Effects of the direct thrombin inhibitor dabigatran on ex vivo coagulation time in orthopaedic surgery patients: a population model analysis

Antiplatelet, Anticoagulant, and Fibrinolytic Activity of Orchids: A Review

Thrombosis is the occlusion of a blood vessel and is responsible for the highest number of deaths worldwide. Its treatment comprises the use of anticoagulants, antiplatelets, and thrombolytics. Although many antithrombotic drugs are currently available, none is completely effective and safe. Plants are a valuable source of compounds with antithrombotic properties. Some orchid species have been used in traditional medicine for their antithrombotic properties. This review informs about the contribution of orchids in this field and the studies that have validated their properties.

Effect of Daridorexant on the Pharmacokinetics of P-Glycoprotein Substrate Dabigatran Etexilate and Breast Cancer Resistance Protein Substrate Rosuvastatin in Healthy Subjects

BACKGROUND AND OBJECTIVE

The dual orexin receptor antagonist daridorexant was approved in 2022 for the treatment of insomnia at doses up to 50 mg once per night. This study aimed at investigating the effect of daridorexant 50 mg at steady state on the pharmacokinetics of dabigatran, the active moiety of dabigatran etexilate, and rosuvastatin, sensitive substrates of P-glycoprotein and breast cancer resistance protein, respectively.

METHODS

This single-center, open-label, fixed-sequence study enrolled 24 healthy male subjects who were dosed orally with dabigatran etexilate 75 mg on days 1 (Treatment A1) and 9 (Treatment C1) as well as rosuvastatin 10 mg on days 3 (Treatment A2) and 11 (Treatment C2). On days 7-14, daridorexant (50 mg once daily) was administered. Blood samples for the pharmacokinetics of both substrates and the pharmacodynamics of dabigatran, i.e., two coagulation tests, were collected and safety assessments performed. Noncompartmental pharmacokinetic parameters and pharmacodynamic variables were evaluated with geometric mean ratios and 90% confidence intervals of Treatment C1/C2 versus A1/A2.

RESULTS

Geometric mean ratios (90% confidence interval) of dabigatran maximum plasma concentration and area under the plasma concentration-time curve were 1.3 (1.0-1.7) and 1.4 (1.1-1.9), respectively, whereas the time to maximum plasma concentration and terminal half-life were comparable between treatments. Pharmacodynamic variables showed a similar pattern as dabigatran pharmacokinetics in both treatments. Rosuvastatin pharmacokinetics were unchanged upon concomitant daridorexant administration. All treatments were well tolerated.

CONCLUSIONS

A mild inhibition of P-glycoprotein was observed after administration of daridorexant (50 mg once daily) at steady state, whereas breast cancer resistance protein was not affected.

CLINICAL TRIAL REGISTRATION

NCT05480475; date of registration: 29 July, 2022.

Delayed concentration effect models for dabigatran anticoagulation

INTRODUCTION

Dabigatran is an anticoagulant with potential use during cardiopulmonary bypass in children and adults. The pharmacokinetic-pharmacodynamic relationship for dabigatran anticoagulation effect was investigated in an intact animal model using rabbits.

METHODS

Ten male New Zealand white rabbits were given a novel preparation of intravenous dabigatran 15 mg.kg^-1 . Blood samples were collected for activated clotting time, thromboelastometric reaction time, and drug assay at 5, 15, 30, 60, 120, 180, 300, and 420 min. Plasma dabigatran concentrations and coagulation measures were analyzed using an integrated pharmacokinetic-pharmacodynamic model using nonlinear mixed effects. Effects (activated clotting and thromboelastometric reaction times) were described using a sigmoidal E_MAX model. Pharmacokinetic parameters were scaled using allometry and standardized to a 70 kg size standard. Pharmacodynamics were investigated using both an effect compartment model and an indirect response (turnover) model.

RESULTS

A two-compartment model described dabigatran pharmacokinetics with a clearance (CL 0.135 L.min^-1 .70 kg^-1 ), intercompartment clearance (Q 0.33 L.min^-1 .70 kg^-1 ), central volume of distribution (V1 12.3 L.70 kg^-1 ), and peripheral volume of distribution (V2 30.1 L.70 kg^-1 ). The effect compartment model estimates for a sigmoid E_MAX model with activated clotting time had an effect site concentration (Ce₅₀ 20.1 mg.L^-1 ) eliciting half of the maximal effect (E_MAX 899 s) and a Hill coefficient (N 0.66). The equilibration half time (T_1/2 keo) was 1.4 min. Results for the reaction time were plasma concentration (Cp₅₀ 65.3 mg.L^-1 ), E_MAX 34 min, N 0.80 with a baseline thromboelastometric reaction time of 0.4 min. The equilibration half time (T_1/2 keo) was 2.04 min.

CONCLUSIONS

Dabigatran reversibly binds to the active site on the thrombin molecule, preventing thrombin-mediated activation of coagulation factors. The effect compartment model performed slightly better than the turnover model and was able to adequately capture pharmacodynamics for both activated clotting and thromboelastometric reaction times. The equilibration half time was short (<2 min). These data can be used to inform future animal preclinical studies for those undergoing cardiopulmonary bypass. These preclinical data also demonstrate the magnitude of parameter values for a delayed effect compartment model that are applicable to humans.

Managing patients on direct factor Xa inhibitors with rapid thrombelastography

The use of direct factor Xa inhibitors rivaroxaban and apixaban (XABANs) has rapidly increased; however, there is no validated test available to monitor the effect on hemostasis. This study aims to assess how hemostatic management based on the Rapid Thromboelastography (R-TEG) variable activated clotting time (ACT) of XABAN patients with ongoing bleedings or in need for acute surgical intervention, affected patient outcome. A total of 343 XABAN patients were included in the main analysis together with 50 healthy volunteers to validate the reference value for ACT. An ACT >120 s (s) was defined as having XABAN-induced coagulopathy. Sixty-five percent of the XABAN patients presented with R-TEG ACT within the normal reference. Patients with XABAN-induced coagulopathy had a significantly increased risk of severe bleeding. Significantly more patients with extra-cerebral bleeding (ECB) and ACT above 120 s were transfused with five red blood cell (RBC) units or more compared to patients with ACT at 120 s or below (17% vs. 3%, p <.05). Significantly more XABAN-patients with ACT above 120 s received pro-hemostatic intervention with prothrombin complex concentrate (PCC) when compared to those with ACT at 120 s or below (ECB: 2% vs. 8%, p =.03, intracranial hemorrhage: 25% vs. 68%, p <.00). Patients who received PCC had a higher 30- and 90-day mortality compared to the rest of the cohort (16% vs. 6%, p = .02 and 21% vs. 7%, p =.00). Patients with XABAN-induced coagulopathy as evaluated by R-TEG ACT presented with more severe bleeding and higher transfusion requirements when compared to those with ACT in the normal range. This suggests that R-TEG ACT measurement in XABAN patients with active hemorrhage or in need for acute surgery may be of clinical value.

