The antithrombotic activity and pharmacokinetics of enoxaparine, a low molecular weight heparin, in humans given single subcutaneous doses of 20 to 80 mg

Anti-factor X Activity Levels with Continuous Intravenous Infusion and Subcutaneous Administration of Enoxaparin after Coronary Artery Bypass Grafting: a Randomized Clinical Trial

BACKGROUND

Low-molecular-weight heparin enoxaparin is widely used in pharmacological thromboprophylaxis after coronary artery bypass grafting (CABG). The aim of this study was to compare anti-factor X activity (anti-Xa) levels when the thromboprophylactic dose of enoxaparin was provided after CABG, with two different administration routes: continuous intravenous infusion (CIV) and subcutaneous bolus (SCB) injection. We hypothesized that the current standard method of SCB administration might lead to lower anti-Xa levels than recommended in other patient groups, due to reduced bioavailability.

METHODS

In this prospective, randomized, controlled clinical trial, 40 patients scheduled for elective CABG were randomized to receive 40 mg of enoxaparin per day either as CIV or SCB for 72 h. Enoxaparin was initiated 6-10 h after CABG. Anti-Xa levels were measured 12-14 times during the study period. The primary outcome i.e. the maximum anti-Xa concentration over 0-24 h (C_max0-24h ), was calculated from these measured values. Secondary outcomes were C_max25-72h and the trough concentration of anti-Xa after 72 h of enoxaparin initiation (C_72h ).

RESULTS

Twenty patients were randomized to the CIV-group and 19 to the SCB-group. The median anti-Xa C_max0-24h was significantly lower in the CIV-group than in the SCB-group: 0.15 [interquartile range (IQR) 0.13-0.19] IU/mL versus 0.25 (IQR 0.18-0.32) IU/mL, p < 0.005. The median anti-Xa C_max25-72h was 0.12 (IQR, 0.1-0.17) IU/mL versus 0.23 (IQR 0.19-0.31) IU/mL, respectively, p < 0.005. At 72 h, there was no difference between the groups in their anti-Xa levels.

CONCLUSIONS

In this low-risk CABG patient population, SCB administration of a thromboprophylactic dose of enoxaparin provided anti-Xa levels that are considered sufficient for thromboprophylaxis in other patient groups. CIV administration resulted in lower anti-Xa levels compared to the SCB route.

Heparin: The Journey from Parenteral Agent to Nasal Delivery

Although the worldwide usage of direct oral anticoagulants has continuously increased over the past decade, heparin remains an important weapon in the current arsenal of anticoagulant drugs. Parenteral heparin administration (i.e., either intravenously or subcutaneously) has represented for decades the only possible route for generating a significant anticoagulant effect, although being notoriously associated with some important drawbacks such as discomfort and risk of low compliance, thus paving the way to searching for more amenable means of administration. We provide here an updated analysis of animal and human studies that have explored the feasibility, suitability, and efficiency of heparin administration through the unconventional nasal route, as a possible alternative to the more traditional parenteral injection. The major hurdles that contribute to impair intranasal absorption and systemic delivery of heparin are represented by its relatively high molecular weight and negative charge. Therefore, although pure drug administration would not be associated with efficient nasal adsorption, or by systemic biological activity (i.e., anticoagulant effect), the combination of low molecular weight heparins and absorption enhancers such as surfactants, mucoadhesive, cyclodextrins, polyethylenimines and encapsulation into (nano)carriers seems effective to at least partially improve drug transport through the nasal route and allow systemic delivery in animals. Besides generating anticoagulant effects, intranasal heparin administration can also produce local pleiotropic effects, mostly related to anti-inflammatory properties, such as attenuating airway allergic inflammation or inhibiting the binding of the spike protein of some coronaviruses (including severe acute respiratory syndrome coronavirus 2) to their host cell receptors. This preliminary evidence represents a valuable premise for planning future studies in humans aimed at establishing the pharmacokinetics and biological activity of locally and systemically delivered intranasal heparin formulations.

Endothelial glycocalyx degradation in multisystem inflammatory syndrome in children related to COVID-19

Abstract

Multisystem inflammatory syndrome in children (MIS-C) represents a rare but severe complication of severe acute respiratory syndrome coronavirus 2 infection affecting children that can lead to myocardial injury and shock. Vascular endothelial dysfunction has been suggested to be a common complicating factor in patients with coronavirus disease 2019 (COVID-19). This study aims to characterize endothelial glycocalyx degradation in children admitted with MIS-C. We collected blood and urine samples and measured proinflammatory cytokines, myocardial injury markers, and endothelial glycocalyx markers in 17 children admitted with MIS-C, ten of which presented with inflammatory shock requiring intensive care admission and hemodynamic support with vasopressors. All MIS-C patients presented signs of glycocalyx deterioration with elevated levels of syndecan-1 in blood and both heparan sulfate and chondroitin sulfate in the urine. The degree of glycocalyx shedding correlated with tumor necrosis factor-α concentration. Five healthy age-matched children served as controls. Patients with MIS-C presented severe alteration of the endothelial glycocalyx that was associated with disease severity. Future studies should clarify if glycocalyx biomarkers could effectively be predictive indicators for the development of complications in adult patients with severe COVID-19 and children with MIS-C.

Key messages

Children admitted with MIS-C presented signs of endothelial glycocalyx injury with elevated syndecan-1 and heparan sulfate level.

Syndecan-1 levels were associated with MIS-C severity and correlated TNF-α concentration.

Syndecan-1 and heparan sulfate may represent potential biomarkers for patients with severe COVID-19 or MIS-C.

Supplementary information

The online version contains supplementary material available at 10.1007/s00109-022-02190-7.

Intestinal Efflux Transporters P-gp and BCRP Are Not Clinically Relevant in Apixaban Disposition

PURPOSE

The involvement of the intestinally expressed xenobiotic transporters P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP) have been implicated in apixaban disposition based on in vitro studies. Recommendations against co-administration of apixaban with inhibitors of these efflux transporters can be found throughout the literature as well as in the apixaban FDA label. However, the clinical relevance of such findings is questionable due to the high permeability and high solubility characteristics of apixaban.

METHODS

Using recently published methodologies to discern metabolic- from transporter- mediated drug-drug interactions, a critical evaluation of all published apixaban drug-drug interaction studies was conducted to investigate the purported clinical significance of efflux transporters in apixaban disposition.

RESULTS

Rational examination of these clinical studies using basic pharmacokinetic theory does not support the clinical significance of intestinal efflux transporters in apixaban disposition. Further, there is little evidence that efflux transporters are clinically significant determinants of systemic clearance.

CONCLUSIONS

Inhibition or induction of intestinal CYP3A4 can account for exposure changes of apixaban in all clinically significant drug-drug interactions, and lack of intestinal CYP3A4 inhibition can explain all studies with no exposure changes, regardless of the potential for these perpetrators to inhibit intestinal or systemic efflux transporters.

Evaluation of prophylactic dosages of Enoxaparin in non-surgical elderly patients with renal impairment

Background

Thromboprophylaxis dosing strategies using enoxaparin in elderly patients with renal disease are limited, while dose adjustments or monitoring of anti-Xa levels are recommended. We sought to evaluate the efficacy and safety of enoxaparin 20 mg versus 30 mg subcutaneously daily by comparing anti-Xa levels, thrombosis and bleeding.

Methods

We conducted a prospective, single-blinded, single-center randomized clinical trial including non-surgical patients, 70 years of age or older, with renal disease requiring thromboprophylaxis. Patients were randomized to receive either 20 mg or 30 mg of enoxaparin. The primary endpoint was peak anti-Xa levels on day 3. Secondary endpoints included trough anti-Xa levels on day 3, achievement of within range prophylactic target peak anti-Xa levels and the occurrence of hemorrhage, thrombosis, thrombocytopenia or hyperkalemia during hospitalization.

Results

Thirty-two patients were recruited and sixteen patients were randomized to each arm. Mean peak anti-Xa level was significantly higher in 30 mg arm (n = 13) compared to the 20 mg arm (n = 11) 0.26 ± 0.11, 95%CI (0.18–0.34), versus 0.14 ± 0.09, 95CI (0.08–0.19) UI/ml, respectively; p = 0.004. Mean trough anti-Xa level was higher in 30 mg arm (n = 10) compared to the 20 mg arm (n = 16), 0.06 ± 0.03, 95CI (0.04–0.08) versus 0.03 ± 0.03, 95CI (0.01–0.05) UI/ml, respectively; p = 0.044. Bleeding events reported in the 30 mg arm were one retroperitoneal bleed requiring multiple transfusions, and in the 20 mg arm one hematuria. No thrombotic events were reported.

Conclusion

Peak anti-Xa levels provided by enoxaparin 20 mg were lower than the desired range for thromboprophylaxis in comparison to enoxaparin 30 mg.

Trial registration

The trial was retrospectively registered on ClinicalTrials.gov identifier: NCT03158792. Registered: May 18, 2017.

