Drug therapy in anticoagulation: which drug for which patient?

Four non-vitamin K oral anticoagulants (NOACs) are now licensed and available in the UK, offering unprecedented choices in anticoagulant therapy for clinicians and patients. NOACs have many clear benefits over warfarin, the most striking being the reduction in intracranial haemorrhage. However, a number of uncertainties remain: their efficacy in certain situations, utility of drug assays, significance of drug interactions and management of bleeding. In the absence of any direct comparative trials, it is not clear that any of the NOACs is significantly better than the others in any of the licensed indications. The differential activities, pharmacokinetics, metabolism, excretion and side effects of the agents should be considered when selecting the most appropriate anticoagulant. In this article, we discuss how, with careful selection for the relevant indication, NOACs can simplify therapy while improving outcomes. We aim to provide clinicians with the information needed to select the most suitable anticoagulant drug for an individual patient in a given situation.

[Bleeding during anticoagulant and antiaggregation therapy as a cause of acute abdomen]

Pradaxa (dabigatrani etexilati mesilas) belongs to a new group of anticoagulants, its pharmacological properties enabling uniform dosage without a need for monitoring the anticoagulant effect. It is an oral direct thrombin inhibitor. Pradaxa is the first NOAC (new oral anticoagulant) with a specific reversal agent called Praxbind (idarucizumab). Dabigatran is indicated for the prophylaxis of venous thromboembolism in elective hip or knee replacements, for the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation, as well as for the treatment of deep vein thrombosis and pulmonary embolism and also their recurrence in adult patients.Key words: dabigatrani etexilati anticoagulant therapy - thromboembolism idarucizumab.

Feasibility and safety of prehospital administration of bivalirudin in patients with ST-elevation myocardial infarction

The selective thrombin inhibitor bivalirudin with a provisional glycoprotein IIb/IIIa inhibitor (GPI) has been shown to be comparable to heparin plus GPI in the rates of ischemic events but to significantly reduce the risk of bleeding complications in patients with acute coronary syndromes. The aim of this preliminary study was to describe the feasibility and safety of a switch from prehospital administration of unfractionated heparin to bivalirudin in ST-elevation acute myocardial infarction (STEMI) patients referred for primary percutaneous coronary intervention. Patients with STEMI treated with a 1-mg/kg bivalirudin bolus in the ambulance followed by infusion during angiography/primary percutaneous coronary intervention were compared with a STEMI control group (from the preceding year) treated with 10,000 U unfractionated heparin in the ambulance followed by in-hospital treatment with a GPI. A total of 102 patients (59%) receiving bivalirudin and 72 receiving heparin were followed during hospitalization. The baseline characteristics and prehospital treatment times were comparable between the 2 groups. The thrombolysis in myocardial infarction flow before and after primary percutaneous coronary intervention was similar. Stents were used significantly more often in the heparin-treated patients (90% versus 76%; p = 0.04), with bailout GPI for those receiving bivalirudin occurring in 30% compared with 83% of those receiving heparin (p <0.001). Significant bleeding complications were seen in <10% of all patients undergoing angiography with no difference between groups. Bivalirudin was easy to administer in the prehospital setting and did not affect the prehospital run times. In conclusion, the results suggest that prehospital bivalirudin administration is as safe and effective as heparin in the treatment of patients with STEMI. Prehospital administration seemed to reduce the need for GPI.

[Abnormality in blood coagulation because of protein S-K196E mutation]

We recently identified protein S-K196E mutation as a genetic risk factor for venous thromboembolism in the Japanese population. The E allele frequency was found to be 0.009. Therefore, a substantial proportion of the Japanese population may be assumed to be carrying the E allele of protein S and is at risk of developing venous thromboembolism.

Interatrial septal defect closure for cerebrovascular accidents: exploring the role of various anticoagulants

BACKGROUND

The role of different anticoagulants in reducing in-hospital complications in patients undergoing closure of interatrial septal defects (IASD) is unknown. In this study, we review our own experience with IASD closure data to determine if in-hospital complications and ambulation time are influenced by the use of various anticoagulants.