Effective Removal of Dabigatran by Idarucizumab or Hemodialysis: A Physiologically Based Pharmacokinetic Modeling Analysis

Background

Application of idarucizumab and hemodialysis are options to reverse the action of the oral anticoagulant dabigatran in emergency situations.

Objectives

The objectives of this study were to build and evaluate a mechanistic, whole-body physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) model of idarucizumab, including its effects on dabigatran plasma concentrations and blood coagulation, in healthy and renally impaired individuals, and to include the effect of hemodialysis on dabigatran exposure.

Methods

The idarucizumab model was built with the software packages PK-Sim® and MoBi® and evaluated using the full range of available clinical data. The default kidney structure in MoBi® was extended to mechanistically describe the renal reabsorption of idarucizumab and to correctly reproduce the reported fractions excreted into urine. To model the PD effects of idarucizumab on dabigatran plasma concentrations, and consequently also on blood coagulation, idarucizumab-dabigatran binding was implemented and a previously established PBPK model of dabigatran was expanded to a PBPK/PD model. The effect of hemodialysis on dabigatran was implemented by the addition of an extracorporeal dialyzer compartment with a clearance process governed by dialysate and blood flow rates.

Results

The established idarucizumab-dabigatran-hemodialysis PBPK/PD model shows a good descriptive and predictive performance. To capture the clinical data of patients with renal impairment, both glomerular filtration and tubular reabsorption were modeled as functions of the individual creatinine clearance.

Conclusions

A comprehensive and mechanistic PBPK/PD model to study dabigatran reversal has been established, which includes whole-body PBPK modeling of idarucizumab, the idarucizumab-dabigatran interaction, dabigatran hemodialysis, the pharmacodynamic effect of dabigatran on blood coagulation, and the impact of renal function in these different scenarios. The model was applied to explore different reversal scenarios for dabigatran therapy.

Electronic supplementary material

The online version of this article (10.1007/s40262-019-00857-y) contains supplementary material, which is available to authorized users.

Updates on Anticoagulation and Laboratory Tools for Therapy Monitoring of Heparin, Vitamin K Antagonists and Direct Oral Anticoagulants

Anticoagulant drugs have been used to prevent and treat thrombosis. However, they are associated with risk of hemorrhage. Therefore, prior to their clinical use, it is important to assess the risk of bleeding and thrombosis. In case of older anticoagulant drugs like heparin and warfarin, dose adjustment is required owing to narrow therapeutic ranges. The established monitoring methods for heparin and warfarin are activated partial thromboplastin time (APTT)/anti-Xa assay and prothrombin time – international normalized ratio (PT-INR), respectively. Since 2008, new generation anticoagulant drugs, called direct oral anticoagulants (DOACs), have been widely prescribed to prevent and treat several thromboembolic diseases. Although the use of DOACs without routine monitoring and frequent dose adjustment has been shown to be safe and effective, there may be clinical circumstances in specific patients when measurement of the anticoagulant effects of DOACs is required. Recently, anticoagulation therapy has received attention when treating patients with coronavirus disease 2019 (COVID-19). In this review, we discuss the mechanisms of anticoagulant drugs—heparin, warfarin, and DOACs and describe the methods used for the measurement of their effects. In addition, we discuss the latest findings on thrombosis mechanism in patients with COVID-19 with respect to biological chemistry.

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.

Pharmacological interventions for the treatment of insomnia: quantitative comparison of drug efficacy

PURPOSE

Although different forms of pharmacological intervention are often prescribed for insomnia disorder, the comparative efficacies among various drugs remain unclear. We therefore conducted this study to quantitatively compare the efficacy of various pharmacotherapies for insomnia by modeling.

METHODS

We searched PubMed, EMBASE and Cochrane Library databases for randomized placebo-controlled trials of insomnia medications that were conducted within a designated time period (from the inception dates to May 16, 2019). Pharmacodynamic models were established to describe the time course of changes from baseline in selected sleep parameters. Sleep quality and dropout rates were also compared by a single-arm meta-analysis.

RESULTS

In sum, 43 studies covering 44 trials (14,535 patients) were included in the analysis. The drugs evaluated included flurazepam, quazepam, temazepam, triazolam, eszopiclone, zaleplon, zolpidem, extended-release zolpidem, suvorexant, ramelteon and doxepin. The established models revealed eszopiclone had the highest efficacy in terms of sleep latency (SL), total sleep time (TST), and sleep quality, and was also associated with the lowest dropout rates. The effect of suvorexant on the parameter 'wake after sleep onset' (WASO) was significantly higher than that of the other drugs analyzed.

CONCLUSIONS

Each drug has its own characteristics in the treatment of insomnia, and this needs to be taken into consideration to meet individual clinical needs. These results serve as a quantitative supplement for clinical practice by reflecting the difference in efficacy of various drugs in the treatment of insomnia.

Quantitative analysis of the placebo response in pharmacotherapy of insomnia and its application in clinical trials

Study Objectives

This study aimed to develop a robust placebo response model for the pharmacotherapy for insomnia to guide drug development and clinical practice.

Methods

PubMed, EMBASE, and Cochrane Library databases were systematically searched for randomized placebo-controlled trials of medications for insomnia dating from the inception dates of the databases to April 18, 2018. Three placebo response models were established to describe the time–course of sleep parameters measured by objective (polysomnography or actigraphy) or subjective methods (sleep diary or questionnaires). The established models were applied to simulate placebo response distribution under different conditions using Monte Carlo simulations.

Results

Fifty-four studies involving 6,416 subjects were included. Placebo response increased over time and reached a plateau at approximately 8 weeks from start of therapy. Established models described the observed data reasonably well based on various diagnostic plots. Baseline sleep parameters affected the placebo response. There were significant positive correlations with placebo response and the severity of sleep latency, wake after sleep onset, and total sleep time at baseline. In addition, placebo response, assessed by subjective and objective methods, was consistent after correcting the baseline levels.

