Fixed dosage of low-molecular-weight heparins causes large individual variation in coagulability, only partly correlated to body weight

Being precise with anticoagulation to reduce adverse drug reactions: are we there yet?

Anticoagulants are potent therapeutics widely used in medical and surgical settings, and the amount spent on anticoagulation is rising. Although warfarin remains a widely prescribed oral anticoagulant, prescriptions of direct oral anticoagulants (DOACs) have increased rapidly. Heparin-based parenteral anticoagulants include both unfractionated and low molecular weight heparins (LMWHs). In clinical practice, anticoagulants are generally well tolerated, although interindividual variability in response is apparent. This variability in anticoagulant response can lead to serious incident thrombosis, haemorrhage and off-target adverse reactions such as heparin-induced thrombocytopaenia (HIT). This review seeks to highlight the genetic, environmental and clinical factors associated with variability in anticoagulant response, and review the current evidence base for tailoring the drug, dose, and/or monitoring decisions to identified patient subgroups to improve anticoagulant safety. Areas that would benefit from further research are also identified. Validated variants in VKORC1, CYP2C9 and CYP4F2 constitute biomarkers for differential warfarin response and genotype-informed warfarin dosing has been shown to reduce adverse clinical events. Polymorphisms in CES1 appear relevant to dabigatran exposure but the genetic studies focusing on clinical outcomes such as bleeding are sparse. The influence of body weight on LMWH response merits further attention, as does the relationship between anti-Xa levels and clinical outcomes. Ultimately, safe and effective anticoagulation requires both a deeper parsing of factors contributing to variable response, and further prospective studies to determine optimal therapeutic strategies in identified higher risk subgroups.

Systems Biology Approach for Personalized Hemostasis Correction

The correction of blood coagulation impairments of a bleeding or thrombotic nature employs standard protocols where the type of drug, its dose and the administration regime are stated. However, for a group of patients, such an approach may be ineffective, and personalized therapy adjustment is needed. Laboratory hemostasis tests are used to control the efficacy of therapy, which is expensive and time-consuming. Computer simulations may become an inexpensive and fast alternative to real blood tests. In this work, we propose a procedure to numerically define the individual hemostasis profile of a patient and estimate the anticoagulant efficacy of low-molecular-weight heparin (LMWH) based on the computer simulation of global hemostasis assays. We enrolled a group of 12 patients receiving LMWH therapy and performed routine coagulation assays (activated partial thromboplastin time and prothrombin time) and global hemostasis assays (thrombodynamics and thrombodynamics-4d) and measured anti-Xa activity, fibrinogen, prothrombin and antithrombin levels, creatinine clearance, lipid profiles and clinical blood counts. Blood samples were acquired 3, 6 and 12 h after LMWH administration. We developed a personalized pharmacokinetic model of LMWH and coupled it with the mechanism-driven blood coagulation model, which described the spatial dynamics of fibrin and thrombin propagation. We found that LMWH clearance was significantly lower in the group with high total cholesterol levels. We generated an individual patient's hemostasis profile based on the results of routine coagulation assays. We propose a method to simulate the results of global hemostasis assays in the case of an individual response to LMWH therapy, which can potentially help with hemostasis corrections based on the output of global tests.

Gerinnungsdiagnostik im klinischen Alltag – Teil 2

Während bei einer Vitamin-K-Antagonisten-Therapie die Therapieüberwachung (International Normalized Ratio [INR]) obligat ist, gilt dies für direkte orale Antikoagulanzien (DOAK) oder niedermolekulares Heparin (NMH) nur in ausgewählten klinischen Szenarien. Bei DOAK steht die Bestimmung von Tal- und Spitzenspiegeln des Medikaments im Plasma im Vordergrund, bei NMH die Anti-Xa-Aktivität. Der Zeitpunkt der Probenabnahme in Relation zur Einnahme ist für die Bewertung essenziell. Eine neu aufgetretene Thrombozytopenie im Rahmen stationärer Behandlungen ist häufig. Einordnung der Grunderkrankung, Tag des Auftretens sowie Erfassung medikamentöser Einflüsse und ihrer Dynamik ermöglichen oft die Eingrenzung der Ursache. Die Thrombophilietestung nach venöser Thromboembolie wird aufgrund fehlender therapeutischer Konsequenz zunehmend seltener durchgeführt. Ein Antiphospholipidsyndrom darf aber nicht übersehen werden, da sowohl die Therapiedauer als auch die Wahl des Antikoagulans davon abhängen.

Monitoring of heparin therapy beyond the anti-Xa activity assay: Evaluation of a thrombin generation assay

INTRODUCTION

Global coagulation assays may be of added value to the anti-Xa assay for monitoring heparin therapy. Unlike most testing methods, the thrombin generation assay (TGA) has the ability to assess the overall function of the hemostatic system, which provides information on the anticoagulation status of patients. We compared the TGA, measured with ST Genesia^® STG-DrugScreen^® reagent, with the anti-Xa assay for monitoring heparin therapy in inflammatory and non-inflammatory patients. We also determined reference values for STG-DrugScreen^® thrombin generation (TG) parameters.

METHODS

Reference values were determined on 120 healthy donors. Furthermore, a spiking experiment with unfractionated heparin (UFH) and low molecular weight heparin (LMWH) was performed, and samples of patients receiving UFH or LMWH were analyzed with ST Genesia^® and the anti-Xa assay.

RESULTS

High discrepancy between TG parameters and anti-Xa activity was observed for low LMWH anti-Xa levels. TG parameters were affected in 36/46 (time to peak) to 42/46 (peak height) patients during UFH therapy with sub-target anti-Xa activity levels.

CONCLUSION

TGA seems insufficiently sensitive for low concentrations of LMWH. There may be an added value of the TGA for monitoring UFH in so-called heparin-resistant patients. Therefore, the TGA has the potential to be introduced as an additional tool for monitoring heparin therapy.

