Is laboratory monitoring of low-molecular-weight heparin therapy necessary? Yes

Finding individualised treatment in obese needing enoxaparin (FIT ONE): a multicentre study of therapeutic enoxaparin and the role of anti-factor Xa monitoring

Enoxaparin is dosed according to actual body weight in treatment of arterial and venous thrombosis. Due to its hydrophilic nature, it distributes according to lean body mass which may be problematic when dosing obese patients as this may increase the risk of bleeding events in this population. The aim was to evaluate current therapeutic enoxaparin dosing strategies, including Antifactor Xa (AFXa) level monitoring, in obese patients and to identify factors that contribute to treatment failure and excess anticoagulation. A retrospective cohort study was conducted reviewing patients administered therapeutic enoxaparin between May 2020 and April 2021. Data were collected on patient characteristics, enoxaparin therapy, AFXa monitoring, and outcomes. Regression models were constructed to assess variables of interest to estimate any association with AFXa levels. In total 762 patients were included in the analysis. The mean initial weight-based dose was 0.95 mg/kg twice daily (SD: ± 0.12, IQR 0.92-1.01) and 1.04 mg/kg once daily (SD: ± 0.26, IQR 0.93-1.12) and 14.4% of patients had AFXa monitoring. Treatment failure was experienced by 2.2%, 5% experienced bleeding. There was no association between the mean actual milligram per kilogram weight-based twice daily doses and subtherapeutic, therapeutic and supratherapeutic AFXa levels (P = 0.135). Obesity was not included in the final regression models due to lack of significance. At a mean therapeutic enoxaparin dose of 0.95 mg/kg twice daily and 1.04 mg/kg once daily no excess in treatment failure or bleeding events were observed in obese patients compared to the product information. Obesity was not an independent variable that affected the achievement of target AFXa levels.

Comparison of enoxaparin 40 mg versus 60 mg dosage for venous thromboprophylaxis in patients undergoing bariatric surgery: A randomized controlled trial

BACKGROUND

Venous thromboembolism (VTE) is a common cause of morbidity and mortality after bariatric surgery. Morbid obesity is an independent risk factor for VTE, with goals of prophylactic anti-factor Xa levels within 0.2-0.5 IU/mL. The recommended dosing regimen of enoxaparin for VTE prophylaxis in patients with morbid obesity is lacking in available guidelines.

OBJECTIVES

To evaluate the achieving prophylactic anti-factor Xa levels with different dosages of enoxaparin for morbid obesity patients.

SETTING

We conducted a study at Chulalongkorn Bariatric and Metabolic Institute, King Chulalongkorn Memorial Hospital.

METHODS

We conducted a randomized controlled trial comparing anti-factor Xa levels 4 h after the administration of enoxaparin. All recruited patients randomly received 40 mg or 60 mg of enoxaparin 12 h before the operation. Blood specimens were collected 4 h after the administration of enoxaparin.

RESULTS

In total, 56 patients who presented between April 2019 and March 2020 at King Chulalongkorn Memorial Hospital were recruited. Of these patients, 28 received 40 mg and 28 received 60 mg of enoxaparin. In both groups, the rates of achieving target levels were 53.57% and 78.57%, respectively (p-value = 0.048). The mean anti-factor Xa levels were 0.19 IU/mL ± 0.06 IU/mL and 0.28 and 0.28 ± 0.10 IU/mL, respectively (p < 0.001). No significant difference was found in the estimated blood loss between the groups. No patient obtained anti-factor Xa levels exceeding 0.5 IU/mL. In both groups, no symptomatic VTE occurred.

CONCLUSIONS

A 60 mg of enoxaparin regimen achieved more prophylactic anti-factor Xa levels than 40 mg in obese patients undergoing bariatric surgery without any adverse events.

An Overview of Heparin Monitoring with the Anti-Xa Assay

Heparin remains a critical therapy in hospitalized patients requiring anticoagulation. Unfractionated heparin (UFH) mediates its therapeutic effect by binding to antithrombin (AT) and inhibiting thrombin and FXa, as well as other serine proteases. Because of its complex pharmacokinetics, monitoring UFH therapy is required, which is usually achieved with either the activated partial thromboplastin time (APTT) or the anti-factor Xa (anti-Xa) assay. Low molecular weight heparin (LMWH) is fast replacing UFH, as it has a more predictable response, negating the need for routine monitoring in most cases. When required, the anti-Xa assay is used for monitoring of LMWH. The APTT has many notable limitations when used for heparin therapeutic monitoring, including biologic, preanalytical, and analytical issues. With its increasing availability, the anti-Xa assay is appealing as it is less affected by patient factors (e.g., acute-phase reactants, lupus anticoagulants, consumptive coagulopathies), known to interfere with the APTT. The anti-Xa assay has shown additional benefits, such as faster time to achieve therapeutic levels, more consistent therapeutic levels, less dose adjustments, and, overall, less tests performed during therapy. However, poor interlaboratory agreement has been observed among anti-Xa reagents, highlighting that further work needs to be done to standardize this assay for use in patient heparin monitoring.