The Role of Tinzaparin in Oncology

Current guidelines recommend low-molecular-weight heparin treatment in patients with cancer with established venous thromboembolism (VTE). The aim of this article was to study the pharmacological properties and effectiveness of tinzaparin in patients with cancer as well as its potential anticancer properties. A search of PubMed and ScienceDirect databases up to March 2016 was carried out to identify published studies that detect the properties and use of tinzaparin in oncology. Protamine sulfate partially (60% to 65%) neutralized tinzaparin’s anti-Xa activity. No dose adjustment of tinzaparin is needed even in patients with severe renal impairment and Creatinine Clearance ≥20 mL/min. Tinzaparin demonstrated a statistically significant decline in VTE recurrence at 1 year post the index thromboembolic event. A statistically significant reduction in minor bleeding rates was also described, whereas major bleeding events did not decrease in patients with cancer treated with tinzaparin versus those who received vitamin K antagonists. Tinzaparin treatment in patients suffering from deep vein thrombosis reduced the incidence of postthrombotic syndrome and venous ulcers. Tinzaparin’s ability to prevent both metastatic dissemination of cancer cells and tumor angiogenesis has been delineated in preclinical research. Current data show that tinzaparin is safe and efficacious either for short-term or for long-term treatment of VTE in patients with cancer. Clinical trials are needed in order to examine the utility of tinzaparin in primary prevention of VTE and validate its potential anticancer advantages exhibited in preclinical research.

Anticoagulant Reversal and Anesthetic Considerations

Bleeding complications are a common concern with the use of anticoagulant agents. In many situations, reversing of neutralizing their effects may be warranted. Prothrombin complex concentrate replaces coagulation factors lowered by warfarin, as does fresh frozen plasma, but in a more concentrated form. Protamine negates the effect of heparin and combines chemically with heparin molecules to form an inactive salt. It also partially reverses the effects of low-molecular-weight heparin. Recombinant activated factor VII is a nonspecific procoagulant that activates the extrinsic clotting pathway, resulting in thrombin generation, but does not directly neutralize the activity of any of the new oral anticoagulants.

Unfractionated and Low-Molecular-Weight Heparins, Basic Mechanism of Action and Pharmacology

Unfractionated heparin has enjoyed sole anticoagulant status for nearly 50 years. Despite a dramatic growth in the development and the introduction of many newer anticoagulant and antithrombotic drugs and polytherapeutic approaches during the past decade, unfractionated and low-molecular-weight heparins remain the drugs of choice for many indications, including surgical anticoagulation, interventional cardiology, and in several additional considerations. Unfractionated heparin has a major role in the areas of vascular medicine and surgery, and it is the only parenteral anticoagulant drug that can be empirically neutralized by such agents as protamine sulfate. The development of low and ultra low-molecularweight heparins, which are a class of depolymerized heparin derivatives with distinct pharmacologic profiles that are largely determined by their composition, represents a refinement for the use of heparin. These drugs produce their major effects by combining with antithrombin Ill and exerting antithrombin and anti-Xa inhibition. The low-molecular-weight heparins also increase non-antithrombin III-dependent effects, such as tissue factor pathway inhibitor release, modulation of adhesion molecules, and the release of profibrinolytic and antithrombotic mediators from the blood vessels. Each of the low-molecular-weight heparins has different cumulative effects, and each product exhibits a distinct profile. Initially developed for the prophylaxis of postsurgical deep vein thrombosis, these drugs are now also used for the treatment of both venous and arterial thrombotic disorders. To a large extent, the low-molecular-weight heparins have replaced unfractionated heparin in most of the subcutaneous indications. This has resulted in a dramatic evolution in anticoagulant management that allows patients with thrombotic disorders to be treated in an outpatient setting. Thus, the introduction of low-molecular-weight heparins represents a major advance in improving the use of heparin. Generic versions of these drugs are likely to be developed as their patents expire. Currently, there are no clear guidelines for the acceptance of the generic versions of branded products. To avoid safety and efficacy-related problems, a generic drug must meet both the chemical and biologic equivalence criterion. Synthetically and biosynthetically derived agents such, as pentasaccharide, will also be introduced for clinical use; however, these drugs will have a narrower therapeutic spectrum due to their monotherapeutic nature. Heparin and its derivatives will continue to have a crucial role in the management of thrombotic and cardiovascular disorders in years to come.

The Treatment of Proximal Vein Thrombosis with Subcutaneous Low-Mole Molecular-Weight Heparin Compared with Continuous Intravenous Heparin

Low-molecular-weight heparin, compared with unfractionated heparin, has a higher bioavailability and a more prolonged half-life. There are limited data comparing the use of low-molecular-weight heparin with unfractionated heparin for the treatment of deep vein thrombosis. We have compared fixed-dose, subcutaneous low-molecular-weight heparin given once daily with adjusted-dose intravenous heparin given by continuous infusion in a multicenter double-blind clinical trial for the initial treatment of patients with proximal vein thrombosis. Clinical outcomes were objectively documented. Six of 213 patients receiving low-molecular-weight heparin (2.8%) and 15 of 219 patients receiving intravenous heparin (6.9%) developed new episodes of venous thromboembolism (p = 0.07; 95% confidence interval for the difference, 0.02%-8.1%). During initial therapy, major bleeding occurred in one patient receiving low-molecular-weight heparin (0.5%) and in 11 patients receiving intravenous heparin (5.0%), a risk reduction of 91% (p = 0.006). This apparent protection against major bleeding was lost during long-term therapy. Minor bleeding complications were rare. During the period of the study, 10 patients receiving low-molecular-weight heparin (4.7%) died, as compared with 21 patients receiving intravenous heparin (9.6%), a risk reduction of 51%(p = 0.049). This study shows that low-molecular-weight heparin is at least as effective as classic intravenous heparin therapy and that there was a reduction in deaths and bleeding complications. Furthermore, low-molecular-weight heparin was more convenient to administer. The simplified therapy with low-molecular-weight heparin given by once-daily subcutaneous injection without monitoring may allow patients with uncomplicated proximal deep vein thrombosis to be cared for as outpatients. Key Words: Low-molecular-weight heparin—Unfractionated heparin—Deep vein thrombosis—Deaths—Bleeding complications.

Non-weight-based enoxaparin dosing subtherapeutic in trauma patients

BACKGROUND

We report our experience dosing and monitoring enoxaparin with anti-factor Xa activity (anti-FXaA) levels for venous thromboembolism prophylaxis in trauma patients (TP).

MATERIALS AND METHODS

TP receiving standard, non-weight-based dosed enoxaparin administered every 12 h for venous thromboembolism prophylaxis with peak anti-FXaA levels measured were prospectively monitored and evaluated and those whose first anti-FXaA levels ≥ or <0.2 IU/mL were compared. Anti-FXaA levels and enoxaparin dose (mg/kg actual body weight) were evaluated for correlation.

RESULTS

Of the fifty-one TP included, initial anti-FXaA levels were <0.2 IU/mL in 37 (72.5%) whose dose was lower than those within target range (0.38 [0.32-0.42] mg/kg versus 0.45 [0.39-0.48] mg/kg, P = 0.003). Thirty-seven TP achieved anti-FXaA level ≥0.2 IU/mL (23 requiring dose increases) at a dose of 0.49 [0.44-0.54] mg/kg. Correlation between dose and anti-FXaA levels for the initial 51 anti-FXaA levels (r = 0.360, P = 0.009) and for all 103 anti-XaA levels (r = 0.556, P < 0.001) was noted.

CONCLUSIONS

Non-weight-based enoxaparin dosing did not achieve target anti-FXaA levels in most TP. Higher anti-FXaA levels correlated with larger weight-based enoxaparin doses. Weight-based enoxaparin dosing (i.e., 0.5 mg/kg subcutaneously every 12 h) would better achieve target anti-FXaA levels.

A practical approach to the use of low molecular weight heparins in VTE treatment and prophylaxis in children and newborns

Low-molecular weight heparins are currently the most commonly used anticoagulants in children and newborns. However, since thrombotic complications rarely occur outside large children's hospitals, physicians often encounter some practical problems in managing these treatments when a pediatric thrombosis specialist is not available. The drug of choice is enoxaparin, due to its favorable FXa/FIIa ratio and the availability of pharmacokinetic and pharmacodynamic data. The treatment of acute thrombosis should be started with two daily injections but when compliance is an issue, a single daily administration schedule could be chosen for secondary prophylaxis ensuring careful measurement of the post 24-hour anti-FXa activity. Furthermore, a subcutaneous device may be a useful tool and a topical dermal anesthetic could be effective in controlling pain without affecting anti-FXa levels. In neonate and toddlers, where mini doses are frequently needed, the dead space of syringes and needles could represent an issue and therefore the use of insulin syringes without dead space is advisable, while a dilution of the drug is useful with other syringes. This article derives from a nonsystematic review of the available literature, with special attention to recent international guidelines and expert recommendations, combined to authors' clinical practice in large tertiary pediatric hospitals and will provide concise and practical information for the use of low-molecular weight heparin in childhood and infancy in a sort of "answering frequently asked questions."