METHODS

Fifty-five consecutive patients with a history of unexplainable stroke or transient ischemic attacks (TIA), with the exception of the presence of an IASD, were included in this study. Multiple variables were collected including age, gender, history of smoking, hypertension, diabetes, hypercholesterolemia, ejection fraction, anticoagulants used pre- and postprocedure, anticoagulants used during the closure procedure, shunt grade across the IASD pre- and postprocedure, defect size, and right-sided filling pressures. Descriptive analysis was performed on all variables including complications frequency and ambulation time, and compared between bivalirudin and indirect thrombin inhibitors.

RESULTS

Of 55 consecutive patients included in this study, 22 patients received bivalirudin and 33 patients received unfractionated heparin (UFH) (n = 26) or enoxaparin (n = 7). The bivalirudin patients were older (60.1 vs 50.8 years; p = 0.028), with a higher incidence of interatrial septal aneurysm (75% vs. 40.7%; p = 0.037). In-hospital complications included 1 (5%) patient with a minor bleed (groin hematoma) in the bivalirudin group, and 3 patients with minor bleed (1 GI bleed, 1 groin hematoma, and 1 transient ischemia on electrocardiogram) in the non-bivalirudin group (9.1%). No patient had a major bleed that required a transfusion or prolonged hospital stay. Ambulation time was not significantly different between the two groups (7.7 +/- 5.9 hours for bivalirudin and 6.9 +/- 5.1 hours for other anticoagulants; p = NS).

CONCLUSION

We conclude that bivalirudin is safe during IASD closure, with a statistically nonsignificant trend toward fewer minor complications than UFH and enoxaparin. No major bleeding occurred in either group. This could be due to the fact that IASD closure is performed via venous access that generally carries a low bleeding complication rate and allows safe early ambulation, irrespective of the anticoagulant utilized and despite the use of 10 and 11 Fr sheaths. Given that major differences do not appear to exist in this exploratory study between the anticoagulants studied, patent foramen ovale closure is currently being performed in our laboratory with UFH.

Protein adsorption on polyurethane catheters modified with a novel antithrombin-heparin covalent complex

Highly anticoagulant covalent antithrombin-heparin complex (ATH) was covalently grafted onto polyurethane catheters to suppress adsorption/activation of procoagulant proteins and enhance adsorption/activation of anticoagulant proteins for blood compatibility. Consistency of catheter coating was demonstrated using immunohistochemical visualization of ATH. The ability of the resulting immobilized ATH heparin chains to bind antithrombin (AT) from plasma, as measured by binding of (125)I-radiolabeled AT, was greater than that for commercially-available heparin-coated catheters, and much greater than for uncoated catheters. Complementary measurements of antifactor Xa (FXa) activity and plasma protein binding were also performed. Both ATH-coated and heparin-coated catheters demonstrated functional binding of exogenous AT. However, the ATH-coated catheters gave a trend towards elevated anti- FXa activities/AT binding ratios, consistent with the higher active pentasaccharide content in starting ATH. Western blot analysis of proteins adsorbed to catheters after incubation with rabbit plasma established protein binding profiles that showed AT and albumin as major plasma proteins adsorbed to ATH-coated catheters, while AT and altered forms of fibrinogen were major plasma protein species adsorbed to heparinized catheters.