Porous Polymers as Universal Reversal Agents for Heparin Anticoagulants through an Inclusion-Sequestration Mechanism

Heparins are widely used anticoagulants for surgical procedures and extracorporeal therapies. However, all of them have bleeding risks. Protamine sulfate, the only clinically approved antidote for unfractionated heparin (UFH), has adverse effects. Moreover, protamine can only partially neutralize low-molecular-weight heparins (LMWHs) and is not effective for fondaparinux. Here, an inclusion-sequestration strategy for efficient neutralization of heparin anticoagulants by cationic porous supramolecular organic frameworks (SOFs) and porous organic polymers (POPs) is reported. Isothermal titration calorimetric and fluorescence experiments show strong binding affinities of these porous polymers toward heparins, whereas dynamic light scattering and zeta potential analysis confirm that the heparin sequences are adsorbed into the interior of the porous hosts. Activated partial thromboplastin time, anti-FXa, and thromboelastography assays indicate that their neutralization efficacies are higher than or as high as that of protamine for UFH and generally superior to protamine for LMWHs and fondaparinux, which is further confirmed by tail-transection model in mice and ex vivo aPTT or anti-FXa analysis in rats. Acute toxicity evaluations reveal that one of the SOFs displays outstanding biocompatibility. This work suggests that porous polymers can supply safe and rapid reversal of clinically used heparins, as protamine surrogates, providing an improved approach for their neutralization.

Quality performance for indirect Xa inhibitor monitoring in patients using international external quality data

Objectives Chromogenic anti-activated factor X (FXa) assays are currently the "gold standard" for monitoring indirect anticoagulants. However, anti-FXa has been shown to vary according to the choice of reagents. In the present study, the performance of anti-FXa measurement was evaluated in order to gain more insight into the clinical applications. Furthermore, the longitudinal coefficient of variation (CV) was studied to investigate whether there is improvement over time. Methods Laboratory tests results were evaluated for samples spiked with unfractionated heparin (UFH), low-molecular-weight-heparin (LMWH), fondaparinux and danaparoid sodium. External quality assessment (EQA) data from multiple years were used from more than 100 laboratories. Results Comparison of the results for all methods showed significant differences in measured values between the frequently used methods (ANOVA: p < 0.001). The largest differences were observed for LMWH and UFH measurements. These differences may be caused by differences in method composition, such as the addition of dextran sulphate. Substantial interlaboratory variation in anti-FXa monitoring was observed for all parameters, particularly at low concentrations. Our results showed that below 0.35 IU/mL, the CVs for UFH and LMWH increase dramatically and results below this limit should be used with caution. Conclusions Our study demonstrates that the choice of the anti-FXa method is particularly important for UFH and LMWH measurement. The variation in measurements may have an effect on clinical implications, such as therapeutic ranges. Furthermore, the longitudinal EQA data demonstrated a constant performance and, in at least 50% of the cases, improvement in the CV% of the anti-Xa results over time.

Antithrombotic and Antiplatelet Drug Toxicity

Anticoagulant and antiplatelet drugs target a specific portion of the coagulation cascade or the platelet activation and aggregation pathway. The primary toxicity associated with these agents is hemorrhage. Understanding the pharmacology of these drugs allows the treating clinician to choose the correct antidotal therapy. Reversal agents exist for some of these drugs; however, not all have proven patient-centered outcomes. The anticoagulants covered in this review are vitamin K antagonists, heparins, fondaparinux, hirudin derivatives, argatroban, oral factor Xa antagonists, and dabigatran. The antiplatelet agents reviewed are aspirin, adenosine diphosphate antagonists, dipyridamole, and glycoprotein IIb/IIIa antagonists. Additional notable toxicities are also reviewed.