Evaluation and Pharmacokinetics of Treatment Dose Enoxaparin in Hospitalized Patients With Morbid Obesity

Background:

The pharmacokinetic properties of enoxaparin may lead to supratherapeutic antifactor Xa (anti-Xa) levels and increased bleeding when standard treatment doses are used in patients with morbid obesity.

Objective:

To evaluate the dose of enoxaparin needed to achieve therapeutic anti-Xa levels in a prospective, masked observational cohort of heterogeneous inpatients with morbid obesity and to determine whether patients with morbid obesity treated with 1 mg/kg of enoxaparin are at increased risk of supratherapeutic levels and bleeding events compared to patients receiving lower doses.

Methods:

Hospitalized patients with a body mass index ≥40 kg/m2 or actual body weight ≥140 kg and prescribed treatment doses of enoxaparin >60 mg per day were enrolled and consented to phlebotomy for determination of anti-Xa levels.

Results:

Forty-one patients were included for data analysis. The dose of enoxaparin that resulted in therapeutic and supratherapeutic anti-Xa levels at steady state was 0.83 mg/kg and 0.98 mg/kg (−0.11; 95% confidence interval [CI] −0.20 to −0.01, P = .02), respectively. Enoxaparin dose as mg/kg of actual body weight was an independent predictor of having a supratherapeutic anti-Xa level. Patients with doses <0.95 mg/kg versus ≥0.95 mg/kg were less likely to have supratherapeutic levels (odds ratio 0.21 [95% CI 0.05-0.84], P = .02) and had similar rates of subtherapeutic levels. Doses <0.95 mg/kg and ≥0.95 mg/kg resulted in similar bleeding rates of 17.9% and 22.2% ( P = .71), respectively.

Conclusion:

Patients with morbid obesity required less than the recommended 1 mg/kg enoxaparin dose to achieve therapeutic peak anti-Xa levels; therefore, initiation with lower dosages is prudent and anti-Xa monitoring should guide dosage adjustments.

Clinical application of enoxaparin

Low-molecular-weight heparins have several important advantages over unfractionated heparin (UFH). Due to a longer plasma half life together with high bioavailability and a linear dose-response relationship, the drugs can be safely and effectively administered in the hospital or ambulatory settings without the need to monitor the anticoagulant effect. Enoxaparin (Lovenox), Aventis Pharma) is a low-molecular-weight heparin which has been studied in a variety of clinical situations. In general surgery the efficacy of enoxaparin to prevent venous thromboembolism is similar to UFH but the tolerability is better. In patients undergoing cancer, orthopedic or vascular surgery the efficacy of enoxaparin is significantly higher with similar rates of bleeding complications. The database for enoxaparin in nonsurgical patients is smaller compared with surgical groups. There is evidence that the efficacy of enoxaparin may be superior to UFH in patients with severe cardiac disease. Efficacy and safety of UFH and enoxaparin are similar for the treatment of deep vein thrombosis. However, enoxaparin can be safely administered by the patients at home which is not possible with UFH. In patients with acute coronary syndromes, enoxaparin has been shown to reduce the rate of deaths and serious cardiac events in comparison with UFH. Furthermore, exonaparin treatment has been shown to be cost-effective, and therefore is the therapy of choice in this setting. In addition, enoxaparin has been shown to be a safe and effective alternative to the combination of UFH and phenprocoumone therapy in patients undergoing electrical cardioversion for atrial fibrillation.

Tinzaparin and other low-molecular-weight heparins: what is the evidence for differential dependence on renal clearance?

Since low-molecular-weight heparins (LMWHs) are eliminated preferentially via the kidneys, the potential for accumulation of these agents (and an increased risk of bleeding) is of particular concern in populations with a high prevalence of renal impairment, such as the elderly and patients with cancer. The risk of clinically relevant accumulation of anticoagulant activity as a result of a reduction in renal elimination appears to differ between LMWHs. This review describes the elimination pathways for LMWHs and assesses whether the relative balance between renal and non-renal (cellular) clearance may provide a mechanistic explanation for the differences in accumulation that have been observed between LMWHs in patients with impaired renal function. Clearance studies in animals, cellular binding studies and clinical studies all indicate that the balance between renal and non-renal clearance is dependent on the molecular weight (MW): the higher the MW of the LMWH, the more the balance is shifted towards non-renal clearance. Animal studies have also provided insights into the balance between renal and non-renal clearance by examining the effect of selective blocking of one of the elimination pathways, and it is most likely that cellular clearance is increased to compensate for decreased renal function. Tinzaparin (6,500 Da) has the highest average MW of the marketed LMWHs, and there is both clinical and preclinical evidence for significant non-renal elimination of tinzaparin, making it less likely that tinzaparin accumulates in patients with renal impairment compared with LMWHs with a lower MW distribution. On the basis of our findings, LMWHs that are less dependent on renal clearance may be preferred in patient populations with a high prevalence of renal insufficiency.

The Pharmacokinetics of Enoxaparin Do Not Correlate With Its Pharmacodynamic Effect in Patients Receiving Dialysis Therapies

The pharmacokinetics and pharmacodynamics of enoxaparin were studied in healthy volunteers and hemodialysis and peritoneal dialysis subjects. Antifactor Xa activity estimated the pharmacokinetics, whereas thrombin generation time (TGT) estimated the pharmacodynamics. Enoxaparin 1 mg/kg was given subcutaneously to all subjects. Antifactor Xa Amax and AUC(0-12) were similar between groups, but the TGTmax was significantly greater in the dialysis groups (P = .001). The thrombin generation time remained significantly more prolonged throughout the 12-hour study period, and there was a trend toward greater TGT AUEC(0-12) for both dialysis groups (P = .07). Patients receiving hemodialysis had greater sensitivity to enoxaparin compared to the other groups. These results suggest that in dialysis patients, there may be accumulation of active heparin metabolites that are undetected by the antifactor Xa assay. Therefore, these subjects exhibit greater thrombin generation time prolongation despite similar antifactor Xa exposure. Further large-scale studies are needed to corroborate the results of this exploratory pilot study.

In situ crosslinkable heparin-containing poly(ethylene glycol) hydrogels for sustained anticoagulant release

Low-molecular weight heparin (LMWH) is widely used in anticoagulation therapies and for the prevention of thrombosis. LMWH is administered by subcutaneous injection usually once or twice per day. This frequent and invasive delivery modality leads to compliance issues for individuals on prolonged therapeutic courses, particularly pediatric patients. Here, we report a long-term delivery method for LMWH via subcutaneous injection of long-lasting hydrogels. LMWH is modified with reactive maleimide groups so that it can be crosslinked into continuous networks with four-arm thiolated poly(ethylene glycol) (PEG-SH). Maleimide-modified LMWH (Mal-LMWH) retains bioactivity as indicated by prolonged coagulation time. Hydrogels comprising PEG-SH and Mal-LMWH degrade via hydrolysis, releasing bioactive LMWH by first-order kinetics with little initial burst release. Separately dissolved Mal-LMWH and PEG-SH solutions were co-injected subcutaneously in New Zealand White rabbits. The injected solutions successfully formed hydrogels in situ and released LMWH as measured via chromogenic assays on plasma samples, with accumulation of LMWH occurring at day 2 and rising to near-therapeutic dose equivalency by day 5. These results demonstrate the feasibility of using LMWH-containing, crosslinked hydrogels for sustained and controlled release of anticoagulants.

Laser-engineered dissolving microneedles for active transdermal delivery of nadroparin calcium

There is an urgent need to replace the injection currently used for low molecular weight heparin (LMWH) multidose therapy with a non- or minimally invasive delivery approach. In this study, laser-engineered dissolving microneedle (DMN) arrays fabricated from aqueous blends of 15% w/w poly(methylvinylether-co-maleic anhydride) were used for the first time in active transdermal delivery of the LMWH nadroparin calcium (NC). Importantly, an array loading of 630IU of NC was achieved without compromising the array mechanical strength or drug bioactivity. Application of NC-DMNs to dermatomed human skin (DHS) using the single-step 'poke and release' approach allowed permeation of approximately 10.6% of the total NC load over a 48-h study period. The cumulative amount of NC that permeated DHS at 24h and 48h attained 12.28±4.23IU/cm(2) and 164.84±8.47IU/cm(2), respectively. Skin permeation of NC could be modulated by controlling the DMN array variables, such as MN length and array density as well as application force to meet various clinical requirements including adjustment for body mass and renal function. NC-loaded DMN offers great potential as a relatively low-cost functional delivery system for enhanced transdermal delivery of LMWH and other macromolecules.