Chronic performance of polyurethane catheters covalently coated with ATH complex: A rabbit jugular vein model

Covalent complexes of antithrombin (AT) and heparin (ATH) have superb anticoagulant activity towards thrombin and factor Xa. Stability of polyurethane central venous catheters covalently modified with radiolabeled ATH was studied using a roller pump with saline or protease P-5147. Saline wash removed loosely bound ATH molecules to decrease graft density from 26 to 12 pmol/cm2. However, only slightly more ATH was removed by strong protease (from 12 to 7 pmol/cm2). To evaluate ATH-coated, heparin-coated, and uncoated catheters, a chronic rabbit jugular vein model was developed with catheters maintained for up to 30-106 days. Lumen occlusion was tested by drawing blood twice daily. Although unmodified or heparin-coated catheters occluded within 5-7 days after insertion, all ATH catheters remained patent throughout the experiment. Scanning electron microscopy (SEM) analysis of heparin and uncoated catheters revealed extensive thrombosis (lumen+mural) while ATH catheters were unaffected. Visual observation showed significant deposition of protein and cells on control and heparin-modified catheters and, to a lesser degree, on ATH-coated surfaces. SEM showed no fibrin inside or outside of ATH catheters, which remained patent in extended studies out to 106 days. Although atomic force microscopy showed ATH coatings to be rough, 6-fold higher anti-factor Xa activity likely contributed to increased patency. Our data confirm that ATH-modified catheters are stable and have superior potency compared to heparin or control catheters.

Provisional glycoprotein IIb/IIIa blockade in a randomized investigation of bivalirudin versus heparin plus planned glycoprotein IIb/IIIa inhibition during percutaneous coronary intervention: predictors and outcome in the Randomized Evaluation in Percutaneous coronary intervention Linking Angiomax to Reduced Clinical Events (REPLACE)-2 trial

BACKGROUND

The REPLACE-2 trial demonstrated the noninferiority of bivalirudin with provisional glycoprotein IIb/IIIa (GPIIb/IIIa) blockade as compared with heparin plus planned GPIIb/IIIa blockade among patients undergoing percutaneous coronary revascularization. Provisional drug was used in 374 (6%) of the 6010 patients. We sought to analyze the predictors for provisional drug use and to assess the outcomes in this cohort.

METHODS

Outcome among the 5.2% of patients in the heparin plus GPIIb/IIIa blockade group and the 7.2% of patients in the bivalirudin group who received provisional placebo or GPIIb/IIIa inhibitor, respectively, was compared against patients without provisional drug use and between randomized arms. Multivariate models identified predictors of provisional drug use and outcome at 30 days, 6 months, and 1 year.

RESULTS

Myocardial infarction, repeat revascularization, and bleeding events occurred more frequently among patients who required provisional drug than those who did not, but there were no differences in 1-year mortality. Ischemic and hemorrhagic end points occurred at similar rates among patients receiving provisional drug in either the heparin plus GPIIb/IIIa group compared with the bivalirudin group. Independent predictors of provisional drug use were randomization to bivalirudin, recent infarction, multilesion intervention, impaired pretreatment coronary flow, and lesion complexity. Provisional drug use, but not randomization to bivalirudin, independently predicted 30-day and 6-month ischemic events.

CONCLUSIONS

Provisional administration of a GPIIb/IIIa inhibitor is associated with more frequent ischemic and bleeding events, reflecting the procedural complications that led to the use of provisional drug. The proportion of bivalirudin-treated patients who will require provisional GPIIb/IIIa blockade, however, is not large enough to have a significant deleterious impact on the overall incidence of ischemic end points or to invalidate the strategy of bivalirudin plus provisional GPIIb/IIIa blockade.

PMEA polymer-coated PVC tubing maintains anti-thrombogenic properties during in vitro whole blood circulation