Anti-Xa Monitoring of Low-Molecular-Weight Heparin during Pregnancy: A Systematic Review

Low-molecular-weight heparin (LMWH) is commonly used for preventing or treating venous thromboembolic disease (VTE) during pregnancy. The physiological changes in maternal metabolism have led to discussions on optimal LMWH dosing strategy and possible need for monitoring. The aim of this systematic review is to summarize and discuss whether LMWH dose adjustment according to anti-Xa provides superior effectiveness and safety compared with weight adjusted or fixed dosed LMWH in pregnant women. A systematic literature search was performed in PubMed, Embase, and Scopus on September 26, 2020. The study is reported according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Effectiveness was defined as episodes of thrombosis and safety as bleeding episodes. In total, 33 studies were included: 4 randomized controlled studies and 29 cohort studies. Prophylactic dosing strategies employing weight dosed, fixed dosed, or anti-Xa adjusted LMWH dosing performed equal in effectiveness and safety. In pregnant women with VTE or high thromboembolic risk, therapeutic weight-adjusted LMWH and weight plus anti-Xa-adjusted LMWH provided equal results in terms of effectiveness and safety. Pregnant women with mechanical heart valves (MHVs) received therapeutic anti-Xa-adjusted LMWH with four out of seven studies presenting mean peak anti-Xa within target ranges. Still, pregnant women with MHV experienced both thrombosis and bleeding with anti-Xa in target. Based on the results of this systematic review, current evidence does not support the need for anti-Xa monitoring when using LMWH as thromboprophylaxis or treatment during pregnancy. Nonetheless, the need for anti-Xa monitoring in pregnant women with MHV may need further scrutiny.

Current opinion and emerging trends on the treatment, diagnosis, and prevention of pregnancy-associated venous thromboembolic disease: a review

Pregnancy associated venous thromboembolism (PA-VTE) is a leading cause of maternal morbidity and mortality worldwide. Despite the availability of international guidance on the prevention, diagnosis and treatment, practice differs between countries and clinical institutions. The evidence base in this area is limited due to the vulnerable population who are affected, with the majority of guidelines deriving their recommendations from experience in surgical and medical venous thromboembolic disease. This review includes best evidence in PA-VTE management, highlighting specific literature which supports current diagnosis, prevention, and treatment strategies. Additionally, we hope to demonstrate emerging trends in the field through discussion of ongoing trials designed to progress towards evidence-based practice in the context of PA-VTE.

Monitoring anti-Xa levels in patients with cancer-associated venous thromboembolism treated with bemiparin

OBJECTIVE

To analyze the relationship between therapeutic (weight-adjusted) dose of bemiparin and anti-Xa activity in patients with venous thromboembolism (VTE) and cancer in comparison with a cohort of patients with VTE without cancer, and its relationship with outcomes.

MATERIALS AND METHODS

This is a prospective cohort study that comprised a cohort of patients with cancer-associated VTE and a cohort of non-cancer patients with VTE, all of them treated with bemiparin. The ethics committee approved the study and informed consent was obtained from the patients.

RESULTS

One hundred patients were included (52 with cancer and 48 without cancer), with a median follow-up of 9.8 months. Mean anti-Xa activity was 0.89 (± 0.33) UI/mL in oncological patients and 0.83 (± 0.30) UI/mL in non-cancer patients (mean difference - 0.05 95% CI - 0.18; 0.06). A multiple linear regression model showed that anti-Xa peak was associated with the dose/kg independently of possible confounding variables (presence of cancer, age, sex and eGFR-estimated Glomerular Filtration Rate), in a way that for every 1 UI of dose/kg increase, the anti-Xa peak activity increased 0.006 UI/mL (95% CI 0.003; 0.009) (p < 0.001). The predictive capacity of anti-Xa peak in the oncology cohort showed an area under the ROC curve of 0.46 (95% CI 0.24-0.68), 0.70 (95% CI 0.49-0.91) and 0.74 (95% CI 0.44-0.94) for death, first bleeding and recurrence of VTE, respectively, and none was statistically significant.

CONCLUSION

In patients with venous thromboembolism treated with bemiparin, anti-Xa levels were not influenced by the presence of cancer.

Clinical features and treatment results in preterm infants with intracardiac thrombus

INTRODUCTION

Thrombus incidence is higher among neonates, especially in preterm infants, due to the associated additional risk factors.

MATERIALS AND METHODS

The medical recordings of premature infants who had been diagnosed as having intracardiac thrombus between January 2016 and January 2019 were evaluated retrospectively. We use recombinant tissue plasminogen activator when the thrombus is relatively large compared to left atrium, pedunculated, mobile, or snake shaped.

RESULTS

A total of 13 premature patients were diagnosed as having intracardiac thrombus during the 3-year period. All were diagnosed during echocardiographic studies. Low molecular weight heparin was administered in four patients. In three, recombinant tissue plasminogen activator was started with low dose (0.01 mg/kg/h) and increased gradually to 0.06 mg/kg/h. In three, recombinant tissue plasminogen activators were started with standard dose (0.5 mg/kg/h). In one recombinant tissue, plasminogen activator was started with low dose (0.01 mg/kg/h) and increased to standard dose. Two patients died before treatment, three patients died during treatment, follow-up was not available for two patients, and thrombus completely resolved in six patients.