"In Less than No Time": Feasibility of Rotational Thromboelastometry to Detect Anticoagulant Drugs Activity and to Guide Reversal Therapy

Anticoagulant drugs (i.e., unfractionated heparin, low-molecular-weight heparins, vitamin K antagonists, and direct oral anticoagulants) are widely employed in preventing and treating venous thromboembolism (VTE), in preventing arterial thromboembolism in nonvalvular atrial fibrillation (NVAF), and in treating acute coronary diseases early. In certain situations, such as bleeding, urgent invasive procedures, and surgical settings, the evaluation of anticoagulant levels and the monitoring of reversal therapy appear essential. Standard coagulation tests (i.e., activated partial thromboplastin time (aPTT) and prothrombin time (PT)) can be normal, and the turnaround time can be long. While the role of viscoelastic hemostatic assays (VHAs), such as rotational thromboelastometry (ROTEM), has successfully increased over the years in the management of bleeding and thrombotic complications, its usefulness in detecting anticoagulants and their reversal still appears unclear.

Updates in Anticoagulation Therapy Monitoring

In the past six decades, heparin and warfarin were the primary anticoagulants prescribed for treatment and prophylaxis of venous thromboembolism worldwide. This has been accompanied by extensive clinical knowledge regarding dosing, monitoring, and reversal of these anticoagulants, and the resources required to do so have largely been readily available at small and large centers alike. However, with the advent of newer oral and parenteral anticoagulants such as low molecular weight heparins, factor Xa inhibitors, and direct thrombin inhibitors in recent years, new corresponding practice guidelines have also emerged. A notable shift in the need for monitoring and reversal agents has evolved as well. While this has perhaps streamlined the process for physicians and is often desirable for patients, it has also left a knowledge and resource gap in clinical scenarios for which urgent reversal and monitoring is necessary. An overview of the currently available anticoagulants with a focus on the guidelines and available tests for anticoagulant monitoring will be discussed in this article.

Heparins: A Shift of Paradigm

Heparins inhibit the thrombin forming capacity of plasma, i. e., the endogenous thrombin potential (ETP), by their anti-thrombin (aIIa) activity, the anti-factor Xa (aXa) activity is of minimal importance. This holds for both unfractionated heparin (UFH) and low molecular weight heparin (LMWH) at aXa/aIIa ratios < 25. Clinical experience and epidemiological evidence show a direct relationship between the ETP and the risk of thrombosis and bleeding. Consequently, the therapeutic potency of a heparin is determined by its aIIa activity, i.e., the concentration of a domain in which 12 sugar flank the high affinity antithrombin-binding pentasaccharide (HA5) at one side. The response of individual plasmas to a fixed dose of any heparin is highly variable. This suggests that individualization of heparin dosage, on basis of the ETP, might reduce bleeding or re-thrombosis. There exist simple laboratory methods for both the ETP and the concentration of the active domain. These methods can be used both for unequivocally characterization of a heparin preparation and for controlling heparin therapy and allow arbitrary units relative to a standard to be abandoned. These tests are as robust as any hematological routine test but not yet routinely available, which severely encumbers progress in the field.

Thrombin generation test as a marker for high risk venous thrombosis pregnancies

Pregnancy is a well-established risk factor for venous thromboembolism and is associated with a state of hypercoagulability. The use of sensitive and specific biological markers to predict risk factors for thrombosis is essential during pregnancy. Our objective was to investigate the usefulness of thrombin generation test (TGT) as a marker to predict the risk of thrombosis in high risk venous thrombosis (HRVT) pregnancies compared to normal pregnancies. This retrospective study enrolled 134 women with HRVT pregnancies, 78 of whom had monozygotic, spontaneous and untreated pregnancies and formed the study group. The control group comprised 106 women with normal pregnancies. Routine assessment of coagulation activation markers: fibrinogen, D-dimer, prothrombin fragments 1 + 2 (F1 + 2), thrombin-antithrombin complexes (TAT) and fibrin monomer complexes (FMC) was performed every 5 weeks in the study group to detect a possible pathological state of hypercoagulability. TGT was performed using platelet-free plasma, 1 and 5 pM tissue factor (TF), supplemented by phospholipids (PL) ± thrombomodulin. Fibrinogen, D-dimer, F1 + 2, and TAT, but not FMC, increased significantly throughout pregnancy in both groups but no difference was shown between the groups. TGT showed an early increase in thrombin generation in both groups, which stabilized during the second month of pregnancy. No correlation was demonstrated between thrombin generation parameters and coagulation activation markers. Based on our results, TGT did not prove conclusive as a marker to predict the risk of thrombosis in HRVT pregnancies. Finding a sensitive and specific biological marker to predict thrombosis risk requires further investigation.

Anwendungen des endogenen Thrombinpotenzials

An overview is given on the method and the applications of thrombin generation assays. Thrombin generation assays provide a tool which can be used to trace the entire thrombin formation and inactivation of a plasma sample. Therefore they are principally different from traditional global assays like PT and aPTT and promise new opportunities for the assessment of bleeding or thrombotic risks.

Thrombodynamics, a new global coagulation test: Measurement of heparin efficiency

The actual coagulation status may be reliably measured using only highly sensitive global functional tests; however, they are not numerous and all of them have disadvantages. Thrombodynamics (TD), a novel global coagulation test, is sensitive to hypo- and hypercoagulable states. The main properties of this test were investigated, and its capabilities for hemostasis analysis were verified through pharmacodynamic monitoring of the most widely used anticoagulants, heparins. The anticoagulant effects in the plasma of donors (n = 20) and patients after hip replacement (n = 20) spiked with unfractionated heparin or enoxaparin were measured in vitro to eliminate the influence of pharmacokinetic factors. Sensitivity for heparins was compared for activated partial thromboplastin time, thrombin generation tests and TD. TD was shown to reliably characterize the pharmacodynamics of any heparin in the entire range of its prophylactic and therapeutic concentrations. Inter-individual variability for the anticoagulant action of heparins was also calculated using the TD data. This variability did not differ between the investigated groups and did not exceed 12% and 20% for the stationary clot growth rate in the presence of unfractionated heparin and enoxaparin, respectively. That finding was in accordance with the values determined earlier using the thrombin generation test. The study results showed that TD has advantages over the other global methods of coagulation analysis. These advantages are good standardization, high reproducibility, independence of the parameter values from patient age and gender, and a narrower parameter distribution in a normal population. These results indicate that TD is a promising universal assessment method that improves the quality of hemostasis analysis because it more reliably detects deviations from the parameters' reference values.

