Comparing Direct Thrombin Inhibitors Using aPTT, Ecarin Clotting Times, and Thrombin Inhibitor Management Testing

Association of Argatroban Dose With Coagulation Laboratory Test in Patients on Extracorporeal Membrane Oxygenation: Activated Clotting Time vs Activated Partial Thromboplastin Time

BACKGROUND

Only some studies have directly compared and analyzed the roles of activated partial thromboplastin time (aPTT) and activated clotting time (ACT) in coagulation monitoring during argatroban administration.

OBJECTIVES

This study aims to assess the correlation of argatroban dose with ACT and aPTT values and to identify the optimal coagulation test for argatroban dose adjustment.

METHODS

We evaluated 55 patients on extracorporeal membrane oxygenation (ECMO) who received argatroban for more than 72 hours. The correlation between argatroban dose and aPTT and ACT values was evaluated. To compare argatroban dose and bleeding events according to liver dysfunction, the patients were divided into 2 groups based on alanine aminotransferase and total bilirubin.

RESULTS

Among the 55 patients, a total of 459 doses and coagulation tests were evaluated. The aPTT and ACT values showed a weak correlation with argatroban dose, with the Pearson correlation coefficients of 0.261 (P < 0.001) and 0.194 (P = 0.001), respectively. The agreement between the target 150 to 180 seconds for ACT and 55 to 75 seconds for aPTT was observed in 140 patients (46.1%). Twenty-four patients (43.6%) had liver dysfunction when they started argatroban. The median argatroban dose was lower in the liver dysfunction group than in the control group (0.094 mcg/kg/min vs 0.169 mcg/kg/min, P = 0.020). Difference was not observed between the 2 groups in the amount of red blood cell (0.47 vs 0.43 pack, P = 0.909) and platelet (0.60 vs 0.08 pack, P = 0.079) transfusion per day.

CONCLUSION AND RELEVANCE

A weak correlation was observed between argatroban dose and the aPTT and ACT values. However, the agreement between aPTT and ACT was only 46.1% regarding the scope of target range. Further research is necessary to determine how to assess the optimal argatroban dose for patients administered argatroban while undergoing ECMO at the intensive care unit.

In vitro Effect of Dalteparin and Argatroban on Hemostasis in Critically Ill Sepsis Patients with New-Onset Thrombocytopenia

Thrombocytopenia is common among critically ill sepsis patients, while they also hold an increased risk for thromboembolic events. Thus, the choice of anticoagulant prophylaxis for this patient population is challenging. We investigated the in vitro effect of low-molecular-weight heparin (dalteparin) and direct thrombin inhibitor (argatroban) on the hemostasis in blood from sepsis patients with new-onset thrombocytopenia. Thrombocytopenia was defined as a platelet count drop of ≥30% and/or from >100 × 10 ⁹ /L to 30 to 100 × 10 ⁹ /L within 24 hours prior to inclusion. We included five healthy individuals and ten patients. Analyses of thrombin generation (Calibrated Automated Thrombogram), thrombin-antithrombin (TAT) complex levels, prothrombin fragment 1+2 (F1+2), and rotational thromboelastometry (ROTEM) were performed. Based on dose-response relationships investigated in healthy blood, patient samples were spiked with prophylactic (0.25 IU/mL) and therapeutic (0.75 IU/mL) dalteparin and low (0.25 µg/mL) and high (0.50 µg/mL) argatroban concentrations, each with a sample without anticoagulant. In patients, the endogenous thrombin potential was markedly lower in therapeutic dalteparin samples than in samples without anticoagulant [median (range): 29 (0-388) vs. 795 (98-2121) nM × min]. In high argatroban concentration samples, thrombin lag time was longer than in samples without anticoagulant [median (range): 15.5 (10.5-20.2) versus 5.3 (2.8-7.3) min]. Dalteparin and argatroban both increased clotting time but did not affect maximum clot firmness in the ROTEM INTEM assay. Six patients had elevated TAT and eight patients had elevated F1 + 2. In conclusion, dalteparin mainly affected the amount of thrombin generated and argatroban delayed clot initiation in critically ill sepsis patients with new-onset thrombocytopenia. Neither anticoagulant affected clot strength.

Assays to Monitor Bivalirudin

Bivalirudin (Angiomax, Angiox) is a parenteral direct thrombin inhibitor (DTI) that is used for patients with heparin-induced thrombocytopenia (HIT), where heparin cannot be used due to the risk of thrombosis. Bivalirudin is also licensed for use in cardiology procedures (e.g., percutaneous transluminal coronary angioplasty; PTCA). Bivalirudin is a synthetic analogue of hirudin found in the saliva of the medicinal leech and has a relatively short half-life of ~25 min. Several assays can be used to monitor bivalirudin; these include the activated partial thromboplastin time (APTT), activated clotting time (ACT), ecarin clotting time (ECT), an ecarin-based chromogenic assay, thrombin time (TT), the dilute TT, and the prothrombinase-induced clotting time (PiCT). Drug concentrations can also be measured using liquid chromatography tandem mass spectrometry (LC/MS) and clotting or chromogenic-based assays with specific drug calibrators and controls.

Treatment of thrombosis in KD Patients using tissue plasminogen activator: a single center study

OBJECTIVE

The most severe complication associated with giant coronary aneurysm in children with Kawasaki disease is ischemic cardiomyopathy (ICM) caused by thrombosis. Addition of tissue plasminogen activator, Alteplase, in the treatment regimen can be an efficient thrombolytic therapy, and therefore can have a significantly positive impact on patients' quality of life in long term.

METHODS

Total four male KD patients with central thromboses in coronary aneurysm were treated in Pediatric Cardiology Department of Shengjing Hospital, China Medical University, from January 2020 to August 2021. These patients received thrombolytic treatments including Alteplase once + Heparin for 1 week followed by continuous oral Warfarin + Aspirin + Clopidogrel.

RESULTS

4 young male KD patients had coronary aneurysm (CAA) complicated with total 7 occurrences of central thrombosis. These patients were given alteplase and heparin/oral Warfarin + Aspirin + Clopidogrel treatment. 9 days to 2 months later, thromboses were significantly dissolved. The treatment successfully diminished the thrombosis complication.