DISCUSSION

In preterm babies with risk factors, intracardiac thrombus should be kept in mind during all echocardiographic studies. In our patients, low and standard dose regimens were used, and the treatment results were similar.

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.

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.

Reduced dosing of enoxaparin for venous thromboembolism in overweight and obese adolescents: a single institution retrospective review

BACKGROUND

The global obesity epidemic has created new challenges, including venous thromboembolisms (VTE) in obese adolescents. The data on whether to reduce the dose of low-molecular heparin in obese adults is conflicting, and information on adolescent patients is scarce.

OBJECTIVES

Our primary goal was to describe dosing, anti-Xa levels, and outcomes of overweight and obese adolescents who received reduced doses of enoxaparin at the initiation of therapy. The secondary goal was to compare their outcomes to overweight and obese adolescents who received standard 1 mg/kg dosing to determine if future trials for dose reduction are warranted.

PATIENTS/METHODS

We performed a retrospective cohort study of overweight and obese patients between the ages of 12 and 18 years old diagnosed with VTE who were treated with reduced dosing (RD) of enoxaparin, comparing their dosing, anti-Xa levels, and outcomes to overweight and obese adolescents who received standard dosing (SD).

RESULTS

RD patients (n=19) achieved therapeutic mean initial anti-Xa levels that were similar to SD patients (n=11). Of the RD patients, 53% did not require dose adjustments during treatment. Two RD patients had thrombus progression. A total of 25 patients ultimately completed therapy with RD.

CONCLUSIONS

Future trials are warranted to evaluate the efficacy and safety of reduced dosing of enoxaparin to treat overweight and obese adolescents with VTE.

Adjustment of therapeutic LMWH to achieve specific target anti-FXa activity does not affect outcomes in pregnant patients with venous thromboembolism

Venous thromboembolism (VTE) remains a leading cause of maternal morbidity and mortality in the developed world. Low molecular weight heparins (LMWH) are routinely used to provide therapeutic anticoagulation during pregnancy for women with VTE, with measurement of plasma anti-FXa activity used to guide dosing in certain patient groups. There is limited evidence to support the use of anti-FXa monitoring in pregnant patients. This study seeks to ascertain whether anti-FXa monitoring of pregnant patients with VTE influences patient outcomes. We performed a single-centre case series including two consecutive groups of pregnant patients treated with LMWH for VTE sustained in the index pregnancy with and without monitoring of anti-FXa levels. 35,394 patients delivered during the study period in a large urban stand-alone maternity hospital, with 26 cases of VTE eligible for inclusion. There was no significant difference between the two groups in any clinical outcome; including maternal blood loss at delivery, recurrent thromboembolic events or rates of planned delivery. These data provide clinical evidence to support current international guideline recommendations that measurement of plasma anti-FXa activity in the majority of patients receiving therapeutic-intensity antenatal LMWH is not warranted.

A fluorescent probe assay (Heparin Red) for direct detection of heparins in human plasma

Heparins are widely used anticoagulant drugs. The current monitoring practice for heparin in plasma, such as the chromogenic anti-factor Xa assay, relies on heparin-triggered activation of antithrombin, an inhibitor of coagulation proteases. Such assays are not applicable to the detection of non-anticoagulant heparins, an emerging class of drug candidates for therapeutic applications unrelated to anticlotting activity. This study describes the application of a commercially available fluorescent probe assay (Heparin Red) for the direct and sensitive detection of the "chemical" heparin in plasma, independent of any anticoagulant activity. The quantification range is about 0-5 μg/mL for both unfractionated heparin (corresponding to 0-1 IU/mL) and the low molecular weight heparin enoxaparin. The Heparin Red assay is of particular value for the quantification of non-anticoagulant heparins, as exemplified by the low molecular weight heparin derivative tafoxiparin and a N-desulfated-N-reacetylated heparin. Heparin octa- and decasaccharides are also detected. Graphical abstract Heparin quantification in plasma by mixing the sample with the Heparin Red reagent and fluorescence readout.