Weight-Based Dosing for Once-Daily Enoxaparin Cannot Provide Adequate Anticoagulation for Venous Thromboembolism Prophylaxis

BACKGROUND

Surgeons commonly provide enoxaparin prophylaxis to high-risk patients to decrease venous thromboembolism risk. The authors' prior work demonstrated that most patients receive inadequate venous thromboembolism prophylaxis, based on anti-factor Xa level, when enoxaparin 40 mg/day is provided and that peak anti-factor Xa level correlates with weight. This study models a weight-based strategy for daily enoxaparin prophylaxis and its impact on anti-factor Xa levels.

METHODS

The authors enrolled plastic surgery patients who received enoxaparin 40 mg/day and had anti-factor Xa levels drawn. The enoxaparin dose of 40 mg was converted to a milligram-per-kilogram dose for each patient. Stratified analysis examined the milligram-per-kilogram dose that produced low, in-range, and high anti-factor Xa levels to identify the appropriate milligram-per-kilogram dose to optimize venous thromboembolism prevention and bleeding events.

RESULTS

Among 94 patients, weight-based dosing ranged from 0.28 to 0.94 mg/kg once daily. For peak and trough anti-factor Xa levels, there was nearly complete overlap for milligram-per-kilogram dosing that produced low versus in-range anti-factor Xa levels. For peak anti-factor Xa, there was nearly complete overlap for milligram-per-kilogram dosing that produced in-range versus high anti-factor Xa levels. Mean milligram-per-kilogram dose was not significantly different between patients who did or did not have postoperative venous thromboembolism (0.41 mg/kg versus 0.52 mg/kg; p = 0.085) or clinically relevant bleeding (0.48 mg/kg versus 0.51 mg/kg; p = 0.73).

CONCLUSIONS

Alterations in enoxaparin dose magnitude based on patient weight cannot allow a high proportion of patients to achieve appropriate anti-factor Xa levels when once-daily enoxaparin prophylaxis is provided. Future research should examine the impact of increased enoxaparin dose frequency on anti-factor Xa levels, venous thromboembolism events, and bleeding.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Thrombin generation test for evaluation of antiplatelet treatment in patients with coronary artery disease after percutaneous coronary intervention

To study the possibility of using thrombin generation tests in platelet-rich and platelet-poor plasma for evaluation of dual antiplatelet therapy efficacy in patients with coronary artery disease (CAD), following percutaneous coronary intervention. Venous blood was analyzed from CAD patients aged 53-75 years who had undergone percutaneous coronary intervention with stenting within one year and had been receiving standard doses of clopidogrel and aspirin (75 and 75-100 mg per day, respectively). The control group comprised age- and sex-matched subjects without clinical signs of CAD who were not receiving these drugs. Thrombin generation tests were performed in platelet-rich and platelet-poor plasma. Intravascular platelet activation, induced platelet aggregation, and routine coagulation were evaluated. Antiplatelet treatment did not influence results of routine coagulation tests or intravascular platelet activation. The dual antiplatelet therapy affects collagen-induced platelet aggregation (44 ± 2.5 vs. 7.9 ± 2.6%, р = 10^-7) and leads to decreases in endogenous thrombin potential (1900 ± 85 vs. 1740 ± 95 nM∙min, p = 0.0045), maximum thrombin concentration (134 ± 9.5 vs. 106 ± 6.5 nM, p = 4∙10^-6), and increases in time to peak thrombin (27 ± 1.5 vs. 31 ± 2 min, p = 0.0012). Decreases in thrombin generation rate showed the highest statistical significance (13 ± 2 vs. 7.9 ± 0.8 nM/min, p = 10^-8). Antiplatelet treatment did not alter thrombogram parameters for platelet-poor plasma.

A century of heparin: past, present and future

Heparin was discovered around 1922 by Howell (Baltimore) and was further developed by the teams of Best (Toronto) and Jorpes (Stockholm). Kakkar (London) propagated its routine use for the prevention of postoperative thrombosis from 1971 onwards. The discovery of low molecular weight heparins (1976, Johnson, London) and their development in the subsequent years led to the present arsenal of clinically useful drugs. In 1976, three teams independently found that a specific structure in heparin binds tightly to antithrombin. This enabled the teams of Lindahl (Stockholm) and Casu (Milan) to determine the pentasaccharide structure responsible for this binding and Petitou, from the Choay team (Paris), to synthesize it (1983). It was found (Olson and others) that heparin facilitates the interaction between antithrombin and a clotting enzyme by allosteric changes in the antithrombin (important for factor Xa) and by facilitating the approach of the enzyme to antithrombin via its "sliding" along the heparin molecule (important for thrombin). Antithrombin action therefore requires a minimum length of seven sugar units next to the pentasaccharide whereas anti-factor Xa action does not. The effect of heparin is almost entirely due to anti-thrombin action (B≐guin), so anti-factor Xa activity does not reflect the concentration of anticoagulant heparin. The anticoagulant effect is poorly reflected by the activated partial thromboplastin time. Because present clinical use is based on the latter tests, it is not generally known that the individual response to heparin shows an extremely wide variation. Individualization of heparin dosage is likely to improve clinical results.