Electrochemical assay of heparin to monitor anticoagulation action in cardiovascular patients

Complications in anticoagulation therapy and long term consequences of the post thrombotic syndromes requires a fast and powerful therapy such as heparin therapy (anticoagulation) to minimize the thrombotic effects in patients. Thus, a simple approach via electrochemical method: Differential pulse polarography (DPP) has been developed for heparin analysis as a powerful clinical tool to monitor anticoagulation action in-patient undergoing heparin therapy. The method has been standardized for determination of heparin activity over the existing methods and a very well defined characteristic reduction peak at -1.25 V in 2 M NaOH was observed for heparin. A linear relation was observed with a regression equation as y = 0.3117x + 0.8069, for 0.1 to 2.0 units/ml heparin. The developed DPP method was observed with excellent precision, accuracy and recovery in human blood plasma samples and in pharmacological formulations. The limit of detection (LOD) and limit of quantification (LOQ) noticed to be 2.04 and 6.8 units/ml respectively. The DPP results compared with pharmacological screening through average thrombin time (TT) and applied to monitor invitro anticoagulation action of heparin in healthy human subjects. Statistical analysis done to validate developed DPP method for heparin analysis and its probable clinical use to monitor anticoagulation action to treat patients suffering from various cerebrovascular disorders (CVD) by proper dosing of heparin.

Parenteral anticoagulants: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article describes the pharmacology of approved parenteral anticoagulants. These include the indirect anticoagulants, unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs), fondaparinux, and danaparoid, as well as the direct thrombin inhibitors hirudin, bivalirudin, and argatroban. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a unique pentasaccharide sequence and catalyze the inactivation of thrombin, factor Xa, and other clotting enzymes. Heparin also binds to cells and plasma proteins other than antithrombin causing unpredictable pharmacokinetic and pharmacodynamic properties and triggering nonhemorrhagic side effects, such as heparin-induced thrombocytopenia (HIT) and osteoporosis. LMWHs have greater inhibitory activity against factor Xa than thrombin and exhibit less binding to cells and plasma proteins than heparin. Consequently, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties, have a longer half-life than heparin, and are associated with a lower risk of nonhemorrhagic side effects. LMWHs can be administered once daily or bid by subcutaneous injection, without coagulation monitoring. Based on their greater convenience, LMWHs have replaced UFH for many clinical indications. Fondaparinux, a synthetic pentasaccharide, catalyzes the inhibition of factor Xa, but not thrombin, in an antithrombin-dependent fashion. Fondaparinux binds only to antithrombin. Therefore, fondaparinux-associated HIT or osteoporosis is unlikely to occur. Fondaparinux exhibits complete bioavailability when administered subcutaneously, has a longer half-life than LMWHs, and is given once daily by subcutaneous injection in fixed doses, without coagulation monitoring. Three additional parenteral direct thrombin inhibitors and danaparoid are approved as alternatives to heparin in patients with HIT.

A Comparison of the Pharmacodynamic Behavior of Branded and Biosimilar Enoxaparin in Primates

Pharmacodynamic behavior of branded and biosimilar enoxaparin was compared in a crossover study in primates. Blood samples collected at baseline and at 1, 4, 6, and 28 hours post-subcutaneous administration of Lovenox or Fibrinox were evaluated using clot-based and amidolytic assays. Anti-Xa levels following Fibrinox and Lovenox administration were not different. Anti-IIa levels were significantly higher in Lovenox-treated animals 1 to 6 hours post-administration. Higher drug levels were measured by Heptest in Fibrinox-treated animals from 4 to 6 hours. Pharmacokinetic differences were not observed using anti-Xa or Heptest assays. The area under the curve (anti-IIa) following Lovenox treatment was significantly larger than following Fibrinox treatment. When drug levels (anti-IIa) were plotted against anti-Xa or Heptest drug levels, a hysteretic relationship which was distinct for Fibrinox- and Lovenox-treated primates was observed suggesting a lack of bioequivalence for the low-molecular-weight heparin tested. In vivo behavior is an important consideration for defining pharmacoequivalence of complex biologic drugs.

Anticoagulant and antithrombotic drugs in pregnancy: what are the anesthetic implications for labor and cesarean delivery?

Neuraxial anesthetic techniques are commonly used during the peripartum period to provide effective pain relief for labor and anesthesia during cesarean delivery. Major neurologic complications are rare after neuraxial anesthesia; however, spinal hematoma is associated with catastrophic neurologic outcomes (including lower-limb paralysis). Anticoagulant and antithrombotic drugs can increase the risk of spinal hematoma after neuraxial anesthesia, and better understanding of the pharmacokinetics and pharmacodynamics of anticoagulants has led to greater appreciation for withholding anticoagulation before and after neuraxial anesthesia. A number of national anesthetic societies have produced guidelines for performing neuraxial anesthesia in patients receiving anticoagulation. However, there is limited information about anesthetic implications of anticoagulation during the peripartum period. This article will review the risks of spinal hematoma after neuraxial anesthesia in pregnant patients; current guidelines for neuraxial anesthesia for anticoagulated patients; and relevant pharmacological data of specific anticoagulant and antithrombotic drugs in pregnancy.

Effects of enoxaparin preparations on thrombin generation and their correlation with their anti-FXa activity

OBJECTIVE

Anticoagulant effect of LMWHs is monitored by anti-factor Xa (anti-FXa) activity assay. Since this test has several limitations, the aim of this study was to explore the activity of two LMWHs by thrombin generation assay (TG, which presents an overall picture of hemostatic balance) and its correlation with their anti-FXa activity.

METHODS

In an open-label, randomized cross-over study, 40  mg of two enoxaparins, the original branded formulation (R) and another one, also marketed in Argentina (T), were daily injected subcutaneously, for 7 days, to 20 healthy volunteers, with a 7-day washout interval. Blood samples were collected before treatment and 180  minutes after the injection on days 3 and 7. TG in platelet-poor plasma activated with tissue factor was assessed by lag time (LT), time to peak (TTP), peak (PTG), and endogenous thrombin potential (ETP). Anti-FXa and anti-FIIa activities, free tissue factor pathway inhibitor (free TFPI), tissue plasminogen activator (t-PA), plasminogen activator inhibitor type 1 (PAI-1), and euglobulin lysis time (ELT) were also assayed.

RESULTS

The mean (SD) anti-FXa (UI/ml) for T and R increased on days 3 and 7. LT and TTP were significantly prolonged by both LMWHs, with no differences between them. The mean ETP (nmol/L) for T and R at 3 and 7 days after treatment were significantly reduced when compared with basal values (p = 0.001 for all). On day 3, a significant correlation was shown between the variables describing TG and anti-FXa for T and R, without differences between them, for LT (r: 0.516 and 0486), ETP (r: 0.532 and 0.574), PEAK (r: 0.482 and 0.501), and TTP (r: 0.577 and 0.503), respectively. This correlation was also significant on day 7. Anti-FIIa activity and free TFPI increased significantly at 3 and 7 days for both LMWHs, without differences between them. R and T decreased ELT and PAI-1, but had no effect on t-PA. There were no differences between both LMWHs in routine hemostatic tests. No adverse events were reported.

CONCLUSIONS

Correlation between TG and anti-FXa activity was good. Both enoxaparins induced similar change of coagulation parameters, with a significant increase in fibrinolytic activity.

Population pharmacokinetics of enoxaparin in infants, children and adolescents during secondary thromboembolic prophylaxis: a cohort study

BACKGROUND

Enoxaparin has been extensively studied in adults on its safety and efficacy during prevention of symptomatic thromboembolism when acute anticoagulation or secondary prevention is required as a result of venous thrombosis or stroke. In children, it is still used off-label and little is known about the pharmacokinetics in children.

OBJECTIVES

The aim of the present study was to evaluate whether a once- or twice-daily dosing regimen would be feasible in children to achieve appropriate plasma levels of enoxaparin.

PATIENTS/METHODS

A population pharmacokinetic model was developed using anti-factor (F)Xa activity data from 126 children (median age: 5.9 years) receiving enoxaparin either as a once- or twice-daily dosing regimen.

RESULTS

A two-compartment model was adequate for describing the enoxaparin kinetics. Body weight proved to be the most predictive covariate for clearance and central volume of distribution: clearance 15 mL h⁻¹ kg⁻¹, central volume of distribution 169 mL kg⁻¹, intercompartmental clearance 58 mL h⁻¹, peripheral volume of distribution 10 L and absorption rate 0.414 h⁻¹. Interindividual variability was found to be 54% for clearance and 42% for volume of distribution.

CONCLUSION

The model is capable of describing all age groups and dosing levels of our population and predicts 12 h and 24 h enoxaparin activities sufficiently. According to our results, a once-daily enoxaparin dosing regimen with frequent monitoring is feasible. In 53.2% of the patients the median 24 h trough level was above the desired range of 0.1 IU mL⁻¹ anti-FXa activity for prophylaxis therapy.

Heparin-induced osteoporosis and pregnancy

PURPOSE OF REVIEW

Osteoporosis is the most common serious side effect of long-term unfractionated heparin use. Until recently, it was unknown whether long-term low-molecular-weight heparin was associated with any change in bone mineral density. With increasing long-term low-molecular-weight heparin use, for a variety of indications, this was an important knowledge gap.

RECENT FINDINGS

We recently completed an a-priori planned substudy to assess the effect of low-molecular-weight heparin on bone mineral density in an ongoing multicenter multinational randomized trial designed to compare the effect of low-molecular-weight heparin prophylaxis on pregnancy outcomes in thrombophilic pregnant women. The results revealed that there is no significant difference in mean bone mineral density between a low-molecular-weight heparin prophylaxis group and a no prophylaxis group. The study was not adequately powered to detect differences in absolute fracture risk.