Extended enoxaparin monotherapy for acute symptomatic pulmonary embolism

We investigated the efficacy and safety of extended enoxaparin monotherapy in symptomatic patients with acute pulmonary embolism (PE). We randomized 40 patients in a 1:1 allocation to enoxaparin monotherapy (1 mg/kg twice daily for 10-18 days, and then 1.5 mg/kg once daily until day 90) ( n = 20) or to enoxaparin 1.0 mg/kg twice daily as a bridge to warfarin with a target international normalized ratio of 2.0-3.0 for 90 days (at least 10 doses of enoxaparin overlapping with warfarin for at least 4 days) ( n = 20). All patients underwent echocardiography, cardiac troponin I (TnI), and brain natriuretic peptide testing to identify patients with an increased likelihood of adverse clinical outcomes. The end-points were newly diagnosed deep venous thrombosis (DVT) or PE and bleeding events through day 90. In 15 patients on extended enoxaparin therapy, we used repeated measure analysis of variance (ANOVA) to investigate differences in anti-Xa levels obtained at 2, 4, 8 and 12 weeks. The patients’ mean age was 52 ± 17 years; the most common comorbidities were obesity (58%), hypertension (30%), concomitant DVT (30%) and cancer (15%). Twelve (30%) patients had elevated cardiac TnI >0.1 mg/l and 11 (28%) had moderate or severe right ventricular dysfunction on echocardiography. Ten (25%) patients received thrombolysis with a continuous infusion of 100 mg alteplase prior to randomization. During a 90-day follow-up, one patient from the enoxaparin monotherapy group suffered symptomatic distal DVT; one from the warfarin group had recurrent symptomatic PE (p= 1.0). None of the study patients had major hemorrhage; two warfarin group patients had minor bleeding compared with none in the enoxaparin monotherapy group (p= 0.49). Repeated measure ANOVA did not reveal significant differences in anti-Xa levels over time (p= 0.217). In patients with acute symptomatic PE, extended enoxaparin monotherapy is feasible and warrants further investigation in a large clinical trial.

The Anti-Factor Xa Range For Low Molecular Weight Heparin Thromboprophylaxis

Low molecular weight heparins (LMWHs) are now the mainstay option in the prevention and treatment of venous thromboembolism. In some patients receiving therapeutic doses of LMWH, activity can be measured by quantifying the presence of Anti-factor Xa (AFXa) for dose adjustment. However, currently there are no guidelines for LMWH monitoring in patients on thromboprophylactic, doses, despite certain patient populations may be at risk of suboptimal dosing. This review found that while the AFXa ranges for therapeutic levels of LMWHs are relatively well defined in the literature, prophylactic ranges are much less clear, thus making it difficult to interpret current research data. From the studies published to date, we concluded that a reasonable AFXa target range for LMWH deep venous thromboses prophylaxis might be 0.2-0.5 IU/mL.

Anticoagulant Treatment of Deep Vein Thrombosis and Pulmonary Embolism: The Present State of the Art

Venous thromboembolism (VTE), a disease entity comprising deep vein thrombosis (DVT) and pulmonary embolism (PE), is a frequent and potentially life-threatening event. To date different agents are available for the effective treatment of acute VTE and the prevention of recurrence. For several years, the standard of care was the subcutaneous application of a low molecular weight heparin (LMWH) or fondaparinux, followed by a vitamin K antagonist (VKA). The so-called direct oral anticoagulants (DOAC) were introduced rather recently in clinical practice for the treatment of VTE. DOAC seem to have a favorable risk-benefit profile compared to VKA. Moreover, DOAC significantly simplify VTE treatment because they are administered in fixed doses and no routine monitoring is needed. Patients with objectively diagnosed DVT or PE should receive therapeutic anticoagulation for a minimum of 3 months. Whether a patient ought to receive extended treatment needs to be evaluated on an individual basis, depending mainly on risk factors determined by characteristics of the thrombotic event and patient-related factors. In specific patient groups (e.g., pregnant women, cancer patients, and elderly patients), treatment of VTE is more challenging than that in the general population and additional issues need to be considered in those patients. The aim of this review is to give an overview of the currently available treatment modalities of acute VTE and secondary prophylaxis. In particular, specific aspects regarding the initiation of VTE treatment, duration of anticoagulation, and specific patient groups will be discussed.

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.

Pathology consultation on anticoagulation monitoring: factor X-related assays

OBJECTIVES

To review various anticoagulation therapies and related laboratory monitoring issues, with a focus on factor X-related chromogenic assays.

METHODS

A case-based approach is used to review pertinent published literatures and product inserts of anticoagulation drugs and to look back on clinical use of factor X-related chromogenic assays.