The modification of the thrombin generation test for the clinical assessment of dabigatran etexilate efficiency

A new oral anticoagulant, dabigatran etexilate (DE, a prodrug of direct thrombin inhibitor (DTI) dabigatran), has been used clinically to prevent thrombosis. The assessment of dabigatran efficiency is necessary in some clinical cases, such as renal insufficiency, risk of bleeding, and drug interactions. However, a specific thrombin generation test (TGT) that is one of the most informative and sensitive to anticoagulant therapy (calibrated automated thrombinography (САТ)) shows a paradoxical increase of test parameters, such as endogenous thrombin potential (ETP) and peak thrombin, in patients receiving DE. The paradoxical behaviour of ETP and peak thrombin in these patients in the presence of DTIs is mostly caused by a decrease in the activity of thrombin in the α₂-macroglobulin-thrombin complex that is used as a calibrator in CAT. For a correct estimation of the TGT parameters in patient’s plasma containing DTIs we proposed to use our previously described alternative calibration method that is based on the measurement of the fluorescence signal of a well-known concentration of the reaction product (7-amino-4-methylcoumarin). In this study, the validity of such approach was demonstrated in an ex vivo study in patients with knee replacement and two special patients with multiple myeloma, who received DE for thrombosis prophylaxis.

Thrombin generation and international normalized ratio in inherited thrombophilia patients receiving thromboprophylactic therapy

BACKGROUND

Thrombin generation assay (TGA) is useful as a global functional test for assessing bleeding or thrombotic risk and its modification with therapy. We investigated TGA to assess anticoagulation status compared with the international normalized ratio (INR) system in patients with primary thrombophilia receiving and not undergoing thromboprophylaxis.

MATERIALS AND METHODS

We studied 50 patients with at least one thrombotic event and a confirmed diagnosis of inherited thrombophilia. Thrombin generation was measured in platelet-poor plasma by calibrated automated thrombography (CAT).

RESULTS

Patients in optimal anticoagulation (INR: 2.0-3.0) showed an endogenous thrombin potential (ETP) of 14-56% of normal and a peak of 18-55% of normal. A significant inverse relationship between INR and thrombin generation parameters (ETP, peak and velocity index) and a linear correlation for lag time was found in patients treated with vitamin-K antagonists (VKA). Receiver-operating characteristics (ROC) analysis showed that the optimal cutoff for ETP was 1600.2 nM · min (111.6% of normal, with a sensitivity of 96.6% and a specificity of 92.9%) and for the peak was 298.3 nM (112.1% of normal, with a sensitivity of 96.4% and a specificity of 100%). According to this analysis, ETP was able to identify patients with increased thrombotic and hemorrhagic risk, correlating with severe clinical complications.

CONCLUSION

TGA showed excellent sensitivity and specificity for assessing anticoagulation status in patients with primary thrombophilia receiving VKA, with significant advantages with regard to INR. Clinical data strongly support ETP as a valuable indicator of thrombotic or hemorrhagic risk in patients receiving or not receiving thromboprophylaxis.

A systematic review on the accumulation of prophylactic dosages of low-molecular-weight heparins (LMWHs) in patients with renal insufficiency

PURPOSE

Although therapeutic dosages of most low-molecular-weight heparins (LMWHs) are known to accumulate in patients with renal insufficiency, for the lower prophylactic dosages this has not been clearly proven. Nevertheless, dose reduction is often recommended. We conducted a systematic review to investigate whether prophylactic dosages of LMWH accumulate in renal insufficient patients.

METHODS

A comprehensive search was conducted on 17 February 2015 using Embase, Medline, Web of Science, Scopus, Cochrane, PubMed publisher, and Google scholar. The syntax emphasized for LMWHs, impaired renal function, and pharmacokinetics. The search yielded 674 publications. After exclusion by reading the titles, abstracts, and if necessary the full paper, 11 publications remained.

RESULTS

For dalteparin and tinzaparin, no accumulation was observed. Enoxaparin, on the other hand, did lead to accumulation in patients with renal insufficiency, although not in patients undergoing renal replacement therapy. Bemiparin and certoparin also did show accumulation. No data were available for nadroparin.

CONCLUSIONS

In this systematic review, we show that prophylactic dosages of tinzaparin and dalteparin are likely to be safe in patients with renal insufficiency and do not need dose reduction based on the absence of accumulation. However, prophylactic dosages of enoxaparin, bemiparin, and certoparin did show accumulation in patients with a creatinine clearance (CrCl) below 30 ml/min, and therefore, dose reduction is required. The differences in occurrence of accumulation seem to depend on the mean molecular weight of LMWHs.

Inverse relationship of bleeding risk with clot burden during pulmonary embolism treatment with LMW heparin

INTRODUCTION

Clinically relevant bleeding occurs three times as frequently as recurrent venous thromboembolism in the modern early treatment of pulmonary embolism (PE) with fixed-dose, unmonitored anticoagulants. Unfractionated heparin (UFH) is monitored and adjusted to assure efficacy and minimize bleeding risk, but low molecular weight heparin (LMWH) is not. PE requires more anticoagulant than isolated deep venous thrombosis. Speculating that PE with low clot burden could lead to excess bleeding with unadjusted LMWH treatment but not with UFH, we compared PE patients receiving either UFH or LMWH with high and low clot burden for clinically significant bleeding in an observational study.

MATERIALS AND METHODS

Patients with acute PE at multiple Chinese teaching hospitals had been randomized to UFH or LMWH for initial treatment. These treatment cohorts had baseline measurement of pulmonary artery obstruction (PAO) score, which was prospectively separated into quartiles, lowest to highest PAO. All patients were followed for bleeding episodes, which were subsequently analyzed by quartile of PAO.

RESULTS

Two hundred seventy-four patients divided between the two groups had similar efficacy and safety outcomes (12 clinically significant bleeds in the UFH group vs 15 in the LMWH group). LMWH recipients with the smallest clot burdens (lowest PAO quartiles) had highest bleeding rates (Cochran-Armitage trend test, P trend = 0.048), but there was no such trend for UFH recipients.