Conclusions

The established placebo response models can serve as a tool to predict placebo response at different baseline levels, which can provide valuable reference for clinical trial design, decision-making in drug development, and clinical practice.

Therapie mit Dabigatran

Summary Dabigatran, an oral, reversible direct factor IIa inhibitor, is approved in Europe for stroke prevention in atrial fibrillation and for the prevention of venous thromboembolism after elective hip and knee replacement. In contrast to vitamin K antagonists, a routine coagulation monitoring during the treatment with dabigatran etexilate is not necessary. However, in specific clinical situations such as invasive emergency procedures or serious haemorrhage, the actual anticoagulant status of dabigatran may be of importance for the treating clinician and can be assessed by clotting tests (aPTT, TT, ECT). The diluted thrombin time test (Hemoclot®), which is specifically calibrated for dabigatran, is useful for quantitative determination of the dabigatran serum concentration. In general, discontinuation of dabigatran etexilate 24 hours before standard elective surgery is sufficient to normalise the bleeding risk in patients with normal renal function. In patients with renal impairment and/or in the case of a high bleeding risk procedure the recommended duration of discontinuation is prolonged. If a bleeding episode occurs in a patient on dabigatran, further treatment should be based on the severity and localisation of the bleeding. A distinct feature of dabigatran is the possibility of effectively removing dabigatran from the circulation by haemodialysis. Recommendation: In the case of clinically minor bleedings, a delay in the administration of the next dabigatran etexilate dose is recommended. The length of the delay is based on the patient’s individual thromboembolic risk. In minor bleedings the use of prothrombin complex concentrates is not indicated. In the case of moderate or major bleedings the main focus should be on stabilising the circulation by using fluids and blood products and, if a lesion can be identified, the local treatment thereof. If time and infrastructure is available, dialysis offers an effective and fast option to remove dabigatran out of the circulation. In the incidence of severe and life threatening bleedings, an additional, more complex haemostasis management is required. Besides haemodynamic stabilisation of the circulation, administration of prothrombin complex concentrates should not be delayed. It has to be kept in mind that standard laboratory coagulation parameters may not accurately reflect the effect of prothrombin complex concentrates in patients on dabigatran. Hence the effect of the prothrombin complex concentrate should be monitored clinically and adjusted by means of onset of coagulation in vivo.

Comparative efficacy of five long-term weight loss drugs: quantitative information for medication guidelines

Quantitative information is scarce in current obesity medication guidelines, and they do not clearly reflect the differences in the efficacy characteristics among various drugs. This study quantitatively assessed the efficacy characteristics of five FDA-approved long-term weight loss drugs. Potentially eligible studies were obtained from public databases. Using the differences in the weight change from baseline between the drug group and the corresponding placebo group as the major indicator of efficacy, a time-effect model was established, and crucial pharmacodynamic parameters, such as the maximal efficacy, drug onset time and rate of body weight regain after the maximal efficacy point, were used to reflect the differences in efficacy among the five drugs. Finally, 50 reports (involving 43,443 participants) were included. After deducting the placebo effects, the maximal efficacies (95% CI) of orlistat (120 mg), lorcaserin, naltrexone-bupropion, phentermine-topiramate (PT, 7.5/46 mg) and liraglutide were -2.94 (-5.82, -1.27), -3.06 (-4.39, -1.71), -6.15 (-9.78, -3.25), -7.45 (-9.76, -3.88) and -5.50 (-10.62, -2.97) kg at weeks 60, 54, 67, 59 and 65 respectively, and their rates of body weight regain were 0.51, 0.48, 0.91, 1.27and 0.43 kg per year respectively. The 1-year dropout rates of orlistat, lorcaserin, naltrexone-bupropion, PT and liraglutide were 29.0, 40.9, 49.1, 34.9 and 24.3% respectively. In addition, a significant dose-effect correlation was observed for orlistat and PT. This study provides valid quantitative information for medication guidelines.

A combined pharmacometric analysis of dabigatran etexilate in healthy volunteers and patients with atrial fibrillation or undergoing orthopaedic surgery

Dabigatran etexilate is the orally bioavailable pro-drug of dabigatran, a direct thrombin inhibitor. Using data from eight clinical studies in healthy volunteers and patients with non-valvular atrial fibrillation (AF) or undergoing orthopaedic surgery (OS), population pharmacokinetic (PK) and pharmacodynamic (PD) models were developed to investigate whether the PK and PD of dabigatran differ across different populations. In both healthy volunteers (n=80) and patients (n=1,965), the PK of dabigatran was best described by a two-compartment disposition model with first-order absorption and elimination. Renal function was the only covariate shown to have a clinically relevant impact on dabig-atran exposure. The patient PK model was successfully applied in predicting exposure observed in the RE-LY trial evaluating dabigatran treatment in patients with non-valvular AF. The relationship between dabigatran plasma concentrations and activated partial thromboplastin time in healthy volunteers and patients (n=762) was best described with a combination of a linear model and a maximum effect (Emax) model, consistent with previous reports. PK/PD relationships were robust across the various populations tested and were not affected by any of the covariates examined. In summary, the PK of dabigatran is sufficiently consistent to allow extrapolation of data generated in healthy volunteers to patients with AF or undergoing OS.

Quantitative analysis of efficacy and associated factors of calcium intake on bone mineral density in postmenopausal women

A model-based meta-analysis method was performed to quantitatively analyze the efficacy characteristics of calcium intake in BMD increase among postmenopausal women. We found that age and calcium intake dose were key factors affecting the efficiency and onset of BMD change, and daily 1200 mg calcium was suggested to be a beneficial dosage.

INTRODUCTION

This paper aims to quantify the efficacy of calcium intake in preventing bone mineral density (BMD) decrease among postmenopausal women and to investigate the factors that may affect the efficacy.

METHODS

Comprehensive literature search was conducted in PubMed and EMBASE from January 2016. Placebo-controlled or no-treatment controlled randomized trials focused on calcium intake for the management of osteoporosis in postmenopausal women were included. The clinical and demographic characteristics of participants and efficacy data, defined as the mean percentage change of spine BMD (L2-L4) at each observation time point compared with that of baseline, were extracted from the studies. Model-based meta-analysis (MBMA) was used to describe the time course of BMD change by calcium intake and identify the related factors.