CONCLUSION

1. Pediatric KD patients complicated with coronary aneurysm thrombosis are prone to recurrence of thrombosis. 2.  In KD patients complicated with coronary aneurysm thrombosis, treatments described in Method can be used for treating either small thromboses formed less than 1 month with strong echo and convex lumen or large thromboses with mixed strong and weak echo. With these treatments, coronary artery blood flow can be improved or completely recovered. 3. Clinical experiences at our center in treating these KD patients suggest that Alteplase can be considered in thrombolytic treatment beyond the limitation of less than 12 h of thrombosis occurrence.

Thromboprophylaxis with argatroban in critically ill patients with sepsis: a review

During sepsis, an initial prothrombotic shift takes place, in which coagulatory acute-phase proteins are increased, while anticoagulatory factors and platelet count decrease. Further on, the fibrinolytic system becomes impaired, which contributes to disease severity. At a later stage in sepsis, coagulation factors may become depleted, and sepsis patients may shift into a hypo-coagulable state with an increased bleeding risk. During the pro-coagulatory shift, critically ill patients have an increased thrombosis risk that ranges from developing micro-thromboses that impair organ function to life-threatening thromboembolic events. Here, thrombin plays a key role in coagulation as well as in inflammation. For thromboprophylaxis, low molecular weight heparins (LMWH) and unfractionated heparins (UFHs) are recommended. Nevertheless, there are conditions such as heparin resistance or heparin-induced thrombocytopenia (HIT), wherein heparin becomes ineffective or even puts the patient at an increased prothrombotic risk. In these cases, argatroban, a direct thrombin inhibitor (DTI), might be a potential alternative anticoagulatory strategy. Yet, caution is advised with regard to dosing of argatroban especially in sepsis. Therefore, the starting dose of argatroban is recommended to be low and should be titrated to the targeted anticoagulation level and be closely monitored in the further course of treatment. The authors of this review recommend using DTIs such as argatroban as an alternative anticoagulant in critically ill patients suffering from sepsis or COVID-19 with suspected or confirmed HIT, HIT-like conditions, impaired fibrinolysis, in patients on extracorporeal circuits and patients with heparin resistance, when closely monitored.

Laboratory methods for monitoring argatroban in heparin-induced thrombocytopenia

INTRODUCTION

The Summary of Product Characteristics for the direct thrombin inhibitor argatroban states monitoring should be by activated partial thromboplastin time (APTT), with a target range of 1.5-3.0 times the patients' baseline APTT. APTT may be influenced by coagulopathies, lupus anticoagulant and raised FVIII levels. Previous studies have shown sensitivity differences of APTT reagents to argatroban. Some recent publications have favoured the use of anti-IIa methods to determine the plasma drug concentration of argatroban. This study aims to compare the anti-IIa assays: Hemoclot thrombin inhibitor assay (HTI) and Ecarin chromogenic assay (ECA) alongside the APTT.

METHODS

Residual plasma of 25 samples from 8 patients (3 with COVID-19 and HIT: n = 18, 5 with HIT: n = 7) was tested at two sites: site A: Sysmex CS5100 by HTI and APTT (Actin FS and SynthASil), and also on Stago STA Compact Max: ECA and APTT (CK Prest); and site B: Stago STA R Max 2 by ECA and APTT (Cephascreen).

RESULTS

Mean APTT ratio was 1.96 (Actin FS), 1.84 (SynthASil), 1.59 (CK Prest) and 2.48 (Cephascreen). Mean argatroban concentration by HTI was 0.60 µg/mL and by ECA was 0.65 µg/mL (site A) and 0.70 µg/mL (site B). There was a poor correlation to HTI in APTT ratios (range r²  = .0235-0.4181) with stronger correlations between ECA methods to HTI (r²  = .8998 site A, r²  = .8734 site B).

CONCLUSION

This study confirms previous publications on the unsuitability of APTT and expands this by being multisited and included APTT reagents that use mechanical clot detection. Both anti-IIa methods are more suitable.

Monitoring and Dosing of Argatroban in a Patient With Antiphospholipid Syndrome

Background: This case reports outlines argatroban dosing and necessary dose adjustments in a 56 year-old male with a past medical history of antiphospholipid syndrome and heparin-induced thrombocytopenia. Method: Argatroban was initiated as a fixed dose of 0.5 µg/kg/min with all initial aPTTs above goal. Argatroban was held for a procedure and re-initiated at 0.25 µg/kg/min. The dose was increased or decreased by 25% from the current rate based on supratherapeutic and subtherapeutic aPTTs, respectively. Results: The patient remained on argatroban for 6 total days, while achieving goal aPTT levels with no VTE or bleeding events. Conclusion: Our patient represents the first reported case of monitoring argatroban with aPTTs in an individual with APS.

DOAC-Stop in lupus anticoagulant testing: Direct oral anticoagulant interference removed in most samples

BACKGROUND

The use of direct oral anticoagulants (DOACs) is a convenient therapeutic option for patients at risk of thrombosis. DOACs interfere with clot-based testing for the identification of lupus anticoagulant antibodies (LACs) in patients with antiphospholipid syndrome (APS), a common cause of acquired thrombotic disease.

OBJECTIVES

To evaluate a commercially available reagent DOAC-Stop for the removal of DOAC interference encountered in LAC testing.

PATIENTS/METHODS

We collected a cohort of 73 test samples from patients on DOAC therapy identified at a large institutional coagulation laboratory from March to December 2019, along with samples from 40 LAC positive and negative control patients not on therapy. Samples were treated with DOAC-Stop and tested for anti-Xa activity and thrombin time for the removal of apixaban, rivaroxaban, argatroban, and dabigatran activity from patient samples. Treated and untreated samples were tested using the activated partial thromboplastin time, silica clotting time, and dilute Russell's viper venom time to evaluate the reliability and utility of DOAC-Stop.

RESULTS

DOAC-Stop markedly reduced DOAC interference from test samples (P < .05). DOAC-Stop had no effect on LAC testing in the absence of DOAC therapy, permitting the identification of all LAC positive and negative controls. DOAC-Stop removed false positives and false negatives resulting from DOAC interference and allows the identification of patients meeting criteria for the diagnosis of APS by LAC testing, as well as the detection of patients on rivaroxaban who are triple positive for APS.

CONCLUSIONS

DOAC-Stop is an effective adjunct for the clinical laboratory faced with DOAC interference in LAC testing.

Prospective Exploratory Experience With Bivalirudin Anticoagulation in Pediatric Extracorporeal Membrane Oxygenation

OBJECTIVES

Objective of this study was to determine if bivalirudin resulted in less circuit interventions than unfractionated heparin. A secondary objective was to examine associations between bivalirudin dose and partial thromboplastin time, international normalized ratio, and activated clotting time.