CONCLUSIONS

For UFH, excess anticoagulant pro-hemorrhagic potential is down-adjusted via activated partial thromboplastin time monitoring, but for LMWH it is not. For PE patients at high bleeding risk, UFH may be safer if the clot burden is small.

Monitoring low molecular weight heparins at therapeutic levels: dose-responses of, and correlations and differences between aPTT, anti-factor Xa and thrombin generation assays

Background

Low molecular weight heparins (LMWH’s) are used to prevent and treat thrombosis. Tests for monitoring LMWH’s include anti-factor Xa (anti-FXa), activated partial thromboplastin time (aPTT) and thrombin generation. Anti-FXa is the current gold standard despite LMWH’s varying affinities for FXa and thrombin.

Aim

To examine the effects of two different LMWH’s on the results of 4 different aPTT-tests, anti-FXa activity and thrombin generation and to assess the tests’ concordance.

Method

Enoxaparin and tinzaparin were added ex-vivo in concentrations of 0.0, 0.5, 1.0 and 1.5 anti-FXa international units (IU)/mL, to blood from 10 volunteers. aPTT was measured using two whole blood methods (Free oscillation rheometry (FOR) and Hemochron Jr (HCJ)) and an optical plasma method using two different reagents (ActinFSL and PTT-Automat). Anti-FXa activity was quantified using a chromogenic assay. Thrombin generation (Endogenous Thrombin Potential, ETP) was measured on a Ceveron Alpha instrument using the TGA RB and more tissue-factor rich TGA RC reagents.

Results

Methods’ mean aPTT at 1.0 IU/mL LMWH varied between 54s (SD 11) and 69s (SD 14) for enoxaparin and between 101s (SD 21) and 140s (SD 28) for tinzaparin. ActinFSL gave significantly shorter aPTT results. aPTT and anti-FXa generally correlated well. ETP as measured with the TGA RC reagent but not the TGA RB reagent showed an inverse exponential relationship to the concentration of LMWH. The HCJ-aPTT results had the weakest correlation to anti-FXa and thrombin generation (R_s0.62–0.87), whereas the other aPTT methods had similar correlation coefficients (R_s0.80–0.92).

Conclusions

aPTT displays a linear dose-respone to LMWH. There is variation between aPTT assays. Tinzaparin increases aPTT and decreases thrombin generation more than enoxaparin at any given level of anti-FXa activity, casting doubt on anti-FXa’s present gold standard status. Thrombin generation with tissue factor-rich activator is a promising method for monitoring LMWH’s.

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.

The study of the thrombin generation mechanism and the effect of low molecular weight heparin as thromboprophylaxis in patients undergoing total knee and hip replacement

INTRODUCTION

The recommended duration of post-operative Low-Molecular-Weight-Heparins (LMWHs) thromboprophylaxis in Total-Hip-Replacement (THR) and Total-Knee-Replacement (TKR) surgery is controversial. Our aim is to study the thrombin generation (TG) modifications induced by surgery and to evaluate the effect of LMWH on TG during and after the recommended duration.

PATIENTS/METHODS

Thirty-one patients received 4000IU anti-Xa/day of enoxaparin, 8-hours post-operatively (15 THR for 30-days and 16 TKR for 15-days). TG assay sensitive to enoxaparin was performed, pre-operatively (D0), 7-hours post-surgery (D1), 8-days post-surgery (D8), and 2-days after thromboprophylaxis withdrawal (D32 and D17), evaluating: lag-time, endogenous thrombin potential (ETP), peak amount of generated thrombin (Peak), time-to-Peak (tt-Peak), and the Mean-Rate-Index [MRI=Peak/(tt-Peak-lag-time)].

RESULTS

TKR surgery decreased lag-time and tt-Peak and increased MRI on D1 vs D0 (p<0.05). In contrast, THR did not significantly modify TG. Enoxaparin effectively reduced thrombin generation in both groups. Thromboprophylaxis withdrawal resulted in rebound increase of TG in the TKR patients (ETP, Peak & MRI significantly increased on D17 vs D0; p<0.05, and vs. D1; p<0.05) but not in THR patients. Variability in the response to enoxaparin was observed among patients of the same group.

CONCLUSIONS

TKR surgery is more thrombogenic than THR surgery. In THR patients TG was efficiently inhibited by 30-day thromboprophylaxis, whereas, in TKR patients treated for 15-days TG was not effectively inhibited. Individual variability of the response to enoxaparin was observed in both groups revealing some form of biological resistance to enoxaparin. TG assay may represent the breakthrough step to efficient antithrombotic strategy in clinical settings with high thrombotic risk.

Lobectomy and postoperative thromboprophylaxis with enoxaparin improve blood hypercoagulability in patients with localized primary lung adenocarcinoma

BACKGROUND

Patients with lung adenocarcinoma undergoing surgery are in high risk for VTE and receive routine post-operative thromboprophylaxis with LWMH.

AIM

We investigated markers of hypercoagulability in patients with primary localized adenocarcinoma and the modifications induced by lobectomy and postoperative administration of enoxaparin.

MATERIALS AND METHODS

Patients suffering from localised primary lung adenocarcinoma (n=15) scheduled for lobectomy were studied. The control group consisted of 15 healthy age and sex-matched individuals. Blood was collected before anaesthesia induction and after surgery, at several intervals until the 7th post-operative day. Samples were assessed for thrombin generation, phosphatidylserin expressing platelet derived microparticles expressing (Pd-MP/PS(+)), tissue factor activity (TFa), FVIIa and TFPI levels, procoagulant phospholipid dependent clotting time and anti-Xa activity.

RESULTS

At baseline, patients showed increased thrombin generation and Pd-MP/PS(+). After lobectomy thrombin generation significantly decreased. Administration of enoxaparin attenuated thrombin generation. In about 50% of samples collected post-operatively an increase of thrombin generation occurred despite the presence of the expected anti-Xa activity in plasma. At the 7th post-operative day, 3 out of 15 patients showed a significant increase of thrombin generation.