RESULTS

The number of anticoagulants available to clinicians has increased greatly in the past decade. Whether and how these anticoagulants should be monitored are areas of uncertainty for clinicians, which can lead to misuse of laboratory assays and suboptimal patient management. Factor X-related assays are of particular concern because of the similar and often confusing test names. Based on a common clinical case scenario and literature review regarding anticoagulant monitoring, an up-to-date discussion and review of the various factor X-related assays are provided, focusing on the differences in test designs and clinical utilities between the chromogenic anti-Xa and chromogenic factor X activity assays.

CONCLUSIONS

Anticoagulation therapy and related laboratory monitoring are rapidly evolving areas of clinical practices. A good knowledge of relevant laboratory assays and their clinical applications is necessary to help optimize patient care.

Non-therapeutic anti-Xa levels in medical patients receiving anticoagulant therapy with enoxaparin

INTRODUCTION

Anticoagulant activity of enoxaparin is not routinely monitored even when previous studies have shown a high pharmacological variability. The aim of this study is to determine the prevalence of non-therapeutic anti-Xa levels among medical patients using enoxaparin as anticoagulant therapy and to point out potential risk factors related to the risk of having a sub-therapeutic level.

MATERIALS AND METHODS

Anti-Xa levels were measured in a cohort of sixty patients with medical indication for enoxaparin. Patients were categorized according to anti-Xa levels as follows: suboptimal anticoagulation (<0.5 IU/ml), optimal anticoagulation (between 0.5 and 1.2 IU/ml) or overanticoagulated (>1.2 IU/ml). Demographic and clinical variables and the use of concomitant medications were described for each group. Univariate and multivariate analysis were performed to assess the relationship between sub-optimal anticoagulation and potential predictive variables. A linear regression analysis was done to assess the relationship between anti-Xa activity, age, weight, body mass index, administered dose/weight and creatinine clearance.

RESULTS

The mean anti-Xa activity was 0.71±0.32 UI/ml. Thirty one percent of patients had anti-Xa levels out of the therapeutic range, most of them (twenty-eight percent of total population) with a sub-therapeutic level. None of the variables were associated with the risk of a sub-therapeutic anti-Xa level.

CONCLUSION

Almost one third of patients receiving enoxaparin had anti-Xa levels out of the therapeutic range. We need more studies to determine the clinical relevance of these findings.

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.

Pulmonary embolism

Pulmonary embolism (PE) remains one of the most challenging medical diseases in the emergency department. PE is a potentially life threatening diagnosis that is seen in patients with chest pain and/or dyspnea but can span the clinical spectrum of medical presentations. In addition, it does not have any particular clinical feature, laboratory test, or diagnostic modality that can independently and confidently exclude its possibility. This article offers a review of PE in the emergency department. It emphasizes the appropriate determination of pretest probability, the approach to diagnosis and management, and special considerations related to pregnancy and radiation exposure.

Anti-Xa Levels 4 h After Subcutaneous Administration of 5,700 IU Nadroparin Strongly Correlate with Lean Body Weight in Morbidly Obese Patients

BACKGROUND: Morbidly obese patients (BMI > 40 kg/m(2)) are at increased risk for venous thromboembolism, especially after surgery. Despite limited evidence, morbidly obese patients are often administered a double dose of nadroparin for thromboprophylaxis compared to non-obese patients. The aim of this study was to evaluate the influence of different body size descriptors on anti-Xa levels after a double dose of nadroparin (5,700 IU) in morbidly obese patients. METHODS: In 27 morbidly obese patients with a mean total body weight of 148 kg (range 107-260 kg), anti-Xa levels were determined peri-operatively until 24 h after administration of a subcutaneous dose of 5,700 IU of nadroparin. RESULTS: Anti-Xa level 4 h after administration (A(4h), mean 0.22 ± 0.07 IU/ml) negatively correlated strongly with lean body weight (r = -0.66 (p < 0.001)) and moderately with total body weight (r = -0.56 (p = 0.003)) and did not correlate with body mass index (r = -0.26 (p = 0.187)). The area under the anti-Xa level-time curve from 0 to 24 h (AUA(0-24h), mean 2.80 ± 0.97 h IU/ml) correlated with lean body weight (r = -0.63 (p = 0.007)), but did not correlate with total body weight (r = -0.44 (p = 0.075)) or body mass index (r = -0.10 (p = 0.709)). CONCLUCIONS: Following a subcutaneous dose of nadroparin 5,700 IU, A(4h) and AUA(0-24h) were found to negatively correlate strongly with lean body weight. From these results, individualized dosing of nadroparin based on lean body weight should be considered in morbidly obese patients.