DESIGN

Prospective observational.

SETTING

Medical-surgical and cardiac PICUs.

PATIENTS

Neonatal and pediatric extracorporeal membrane oxygenation patients who received bivalirudin anticoagulation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Twenty extracorporeal membrane oxygenation runs in 18 patients used bivalirudin; 90% were venoarterial. Median (interquartile range) age was 4.5 months (1.6-35 mo). Thirteen patients (72%) had an underlying cardiac diagnosis. Of the 20 runs using bivalirudin, 16 (80%) were initially started on unfractionated heparin and transitioned to bivalirudin due to ongoing circuit thrombosis despite therapeutic anti-Xa levels (n = 13), ongoing circuit thrombosis with unfractionated heparin greater than or equal to 40 U/kg/hr (n = 2), or absence of increase in ACT after bolus of 100 U/kg of unfractionated heparin and escalation of unfractionated heparin infusion (n = 1). Initial bivalirudin dose ranged from 0.2 to 0.5 mg/kg/hr; no bolus doses were used. Median (range) bivalirudin dose was 0.9 mg/kg/hr (0.15-1.6 mg/kg/hr). Median (interquartile range) time on extracorporeal membrane oxygenation was 226.5 hours (150.5-393.0 hr) including 84 hours (47-335 hr) on bivalirudin. Nonparametric results are as follows: the rate of circuit intervention was significantly lower in patients on bivalirudin than on unfractionated heparin (median [interquartile range]: 0 [0-1] and 1 [1-2], respectively; Wilcoxon p = 0.0126). Bivalirudin dose was correlated to PTT (rs = 0.4760; p < 0.0001), INR (rs = 0.6833; p < 0.0001), and ACT (rs = 0.6161; p < 0.0001). Four patients had a significant bleeding complication on bivalirudin. Survival to hospital discharge was 56%.

CONCLUSIONS

Bivalirudin appears to be a viable option for systemic anticoagulation in pediatric extracorporeal membrane oxygenation patients who have failed unfractionated heparin, but questions remain namely its optimal monitoring strategy. This pilot study supports the need for larger prospective studies of bivalirudin in pediatric extracorporeal membrane oxygenation, particularly focusing on meaningful monitoring variables.

Ecarin based coagulation testing

Ecarin is derived from venom of Echis carinatus, and will activate prothrombin into meizothrombin which will then cleave fibrinogen to result in clot formation. Ecarin based testing has been described for decades, but these assays were typically restricted to reference or speciality coagulation laboratories. This test was initially described for the assessment of direct thrombin inhibitors (eg, bivalirudin lepirudin, or argatroban) and was not affected by heparins or heparinoids. Ecarin based assays were rarely used for anticoagulation monitoring until the emergence of the direct oral thrombin inhibitor dabigatran etexilate in 2010. As this test was mentioned in the prescribing information for dabigatran etexilate, there was increased interest for use by clinical laboratories as the preferred method for assessing the anticoagulant effect of this drug. The purpose of this document is to review the current status of ecarin based assays for assessing dabigatran. This is with the understanding that these methods can also be exploited for determining the anticoagulation effect of parenteral direct thrombin inhibitors, such as argatroban and bivalirudin.

Bivalirudin Dosing Requirements in Adult Patients on Extracorporeal Life Support With or Without Continuous Renal Replacement Therapy

Systemic anticoagulation with unfractionated heparin is standard of care for patients receiving extracorporeal life support (ECLS); however, an alternative anticoagulant may be necessary when challenges with heparin therapy arise. Evidence for alternative anticoagulation in ECLS patients is limited. This retrospective analysis evaluated the dosing and outcomes associated with bivalirudin use in 14 adult ECLS patients. Indications for bivalirudin included heparin-induced thrombocytopenia, heparin resistance, or persistent clotting or bleeding while on heparin. The median initial bivalirudin dose to achieve target activated partial thromboplastin time was 0.15 mg/kg/h (range 0.04-0.26 mg/kg/h). Dosing requirements increased by 75-125% when renal replacement was included. Median time on bivalirudin was 5.2 days (range 0.9-28 days). Five patients (36%) required a circuit change while on bivalirudin because of clotting or failing oxygenation, and four (28.6%) had bleeding significant enough to require either reduction in activated partial thromboplastin time goals or temporary holding of anticoagulation. Bivalirudin appears to be a potential option for adult patients on ECLS who are unable to receive or fail heparin therapy; however, the wide variation in dosing suggests the need for careful management.

Advances in monitoring anticoagulant therapy

Anticoagulant drugs directly or indirectly influence coagulation factors preventing fibrin formation, thus preventing blood clotting. They are classified into two groups according to the mode of application, namely parenteral and oral drugs. Among the latter, vitamin K antagonists (most often warfarin) were most widely used for almost a century. In recent years new oral anticoagulant drugs have become available that directly target either factor IIa or Xa (direct oral anticoagulants, DOACs). The proportion of patients to whom DOACs are prescribed is increasing because clinical studies have proved they are at least as effective and safe as vitamin K antagonists. Some of the anticoagulant drugs require regular laboratory monitoring, while others only need assessment of blood drug levels in specific clinical situations. This chapter provides an overview of appropriate laboratory tests used for either regular laboratory monitoring of therapy or occasional assessment of the anticoagulant effect of both parenteral and oral anticoagulant drugs used in clinical practice.

Argatroban and Bivalirudin for Perioperative Anticoagulation in Cardiac Surgery

Argatroban and bivalirudin are used as replacement anticoagulants for heparin. The authors review clinical studies for these drugs in the perioperative setting of cardiac surgical patients including extracorporeal management and mechanical support therapy.

Monitoring of Argatroban and Lepirudin: What is the Input of Laboratory Values in "Real Life"?