CONCLUSION

In patients with localized lung adenocarcinoma, hypercoagulability is characterized by high thrombin generation and increased concentration of Pd-MP/PS(+). Tumor mass resection is related with attenuation of thrombin generation, which is inhibited by postoperative thromboprophylaxis with enoxaparin. The response to enoxaparin is not predicted by the concentration of the anti-Xa activity in plasma. The assessment of thrombin generation during prophylaxis with enoxaparin allows to identify patients with high residual plasma hypercoagulability.

The effects of location and low-molecular-weight heparin administration on deep vein thrombosis outcomes in trauma patients

BACKGROUND

Deep vein thrombosis (DVT) is common after trauma. Pulmonary embolism (PE) is a feared complication of DVT. Standard doses of low-molecular-weight heparin (LMWH) are commonly used to prevent and treat DVT and PE. There is variable bioavailability of LMWH with standard therapy. The traditional concept that below-knee DVT is associated with a lower risk of subsequent PE may result in less aggressive therapy. The purposes of this study were to assess the rates of PE in above-knee versus below-knee DVT and longitudinally evaluate outcomes of DVT treated with LMWH therapy.

METHODS

This was a retrospective review of patients at a university Level I trauma center during the years 2005 through 2010. Patients diagnosed with lower-extremity DVT were included in this study. Patients were classified by location of lower-extremity DVT and type of LMWH therapy received. All high-risk trauma patients were evaluated with weekly duplex Doppler ultrasonography. All duplex studies were reviewed for DVT resolution or improvement. Symptomatic patients were evaluated with computed tomographic angiography to rule out PE. Demographics, total length of hospital stay, length of intensive care unit stay, and Injury Severity Score (ISS) were collected.

RESULTS

Three-hundred eight trauma patients with lower-extremity DVT were included. More patients developed below-knee DVT (65.6%) compared with above-knee DVT (34.4%). Increased length of hospital stay, intensive care unit stay, and higher ISS were noted in patients with above-knee DVT. More patients had below-knee DVT in the prophylactic dosing group. With LMWH therapy, three PEs occurred in patients in the prophylactic dosing group with below-knee DVT, and no PEs occurred in the therapeutic treatment group. The incidence of PE between patients with below-knee DVT compared with above-knee DVT overall was not different (3.3% and 4.7%, p = 0.59). To assess DVT outcomes, 157 of the 308 patients had serial duplex studies following diagnosis of lower-extremity DVT. The number of patients receiving either therapeutic or prophylactic LMWH was similar (51% and 49%). There was no difference in rates of resolution or improvement between LMWH dosing groups or location of DVT.

CONCLUSION

In screened trauma patients, below-knee DVT is more common than above-knee DVT. There was no difference in the incidence of PE between groups. Standard prophylactic and therapeutic dosing of LMWH does not affect the rates of resolution or improvement of lower-extremity DVT. Rates of resolution and improvement of DVT is not dependent of location of lower-extremity DVT.

LEVEL OF EVIDENCE

Therapeutic study, level IV; epidemiologic study, level III.

Bioactivity of enoxaparin in critically ill patients with normal renal function

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Venous thromboembolism is a frequent complication in critically ill patients that has a negative impact on patient outcomes. Critically ill patients have significantly lower plasma anti-factor-Xa activity levels compared with control patients after administration of subcutaneous heparin. The clinical relevance of the different anti-factor-Xa levels after prophylactic doses of low molecular weight heparin (LMWH) in critically ill patients is not completely understood.

WHAT THIS STUDY ADDS

The standard dose of 40 mg enoxaparin led to a significant increase in anti-FXa levels in this selected cohort of ICU patients with normal renal function. This study found only subtle pharmacokinetic differences, but a comparable pharmacodynamic action, after enoxaparin administration in critically ill and normal medical ward patients. Thrombin generation with TGA RC-low and TGARC-high reagents was significantly reduced in ICU and normal ward patients after receiving LMWH. Both readouts appear equally useful for estimating the pharmacodynamics of enoxaparin. The ex vivo model of thrombosis was used for the first time in patients to evaluate the anti-thrombotic activity of LMWH. This method did not show any difference in thrombus formation after administration of enoxaparin in the individual group of patients.

AIM

In critically ill patients, reduced anti-FXa plasma activity following subcutaneous administration of enoxaparin or nadroparin has been described. In this study, we aimed to investigate the bioactivity of enoxaparin in critically ill patients and controls.

METHODS

A prospective, controlled, open label study was performed on a medical intensive care unit (ICU) and a general medical ward. Fifteen ICU patients (male = 12, median age 52 years [IQR 40-65], with a median Simplified Acute Physiology Score of 30 [IQR 18-52]) and sex- and age-matched medical ward patients were included. The anti-FXa plasma activity was measured after a single subcutaneous dose of40 mg enoxaparin. The thrombus size of a clot formed in an ex vivo perfusion chamber and endogenous thrombin potential (ETP) were measured.

RESULTS

The anti-FXa plasma activity increased significantly after enoxaparin administration, with peak levels at 3 h after treatment, but was comparable between the ICU and medical ward groups (median 0.16 IU ml-1 [IQR 0-0.22 IU ml-1] vs. 0.2 IU ml-1 [IQR 0.15-0.27 IU ml-1],respectively, P = 0.13). The area under the anti-FXa activity curve from 0–12 h was similar between the groups (median 0.97 IU ml-1 h [IQR0.59-2.1] and 1.48 IU ml-1 h1 [IQR 0.83-1.62], P = 0.42 for the ICU group compared with the control group, respectively). The ETP was lower in the ICU group (P < 0.05) at baseline, but it was comparable at 3 h between the groups. Thrombus size decreased at 3 h compared with pre-dose (P = 0.029) and was not different between the groups.