SUMMARY

Recent results suggest that the use of long-term prophylactic low-molecular-weight heparin in pregnancy is not associated with a significant decrease in bone mineral density. Whether higher doses might be a risk factor for osteoporosis is still an unanswered question. It is also possible that subgroups are more susceptible. Overall, women should be reassured regarding the risk of osteoporosis associated with the use of prophylactic dose of low-molecular-weight heparin during their pregnancy.

Biomarkers and coagulation tests for assessing the biosimilarity of a generic low-molecular-weight heparin: results of a study in healthy subjects with enoxaparin

Low-molecular-weight heparins (LMWHs) differ considerably in their influence on clotting tests and release of tissue factor pathway inhibitor (TFPI). Biosimilarity therefore becomes an issue when generic forms of LMWHs are developed. So far, no bioequivalence study with a generic LMWH has been reported. A generic enoxaparin (test) was compared with the originator (reference) in 20 volunteers after single-dose subcutaneous administration (40 mg enoxaparin sodium, 4000 IU/mL anti-factor Xa (anti-FXa; activity). Target variables were anti-FXa and anti-FIIa activity, activated partial thromboplastin time (aPTT), prothrombinase-induced clotting time (PiCT), and TFPI over 24 hours. The statistical evaluation of the anti-FXa activity profile demonstrated bioequivalence of test and reference with confidence intervals of area under the plasma concentration-time curve (AUC0-tlast) (93%-99%) and Amax (88%-95%). Confidence intervals of AUC(0-tlast) (89%-102%) and Amax (90%-103%) of anti-FIIa activity also fulfill bioequivalence criteria. The 90% confidence interval for the maximum concentration of TFPI ranged from 90% to 113%. The claim of similarity was also supported by aPTT and PiCT profiles. Bioequivalence with the originator enoxaparin could be demonstrated by ex vivo inhibition of FXa and FIIa activity, by coagulation tests (aPTT and PiCT), and by in vivo release of TFPI. Whether such data also prove biosimilarity of the generic enoxaparin needs to be determined.

AFFECT: a prospective, open-label, multicenter trial to evaluate the feasibility and safety of a short-term treatment with subcutaneous certoparin in patients with persistent non-valvular atrial fibrillation

BACKGROUND

Patients with persistent atrial fibrillation (AF) scheduled for electrical cardioversion need immediate anticoagulation. Unfractionated heparin (UFH) is often used for early anticoagulation in these patients before oral anticoagulation becomes effective. However, dose adjustment is required to achieve a two- to three-fold prolongation of the activated partial thromboplastin. Low molecular weight heparins, given in body weight-adjusted or independent fixed dosage, require less laboratory monitoring and are also effective within hours of first dosing. They seem to be an attractive alternative to UFH. Previous evidence has shown that these drugs are safe and effective in this indication.

PATIENTS AND METHODS

In this prospective, open-label, multicenter pilot study, 203 patients were enrolled with persistent non-valvular AF scheduled for electrical cardioversion. Patients received a fixed dose of 8000 U anti-Xa certoparin twice daily starting immediately after enrolment and before cardioversion was performed. Patients with AF > 48 h underwent transoesophageal echocardiography (TEE) before cardioversion to exclude intra-atrial thrombi. After cardioversion, overlapping oral anticoagulation was started. Treatment with certoparin was stopped only after two consecutive days with INR values >2.

OBJECTIVES

The objective was to document the feasibility and safety of a short-term treatment with a fixed, body weight-independent certoparin regimen (2 x 8000 U anti-Xa).

RESULTS

Out of 203 patients enrolled, 200 received at least one dose of certoparin and were included in the analysis (safety population). Median treatment duration with certoparin was 7 days. Bleedings were observed in 8 patients (4.0%) and were classified as major (1.5%) or minor (2.5%). Cerebral ischemia was reported for 1 patient (0.5%). One patient showed mild thrombocytopenia (0.5%). There were no reports of venous thromboembolism or death during the treatment period.

CONCLUSION

Certoparin administered at 8000 U anti-Xa twice daily independent of body weight was safe and appeared to be effective in patients with non-valvular AF undergoing electrical cardioversion. Its ease of use and the possibility of treatment on an outpatient basis make it an attractive option for early anticoagulation in AF.

Suboptimal doses of low molecular weight heparin and acute venous thromboembolism. Data from the RIETE registry

The objective was to assess the use of suboptimal doses (60-149 UI kg(-1) day(-1)) of low molecular weight heparin (LMWH) in the treatment of acute venous thromboembolism (VTE) in actual clinical practice and to evaluate the outcomes compared to standard doses (> or = 150 UI kg(-1) day(-1)). Retrospective analysis of data from a multicenter registry of patients with VTE (RIETE; Registro Informatizado de Enfermedad TromboEmbólica). Patient characteristics, antithrombotic treatments, and 3-month outcomes were analyzed. We studied 12,302 patients with VTE; 10,524 patients were treated initially only with LMWH; 1,547 patients received suboptimal LMWH (mean = 122 UI kg(-1) day(-1)), and 8,977 patients received full-dose LMWH (mean = 191 UI kg(-1) day(-1)). The suboptimal group included significantly more patients with recent major bleeding, weight more than 100 kg, raised creatinine, or deep vein thrombosis. No significant differences in mortality rate (7.7 vs 7.8%), VTE recurrence (2.7 vs 2.3%), or fatal hemorrhage (0.6 vs 0.6%) occurred between the suboptimal and the standard group. Major bleeding episodes occurred more frequently in the patients with pulmonary embolism treated with suboptimal LMWH (4.5 vs 2.4%; p = 0.02). In the multivariate analysis, after adjusting for bleeding risk factors, major hemorrhage was not associated with the heparin dose. Suboptimal doses of LMWH are used in actual clinical practice in a reduced group of patients at an outcome rate not very different to that of standard doses. Bleeding episodes depend more on the patient's characteristics than on the LMWH dose. Randomized trials should be performed to corroborate these results.

Platelet activity, coagulation, and fibrinolysis during exercise in healthy males: effects of thrombin inhibition by argatroban and enoxaparin

BACKGROUND

Relationships between exercise-induced activation of platelets, blood coagulation, and fibrinolysis, and the importance of thrombin for responses to exercise are not clear.

METHODS AND RESULTS

Effects of thrombin inhibition on hemostatic parameters were examined in a double-blind crossover study comparing the direct thrombin inhibitor argatroban (350 microg/kg intravenous bolus followed by 25 microg/kg per minute of infusion), the indirect thrombin inhibitor enoxaparin (0.75 mg/kg, intravenous bolus), or placebo (saline) in 21 healthy males. Measurements were made at rest, before and during/after thrombin inhibitor treatment, and immediately after exhaustive exercise. At rest argatroban abolished, and enoxaparin attenuated platelet activation by thrombin, but not by adenosine diphosphate. Argatroban and, even more so, enoxaparin decreased thrombin generation (prothrombin F1+2) and the coagulation potential, and increased the fibrinolytic potential. Exercise increased circulating activated platelets (from 5.5+/-0.3 to 9.4+/-0.9x10(9)/L; P<0.001), circulating platelet-platelet microaggregates, the platelet responsiveness to in vitro stimulation, leukocyte activation (leukocyte CD11b expression and plasma elastase), and platelet-leukocyte aggregation (P<0.01 for all). Exercise increased coagulation (F1+2; P<0.01) and fibrinolysis, but did not alter the balance between them; fibrin gel permeability increased (P<0.01), probably because of release of endogenous tissue plasminogen activator from the vessel wall. Neither argatroban nor enoxaparin counteracted exercise-induced platelet or leukocyte activation. Both thrombin inhibitors augmented exercise effects on fibrinolysis.

CONCLUSIONS

Strenuous exercise enhances platelet and leukocyte activation independently of thrombin. Exercise augments both coagulation and fibrinolysis, but the balance between them appears to be maintained. At therapeutic dosages argatroban counteracted thrombin-induced platelet activation most efficiently, whereas enoxaparin had somewhat stronger anticoagulant and profibrinolytic effects.

Thrombin generation time is a novel parameter for monitoring enoxaparin therapy in patients with end-stage renal disease

BACKGROUND

Patients with end-stage renal disease (ESRD) who receive enoxaparin are at increased risk for adverse bleeding episodes. This phenomenon appears to occur despite judicious monitoring of antifactor Xa (aFXa) activity. Better monitoring parameters are needed to quantify the anticoagulant effects of enoxaparin in the ESRD population.

OBJECTIVES

The objective of this study was to determine the utility of using thrombin generation time (TGT), platelet contractile force (PCF) and clot elastic modulus (CEM) to monitor the degree of anticoagulation in ESRD subjects, and to compare these results to aFXa activity, the current gold-standard monitoring parameter.