Monitoring of direct thrombin inhibitors (DTIs) in patients with heparin-induced thrombocytopenia (HIT) is primarily performed using the activated partial thromboplastin time (aPTT). This assay is poorly standardized, reagent dependent, and not DTI specific. We compared aPTT, thrombin time (TT), and prothrombin time (PT) to drug levels obtained by the ecarin chromogenic assay (ECA). We analyzed 495 samples of patients with confirmed or suspected HIT on treatment with either argatroban (n = 37) or lepirudin (n = 80). Mean DTI levels ± standard deviation (SD) were 0.41 ± 0.36 µg/mL for argatroban and 0.20 ± 0.21 µg/mL for lepirudin. Results of aPTT were highly variable: 67 ± 22 seconds for argatroban and 55 ± 20 seconds for lepirudin. Significant correlations ( P < .01) were found between ECA-based DTI level and TT (argatroban, r = .820 and lepirudin, r = .830), PT (argatroban, r = -.544), and aPTT (lepirudin, r = .572). However, there was no correlation of aPTT with argatroban or PT with lepirudin concentration. Multiple regression analyses revealed that the TT predicted 54% of argatroban and 42% of lepirudin levels, but no significant impact was seen for PT or aPTT. The aPTT-guided monitoring of DTI therapy leads to a high percentage of patients with inaccurate plasma levels, hence resulting to either undertreatment or overtreatment. Knowledge of baseline values prior to DTI therapy and inclusion of clinical settings are essential for dosing DTIs when using aPTT. However, due to several limitations of aPTT, monitoring according to exact plasma concentrations as obtained by specific tests such as ECA may be more appropriate.

Anticoagulation Monitoring Part 1: Warfarin and Parenteral Direct Thrombin Inhibitors

OBJECTIVE:

To review the availability, mechanisms, limitations, and clinical application of point-of-care (POC) devices used in the management of warfarin and parenteral direct thrombin inhibitors.

DATA SOURCES:

Scientific articles were identified through a MEDLINE search (1966–August 2004), manufacturer Web sites, additional references listed in articles and Web sites, and abstracts from scientific meetings.

STUDY SELECTION AND DATA EXTRACTION:

English-language literature from clinical trials was reviewed to evaluate the accuracy, reliability, and clinical application of POC monitoring devices.

DATA SYNTHESIS:

The prothrombin time expressed as the international normalized ratio (PT—INR) is a well-established test for monitoring warfarin anticoagulation. Multiple devices are available for POC testing. Because there is no universally accepted standard, the performance of each device is typically tested against a standard test performed in a reference laboratory. Performance of currently available devices, as measured by correlations to a standard reference laboratory PT—INR, may be considered very good and acceptable for use in patient care. Utilization of patient self-testing and patient self-monitoring of warfarin anticoagulation using POC devices is increasing. Parenteral direct thrombin inhibitors are typically monitored using a standard laboratory activated partial thromboplastin time. Some research has shown that POC monitoring of direct thrombin inhibitors using the ecarin clotting time is helpful for patients undergoing cardiopulmonary bypass surgery, although that test is not readily available.

CONCLUSIONS:

POC testing for anticoagulation therapy has been available for >20 years. Multiple POC devices are available to monitor warfarin. There is some variability in results between devices and between reagents used in the same device. Despite these limitations, POC monitoring of warfarin via the PT—INR is an integral part of clinical practice. Additional research evaluating POC monitoring of direct thrombin inhibitors is necessary.

Pathology consultation on monitoring direct thrombin inhibitors and overcoming their effects in bleeding patients

OBJECTIVES

Direct thrombin inhibitors (DTIs), a relatively new class of anticoagulants, present several challenges regarding monitoring of their anticoagulant effects and overcoming bleeding associated with their use. The aim of this article is to (1) briefly present the pharmacologic properties of currently available DTIs, (2) discuss approaches to laboratory assessment of these drugs, and (3) review management of bleeding associated with their use.

METHODS

Published literature on DTIs, including clinical trials, case reports, and experimental animal models, was reviewed. The primary authors also reviewed their first-hand experiences with DTI anticoagulation.

RESULTS

Based on the literature review and the practical experiences of the authors, suggestions for the monitoring of DTIs and algorithmic approaches for the management of DTI-associated bleeding were developed.

CONCLUSIONS

Routine coagulation assays (eg, the prothrombin time) show a relatively poor correlation with the degree of anticoagulation and DTI drug concentrations. Newer assays, such as the ecarin clotting time and dilute thrombin time, may be more useful in assessing DTI anticoagulation, but these assays are not yet widely available. Low-grade DTI-associated bleeds are best managed with cessation of the drug and supportive care, while higher-grade and/or life-threatening bleeds may best be reversed by active drug removal (eg, via the administration of activated charcoal or hemodialysis). At present there is little evidence to suggest that transfusion products such as factor concentrates or thawed plasma are of any particular benefit in DTI reversal; however, these products may play a supportive role in the management of bleeding.

Warfarin-related nephropathy is the tip of the iceberg: direct thrombin inhibitor dabigatran induces glomerular hemorrhage with acute kidney injury in rats

BACKGROUND

Excessive anticoagulation with warfarin can result in acute kidney injury (AKI) by causing glomerular hemorrhage and renal tubular obstruction by red blood cell (RBC) casts in some patients, especially in those with chronic kidney disease (CKD). This condition was described as warfarin-related nephropathy (WRN). Recent evidence suggests that WRN-like syndromes are not confined to anticoagulation with warfarin, but may be seen with other anticoagulants, such as dabigatran. The aim of this study was to investigate dabigatran effects on kidney function in an animal model of CKD and possible pathogenic mechanisms of AKI.

METHODS

Control and 5/6 nephrectomy rats were treated with different doses of dabigatran and protease-activated receptor 1 (PAR-1) inhibitor SCH79797.

RESULTS

Dabigatran resulted in changes in coagulation in rats similar to those in humans at 50 mg/kg/day. Dabigatran resulted in a dose-dependent increase in serum creatinine (Scr) and hematuria in both control and 5/6 nephrectomy rats. SCH79797 also increased Scr and hematuria, more prominent in animals with CKD. Morphologically, numerous RBC tubular casts were seen in 5/6 nephrectomy rats treated with either dabigatran or SCH79797 and only occasional RBC casts in control rats.

CONCLUSIONS

Our data indicate that WRN represents part of a broader syndrome, anticoagulant-related nephropathy (ARN). ARN, at least partially, is mediated via PAR-1. Our findings suggest that not only CKD patients, but other patients as well, are at high risk of developing AKI if the therapeutic range of anticoagulation with dabigatran is exceeded. Close monitoring of kidney function in patients on dabigatran therapy is warranted.

Utilization of coagulation assays in clinical therapeutics

With the emergence of new anticoagulants, clinicians need a thorough understanding of coagulation assays. Various laboratory assays exist to measure the effectiveness of anticoagulants. Coagulation assays are the primary method for measuring the effectiveness of anticoagulants; therefore, a comprehensive understanding of the various assays is critical to interpret the results appropriately. Coagulation test results can be affected by multiple factors including diseases, drugs, and genetic variations. This article reviews the indications, limitations, and interpretation of coagulation assays.