RESULTS

This study includes 17 trials involving 2537 subjects. The results showed that a classic pharmacodynamic maximal effect (E _max) model could describe the time course of BMD change by calcium intake. Using this model, we found that age and calcium intake dose were key factors affecting the efficiency and onset of BMD change. A 60-year-old woman administered with 800 mg/day calcium can achieve a maximum BMD increasing rate of 2.38%, and the time to reach 50% of this maximum (known as onset time) was 9.44 months. An increase of 0.0817% per year was noted in the maximal effect value for women aged between 50 and 83 years. For calcium dose interval from 250 to 2000 mg/day, the onset time was expressed as 9.44 × (dose/800)^-1.33 months. Two-year calcium intake of 700, 1200, and 2000 mg/day resulted in a maximum efficacy of BMD of 68.0, 81.3, and 89.6%, respectively. This indicates that the final efficacy had already reached the plateau (>80% E _max) under the 1200-mg/day dose.

CONCLUSION

Calcium intake can effectively postpone the tendency of BMD decrease in postmenopausal women. An increased calcium dose contributes to the shortening of the onset time. Considering the drug-acting rate and safety into account, menopausal women can be administered with a rational dose of 1200 mg/day to reduce bone loss.

Laboratory Assessment of the Anticoagulant Activity of Direct Oral Anticoagulants: A Systematic Review

BACKGROUND

Direct oral anticoagulants (DOACs) are the treatment of choice for most patients with atrial fibrillation and/or noncancer-associated venous thromboembolic disease. Although routine monitoring of these agents is not required, assessment of anticoagulant effect may be desirable in special situations. The objective of this review was to summarize systematically evidence regarding laboratory assessment of the anticoagulant effects of dabigatran, rivaroxaban, apixaban, and edoxaban.

METHODS

PubMed, Embase, and Web of Science were searched for studies reporting relationships between drug levels and coagulation assay results.

RESULTS

We identified 109 eligible studies: 35 for dabigatran, 50 for rivaroxaban, 11 for apixaban, and 13 for edoxaban. The performance of standard anticoagulation tests varied across DOACs and reagents; most assays, showed insufficient correlation to provide a reliable assessment of DOAC effects. Dilute thrombin time (TT) assays demonstrated linear correlation (r2 = 0.67-0.99) across a range of expected concentrations of dabigatran, as did ecarin-based assays. Calibrated anti-Xa assays demonstrated linear correlation (r2 = 0.78-1.00) across a wide range of concentrations for rivaroxaban, apixaban, and edoxaban.

CONCLUSIONS

An ideal test, offering both accuracy and precision for measurement of any DOAC is not widely available. We recommend a dilute TT or ecarin-based assay for assessment of the anticoagulant effect of dabigatran and anti-Xa assays with drug-specific calibrators for direct Xa inhibitors. In the absence of these tests, TT or APTT is recommended over PT/INR for assessment of dabigatran, and PT/INR is recommended over APTT for detection of factor Xa inhibitors. Time since last dose, the presence or absence of drug interactions, and renal and hepatic function should impact clinical estimates of anticoagulant effect in a patient for whom laboratory test results are not available.

Sensitivity of routine coagulation assays to direct oral anticoagulants: patient samples versus commercial drug-specific calibrators

Most studies on the sensitivities of coagulation assays to direct oral anticoagulants (DOACs) are based on normal plasma spiked with anticoagulant in the laboratory. Recent studies have shown that reagent sensitivity varies significantly depending on whether spiked or patient samples are used. The aim of this study was to compare the sensitivities of routine coagulation assays in patient samples and commercial drug specific calibrators using commonly used activated partial thromboplastin time (APTT) and prothrombin time (PT) reagents (i.e., Actin FS and Neoplastine CI Plus for APTT and PT, respectively) in Australian laboratories. Samples collected at Pathology North Hunter (PN-H) for dabigatran (n=39), rivaroxaban, (n=56) or apixaban levels (n=22) between February 2013 and November 2015 were analysed and compared to two different commercial drug specific calibrators from different manufacturers for each DOAC. Our results show that dabigatran (Hyphen and Technoclone) and rivaroxaban (Stago) calibrators tend to overestimate the APTT but are similar to patient samples for PT. A cut-off DOAC level of 50 ng/mL based on results from patient samples within the laboratory can be used as the lower limit which will result in prolongation of APTT for dabigatran (sensitivity 96%, n=25) and PT for rivaroxaban (sensitivity 97%, n=29), respectively. Individual laboratories should be familiar with the sensitivity of their coagulation reagents to different DOACs including differences between patient samples versus different commercial drug specific calibrators.

Laboratory Monitoring: A Turning Point in the Use of New Oral Anticoagulants

Large clinical trials have demonstrated that new oral anticoagulants (NOACs) are at least as efficient as vitamin K antagonists (VKAs) in preventing thromboembolic events, while providing a better safety profile. The relatively stable pharmacokinetics and pharmacodynamics, the reduced reports on food and drug interactions, and the wide therapeutic windows of NOACs appear to provide a more predictable anticoagulant effect than that observed with VKAs, enabling the use of fixed doses without the need for monitoring. However, the safe implementation of NOACs may require additional judgment, and one should not have the erroneous impression that NOACs are free from interactions or that inter- and intra-individual variability is absent with NOACs. In fact, a consensus seems to have been reached concerning the usefulness of "circumstantial" testing in certain clinical scenarios. Recent data also suggest that factors such as intercurrent diseases, drug interactions, and inexplicable variability may occasionally alter the anticoagulant effect of NOACs. Furthermore, the issue of nonadherence, already high in VKA-treated patients, may represent an even greater clinical concern with NOACs, given their short half-lives. This review aims to underline the main arguments that support the need for NOAC monitoring, at least in selected categories of patients. Additionally, an overview of classic coagulation assays and novel laboratory techniques that may provide a tool for NOAC monitoring is also provided.