METHODS

Eight healthy volunteers without renal dysfunction and eight ESRD subjects were enrolled into this study. Subjects received a single dose of enoxaparin 1 mg kg(-1) subcutaneously, and blood samples were obtained for the determination of aFXa activity, TGT, PCF and CEM at baseline, 4, 8, and 12 h postdose.

RESULTS

Baseline, 4, 8, and 12-h aFXa activity concentrations were not different between groups. However, the corresponding TGT at 8 and 12 h was significantly prolonged in the ESRD group (P = 0.04, and P = 0.008, respectively). The 4-h peak TGT trended toward significance (P = 0.06). There were no differences in PCF or CEM across time.

CONCLUSIONS

These data suggest that the parameter aFXa activity is a poor predictor of the anticoagulant effect of enoxaparin in patients with ESRD. Thrombin generation time appears to be more sensitive to the antithrombotic effects of enoxaparin in this population. Further large-scale trials are needed to corroborate these data.

Quality of anticoagulation with unfractionated heparin plus phenprocoumon for the prevention of thromboembolic complications in cardioversion for non-valvular atrial fibrillation. Sub-analysis from the Anticoagulation in Cardioversion using Enoxaparin (ACE) trial

INTRODUCTION

Anticoagulation in cardioversion for atrial fibrillation is performed using unfractionated heparin and oral anticoagulants. TEE-guided cardioversion, after achievement of therapeutic anticoagulation (1-3 days), may be an alternative to the traditional procedure (3-week anticoagulation followed by cardioversion). The quality of anticoagulation in atrial fibrillation has not been investigated in a randomised trial with TEE-guided cardioversion. We analysed respective data from the ACE trial on the quality of conventional anticoagulation, where most participating centres chose the TEE-guided approach.

MATERIALS AND METHODS

In a randomised, prospective, multicentre trial, we analysed the efficacy of unfractionated heparin plus phenprocoumon in 248 patients on an intention-to-treat basis. There were 2373 evaluable anticoagulation measurements (out of 2925 measurements) and 4 categories of anticoagulation quality (under-, target, over- and severe over-anticoagulation). Of patients with evaluable measurements, 88% received short-term anticoagulation (4 weeks) in TEE-guided cardioversion.

RESULTS

The median time to achieve therapeutic anticoagulation (aPTT> or =60 and <80 s or INR> or =2 and <3) was 3 days. Anticoagulation values were out of therapeutic range in 69.5% of measurements during 4- or 7-week follow-up, and never within therapeutic range in 10% of patients. Of the 15 primary endpoints observed (death, thromboembolism and major bleeding complications), only 3 were in patients with anticoagulation measurements within therapeutic range.

CONCLUSIONS

In this study setting, with predominance of 4 weeks anticoagulation in TEE-guided cardioversion for atrial fibrillation, therapeutic anticoagulation was reached within 3 days using conventional anticoagulation. Despite careful dose adjustments, anticoagulation was out of therapeutic range in almost 70% of total measurements and 80% of primary endpoints.

Antifactor Xa activity in critically ill patients receiving antithrombotic prophylaxis with standard dosages of certoparin: a prospective, clinical study

Introduction

Deep venous thrombosis with subsequent pulmonary embolism or post-thrombotic syndrome is a feared complication in the intensive care unit. Therefore, routine prophylactic anticoagulation is widely recommended. Aside from unfractionated heparin, low molecular weight heparins, such as certoparin, have become increasingly used for prophylactic anticoagulation in critically ill patients. In this prospective study, we evaluated the potency of 3,000 IU certoparin administered once daily to reach antithrombotic antifactor Xa (aFXa) levels of 0.1 to 0.3 IU/ml in 62 critically ill patients.

Methods

AFXa levels were determined 4, 12 and 24 h after injection of certoparin. Prothrombin time, activated partial thromboplastin time, antithrombin, fibrinogen, hemoglobin, platelet count, serum urea and creatinine concentrations were documented before and 12 and 24 h after injection of certoparin.

Results

Four hours after certoparin injection (n = 32), 28% of patients were within the antithrombotic aFXa range. After 12 and 24 h, 6% achieved antithrombotic aFXa levels. Because of a severe pulmonary embolism in one study patient, an interim analysis was performed, and the dosage of certoparin was increased to 3,000 IU twice daily. This regime attained recommended antithrombotic aFXa levels in 47%, 27%, 40% and 30% of patients at 4, 12, 16 and 24 h, respectively, after twice daily certoparin injection (n = 30). Antithrombin and fibrinogen concentrations slightly increased during the observation period. Low antithrombin concentrations before certoparin were independently correlated with underdosing of certoparin. Patients with aFXa levels <0.1 IU/ml 4 h after certoparin injection required vasopressors more often and had lower serum concentrations of creatinine and urea than patients with antithrombotic aFXa levels.

Conclusion

Standard dosages of certoparin of 3,000 IU given once or twice daily are ineffective for attaining the recommended aFXa levels of 0.1 to 0.3 IU/ml in critically ill patients. Low antithrombin levels before certoparin administration were independently associated with low aFXa levels. Renal function and vasopressor therapy may further influence the effectiveness of certoparin in ensuring adequate antithrombotic prophylaxis.

Heparin in interventional radiology: a therapy in evolution

Interventional radiology techniques made possible by the antithrombotic properties of heparin have revolutionized treatment for a myriad of disorders. Newer low-molecular-weight heparins (LMWHs) offer several advantages over unfractionated heparin (UFH), especially in chronic settings. They are increasing in popularity for use during vascular procedures. However, LMWH shares limitations with UFH such as heterogeneity, nonspecificity, and induction of thrombocytopenia. These drawbacks have led to a search for the next generation of antithrombotic agents. Homogeneous drugs targeting specific coagulation cascade molecules are now available. The number of alternative anticoagulant drug combinations presents clinicians with a confusing array of choices. The strengths and weaknesses of UFH, LMWH, and direct antithrombin agents are presented. The promising future of LMWH and hirudins is discussed.

Unfractionated Heparin, Low Molecular Weight Heparins, and Pentasaccharide: Basic Mechanism of Actions, Pharmacology, and Clinical Use

During the past decade, a large number of new anticoagulant and antithrombotic drugs have been developed. These agents represent a wide variety of substances that are derived using natural sources, biotechnology-based methods, and synthetic approaches. Because of the structural and molecular characteristics, these agents exhibit physicochemical and functional diversities. Thus, each of these classes of drugs controls thrombogenesis by way of distinct mechanisms. The main classes of these new drugs include peptides, peptidomimetics, heparinomimetics, and recombinant proteins. Despite these significant developments, heparin and heparin-derived drugs have continued to play a major role in the management of thrombotic and cardiovascular disorders.

Pharmacokinetics of UH and LMWH are similar with respect to antithrombin activity

BACKGROUND

The ability to administer low molecular weight heparins (LMWH) subcutaneously without laboratory monitoring contributes to their popularity for the treatment of thrombotic disorders. Subcutaneous unfractionated heparin, although less expensive, is deemed to require routine laboratory monitoring on the basis of more variability in drug effect compared to LMWH. However, the more predictable pharmacokinetic profiles of low molecular weight heparins are largely based on anti-Xa activity, while antithrombin activity may be at least as important to their mechanisms of action.

METHODS

We performed a clinical pharmacokinetic trial to compare the variability in peak antithrombin effect between subcutaneous unfractionated heparin and various LMWHs, all given in recommended weight-adjusted treatment doses. Sixty-one patients enrolled in a warfarin clinic were randomized to receive one of four different weight-adjusted subcutaneous heparin doses: unfractionated heparin, 250 units/kg (n=15); tinzaparin, 175 units/kg (n=15); dalteparin, 200 units/kg (n=15); or enoxaparin, 1 mg/kg (n=16). The areas under the curves of antithrombin levels during the first 3 h after administration were determined for each patient, and the coefficients of variation (CV) and 95% confidence intervals of the AUCs were compared among the treatment groups.

RESULTS

There was no statistically significant difference in the coefficients of variation of antithrombin effect between unfractionated heparin (52.8, 95% CI: 32.6-72.9) and enoxaparin (56.5, 95% CI: 35.7-77.4) or dalteparin (43.5, 95% CI 25.4-61.6). Tinzaparin had statistically significant decrease in coefficients of variation (21.6, 95% CI: 12.2-30.9) relative to unfractionated heparin, dalteparin and enoxaparin.

CONCLUSIONS

LMWHs, as a class of drugs, are no more predictable in antithrombin effect after subcutaneous injection than unfractionated heparin. There were considerable differences among LMWHs in the observed variability of antithrombin effects, with tinzaparin being somewhat more predictable than the other drugs tested.