Bivalirudin in pediatric patients maintained on extracorporeal life support

OBJECTIVE

Anticoagulation with heparin is standard of care for patients maintained on extracorporeal life support. Very limited evidence exists for the use of alternative anticoagulants during extracorporeal life support. Patients with heparin-induced thrombocytopenia, heparin resistance, and evidence of significant thrombosis while on heparin may be candidates for alternative anticoagulation. The objective of this analysis is to present evidence for the use of bivalirudin during extracorporeal life support in pediatric patients.

DESIGN

Case series.

SETTING

University of California, Davis Medical Center.

PATIENTS

Twelve critically ill, pediatric patients receiving bivalirudin for anticoagulation during extracorporeal life support.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Twelve patients meeting entry criteria received bivalirudin during the study period. The median patient age was 8 days (range, 1 d to 6 yr). Eight patients were neonates. Eight patients were male. Nine patients were supported with venoarterial extracorporeal life support. Median duration of extracorporeal life support was 226 hours (range, 111-913) and median time on bivalirudin was 92 hours (range, 60-230). Bivalirudin bolus doses were administered to select patients without bleeding complications. The maintenance dose that corresponded with initial target activated partial thromboplastin time ranged from 0.045 to 0.48 mg/kg/hr with a median rate of 0.16 mg/kg/hr. The median dose for days 1, 3, and 5 was 0.135, 0.175, and 0.267 mg/kg/hr, respectively. The correlation (r2) between dose adjustment and activated partial thromboplastin time response was 0.264.

CONCLUSIONS

This is the largest case series describing the use of a direct thrombin inhibitor in pediatric extracorporeal life support patients. The maintenance dose range reflected considerable inter-patient variability. There was an observed increase in dose requirements with time. Bivalirudin, with close monitoring, is a potential option for pediatric patients on extracorporeal life support who have developed heparin-induced thrombocytopenia, heparin resistance, or significant thrombosis while on heparin.

Disseminated intravascular coagulation does not play a major role in the pathogenesis of classical swine fever

Classical swine fever (CSF) is a multi-systemic disease that can be accompanied by severe haemorrhagic lesions. The underlying pathogenetic mechanisms are still far from being understood, though disseminated intravascular coagulation (DIC) was discussed as a major factor. In the presented study, the direct thrombin inhibitor hirudin was used in an attempt to elucidate the role of the coagulation system in the pathogenesis of CSF-induced haemorrhagic lesions. Two groups of piglets (n=5) were infected with highly virulent CSF virus (CSFV) strain CSF0634. One group underwent daily treatment with hirudin, the other served as untreated challenge infection control. Assessment of clinical signs using a clinical score system, coagulation tests, and blood counts were performed daily. Both groups developed acute-lethal CSF with haemorrhagic lesions. Although changes in the coagulation system were seen in the late stages of CSFV infection, our results strongly suggest that DIC does not present the crucial event in the pathogenesis of haemorrhagic lesions.

Measuring direct thrombin inhibitors with routine and dedicated coagulation assays: which assay is helpful?

The use of direct thrombin inhibitors (DTIs) for prophylactic or therapeutic anticoagulation is increasing because of the predictable bioavailability and short half-life of these DTIs. However, in certain situations, indication of the concentration is warranted. We investigated the effects of 3 DTIs (lepirudin, argatroban, and bivalirudin) in 6 pooled plasma specimens on routine coagulation assays (activated partial thromboplastin time [aPTT], prothrombin time [PT], and thrombin time [TT]) and dedicated DTI assays (Hemoclot, HemosIL, the ecarin clotting time, and a chromogenic ecarin clotting time) on 2 coagulation analyzers. We found routine tests to be nondiscriminative between concentrations of different DTIs in the aPTT. Moreover, for PT and TT, the responses for different DTIs differed. This was similar for ecarin clotting assays. The Hemoclot and HemosIL assays showed identical linear increases for all 3 DTIs. We conclude that dedicated calibrated assays based on a diluted TT (Hemoclot and HemosIL) appear to be the most suitable for monitoring purposes.

High-dose argatroban for treatment of heparin-induced thrombocytopenia with thrombosis: a case report and review of laboratory considerations

PURPOSE

A case report describing high-dose argatroban for the treatment of heparin-induced thrombocytopenia (HIT) with thrombosis and associated considerations in interpreting laboratory monitoring data are presented.

SUMMARY

A 51-year-old woman with an extensive history of coronary artery disease arrived at the emergency department with complaints of chest pain. The patient was admitted, and coronary artery bypass graft surgery was ultimately performed. The patient had a baseline platelet count of 177,000 cells/μL. During hospitalization, the patient received heparin, and her platelet count dropped to 12,000 cells/μL 13 days after the initiation of heparin. The patient developed swelling around a peripherally inserted central catheter and later developed deep vein thrombosis. An argatroban infusion of 2 μg/kg/min was initiated, with a target activated partial thromboplastin time (aPTT) of 40-80 seconds. After 5 days of therapy, the patient had increased swelling in her right arm and an aPTT of 56 seconds. Her goal aPTT was subsequently increased. Six days later, the patient developed a left-lower-extremity DVT despite aPTTs within the goal range. A new aPTT target of >75 seconds was set. The infusion rate was increased to 15.5 μg/kg/min to attain the target aPTT. Results of an in vitro test led to an alternative interpretation of aPTT and International Normalized Ratio values that aided in the monitoring of argatroban during the high-dose infusion.

CONCLUSION

A patient with HIT with thrombosis was successfully treated with unusually high dosages of argatroban and may have had serum argatroban concentrations exceeding what has commonly been thought to be the therapeutic range.

Hospital-based clinical implications of the novel oral anticoagulant, dabigatran etexilate, in daily practice

Dabigatran etexilate is an oral direct thrombin inhibitor that has been approved by the US Food and Drug Administration for the prevention of stroke and systemic embolization in patients with nonvalvular atrial fibrillation. It has also been studied for the prevention of venous thromboembolism in patients after hip and knee arthroplasty and for treatment of venous thromboembolism. Although routine laboratory monitoring is not needed, there are clinical scenarios in which physicians will need to have a clear understanding of drug pharmacology, laboratory assessment, and reversibility of this drug to make appropriate clinical decisions. We review the pharmacology of dabigatran etexilate, pertinent clinical trials, and the effects of dabigatran etexilate on prothrombin time, activated partial thromboplastin time, thrombin time, and ecarin clotting time. We also provide an approach to patients on dabigatran etexilate who are bleeding, have a suspected therapeutic failure, or require periprocedural management.

