiparin (3500 IU, anti-Xa) and tinzaparin (4500 IU, anti-Xa) administered subcutaneously to 12 healthy male volunteers were compared in a monocentric study. Each of the 12 subjects underwent successively the two low-molecular-weight heparin (LMWH) preparations in a randomised order and was considered as its own control. Anti-Xa activity, free and total tissue factor pathway inhibitor (TFPI), and thromboplastin-thrombomodulin-mediated time were determined as main variables. Activated partial thromboplastin time (APTT), thrombin clotting time, and anti-IIa activity were also determined. Bemiparin (3500 IU, anti-Xa) exerts a significantly more rapid, more potent, and more prolonged anti-Xa activity than tinzaparin (4500 IU, anti-Xa). The plasma level increase for free and total TFPI is significantly lower with bemiparin than with tinzaparin. Free and total TFPI peak levels occur earlier than anti-Xa activity peak levels for both LMWH preparations, but no statistical difference appeared between the two preparations for TFPI T(max). No significant effect was observed for both preparations for thromboplastin-thrombomodulin-mediated time. Subcutaneous injection of bemiparin exerts only minimal anti-IIa activity and does not prolong thrombin time, whereas tinzaparin elicits significant anti-IIa activity and prolongs thrombin clotting time. Bemiparin exerts a significantly lower prolongation of APTT than tinzaparin. No difference was observed for APTT prolongation T(max) between the two preparations. Globally, the overall tolerability of both formulations revealed no relevant adverse effects. In conclusion, bemiparin and tinzaparin are not bioequivalent. Bemiparin exerts an important and more prolonged anti-Xa activity in comparison with tinzaparin. An original finding of this study is the difference observed between the two formulations for free TFPI release.

Effectiveness and safety of bemiparin versus low-molecular weight heparins in orthopaedic surgery

OBJECTIVE

To evaluate the effectiveness and safety of bemiparin in the prophylaxis of thromboembolism in orthopaedic surgery with respect to other low-molecular-weight heparins.

METHODS

A meta-analysis of effectiveness and safety of low-molecular weight heparins versus standard heparin in orthopaedic surgery was performed. A literature search was done of Medline and Excerpta Medica from 1988 to 1998. Only controlled clinical trials were selected for meta-analysis. Differences between groups were expressed as odds ratios and these were combined by the Mantel-Haenszel method.

MAIN OUTCOME MEASURES

Rates of deep vein thrombosis, pulmonary embolism and wound haematoma.

RESULTS

Twenty-one studies involving 4605 patients were included in the meta-analysis. Bemiparin significantly reduces the rates of deep vein thrombosis (OR; 95% CI = 0.38, 0.15-0.90). No significant differences were found in pulmonary embolism and wound haematoma. The incidence of deep vein thrombosis is also lower with enoxaparin than with unfractionated heparin. However, only nadroparin reduced the incidence of pulmonary embolism (ORs = 0.24, 95% CI = 0.05-0.94). In any case, the incidence of wound haematoma was not significant.

CONCLUSION

Bemiparin seems to be as effective and safe as the other low-molecular-weight heparins in the prevention of thromboembolic complications in orthopaedic surgery.