Pharmacokinetics of the low molecular weight heparin dalteparin in cats

Low molecular weight heparin (LMWH) is used as an anticoagulant in cats although only limited pharmacokinetic data are available in this species. The aim of the present study was to establish the pharmacokinetics of dalteparin in cats based on anti-FXa heparin activities. Groups of clinically healthy cats (six animals per treatment) received individual LMWH injections at three different doses intravenously (IV) (25, 50, 100 anti-factor Xa international units [IU anti-FXa]/kg) or subcutaneously (SC) (50, 100, 200 IU anti-FXa/kg). Blood samples were collected before and at various times after injection. Anti-FXa activity was measured with a chromogenic substrate test. Following IV injection, maximum plasma heparin activities (C(max)) were 0.67 ± 0.14, 1.44 ± 0.22 and 2.87 ± 0.38 IU anti-FXa/mL, respectively. The calculated mean half-life (t(½)) was between 39 and 57 min and was not significantly dose-dependent (P=0.139). The volume of distribution (35-39 mL/kg) was almost equivalent to the plasma volume. After SC injection, C(max) values of 0.41 ± 0.10, 0.86 ± 0.17 or 1.91 ± 0.16 IU anti-FXa/mL, respectively, were calculated at 91-110 min post-injection. The t(½) values were between 106 and 122 min and were not significantly influenced by dose (P=0.784). The bioavailability after SC injection was approximately 100%. The high bioavailability of the SC administered LMWH dalteparin in cats was consistent with other species and indicated predictable blood levels. However, the comparatively short t(½) may indicate the necessity of multiple daily injections, which should be verified in clinical trials.

No accumulation of the peak anti-factor Xa activity of tinzaparin in elderly patients with moderate-to-severe renal impairment: the IRIS substudy

BACKGROUND

In the elderly, concerns have been raised regarding the risk of accumulation of low molecular weight heparins, owing to their renal elimination. Although data exist for tinzaparin, they are observational.

OBJECTIVES

To assess whether: (i) there was an accumulation of anti-factor Xa activity; and (ii) there was any relationship between anti-FXa activity and age, weight, creatinine clearance or clinical outcomes in patients with moderate-to-severe renal impairment receiving tinzaparin (175 IU kg(-1) per 24 h) for acute venous thromboembolism.

METHODS

In 38 centers participating in the Innohep in Renal Insufficiency Study (IRIS), peak plasma anti-FXa activity was measured on day 2/day 3 and on day 5 or at visit S (VS) (end of tinzaparin treatment). There was considered to be absence of accumulation if the 90% confidence interval (CI) of the (anti-FXa day 5/VS)/(anti-FXa day 2/3) ratio did not exceed the predefined limit of 1.25.

RESULTS

Eighty-seven patients, with a mean age of 83 ± 5 years (range: 75-99 years) and a mean creatinine clearance (CrCl) of 40.8 mL min(-1) , 24.1% of whom had severe renal impairment, were included. The mean duration of tinzaparin treatment was 8.4 days. No significant accumulation was detected: the mean accumulation ratio was 1.06 (90% CI 1.01-1.11). There was no correlation between the accumulation ratio and age, weight, or CrCl. The mean anti-FXa activity did not differ significantly between the eight patients who experienced clinically relevant bleeding and those who did not.

CONCLUSIONS

No accumulation of anti-FXa activity was observed in elderly patients with renal impairment receiving therapeutic doses of tinzaparin, suggesting that there is no need for systematic anti-FXa monitoring in these patients. The high proportion of high molecular weight moieties in tinzaparin may account for its reduced dependence on renal elimination.

Prevention of venous thromboembolism in obesity

Venous thromboembolism (VTE) is a significant cause of morbidity and mortality in hospitalized patients. Where appropriate, evidence-based methods of prophylaxis are implemented and the burden of VTE can be reduced substantially. Obesity, including morbid obesity, is associated with a high risk of VTE and, unfortunately, fixed doses of US FDA-approved anticoagulant regimens, including unfractionated heparins, low-molecular-weight heparins and factor Xa inhibitors, may not provide optimal VTE prophylaxis in these patients. Although the data are still limited, a rapidly growing body of literature and cumulative evidence suggests that anticoagulant dose adjustments in morbidly obese patients may optimize pharmacodynamic activity and reduce VTE risk. With the prevalence of morbid obesity continuing to rise, more high-quality clinical data are needed to better understand the pathobiology of VTE in obesity and provide effective, yet safe, prevention strategies.

An Official ATS/ERS/ESICM/SCCM/SRLF Statement: Prevention and Management of Acute Renal Failure in the ICU Patient: an international consensus conference in intensive care medicine

OBJECTIVES

To address the issues of Prevention and Management of Acute Renal Failure in the ICU Patient, using the format of an International Consensus Conference.