Coagulation-induced shedding of platelet glycoprotein VI mediated by factor Xa

This study evaluated shedding of the platelet collagen receptor, glycoprotein VI (GPVI) in human plasma. Collagen or other ligands induce metalloproteinase-mediated GPVI ectodomain shedding, generating approximately 55-kDa soluble GPVI (sGPVI) and approximately 10-kDa platelet-associated fragments. In the absence of GPVI ligands, coagulation of platelet-rich plasma from healthy persons induced GPVI shedding, independent of added tissue factor, but inhibitable by metalloproteinase inhibitor, GM6001. Factor Xa (FXa) common to intrinsic and tissue factor-mediated coagulation pathways was critical for sGPVI release because (1) shedding was strongly blocked by the FXa-selective inhibitor rivaroxaban but not FIIa (thrombin) inhibitors dabigatran or hirudin; (2) Russell viper venom that directly activates FX generated sGPVI, with complete inhibition by enoxaparin (inhibits FXa and FIIa) but not hirudin; (3) impaired GPVI shedding during coagulation of washed platelets resuspended in FX-depleted plasma was restored by adding purified FX; and (4) purified FXa induced GM6001-inhibitable GPVI shedding from washed platelets. In 29 patients with disseminated intravascular coagulation, mean plasma sGPVI was 53.9 ng/mL (95% confidence interval, 39.9-72.8 ng/mL) compared with 12.5 ng/mL (95% confidence interval, 9.0-17.3 ng/mL) in thrombocytopenic controls (n = 36, P < .0001), and 14.6 ng/mL (95% confidence interval, 7.9-27.1 ng/mL) in healthy subjects (n = 25, P = .002). In conclusion, coagulation-induced GPVI shedding via FXa down-regulates GPVI under procoagulant conditions. FXa inhibitors have an unexpected role in preventing GPVI down-regulation.

Monitoring of the anticoagulants argatroban and lepirudin: a comparison of laboratory methods

Monitoring of direct inhibitors of thrombin (DTI) is critical for their safe and effective use as anticoagulants. We examined samples containing several concentrations of argatroban or lepirudin in reconstituted standard human plasma and plasma from medical outpatients and intensive care patients. Prothrombin time (PT), activated partial thromboplastin time (aPTT), and thrombin time (TT) were determined using automated analyzers. Ecarin clotting time (ECT) was measured using a 10 IU/mL dilution of ecarin in 0.05 mol/L CaCl(2). Calibration curves were approximately linear for TT and ECT in samples containing argatroban and lepirudin, respectively. Activated partial thromboplastin curves reached a plateau at DTI concentrations ≥2 µg/mL, suggesting that the aPTT may not reliably detect overdosing. Prothrombin time increased exponentially. A broad range of clotting times was seen in patient samples with all tests suggesting that individual morbidity and therapies may strongly influence test results and may lead to underestimation of DTI doses.

Laboratory monitoring of new anticoagulants

Maintaining a balance between bleeding and clotting has always been a challenge in treating coagulation disorders. A perturbation in that balance can be associated with substantial morbidity and mortality. As a result, anticoagulant monitoring is extremely important, and inappropriate testing may lead to complications. There are now a variety of new anticoagulant drugs in clinical use including several direct thrombin inhibitors (DTIs), such as argatroban, bivalirudin, and hirudin, as well as a Factor Xa inhibitor, fondaparinux. There are pitfalls associated with some of the currently used laboratory monitoring tests, and newer alternative laboratory monitoring tests have been investigated (Walenga and Hoppensteadt, Semin Thromb Hemost 2004;30:683-695). In addition, laboratory testing can assist with transitioning patients from DTI to warfarin therapy.

Dosing Nomograms: Silos on a Slope

Developing dosing management guidelines or protocol approaches to pharmacotherapy can provide several benefits for standardization of care. Frequently, clinicians may need to incorporate multiple influencing factors to individualize management. In some cases, preestablished, standardized approaches may create barriers to individualized care, potentially categorizing patients into dosing categories (silos) that minimize their individualized needs. Approaches to managing direct thrombin inhibitor therapy have been recently explored and dosing approaches different from those provided in the prescribing information have been proposed. Considerations regarding individualized management of anticoagulant therapy, including the use of standardized dosing or monitoring protocols, are discussed here.

Pharmacokinetics and pharmacodynamics of the direct oral thrombin inhibitor dabigatran in healthy elderly subjects

OBJECTIVES

To investigate the pharmacokinetic and pharmacodynamic profile of dabigatran in healthy elderly subjects; to assess the intra- and interindividual variability of dabigatran pharmacokinetics in order to assess possible gender differences; and to assess the effect of pantoprazole coadministration on the bioavailability of dabigatran.

STUDY DESIGN AND SETTING

Open-label, parallel-group, single-centre study, consisting of a baseline screening visit, 7-day treatment period and post-study examination visit.

SUBJECTS AND INTERVENTION

36 healthy elderly subjects (aged > or =65 years) with a body mass index of 18.5-29.9 kg/m(2). Subjects were randomized to receive dabigatran etexilate either with or without coadministration of pantoprazole. Dabigatran etexilate was administered as capsules at 150 mg twice daily over 6 days and once on the morning of day 7. Pantoprazole was administered at 40 mg twice daily, starting 2 days prior to dabigatran etexilate administration and ending on the morning of day 7.

MAIN OUTCOME MEASURES

The primary pharmacokinetic measurements included the area under the plasma concentration-time curve at steady state (AUC(ss)), maximum (C(max,ss)) and minimum (C(min,ss)) plasma concentrations at steady state, terminal half-life (t((1/2))), time to reach C(max,ss) and renal clearance of dabigatran. The secondary pharmacokinetic parameters included the mean residence time, total oral clearance and volume of distribution. The pharmacodynamic parameters measured were the blood coagulation parameters ecarin clotting time (ECT) and activated partial thromboplastin time (aPTT).