CONCLUSION

Similar bioactivity was achieved with a standard dose of subcutaneous enoxaparin in this selected cohort of ICU and general ward patients with normal renal function.

Large inter-individual variation of the pharmacodynamic effect of anticoagulant drugs on thrombin generation

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

Heparin-grafted dialysis membrane allows minimal systemic anticoagulation in regular hemodialysis patients: a prospective proof-of-concept study

This prospective, multicenter, proof-of-concept study aimed to evaluate the possibility to reduce the ordinary heparin dose and the systemic anti-Xa activity during hemodialysis (HD) sessions using a new heparin-grafted HD membrane. In 45 stable HD patients, the use of a heparin-grafted membrane with the ordinary heparin dose was followed by a stepwise weekly reduction of dose. Reduction was stopped when early signs of clotting (venous pressure, quality of rinse-back) occurred during two out of three weekly HD sessions. Heparin dose was decreased for 67% of patients resulting in the lowering of these patients' anti-Xa activity by 50%. Dose reductions were achieved with both types of heparin (low-molecular-weight heparin: 64 ± 14 to 35 ± 12 IU/kg, P < 0.0001; unfractionated heparin: 82 ± 18 to 46 ± 13 IU/kg, P < 0.0001) resulting in a decrease of anti-Xa activity at dialysis session end (low-molecular-weight heparin: 0.51 ± 0.25 to 0.25 ± 0.11 IU/mL, P < 0.0001; unfractionated heparin: 0.28 ± 0.23 to 0.13 ± 0.07 IU/mL, P < 0.0001). Failure to further decrease heparin dose was related to signs of clotting in blood lines (57% of sessions), in dialyzer (9%), or both (34%). Significant reduction of heparin dose and anti-Xa activity at the end of HD sessions was possible in stable HD patients using heparin-grafted membrane. HD patients who require low anti-Xa activity at the end of HD sessions might benefit from a heparin-grafted membrane to reduce bleeding risk and other heparin adverse events.

Monitoring platelet dependent thrombin generation in mice

Calibrated automated thrombin generation assay was adapted to measure thrombin generation in platelet rich plasma from mice. Vena cava phlebotomy appeared the best technique for blood sampling. The concentration-effect curves of tissue factor and platelet count have been determined. Corn trypsin inhibitor 2μM inhibits contact activation effectively. Recombinant human thrombomodulin does not inhibit thrombin generation in mouse plasma but activated protein C (20nM) does. Thrombin generation was dose dependently diminished by low molecular weight heparin and increased by high concentrations of exogenous factor VIII i.e. the assay can detect both hypo- and hypercoagulability.

Thrombelastography versus AntiFactor Xa levels in the assessment of prophylactic-dose enoxaparin in critically ill patients

BACKGROUND

A standard dose of enoxaparin is frequently used for deep venous thrombosis (DVT) prophylaxis. Evidence suggests inconsistent bioavailability in intensive care unit (ICU) patients. Antifactor Xa activity (anti-Xa) has been used to monitor enoxaparin dosing but its accuracy and availability are problematic. Thrombelastography (TEG) is used to evaluate coagulation in diverse settings. The purpose of this study was to analyze whether TEG could be used to predict which enoxaparin-treated patients would develop DVT.

METHODS

Two hundred sixty-one simultaneous enoxaparin-active (active) and enoxaparin-neutralized (neutral) TEGs were performed in 61 surgical ICU patients over four consecutive days. Patient characteristics and anti-Xa were collected. DVT screening was per ICU protocol.

RESULTS

Mean (+/-SEM) age was 54 (+/-2.3) years and Acute Physiology and Chronic Health Evaluation II score was 17 (+/-0.7). There were 30 trauma and 31 general surgery patients (69% men). The DVT rate was 28%. Time to clot formation (R) and percent lysis at 30 minutes were different between active versus neutralized blood (p < 0.001). R time was 1.5 minutes shorter in patients with DVT versus those without (p < 0.001) indicating hypercoagulability in DVT patients. Anti-Xa levels were similar in patients with (0.135 +/- 0.012) and without (0.135 +/- 0.007) DVT (p = 0.97). There were no differences in age, body mass index, injury severity score, Acute Physiology and Chronic Health Evaluation II score, or trauma status between DVT and non-DVT groups.

CONCLUSIONS

TEG demonstrates differences between enoxaparin-neutralized and enoxaparin-active blood in ICU patients that may be used to guide dosing. TEG differentiates enoxaparin-treated patients who subsequently develop DVT while anti-Xa levels do not. TEG demonstrates an enoxaparin-related increase in fibrinolysis.

Study of bioaccumulation of dalteparin at a prophylactic dose in patients with various degrees of impaired renal function

BACKGROUND

Low-molecular-weight heparins (LMWH) have been shown to be effective and safe for prophylaxis of thromboembolic diseases. However, issues regarding safety and optimal use of LMWH arise in patients with renal insufficiency (RI).

OBJECTIVES

To compare pharmacokinetic data of dalteparin for up to 3 weeks in patients with various degrees of RI.

PATIENTS AND METHODS

Patients from general medical and surgical wards were included in this prospective cohort study and divided into three groups according to renal function: A=normal (GFR>or=60 mL min(-1)1.73 m(-2)), B=mild RI (GFR 30-59 mL min(-1)1.73 m(-2)), C=severe RI (GFR<30 mL min(-1)1.73 m(-2)). Dalteparin was injected s.c. once daily at a prophylactic dose. Peak anti-Xa activity levels (anti-Xa) were measured 4+/-1 h after injection on day 1 and every third day up to 3 weeks. Primary objectives were peak anti-Xa levels and adjusted anti-Xa levels, adjustment being carried out for dose and body weight.

RESULTS

A total of 42 patients could be analyzed during a median of 10 days (interquartile range IQR 4-13, range 1-20). In all groups, adjusted peak anti-Xa levels were not different on day 10 compared with day 1. No bioaccumulation>30% could be found up to day 10 even in patients with severe RI.