Pharmacokinetics, pharmacodynamics and food effect of LB30870, a novel direct thrombin inhibitor, after single oral doses in healthy men

1. The safety, tolerability, pharmacokinetics, pharmacodynamics, and food effect of LB30870, a new selective thrombin inhibitor, were studied in 16 healthy men. 2. A double-blind, placebo-controlled single ascending dose study was done at oral doses of 5, 15, 30, 60, 120, and 240 mg under fasting conditions. An open, randomized, balanced cross-over food effect study was done at 60 mg dose. Plasma and urinary concentrations were measured up to 48 h post-dose. Coagulation and thrombin activity markers were measured at selected time points. 3. Cmax of LB30870 was at 1.3-3.0 h post-dose with a mean apparent terminal half-life (t1/2) of 2.8-4.1 h. AUC after doses above 15 mg appeared greater than dose-proportional. In fed state, AUC showed 80% reduction relative to fasting condition. 4. At doses 60 and 120 mg, peak activated partial thromboplastin time (aPTT) increased by 1.5- and 2-fold, respectively, from baseline. The aPTT and international normalized ratio (INR) were concentration-dependent, with less within-individual variability than ecarin clotting time (ECT), prothrombin time (PT), or thrombin time (TT). 5. Single oral doses of LB30870 up to 240 mg were well tolerated. The food effect must be overcome if LB30870 is to be used as an oral anti-coagulant.

Laboratory measurement of the anticoagulant activity of the non-vitamin K oral anticoagulants

BACKGROUND

Non-vitamin K oral anticoagulants (NOACs) do not require routine laboratory monitoring. However, laboratory measurement may be desirable in special situations and populations.

OBJECTIVES

This study's objective was to systematically review and summarize current evidence regarding laboratory measurement of the anticoagulant activity of dabigatran, rivaroxaban, and apixaban.

METHODS

We searched PubMed and Web of Science for studies that reported a relationship between drug levels of dabigatran, rivaroxaban, and apixaban and coagulation assay results. Study quality was evaluated using QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies 2).

RESULTS

We identified 17 eligible studies for dabigatran, 15 for rivaroxaban, and 4 for apixaban. For dabigatran, a normal thrombin time excludes clinically relevant drug concentrations. The activated partial thromboplastin time (APTT) and prothrombin time (PT) are less sensitive and may be normal at trough drug levels. The dilute thrombin time (R(2) = 0.92 to 0.99) and ecarin-based assays (R(2) = 0.92 to 1.00) show excellent linearity across on-therapy drug concentrations and may be used for drug quantification. For rivaroxaban and apixaban, anti-Xa activity is linear (R(2) = 0.89 to 1.00) over a wide range of drug levels and may be used for drug quantification. Undetectable anti-Xa activity likely excludes clinically relevant drug concentrations. The PT is less sensitive (especially for apixaban); a normal PT may not exclude clinically relevant levels. The APTT demonstrates insufficient sensitivity and linearity for quantification.

CONCLUSIONS

Dabigatran, rivaroxaban, and apixaban exhibit variable effects on coagulation assays. Understanding these effects facilitates interpretation of test results in NOAC-treated patients. More information on the relationship between drug levels and clinical outcomes is needed.

Interrupting anticoagulation in patients with nonvalvular atrial fibrillation

Three target-specific oral anticoagulants (TSOACs)-dabigatran, rivaroxaban, and apixaban-have been approved by the FDA to reduce the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation; however, no agents are currently approved to reverse the anticoagulant effects of these TSOACs in cases of active bleeding. This review discusses the benefits and risks of these TSOACs from a clinician's perspective, with a focus on the interruption of treatment for either elective or emergent surgery, monitoring, and reversal of anticoagulation. Available coagulation assays are not ideal for monitoring the effects of TSOACs and do not provide reliable quantitative measurement of their anticoagulant effects. When necessary, activated partial thromboplastin time (aPTT) may provide qualitative information on dabigatran, and prothrombin time (PT) may provide qualitative assessment of the presence of the factor Xa inhibitors, rivaroxaban and apixaban. Current recommendations for reversal of TSOACs are based largely on limited and sometimes conflicting data from in vitro or in vivo animal models, and clinical experience with these recommendations is also limited. Methods that have been investigated for effectiveness for reversal of the pharmacodynamic effects of the TSOACs include dialysis, activated charcoal, prothrombin complex concentrate (PCC), and recombinant activated factor VII. It is important to note that even within a class of anticoagulant drugs, compounds respond differently to reversal agents; therefore, recommendations for one agent should not be extrapolated to another, even if they are from the same therapeutic class. New antidotes are being explored, including a mouse monoclonal antibody to dabigatran; andexanet alfa, a potential universal factor Xa inhibitor reversal agent; and a synthetic small molecule (PER977) that may be effective for the reversal of factor Xa inhibitors and direct thrombin inhibitors. Given the short half-lives of TSOACs, watchful waiting, rather than reversal, may be the best approach in some circumstances.

Practical considerations in the use of novel oral anticoagulants for stroke prevention in nonvalvular atrial fibrillation

Atrial fibrillation (AF) is a highly prevalent cardiac arrhythmia associated with an increased risk of stroke. The role of anticoagulation therapy in the prevention of thrombosis and stroke is of critical importance for patients with AF. Limitations with vitamin K antagonists (VKAs), the current standard of care, have led to the development of novel oral anticoagulants (NOACs) that target either thrombin (dabigatran etexilate) or activated factor X (rivaroxaban, apixaban, and edoxaban). In comparison with traditional VKAs such as warfarin, these NOACs offer several pharmacologic advantages, including rapid onset of action, no significant food interactions, low potential for drug-drug interactions, and no requirement for routine coagulation monitoring. Completed phase-III clinical trials have demonstrated the therapeutic potential of dabigatran, rivaroxaban, and apixaban in comparison with warfarin for stroke prevention in patients with nonvalvular AF (NVAF). While the future utility of NOACs in preventing stroke in patients with NVAF looks promising, several practical issues, including the current lack of a reversal strategy and use of these agents in older patients with renal dysfunction, must be considered. Clinician and patient understanding of such issues will be important for the safe and effective use of NOACs.

Determination of dabigatran, rivaroxaban and apixaban by ultra-performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) and coagulation assays for therapy monitoring of novel direct oral anticoagulants

BACKGROUND

Three novel direct oral anticoagulants (DOACs) have recently been registered by the Food and Drug Administration and European Medicines Agency Commission: dabigatran, rivaroxaban, and apixaban. To quantify DOACs in plasma, various dedicated coagulation assays have been developed.

OBJECTIVE

To develop and validate a reference ultra-performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) method and to evaluate the analytical performance of several coagulation assays for quantification of dabigatran, rivaroxaban, and apixaban.