RESULTS

With twice-daily administration of dabigatran etexilate, plasma concentrations of dabigatran reached steady state within 2-3 days, which is consistent with a t((1/2)) of 12-14 hours. The mean (SD) peak plasma concentrations on day 4 of treatment in male and female elderly subjects were 256 ng/mL (21.8) and 255 ng/mL (84.0), respectively. The peak plasma concentrations were reached after a median of 3 hours (range 2.0-4.0 hours). Coadministration with pantoprazole decreased the average bioavailability of dabigatran (the AUC(ss)) by 24% (day 4; 90% CI 7.4, 37.8) and 20% (day 7; 90% CI 5.2, 33.3). Intra- and interindividual pharmacokinetic variability in the overall population was low (<30% coefficient of variation), indicating that dabigatran has a predictable pharmacokinetic profile. Prolongation of the ECT and aPTT correlated with, and paralleled, the plasma concentration-time profile of dabigatran, which demonstrates a rapid onset of action without a time delay, and also illustrates the direct mode of action of the drug on thrombin in plasma. The ECT increased in direct proportion to the plasma concentration, and the aPTT displayed a linear relationship with the square root of the plasma concentration. The mean AUC(ss) was 3-19% higher in female subjects than in male subjects, which was likely due to gender differences in creatinine clearance. The safety profile of dabigatran was good, with and without pantoprazole coadministration.

CONCLUSIONS

Dabigatran demonstrated reproducible and predictable pharmacokinetic and pharmacodynamic characteristics, together with a good safety profile, when administered to healthy elderly subjects. Minor gender differences were not considered clinically relevant. The effects of pantoprazole coadministration on the bioavailability of dabigatran were considered acceptable, and dose adjustment is not considered necessary.

Heparin-induced thrombocytopenia in intensive care patients

OBJECTIVE

To summarize new information on frequency of heparin-induced thrombocytopenia (HIT) in patients treated in intensive care units (ICU), developments in the interpretation of assays for detecting anti-PF4/heparin antibodies, and treatment of HIT patients.

STUDY SELECTION

All data on the frequency of laboratory-confirmed HIT in ICU patients were included; for laboratory testing of HIT and treatment of patients, this review focuses on recent data that became available in 2005 and 2006.

DATA EXTRACTION AND SYNTHESIS

HIT is a potentially life-threatening adverse effect of heparin treatment caused by platelet-activating antibodies of immunoglobulin G class usually recognizing complexes of platelet factor 4 and heparin. HIT is more often caused by unfractionated heparin than low-molecular-weight heparin and is more common in postsurgical than in medical patients. In the ICU setting, HIT is uncommon (0.3-0.5%), whereas thrombocytopenia from other causes is very common (30-50%). For laboratory diagnosis of HIT antibodies, both antigen assays and functional (platelet activation) assays are available. Both tests are very sensitive (high negative predictive value) but specificity is problematic, especially for the antigen assays, which also detect nonpathogenic immunoglobulin M and immunoglobulin A class antibodies. Detection of immunoglobulin M or immunoglobulin A antibodies could potentially lead to adverse events such as bleeding if a false diagnosis of HIT prompts replacement of heparin by an alternative anticoagulant. For treatment of HIT, three alternative anticoagulants are approved: the direct thrombin inhibitors, lepirudin and argatroban, and the heparinoid, danaparoid (not approved in the United States). Recent data indicate that the approved dosing regimens of the direct thrombin inhibitors are too high, especially in ICU patients.

CONCLUSIONS

HIT affects <1% of ICU patients even though 30-50% develop thrombocytopenia. The choice of the optimal alternative anticoagulant depends on patient characteristics. Many ICU patients require lower doses of alternative anticoagulant than those recommended by the manufacturer.

The pharmacokinetics, pharmacodynamics and tolerability of dabigatran etexilate, a new oral direct thrombin inhibitor, in healthy male subjects

AIMS

The novel direct thrombin inhibitor (DTI), dabigatran etexilate (Boehringer Ingelheim Pharma GmbH & Co. KG), shows potential as an oral antithrombotic agent. Two double-blind, randomized trials were undertaken to investigate the pharmacokinetics (PK), pharmacodynamics (PD) and tolerability of orally administered dabigatran etexilate in healthy male subjects.

METHODS

Dabigatran etexilate or placebo was administered orally at single doses of 10-400 mg (n = 40) or at multiple doses of 50-400 mg three times daily for 6 days (n = 40). Plasma and urine samples were collected over time to determine the PK profile of dabigatran. PD activity was assessed by its effects on blood coagulation parameters: activated partial thromboplastin time (aPTT), prothrombin time (PT), reported as international normalized ratio (INR), thrombin time (TT), and ecarin clotting time (ECT). All adverse events were recorded.

RESULTS

Dabigatran etexilate was rapidly absorbed with peak plasma concentrations of dabigatran reached within 2 h of administration. This was followed by a rapid distribution/elimination phase and a terminal phase, with associated estimated half-lives of 8-10 h and 14-17 h with single and multiple dose administrations, respectively. Dabigatran exhibited linear PK characteristics with dose-proportional increases observed in maximum plasma concentration and area under the curve. Steady-state conditions were reached within 3 days with multiple dosing. The mean apparent volume of distribution during the terminal phase (V(z)/F) of 1860 l (range 1430-2400 l) and the apparent total clearance after oral administration (CL(tot)/F) of 2031 ml min(-1) (range 1480-2430), were dose independent. Time curves for aPTT, INR, TT and ECT paralleled plasma concentration-time curves with values increasing rapidly and in a dose-dependent manner. At the highest dose of 400 mg administered three times daily, maximum prolongations over baseline of 3.1 (aPTT), 3.5 (INR), 29 (TT) and 9.5-fold (ECT) were observed. Dabigatran underwent conjugation with glucuronic acid to form pharmacologically active conjugates that accounted for approximately 20% of total dabigatran in plasma. Overall, variability in PK parameters was low to moderate, with an average interindividual coefficient of variation (CV) of approximately 30% and variability in PD parameters was low, with CV < 10%. Of the four assays, TT and ECT exhibited the greatest sensitivity and precision within the anticipated therapeutic dose range. Bleeding events were few and were mild-to-moderate in intensity, occurring only in the higher, multiple dose groups.

CONCLUSIONS

These data suggest that dabigatran etexilate is a promising novel oral DTI with predictable PK and PD characteristics and good tolerability. Further investigation of dabigatran etexilate for the treatment and prophylaxis of patients with arterial and venous thromboembolic disorders, acute coronary syndromes and other medical conditions is warranted.