METHODS AND QUESTIONS

Five main questions formulated by scientific advisors were addressed by experts during a 2-day symposium and a Jury summarized the available evidence: (1) Identification and definition of acute kidney insufficiency (AKI), this terminology being selected by the Jury; (2) Prevention of AKI during routine ICU Care; (3) Prevention in specific diseases, including liver failure, lung Injury, cardiac surgery, tumor lysis syndrome, rhabdomyolysis and elevated intraabdominal pressure; (4) Management of AKI, including nutrition, anticoagulation, and dialysate composition; (5) Impact of renal replacement therapy on mortality and recovery.

RESULTS AND CONCLUSIONS

The Jury recommended the use of newly described definitions. AKI significantly contributes to the morbidity and mortality of critically ill patients, and adequate volume repletion is of major importance for its prevention, though correction of fluid deficit will not always prevent renal failure. Fluid resuscitation with crystalloids is effective and safe, and hyperoncotic solutions are not recommended because of their renal risk. Renal replacement therapy is a life-sustaining intervention that can provide a bridge to renal recovery; no method has proven to be superior, but careful management is essential for improving outcome.

Bleeding the system: a case of feigned enoxaparin overdose

BACKGROUND

Low-molecular-weight heparins (LMWHs) have become ubiquitously used as anticoagulants because of their comparative safety and ease of use; however they may be fatal if taken in overdose, and lack of familiarity with their pharmacology may hinder appropriate care.

OBJECTIVE

The author reports a case of feigned LMWH overdose so as to alert practitioners to this diagnostic possibility.

METHOD

This is a case report of a 49-year-old homeless man who reported a deliberate overdose of an injectable LMWH. The author reviews the mechanism of action and monitoring of LMWHs.

RESULTS

On the basis of his unusual presentation and previously documented history and medical work-up, he was ultimately diagnosed with malingering.

DISCUSSION

Feigned LMWH overdose is ideally suited to the purposes of malingering, since it represents a medical emergency that requires inpatient medical hospitalization and testing at outside laboratory facilities to verify the overdose.

[Care of acute pulmonary embolism]

Pulmonary embolism (PE) is common and potentially serious. Three stages are described: mild PE, moderate PE (associated with an ultrasound right ventricular dysfunction) and severe PE (associated with a shock). In the first category, the prognosis is highly favourable (mortality under 5%) and the initial phase of anticoagulant treatment is well documented and codified: the treatment is based on heparin therapy (non fractionated or derivatives) and oral anticoagulants. In the severe forms, fibrinolysis is indicated in addition to the heparin therapy, given the very high mortality (up to 50%). However, the optimum care of moderate PE (intermediate mortality between 10 and 15%) remains uncertain, due to the inability to demonstrate a benefits-risk ratio in favour of fibrinolysis. In addition, this entity is still poorly defined. Although cardiac ultrasound data is useful, other parameters, such as pro-BNP, provide a better identification of these forms of intermediate prognosis. Although the evaluation of the new oral and injectable anticoagulants is promising, it mainly concerns mild PE. In addition, trials are currently under way in patients with a gloomier prognosis. The purpose is to validate or invalidate the indication of classic treatments (fibrinolysis) or new treatments (optional caval filters).

No correlation between anti-factor Xa levels, low-molecular-weight heparin, and bleeding after gastric bypass

BACKGROUND

Pulmonary embolism (PE) remains a leading cause of death after Roux-en-Y gastric bypass. Currently, various regimens of low-molecular-weight heparin (LMWH) are used for perioperative deep vein thrombosis (DVT) prophylaxis. Anti-factor Xa (AFXa) has been suggested as a potential marker of LMWH activity. We have developed a perioperative prophylactic DVT regimen for our bariatric patients in which the dosage of LMWH they receive is based on their body mass index (BMI). We looked at whether AFXa levels correlated with bleeding risk.

METHODS

A retrospective, single institution review of 102 patients undergoing a gastric bypass from November 2003 to April 2004 was performed. Twelve patients received transfusions. AFXa levels were present for 7 of 12 patients requiring transfusions and 74 of 90 patients not requiring transfusions. The average AFXa level for each group was compared.

RESULTS

The transfusion rate for the group was 11.7%, with an average of 2.6 units of blood given (SD 1.2). There was no statistical difference between the average AFXa value for transfused and nontransfused patients (0.13 +/- 0.08 vs. 0.16 +/- 0.19, P = .7).

CONCLUSION

AFXa levels do not appear to correlate with bleeding risk in patients receiving LMWH prophylaxis following gastric bypass. Determining such risk seems to require another marker.