CONCLUSION

The use of dalteparin at a prophylactic dose was not associated with a bioaccumulation>30% even in patients with severe renal insufficiency during a median follow-up of 10 days (IQR 4-13, range 1-20).

Differential effects of factor IIa inhibitors on the endogenous thrombin potential

Calibrated automated thrombin generation measurement in clotting plasma (endogenous thrombin potential, ETP) is being used increasingly to monitor the effects of anticoagulant drugs. Calibrated automated thrombography measures the concentration of thrombin in clotting plasma by monitoring the cleavage of a fluorogenic substrate (Z-Gly-Gly-Arg-7-amino-4-methylcoumarin) and comparing it with a constant known thrombin activity in a parallel nonclotting sample. This study compared the concentration-dependent effects of different factor IIa inhibitors on the ETP. In accordance with a theoretical prediction, the monovalent factor IIa inhibitors melagatran and argatroban reduced peak thrombin concentrations without a marked effect on the lag time of thrombin generation. However, both bivalent factor IIa inhibitors lepirudin and bivalirudin markedly prolonged the lag time of thrombin generation and thus behaved like "super" factor Xa inhibitors according to the theoretical model. These findings have important consequences for therapeutic drug monitoring using thrombin generation assays. For monitoring of hirudins, the lag time of thrombin generation seems to be a very sensitive parameter. In contrast, for monitoring of argatroban, the evaluation of the ETP seems to be useful.

Thrombin generation testing in routine clinical practice: are we there yet?

Thrombin is the central enzyme in the coagulation cascade. Estimation of an individual's potential to generate thrombin may correlate more closely with a hyper- or hypo-coagulable phenotype, compared to traditional coagulation tests. The possible correlation and recent technical advances in thrombin generation measurement has caused a significant interest in the method and the development of commercial assays. Several variations of the assay exist depending on the defect to be investigated. Fluorogenic thrombin generation assays have acceptable intra-laboratory variation but a higher inter-laboratory variation. Variation in preanalytical variables makes comparisons between studies difficult. Thrombin generation is highly variable between individuals and there are suggestions that this may allow individualized treatment based on global haemostatic response in patients with bleeding disorders or on anticoagulant therapy. In patients with thrombotic disorders it may be possible to identify those at higher risk of recurrent thrombosis. For both scenarios, however, data from large prospective studies are lacking or inconclusive and a good relationship between thrombin generation and phenotype remains to be established. Further standardization of the assay is needed before large multicentre studies can be conducted and until then thrombin generation in routine clinical practice is not yet a reality.

Heparin-induced thrombocytopenia: a stoichiometry-based model to explain the differing immunogenicities of unfractionated heparin, low-molecular-weight heparin, and fondaparinux in different clinical settings

INTRODUCTION

Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating antibodies that recognize platelet factor 4 (PF4)/heparin complexes. The frequency of HIT is highly variable in different clinical settings, and is more frequent with unfractionated heparin (UFH) than with low-molecular-weight heparin (LMWH), despite the in vitro observation that HIT antibodies activate platelets similarly well with LMWH as with UFH. An important difference between UFH, LMWH, and fondaparinux is their widely differing plasma concentrations. We aimed to provide a model that included anticoagulant concentrations and PF4 availability as risk factors influencing the anti-PF4/heparin immune response.

MATERIALS AND METHODS

By photon correlation spectroscopy we determined the concentrations at which UFH, LMWH, and fondaparinux form complexes optimally with PF4. Plasma concentrations of UFH and LMWH were calculated based on ex vivo pharmacokinetic data, with information on fondaparinux and PF4 concentrations taken from the literature.

RESULTS AND CONCLUSIONS

The main features of our model are: optimal complex formation occurs at prophylactic-dose UFH and high PF4 levels, whereas therapeutic-dose LMWH concentrations are too high for optimal complex formation; in contrast, concentrations of fondaparinux are usually below the optimal stoichiometric range. Thus, immunization should occur more often in situations with major rather than minor platelet activation, and--for a given degree of platelet activation (PF4 availability)--as: prophylactic-dose UFH>therapeutic-dose UFH>prophylactic-dose LMWH, fondaparinux>therapeutic-dose LMWH. Our model provides a framework for explaining empirical observations that LMWH induces less anti-PF4/heparin antibodies than does UFH, and that anti-PF4/heparin antibodies are more often found in patients undergoing major surgery than in medical patients.

Recollections on thrombin generation

Against an autobiographic background, a historical sketch is given of the development of the technique of thrombin generation, from subsampling to duly calibrated continuous measurement with fluorogenic substrates. Its application to various problems in the pathophysiology of hemostasis and thrombosis is discussed.

[Stereophotography of the ocular fundus. 2. Observation method]

Traditional anticoagulant agents such as vitamin K antagonists (VKAs), unfractionated heparin (UFH), low molecular weight heparins (LMWHs) and fondaparinux have been widely used in the prevention and treatment of thromboembolic diseases. However, these agents are associated with limitations, such as the need for regular coagulation monitoring (VKAs and UFH) or a parenteral route of administration (UFH, LMWHs and fondaparinux).

Several non-VKA oral anticoagulants (NOACs) are now widely used in the prevention and treatment of thromboembolic diseases and in stroke prevention in non-valvular atrial fibrillation. Unlike VKAs, NOACs exhibit predictable pharmacokinetics and pharmacodynamics. They are therefore usually given at fixed doses without routine coagulation monitoring. However, in certain patient populations or special clinical circumstances, measurement of drug exposure may be useful, such as in suspected overdose, in patients experiencing a hemorrhagic or thromboembolic event during the treatment’s period, in those with acute renal failure, in patients who require urgent surgery or in case of an invasive procedure. This article aims at providing guidance on laboratory testing of classic anticoagulants and NOACs.