Heparin-Induced Thrombocytopenia: Treatment Options and Special Considerations

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse effect that typically manifests several days after the start of heparin therapy, although both rapid- and delayed-onset HIT have been described. Its most serious complication is thrombosis. Although not all patients develop thrombosis, it can be life threatening. The risk of developing HIT is related to many factors, including the type of heparin product administered, route of administration, duration of therapy, patient population, and previous exposure to heparin. The diagnosis of HIT is typically based on clinical presentation, exposure to heparin, and presence of thrombocytopenia with or without thrombosis. Antigen and activation laboratory assays are available to support the diagnosis of HIT. However, because of the limited sensitivity and specificity of these assays, bedside probability scales for HIT were developed. When HIT is suspected, prompt cessation of all heparin therapy is necessary, along with initiation of alternative anticoagulant therapy. Two direct thrombin inhibitors--argatroban and lepirudin--are approved for the management of HIT in the United States, and bivalirudin is approved for use in patients with HIT who are undergoing percutaneous coronary intervention. Other agents, although not approved to manage HIT, have also been used; however, their role in therapy requires further evaluation. A comprehensive HIT management strategy involves the evaluation of numerous factors. Many patients, including those undergoing coronary artery bypass surgery, those with acute coronary syndromes, those with hepatic or renal insufficiency, and children, require special attention. Clinicians must become familiar with the available information on this serious adverse effect and its treatment so that optimum patient management strategies may be formulated.

Argatroban Dosing of Patients with Heparin-Induced Thrombocytopenia and an Elevated aPTT Due to Antiphospholipid Antibody Syndrome

Objective:

To describe the clinical characteristics, management, and outcomes of patients with heparin-induced thrombocytopenia with thrombosis (HITTS) or without thrombosis (HIT) who also had an elevated baseline activated partial thromboplastin time (aPTT) due to antiphospholipid antibody syndrome (APS).

Case Summary:

Four patients with HIT/HITTS and an elevated baseline aPTT due to APS were identified. Two patients had venous thrombosis, 1 had limb ischemia, and 1 had isolated HIT. All 4 were managed with a weight-based fixed dose of argatroban without laboratory monitoring. None of the patients had thrombotic or bleeding complications once therapy was initiated.

Discussion:

Management of patients with HIT/HITTS and an abnormal baseline aPTT due to APS is problematic. We review alternative management strategies, such as monitoring direct thrombin inhibitors with the ecarin clotting time or thrombin inhibition time or using an alternative anticoagulant, such as fondaparinux. As of March 13, 2006, none of these management strategies has been evaluated in a clinical trial for this patient population. We report the successful use of weight-based, fixed-dose argatroban without laboratory monitoring in patients with APS.

Conclusions:

Use of a fixed-dose argatroban regimen without laboratory monitoring is a potential management strategy for patients with HIT/HITTS and an elevated baseline aPTT due to APS.

Recognition, treatment, and prevention of heparin-induced thrombocytopenia: Review and update

Heparin-induced thrombocytopenia (HIT) is one of the most important life- and limb-threatening adverse drug events encountered by physicians. Serious sequelae associated with HIT can be avoided with early recognition and appropriate treatment. This review examines the recommendations published in 2004 by the American College of Chest Physicians on the recognition, treatment, and prevention of HIT together with more recent data, especially regarding treatment with direct thrombin inhibitors.

Argatroban in Post-Cardiovascular Surgery Patient with Heparin-Induced Thrombocytopenia Requiring Hemodialysis and Continuous Hemofiltration

Objective:

To describe the use of argatroban in a postoperative cardiovascular surgery patient with heparin-induced thrombocytopenia (HIT) requiring hemodialysis and continuous veno-veno hemofiltration (CVVH).

Case Summary:

A 23-year-old white woman with HIT developed acute renal failure after cardiovascular surgery. Argatroban was used as a substitute for heparin during hemodialysis and CVVH. Both activated partial thromboplastin time (aPTT) and activated clotting time (ACT) were used to guide the dosage of argatroban. The patient was successfully dialyzed without clotting of the circuit. The dosage required in our patient was much lower than the manufacturer's recommendation.

Discussion:

Argatroban is a selective thrombin inhibitor that does not cross-react with heparin-induced antibodies. It is metabolized by the liver, and dosage adjustment is recommended in patients with severe hepatic impairment. The correct dosage for patients with unstable hemodynamics is not known. Our patient had apparently normal hepatic function at the initiation of therapy, but the dosage of argatroban recommended by the manufacturer resulted in prolonged elevation of the aPTT and ACT with associated gastrointestinal bleeding. This may be due to hepatic congestion secondary to poor cardiac function and/or severe generalized edema.

Conclusions:

When argatroban is considered for therapy in place of heparin for CVVH, it needs to be used with extreme caution since the correct initial dosage in patients with mild hepatic impairment and unstable hemodynamics is unclear.

Ximelagatran: an oral direct thrombin inhibitor

OBJECTIVE

To present the chemistry, pharmacology, and pharmacokinetics of ximelagatran, an oral direct thrombin inhibitor (DTI), and to review available comparative clinical trial data evaluating its efficacy and safety relative to other antithrombotic agents in the prevention and treatment of thromboembolism.

DATA SOURCES

A search of the PubMed and Cochrane databases (1995-August 2004), supplemented by a manual search of article bibliographies, conference abstracts, and data on file from the manufacturer, was conducted. Key search terms were ximelagatran, melagatran, H376/95, and direct thrombin inhibitors.

STUDY SELECTION AND DATA EXTRACTION

Pertinent information from available clinical trials, including study design, patient demographics, dosing regimens, anticoagulant comparators, methods for evaluating effectiveness, treatment outcomes, adverse events, and pharmacokinetic and pharmacodynamic evaluations, was extracted.

DATA SYNTHESIS

Ximelagatran is an orally administered DTI under development for use in the treatment of venous thromboembolism (VTE), long-term prevention of a second VTE event, stroke secondary to atrial fibrillation, prevention of VTE after orthopedic procedures, and recurrent ischemic events after acute myocardial infarction.

CONCLUSIONS

Ximelagatran, in twice-daily doses of 24 or 36 mg, is an alternative to low-molecular-weight heparins or warfarin in thromboprophylaxis following orthopedic knee replacement, atrial fibrillation, or initial treatment of VTE. Improved outcomes versus placebo were seen in the long-term prevention of VTE in patients who completed an initial 6 months of treatment. Liver-related effects need further clarification.