Lepirudin: a bivalent direct thrombin inhibitor for anticoagulation therapy

Lepirudin (Refludan), Berlex Laboratories, USA and Canada; Pharmion, all other countries), a recombinant derivative of the naturally occurring leech anticoagulant hirudin, was the first direct thrombin inhibitor to be approved by the European Agency for the Evaluation of Medicinal Products and the US Food and Drug Administration for the treatment of heparin-induced thrombocytopenia. Since its introduction into Europe and the USA, it has been studied in over 7000 patients requiring anticoagulation in conditions including acute coronary syndromes, percutaneous coronary intervention, cardiopulmonary bypass and heparin-induced thrombocytopenia. Three European clinical trials, designated Heparin-Associated Thrombocytopenia (HAT)-1, -2 and -3, demonstrated the efficacy and safety of lepirudin in the prevention and treatment of thrombosis in patients with antibody-confirmed heparin-induced thrombocytopenia. A postmarketing, observational study, termed the Drug-Monitoring Program, evaluated lepirudin in over 1000 patients with heparin-induced thrombocytopenia in the setting of routine clinical practice. In the Drug-Monitoring Program, adverse events were substantially reduced compared with clinical trials, while clinical efficacy was maintained; suggesting that insight gained through clinical experience was translated into improved safety. Here, pharmacotherapy using lepirudin is reviewed, with particular reference to clinical studies in heparin-induced thrombocytopenia, and some recommendations based on this extensive clinical experience with lepirudin are provided. Although only approved for the treatment of heparin-induced thrombocytopenia, the use of lepirudin in acute coronary syndromes, percutaneous coronary intervention, vascular surgery and coronary artery bypass grafting is also discussed. The review concludes with a discussion of pharmacokinetic and clinical data supporting the potential for subcutaneous administration of lepirudin.

Retrospective evaluation of a pharmacokinetic program for adjusting enoxaparin in renal impairment

BACKGROUND

Although clinical trials have found that enoxaparin clearance is prolonged in renal impairment, only one letter describes experience with adjusting doses. Only pharmacokinetic studies exist to guide dose adjustment in response to anti-Xa levels. Unfractionated heparin has comparable major bleeding in renal impairment compared with unadjusted enoxaparin. This necessitates a pharmacokinetic program to adjust enoxaparin with anti-Xa monitoring.

METHODS

A pharmacokinetic program was created in response to adverse events and physician interest in a service. A program was designed providing all patients a loading dose of 1 mg/kg enoxaparin. Subsequent doses were 0.50 mg/kg per dose subcutaneously (SC) every 12 hours (q12h) for patients with a creatinine clearance (CrCl) < or =30 mL/min (severe group) and 0.75 mg/kg per dose SC q12h for patients with CrCl of 30 to 60 mL/min (moderate group). A 1-year review of 170 hospitalized patients is reported.

RESULTS

The mean +/- SD [95% CI] anti-Xa level 4 hours after the third dose was 0.65 +/- 0.19 [0.59 to 0.70] IU/mL for the severe group and 0.82 +/- 0.18 [0.79 to 0.85] IU/mL for the moderate group (P <.001). Eighty percent of patients with moderate renal failure and 60% of the patients with severe renal failure were in the therapeutic anti-Xa range after the third dose. A dose-adjustment ratio was used to adjust doses in patients whose levels were outside the therapeutic range: New dose = [(Current dose) x (Goal anti-Xa level)]/(Current anti-Xa level). An incidence of bleeding comparable to that found in normal patients was found.

CONCLUSIONS

In high-risk patients, it is reasonable to limit the exposure of patients to low molecular weight heparins by using anti-Xa levels as a marker. The enoxaparin protocol for renally impaired patients successfully placed patients in the therapeutic range established by consensus guidelines. The dose-adjustment ratio adds significant understanding to the pharmacokinetics of dose adjustment.

Heparin and Low-Molecular-Weight Heparin

This article about unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) is part of the Seventh American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a pentasaccharide, catalyzing the inactivation of thrombin and other clotting factors. UFH also binds endothelial cells, platelet factor 4, and platelets, leading to rather unpredictable pharmacokinetic and pharmacodynamic properties. Variability in activated partial thromboplastin time (aPTT) reagents necessitates site-specific validation of the aPTT therapeutic range in order to properly monitor UFH therapy. Lack of validation has been an oversight in many clinical trials comparing UFH to LMWH. In patients with apparent heparin resistance, anti-factor Xa monitoring may be superior to measurement of aPTT. LMWHs lack the nonspecific binding affinities of UFH, and, as a result, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties. LMWHs have replaced UFH for most clinical indications for the following reasons: (1) these properties allow LMWHs to be administered subcutaneously, once daily without laboratory monitoring; and (2) the evidence from clinical trials that LMWH is as least as effective as and is safer than UFH. Several clinical issues regarding the use of LMWHs remain unanswered. These relate to the need for monitoring with an anti-factor Xa assay in patients with severe obesity or renal insufficiency. The therapeutic range for anti-factor Xa activity depends on the dosing interval. Anti-factor Xa monitoring is prudent when administering weight-based doses of LMWH to patients who weigh > 150 kg. It has been determined that UFH infusion is preferable to LMWH injection in patients with creatinine clearance of < 25 mL/min, until further data on therapeutic dosing of LMWHs in renal failure have been published. However, when administered in low doses prophylactically, LMWH is safe for therapy in patients with renal failure. Protamine may help to reverse bleeding related to LWMH, although anti-factor Xa activity is not fully normalized by protamine. The synthetic pentasaccharide fondaparinux is a promising new antithrombotic agent for the prevention and treatment of venous thromboembolism.

Correlation of plasma coagulation parameters with thromboprophylaxis, patient characteristics, and outcome in the MEDENOX study

CONTEXT

Plasma anti-Xa and anti-IIa activities correlate with the dose of low-molecular-weight heparin, and D-dimer and thrombin-antithrombin complexes are markers of procoagulant activity.

OBJECTIVE

To investigate the relationship between plasma coagulation parameters and patient characteristics, including renal function, thromboprophylaxis, and incidence of venous thromboembolism (VTE) in the MEDENOX study population.

DESIGN

Controlled, multicenter, double-blind, randomized study.

PATIENTS

Two hundred twenty-four acutely ill medical patients.

INTERVENTIONS

Either 20 or 40 mg of enoxaparin administered subcutaneously or a placebo once daily for 10 (+/-4) days.

MAIN OUTCOME MEASURES

VTE and plasma anti-Xa and anti-IIa activities, D-dimer, and thrombin-antithrombin levels in blood collected before prophylaxis was given (day 0) and after the last injection of the study drug.

RESULTS AND CONCLUSIONS

Anti-Xa activity correlated with the dose of enoxaparin. In patients with mild or moderate renal impairment, there was no significant relationship between anti-Xa activity and the creatinine clearance rate. D-dimer concentrations were lower at day 10 (+/-4) in the 40-mg group, which had a 63% lower VTE incidence, than at day 0. No venographically confirmed thromboses were found in patients with a normal D-dimer concentration (<0.5 microg/mL [0.5 mg/L]). D-dimer levels were higher in patients with VTE than in those without VTE, but no predictive value could be demonstrated for individual patients.

Tissue distribution of the low molecular weight heparin, tinzaparin, following administration to rats by the oral route

Heparins are antithrombotic drugs given by intravenous and subcutaneous routes. However, we have observed that heparins have antithrombotic activity in a rat model when administered orally despite low plasma levels, with low molecular weight heparins (LMWHs) being effective at lower single doses than unfractionated heparins (UFH). Since LMWHs may have other pharmaceutical uses and little is known regarding the pharmacokinetics of oral LMWHs, our objectives were to determine the distribution of the LMWH tinzaparin (Logiparin) following oral dosing. To study distribution at different doses, 0.025-15 mg/kg tinzaparin was given by stomach tube to rats. Gut and non-gut tissues were sampled 4 h later. In a time course study, plasma and tissue samples were collected at eight time points within 24 h after oral administration (60 mg/kg, 4 rats/time interval). Accumulated urine and faeces were collected over 4 and 24 h using metabolic cages. Gut tissue and washes, faeces, urine and non-gut tissue were extracted and analysed for heparin by agarose gel electrophoresis with toluidine blue staining. Activated partial thromboplastin time (APTT) and anti-Xa activity, by Heptest and chromogenic assay, estimated plasma tinzaparin concentrations. Stomach and lung tinzaparin concentrations demonstrated a dose-effect. Peak concentrations in tissue and washes of stomach, duodenum, jejunum, ileum and colon were at 6-30, 15-30, 30 min, 2 and 4 h, respectively. Amounts found at peak times in combined tissue and washes accounted for 46% and 0.5% in stomach (15 min) and colon (4 h), respectively. Tinzaparin was recovered from liver, lung, endothelial samples, and urine at 24 h, but not in faeces. Non-significant increases were seen in APTT and the Heptest, however, anti-Xa activity was significantly greater than control at all times examined, peaking at 2 h. No bleeding was observed. Results are consistent with oral absorption of tinzaparin with wide tissue distribution, likely on endothelium with little in plasma, as previously observed for UFH. Oral administration of LMWHs should be further studied.