METHODS

The developed UPLC-MS/MS method was validated by determination of precision, accuracy, specificity, matrix effects, lower limits of detection, carry-over, recovery, stability, and robustness. The following coagulation assays were evaluated for accuracy and precision: laboratory-developed (LD) diluted thrombin time (dTT), Hemoclot dTT, Pefakit PiCT, ECA, Liquid anti-Xa, Biophen Heparin (LRT), and Biophen DiXal anti-Xa. Agreement between the various coagulation assays and UPLC-MS/MS was determined with random samples from patients using dabigatran or rivaroxaban.

RESULTS

The UPLC-MS/MS method was shown to be accurate, precise, sensitive, stable, and robust. The dabigatran coagulation assay showing the best precision, accuracy and agreement with the UPLC-MS/MS method was the LD dTT test. For rivaroxaban, the anti-factor Xa assays were superior to the PiCT-Xa assay with regard to precision, accuracy, and agreement with the reference method. For apixaban, the Liquid anti-Xa assay was superior to the PiCT-Xa assay.

CONCLUSIONS

Statistically significant differences were observed between the various coagulation assays as compared with the UPLC-MS/MS reference method. It is currently unknown whether these differences are clinically relevant. When DOACs are quantified with coagulation assays, comparison with a reference method as part of proficiency testing is therefore pivotal.

A clinician's perspective: novel oral anticoagulants to reduce the risk of stroke in nonvalvular atrial fibrillation--full speed ahead or proceed with caution?

Over the past few years, three novel oral anticoagulants, dabigatran, rivaroxaban, and apixaban, have been approved in the USA and Europe to reduce the risk of stroke or systemic embolism in patients with nonvalvular atrial fibrillation, and the results of a Phase III trial for a fourth novel oral anticoagulant, edoxaban, have recently been published. The aim of this review is to examine this indication from a clinician's perspective, highlighting efficacy and safety results from the major trials with these novel oral agents. Clinical issues regarding bleeding, monitoring, and reversal are discussed, along with requirements to consider when interrupting treatment with a novel oral anticoagulant for the purpose of transitioning to another anticoagulant and prior to cardioversion, ablation, percutaneous coronary intervention, or emergency surgery. The cost-effectiveness of each of the approved novel oral anticoagulants is reviewed, and the author provides recommendations for selecting appropriate patients for these agents.

Potential use of NOACs in developing countries: pros and cons

PURPOSE

Although vitamin K antagonists (VKAs) are effective for long-term thromboprophylaxis in atrial fibrillation (AF), their limitations have led to widespread underutilisation, especially in the developing world. Novel oral anticoagulants (NOACs) have emerged as promising alternatives to VKAs, although there are some particular considerations and challenges to their introduction in developing countries. This review summarises the current state of antithrombotic management of AF in the developing world, explores the early evidence for the NOACs and describes some of the special considerations that must be taken into account when considering the role of the NOACs within developing countries' health care systems.

METHODS

A literature search was conducted via PubMed and Google Scholar to find articles published in English between the years 2000 to 2014. Search terms used were "atrial fibrillation", "oral anticoagulants", "warfarin", "NOACs", "dabigatran", "rivaroxaban", "apixaban", "edoxaban", "time in therapeutic range", "International Normalized Ratio" "cost-effectiveness", "stroke", "adverse-drug reactions" and "drug-drug interactions", together with the individual names of developing countries as listed by the World Bank. We reviewed the results of randomized clinical trials, relevant retrospective and prospective studies, case-studies and review articles.

RESULTS

Many developing countries lack or have sporadic data on the quality of AF management, making it difficult to anticipate the potential impact of NOACs in these settings. The utilisation of anticoagulants for AF appears highly variable in developing countries. Given the issues associated with VKA therapy in many developing countries, NOACs offer some potential advantages; however, there is insufficient evidence to advocate the widespread replacement of warfarin at present. VKAs may continue to have a role in selected patients or countries, especially if alternative monitoring strategies can be utilised.

CONCLUSION

The evaluation of the introduction of NOACs should consider safety, budget concerns and the quality of oral anticoagulation care achieved by each country. Prospective registries will be important in developing countries to better elucidate the comparative safety, efficacy and cost-effectiveness of NOACs and VKAs as NOACs are introduced into practice.

The role of prothrombin complex concentrates in reversal of target specific anticoagulants

Over the past several years a new era for patients requiring anticoagulation has arrived. The approval of new target specific oral anticoagulants offers practitioners several advantages over traditionally used vitamin K antagonist agents including predictable pharmacokinetics, rapid onset of action, comparable efficacy and safety, all without the need for routine monitoring. Despite these benefits, hemorrhagic complicates are inevitable with any anticoagulation treatment. One of the major disadvantages of the new oral anticoagulants is lack of specific antidotes or reversal agents for patients with serious bleeding or need for urgent surgery. As use of the new target specific oral anticoagulants continues to increase, practitioners will need to understand both the pharmacodynamics and pharmacokinetic properties of the agents, as well as, the available literature with use of non-specific therapies to reverse anticoagulation. Four factor prothrombin complex concentrates have been available for several years in Europe, and recently became available in the United States with approval of Kcentra. These products have shown efficacy in reversing anticoagulation from vitamin K antagonists, however their usefulness with the new target specific oral anticoagulants is poorly understood. This article will review the properties of dabigatran, rivaroxaban and apixaban, as well as the limited literature available on the effectiveness of prothrombin complex concentrates in reversal of their anticoagulant effects. Additional studies are needed to more accurately define the role of prothrombin complex concentrates in patients with life threatening bleeding or who require emergent surgery, as current data is both limited and conflicting.

Measuring the anticoagulant effects of target specific oral anticoagulants-reasons, methods and current limitations

To simplify and optimize oral anticoagulation, new target-specific oral anticoagulants (TSOAs) have been developed. The direct thrombin-inhibitor dabigatran and the direct factor Xa inhibitors rivaroxaban, apixaban and edoxaban are the first such compounds to receive approval in certain countries for various indications. Due to the predictable pharmacokinetic and pharmacodynamic profiles of these drugs, routine monitoring of patients receiving TSOA therapy has not been considered necessary. However, it has now been realized that in routine clinical settings, there are several situations where it may be prudent to assess the level of TSOA anticoagulation. Several studies evaluating the influence of TSOAs on various coagulation assays have been performed to identify systems that can be used to monitor these drugs. With a particular focus on dabigatran and rivaroxaban, we will describe and discuss the potential of several methods for measuring the anticoagulant effect of TSOAs, as well as their methodological limitations and the restrictions in transferring their results into clinical context.