Pharmacodynamic and pharmacokinetic properties of enoxaparin : implications for clinical practice

Enoxaparin is a low-molecular-weight heparin (LMWH) that differs substantially from unfractionated heparin (UFH) in its pharmacodynamic and pharmacokinetic properties. Some of the pharmacodynamic features of enoxaparin that distinguish it from UFH are a higher ratio of anti-Xa to anti-IIa activity, more consistent release of tissue factor pathway inhibitor, weaker interactions with platelets and less inhibition of bone formation. Enoxaparin has a higher and more consistent bioavailability after subcutaneous administration than UFH, a longer plasma half-life and is less strongly bound to plasma proteins. These properties mean that enoxaparin provides a more reliable anticoagulant effect without the need for laboratory monitoring, and also offers the convenience of once-daily administration. Clinical studies have confirmed that these pharmacological advantages translate into improved outcomes. There are important pharmacokinetic and pharmacodynamic differences between enoxaparin, other LMWHs and UFH, and therefore these molecules cannot be regarded as interchangeable.

Pharmacokinetics of enoxaparin in patients undergoing percutaneous coronary intervention with and without glycoprotein IIb/IIIa therapy

The pharmacokinetic profile of enoxaparin was established in a substudy involving 1054 patients undergoing percutaneous coronary intervention. Patients enrolled in the National Investigators Collaborating on Enoxaparin 1 (NICE-1) trial received enoxaparin as a 1.0-mg/kg intravenous bolus. Patients enrolled in the NICE-4 trial received enoxaparin as a 0.75-mg/kg intravenous bolus followed by abciximab as a 0.25-mg/kg bolus and a 0.125-mcg/kg/min 12-hour infusion. Blood samples were collected at six time points over 12 hours and analyzed for plasma anti-Xa, anti-IIa, and Heptest (Haemachem Inc., St. Louis, MO) activity using specific and sensitive assay methods. Data were similar in both trials. Plasma anti-Xa, anti-IIa, and Heptest activity peaked shortly after the enoxaparin bolus and declined in parallel over the ensuing 12 hours. Area under the curve and peak activity were greatest for Heptest activity and least for anti-IIa activity. Values for clearance, volume of distribution, volume of distribution at steady state, and elimination rate constant were on the order of 10 mL/h/kg, 48 mL/kg, 45 mL/kg, and 0.22/h, respectively. These measures suggest that the use of abciximab in combination with enoxaparin during percutaneous coronary intervention is unlikely to affect the pharmacokinetics of enoxaparin.

Prophylactic anticoagulation with enoxaparin: Is the subcutaneous route appropriate in the critically ill?

BACKGROUND

Subcutaneously administered low-molecular-weight heparins are widely used for prevention of venous thromboembolism. The appropriateness of the subcutaneous route in critically ill patients has never been established.

OBJECTIVE

To determine anti-Xa activities in critically ill patients and in noncritically ill patients receiving prophylactic doses of subcutaneous enoxaparin.

DESIGN

Prospective, controlled, open-labeled study.

SETTING

Tertiary medical-cardiologic-postoperative intensive care unit and a general medical ward at a university hospital.

PATIENTS

A total of 16 intensive care unit patients (group 1; age, 61.1 +/- 16 yrs; male/female ratio, 7/9; Acute Physiology and Chronic Health Evaluation II score, 20.9 +/- 7; mechanical ventilation, n = 15; vasopressors, n = 13) and 13 noncritically ill medical patients (group 2; age, 61.7 +/- 9 yrs; male/female ratio, 7/6) were studied. Body mass index (25.7 +/- 5 vs. 24 +/- 6 kg/m2, p = not significant) was comparable and serum creatinine levels (0.83 +/- 0.25 vs. 1.07 +/- 0.3 mg/dL, group 1 vs. 2) were within the normal range in both groups. Patients with impaired renal function, receiving hemofiltration, or requiring therapeutic anticoagulation were not eligible.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Anti-Xa activities were determined at 0, 1, 3, 6, and 12 hrs after a single daily subcutaneous dose of 40 mg enoxaparin on day 1 and at 3 hrs after 40 mg of enoxaparin on days 2-5. Mean anti-Xa levels at 0 to 12 hrs were consistently lower in group 1 compared with group 2 by analysis of variance (p =.001 between groups and over time), as was the area under the curve at 0 to 12 hrs (2.6 +/- 1 vs. 4.2 +/- 1.7 units x mL(-1) x hr(-1), group 1 vs. 2, p =.008). Significant differences in anti-Xa activity were also found on days 2-5 (p =.001). Peak anti-Xa activities at 3 hrs after administration were negatively correlated with the body mass index (r = -.41, p <.03). No correlation was found between the anti-Xa activity at 3 hrs and the dose of norepinephrine (r =.12, p =.7).

CONCLUSION

Critically ill patients with normal renal function demonstrated significantly lower anti-Xa levels in response to a single daily dose of subcutaneous enoxaparin when compared with medical patients in the normal ward.

Heparin and low molecular weight heparin: background and pharmacology

The various LMWHs available for therapeutic use have multiple mechanisms of action, most of which are similar to the mechanisms of UH. The relative potencies of expression of the mechanisms differ between LMWH and UH and among specific LMWHs. The pharmacokinetics of LMWHs and UH are often measured according to the results of anti-Xa assays, although the correlation between anti-Xa levels and the antithrombotic activities of the drugs is questionable. Animal models of thrombosis give some information regarding the antithrombotic efficacy of different LMWHs when compared with UH and with other LMWHs, but the results are not directly applicable to human thrombosis. Unfortunately, no single measure of antithrombosis has been developed in humans whereby the potencies of LMWHs, UH, and other new anticoagulants can be directly compared. Large clinical outcome studies are expensive and difficult to carry out. Perhaps for this reason, different subcutaneous LMWHs have not been compared with each other in this format. Various LMWHs have demonstrated equivalent efficacy and safety when compared with intravenous UH and high-dose subcutaneous UH, and it is reasonable to assume that there would not be large differences in efficacy and safety among different agents. The superiority of one subcutaneous regimen over another can be confirmed (or refuted) only by the performance of well-planned clinical studies.

Inhibition of factor VIIa generation and prothrombin activation by treatment with enoxaparin in patients with unstable angina

Factor VIIa (FVIIa) and thrombin generation occur in patients suffering an acute coronary event. We studied the effect of treatment with enoxaparin on FVIIa and prothrombin activation in patients with unstable angina. Anti-Xa activity, FVIIa, FVII coagulant activity (FVII:C) and FVII antigen (FVII:Ag), free tissue factor pathway inhibitor (TFPI), and prothrombin fragments 1 + 2 (F1+2) were measured in patients' plasma, over a 24-h treatment period with enoxaparin. All 14 patients recruited in the study (mean age 68 years) were treated with a subcutaneous injection of enoxaparin, 1 mg/kg twice daily. Blood was drawn just before, and at different time intervals after, the first injection. Before enoxaparin administration, the levels of FVIIa (4.02 +/- 0.8 ng/ml) and F1+2 (2.68 +/- 0.2 nmol/l) were significantly increased as compared with control subjects (2.3 +/- 0.3 ng/ml and 0.9 +/- 0.1 nmol/l respectively, P < 0.05). Free TFPI, FVII:C and FVII:Ag were within normal ranges. One hour after the first injection of enoxaparin, FVIIa and F1+2 levels decreased by 65% and 50%, respectively, and no significant fluctuations were noted throughout the observation period. The concentrations of FVII:C and FVII:Ag were not modified as compared with baseline values. After each injection, the peak concentrations of free TFPI and anti-Xa activity were observed at 2 and 4 h respectively. The kinetics of FVIIa and F1+2 inhibition did not follow those of anti-Xa activity and TFPI release.

Comparison of pharmacokinetic variables for two low-molecular-weight heparins after subcutaneous administration of a single dose to horses

OBJECTIVE

To determine pharmacokinetic variables and to evaluate the influence on clotting times after SC administration of single doses of dalteparin and enoxaparin to horses.

ANIMALS

5 healthy adult horses.

PROCEDURES

The study was designed as a 4-period crossover study. Each horse received a single SC injection of dalteparin (50 and 100 anti-Xa U/kg) and enoxaparin (40 and 80 anti-Xa U/kg). Plasma anti-Xa activities and clotting times were measured, and pharmacokinetic variables were determined. Absolute and relative maximal prolongation of clotting times was calculated, and correlation between plasma anti-Xa activities and clotting times was determined.

RESULTS

The SC administration of each of the doses of the 2 preparations was well tolerated. Time course of the anti-Xa activities could be described in a 1-compartment model. Comparison of low- and high-dose treatments revealed a disproportionate increase of the area under the plasma activity-time curve and prolongation of the terminal half-life, but the increase in maximum plasma activity was proportionate, and peak plasma concentrations corresponded with concentrations recommended in human medicine. There were only mild changes in activated partial thromboplastin time (aPTT), whereas the influence on thrombin time (TT) was greater, dose-dependent, and more variable. A weak-to-moderate correlation between aPTT and plasma anti-Xa activities and a moderate-to-strong correlation between TT and plasma anti-Xa activities were found.

CONCLUSIONS AND CLINICAL RELEVANCE

Pharmacokinetic and anticoagulatory properties of low-molecular-weight heparins in horses are similar to those found in humans. Once-daily SC administration of dalteparin or enoxaparin may be useful as an anticoagulatory treatment in horses.