A semi-mechanistic absorption model to evaluate drug-drug interaction with dabigatran: application with clarithromycin

AIM

The aim of this study was to develop a PK/PD model to assess drug-drug interactions between dabigatran and P-gp modulators, using the example of clarithromycin, a strong inhibitor of P-gp.

METHODS

Ten healthy male volunteers were randomized to receive in the first treatment period a single 300 mg dose of dabigatran etexilate (DE) and in the second treatment period 500 mg clarithromycin twice daily during 3 days and then 300 mg DE plus 500 mg clarithromycin on the fourth day, or the same treatments in the reverse sequence. Dabigatran plasma concentration and ecarin clotting time (ECT) were measured on 11 blood samples. Models were built using a non-linear mixed effect modelling approach.

RESULTS

The best PK model was based on an inverse Gaussian absorption process with two compartments. The relationship between dabigatran concentration and ECT was implemented as a linear function. No continuous covariate was associated with a significant decrease in the objective function. The concomitant administration of clarithromycin induced a significant change only in DE bioavailability, which increased from 6.5% to 10.1% in the presence of clarithromycin. Clarithromycin increased peak concentration and AUC by 60.2% and 49.1% respectively.

CONCLUSION

The model proposed effectively describes the complex PK of dabigatran and takes into account drug-drug interactions with P-gp activity modulators, such as clarithromycin.

Dabigatran, intracranial hemorrhage, and the neurosurgeon

Dabigatran etexilate (Pradaxa) is a novel oral anticoagulant that has gained FDA approval for the prevention of ischemic stroke and systemic embolism in patients with nonvalvular atrial fibrillation. In randomized trials, the incidence of hemorrhagic events has been demonstrated to be lower in patients treated with dabigatran compared with the traditional anticoagulant warfarin. However, dabigatran does not have reliable laboratory tests to measure levels of anticoagulation and there is no pharmacological antidote. These drawbacks are challenging in the setting of intracerebral hemorrhage. In this article, the authors provide background information on dabigatran, review the existing anecdotal experiences with treating intracerebral hemorrhage related to dabigatran therapy, present a case study of intracranial hemorrhage in a patient being treated with dabigatran, and suggest clinical management strategies. The development of reversal agents is urgently needed given the growing number of patients treated with this medication.

Review article: Venous thromboembolism after total joint replacement

Venous thromboembolism can occur in up to 84% of cases following total joint replacement. It can result in pain, swelling, chronic post-thrombotic syndrome, and pulmonary embolism. Its prevention is vital to the success of the surgery. To achieve a safe and effective prophylaxis, a combination of mechanical and pharmacologic agents should be used. New generation of thromboprophylactic agents target different factors of the coagulation pathway.

Importance of pharmacokinetic profile and variability as determinants of dose and response to dabigatran, rivaroxaban, and apixaban

Warfarin has been the mainstay oral anticoagulant (OAC) medication prescribed for stroke prevention in atrial fibrillation (AF) patients. However, warfarin therapy is challenging because of marked interindividual variability in dose and response, requiring frequent monitoring and dose titration. These limitations have prompted the clinical development of new OACs (NOACs) that directly target the coagulation cascade with rapid onset/offset of action, lower risk for drug-drug interactions, and more predictable response. Recently, NOACs dabigatran (direct thrombin inhibitor), and rivaroxaban and apixaban (factor Xa [FXa] inhibitors) have gained regulatory approval as alternative therapies to warfarin. Though the anticoagulation efficacy of these NOACs has been characterized, differences in their pharmacokinetic and pharmacodynamic profiles have become a significant consideration in terms of drug selection and dosing. In this review, we outline key pharmacokinetic and pharmacodynamic features of each compound and provide guidance on selection and dosing of the 3 NOACs relative to warfarin when considering OAC therapy for AF patients. Importantly, we show that by better understanding the effect of clinical variables such as age, renal function, dosing interval, and drug metabolism (CYP3A4) and transport (P-glycoprotein), we might be able to better predict the risk for sub- and supratherapeutic anticoagulation response and individualize OAC selection and dosing.

Dabigatran and kidney disease: a bad combination

Dabigatran is an oral direct thrombin inhibitor widely used to prevent and treat various thromboembolic complications. An advantage of this agent over other anticoagulants is that routine laboratory monitoring and related dose adjustments are considered unnecessary. A major disadvantage is the absence of a reliable means of reversing its anticoagulant effect. After U.S. Food and Drug Administration approval, recently emerged data suggest a higher bleeding risk with dabigatran, especially in the elderly. Clinicians are thus faced with caring for patients with serious bleeding events without readily available tests to measure drug levels or the anticoagulant effects of dabigatran and without effective antidotes to rapidly reverse the anticoagulant effect. On the basis of dabigatran's pharmacokinetic profile, hemodialysis and continuous renal replacement therapy have been used to remove dabigatran with the hope, still unproven, that this would rapidly reverse the anticoagulant effect and reduce bleeding in patients with normal and those with reduced kidney function. However, the best clinical approach to the patient with serious bleeding is not known, and the risks of placing a hemodialysis catheter in an anticoagulated patient can be substantial. This article reviews this issue, addressing clinical indications, drug pharmacokinetics, clinical and laboratory monitoring tests, and dialytic and nondialytic approaches to reduce bleeding in dabigatran-treated patients.

The role of the laboratory in treatment with new oral anticoagulants

Orally active small molecules that selectively and specifically inhibit coagulation serine proteases have been developed for clinical use. Dabigatran etexilate, rivaroxaban and apixaban are given at fixed doses and do not require monitoring. In most circumstances, these drugs have predictable bioavailability, pharmacokinetic effects, and pharmacodynamic effects. However, there will be clinical circumstances when assessment of the anticoagulant effect of these drugs will be required. The effect of these drugs on laboratory tests has been determined in vitro by spiking normal samples with a known concentration of active compound, or ex vivo by using plasma samples from volunteers and patients. Data on the sensitivity of different reagents are now available, and so guidance as to the effect and interpretation of a test result is now possible. Laboratories should be aware of the sensitivity of their own assays to each drug. This may be achieved by using appropriate calibrated plasma samples.

Extracorporeal therapy for dabigatran removal in the treatment of acute bleeding: a single center experience

BACKGROUND AND OBJECTIVES

Dabigatran is an oral direct thrombin inhibitor that is Food and Drug Administration-approved for prevention of stroke in patients with atrial fibrillation. No antidote is available for reversal of dabigatran's anticoagulant effect. Despite limited clinical data, hemodialysis has been suggested as a strategy to remove dabigatran during acute bleeding. This work presents five cases, in which extracorporeal therapy was performed for dabigatran removal in acutely bleeding patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The series is comprised of five consecutive cases of patients receiving dabigatran 150 mg per os two times daily who were admitted with life-threatening bleeding between March of 2012 and January of 2013. Dabigatran plasma concentrations ranged from 149 to 1200 ng/ml. Treatment included administration of blood products to all patients and then, high-flux intermittent hemodialysis alone or followed by continuous renal replacement therapy.

RESULTS

Dabigatran concentrations decreased by 52%-77% during intermittent hemodialysis but rebounded up to 87% within 2 hours after completion of dialysis. Initiation of continuous renal replacement therapy after intermittent hemodialysis attenuated the rebound effect in one patient and contributed to a reduction in dabigatran concentrations of 81% over 30 hours.

CONCLUSIONS

Extracorporeal therapy lowered dabigatran concentrations, suggesting that it removed the drug and may effectively accelerate total clearance, especially in patients with impaired kidney function. The use of prolonged intermittent hemodialysis or intermittent hemodialysis followed by continuous renal replacement therapy is recommended for the management of life-threatening bleeding in patients receiving dabigatran. The advantage of extracorporeal therapy should be weighed against the risk of bleeding with catheter insertion.

Dabigatran in the peri-procedural period for radiofrequency ablation of atrial fibrillation: efficacy, safety, and impact on duration of hospital stay

Purpose

Dabigatran is effective for both the prevention of stroke and bleeding in patients with atrial fibrillation (AF). However, the safety and efficacy of the use of dabigatran in the peri-procedural period for radiofrequency catheter ablation (RFCA) of AF is unknown. Therefore, the purpose of this study was to evaluate the safety and efficacy of dabigatran in the peri-procedural period for RFCA of AF and the duration of hospital stay.

Methods

Consecutive patients (n = 227) who underwent RFCA for AF were prospectively analyzed. Peri-procedural anticoagulant therapy with dabigatran (n = 101, D group) was compared with warfarin and heparin bridging (n = 126, W group). Dabigatran was discontinued 12–24 h before and restarted 3 h after the procedure. Warfarin was stopped 3 days before the procedure and unfractionated heparin was administered.

Results

Ischemic stroke occurred in one patient of the D group (0.8 %). There was no significant difference between the two groups in the incidence of major bleeding (three cases of cardiac tamponade in each group and one case of intracranial bleeding in the W group, p = 0.93) or minor bleeding (five cases in the D group vs. five in the W group, p = 0.54). The duration of hospital stay was significantly shorter in the D group than in the W group (7.2 vs. 10.3 days, p = 0.0001).

Conclusions

Peri-procedural anticoagulation therapy with dabigatran for RFCA of AF was equally safe and effective compared with warfarin and heparin bridging. The use of dabigatran for RFCA of AF shortened the duration of hospital stay.

[Dealing with massive bleeding and associated perioperative coagulopathy: recommendations for action of the German Society of Anaesthesiology and Intensive Care Medicine]

Massive bleeding with coagulopathy and hemorrhagic shock poses a potential threat to life in numerous clinical settings. Optimal treatment including the prevention of exsanguination necessitates a standardized and interdisciplinary approach. Several studies have shown the importance of massive transfusion protocols and standardized coagulation algorithms to improve survival of severely bleeding patients and to avoid secondary complications. Thus, the Helsinki declaration for patient safety in anesthesiology demands the implementation of clinical practice guidelines for the treatment of patients requiring massive transfusion. This paper introduces a standardized algorithm for the treatment of patients with massive bleeding which was developed in consensus with the German Society of Anaesthesiology and Intensive Care Medicine (DGAI).

Differences in intraprocedural ACTs with standardized heparin dosing during catheter ablation for atrial fibrillation in patients treated with dabigatran vs. patients on uninterrupted warfarin

PURPOSE

Effective intraprocedural anticoagulation for catheter ablation for atrial fibrillation is critical to minimize the risk of cerebral thromboembolism. The effect of dabigatran on anticoagulation with heparin during the procedure is unknown. This study compares heparin anticoagulation in patients treated with dabigatran vs. patients on uninterrupted warfarin.

METHODS

Seventy-six consecutive patients (24 dabigatran and 52 warfarin) subjected to a standard intraprocedural heparin protocol were included. Heparin administration and rapidity and degree of anticoagulation were compared between the groups.

RESULTS

Despite greater administration of heparin (52.5 ± 22.0 vs. 33.2 ± 10.1 units kg(-1) h(-1); p < 0.001), the mean (320.3 ± 19.5 s) and peak (358.8 ± 28.6 s) activated clotting time (ACT) for the dabigatran group were significantly lower than for the warfarin group (mean, 362.9 ± 35.9 and peak, 410.4 ± 49.7; p < 0.001). The time from initial heparin bolus to first ACT of ≥300 s in the dabigatran group was more than twice that observed in the warfarin group (45.0 ± 30.4 vs. 20.9 ± 14.5 min; p < 0.001). The time to first ACT of ≥350 s was similarly prolonged (109.1 ± 60.0 vs. 55.2 ± 51.1 min; p < 0.001) in the dabigatran group, with eight patients (33 %) failing to reach this target. Outcome differences persisted following analysis using linear models and Cox proportional hazard regression with adjustment for propensity scores.

CONCLUSION

A standard intraprocedural heparin protocol results in delayed and lower levels of anticoagulation as measured by the ACT for patients treated with dabigatran compared with those on uninterrupted warfarin.

[Clinical management of the new anticoagulants]

The vitamin K antagonists (VKA) available for stroke prevention in patients with atrial fibrillation have many drawbacks due to their difficult clinical use and high risk of bleeding. Currently, several drugs are being developed as possible substitutes for VKA that have many advantages such as the lack of monitoring requirement and scarce pharmacologic and food interactions. The present article provides an update on the new oral anticoagulants that are in a more advanced stage of clinical research, their pharmacologic properties, advantages and disadvantages and their results in recent clinical trials.