Poly(2-methoxyethylacrylate) (PMEA) is a new coating material that appears to reduce protein and platelet adsorption. However, the exact performance of PMEA coated circuit remains to be revealed in well-controlled experiments. Therefore, we compared its hemocompatibility with covalent-bound heparin-, and non-coated circuits during 6 hours of in vitro circulation, using donor blood from six volunteers. In our model, simple tubing circuits containing one-way ball valve were placed on the rotary table, which moved alternatively to generate pulsatile recirculation of heparinized human blood inside the tubing. Using this model, we expected fine assessment of the material surface, because we could reduce blood damage by avoiding air and a blood pump. Moreover, the small capacity of circuit allowed us to compare three kinds of circuits using a single unit of donor blood, eliminating effects by possible variations between blood donors. The anti-thrombin capacity of the PMEA-coated circuits was maintained even after six hours blood circulation, whereas surface thrombin generation increased markedly after use in non-coated circuits (P<0.05). Deposition of fibrin onto PMEA circuits was reduced more than 30% compared with heparin and non-coated circuits (P<0.05). However, the increase of plasma Factor XIIa was similar in all circuits. Increase of CD11b expression on circulating leukocytes and of plasma C3a was ameliorated in the heparin- and PMEA-coated circuits (P<0.05). PMEA-coated circuits appear to maintain their anti-thrombogenicity during use, otherwise PMEA-coated and heparin-coated circuits showed a similar character in hemocompatibility. This long-standing anti-thrombogenicity might be attributable to less adsorption of activated blood components onto the surface.

Functionality and stability of heparin immobilized onto poly(dimethylsiloxane)

Poly(dimethylsiloxane) (PDMS) has become an attractive material when working in the field of microfluidics, mainly because of the rapid prototyping process it involves. The increased surface volume ratio in microchannels makes the interaction between sample and material surface highly important, evident when handling complex biological samples such as plasma or blood. This study demonstrates a new grade of non-covalent heparin surface that adds efficient anticoagulant property to the PDMS material. The surface modification is a simple and fast one-step process performed at neutral pH, optimal when working with closed microsystems. The heparin formed a uniform and functional coating on hydrophobic PDMS with comparatively high level of antithrombin-binding capacity. In addition, long-term studies revealed that the immobilized heparin was more or less stable in the microchannels over a time of three weeks. Recalcified plasma in contact with native PDMS showed complete coagulation after 1h, while no fibrin formation was detected in plasma incubated on heparin-coated PDMS within the same time. In conclusion, we see the heparin coating developed and evaluated in this study as a tool that greatly facilitates the use of PDMS in microfluidics dealing with plasma or blood samples.

Chromogenic methods in coagulation diagnostics

Chromogenic peptide substrates were developed more than 30 years ago. Although the use of chromogenic substrate methods in coagulation and fibrinolysis diagnostics was not as rapidly implemented as initially believed, they are now well established for several analytes such as antithrombin, FVIII, protein C, plasminogen, plasmin inhibitor, heparins, and pentasaccharides. The advent of direct thrombin and factor Xa inhibitors has stimulated the development of new, specific chromogenic methods and these may find their way into routine use if these new drug candidates will prove to be valid replacements for coumarin derivatives. A large number of chromogenic research methods for other analytes were developed, too. The current interest in global chromogenic methods for thrombin generation and the protein C pathway may turn out as clinically important and thus enter into routine use.

Bivalirudin versus heparin as an antithrombotic agent in patients who undergo percutaneous saphenous vein graft intervention with a distal protection device

Bivalirudin (Angiomax) is increasingly used as a substitute for heparin in a variety of percutaneous coronary interventions, and data on its usage in saphenous vein graft interventions are limited. This retrospective, observational study evaluated the efficacy and safety of bivalirudin compared with heparin as an antithrombotic regimen in patients who underwent saphenous vein graft intervention with distal protection devices. We found that bivalirudin use is clinically safe and feasible, with fewer vascular and ischemic complications compared with heparin.

Effect of bivalirudin on length of stay in the recovery area after percutaneous coronary intervention compared with heparin alone, heparin + abciximab, or heparin + eptifibatide

Three hundred nine patients were followed during their recovery area stay after percutaneous coronary intervention. Recovery area times for patients who received bivalirudin during percutaneous coronary intervention showed an average reduction in total recovery area length of stay of 36 minutes (p <0.0001) compared with patients who received heparin alone. This reduction was also seen when compared with the heparin + abciximab group (46-minute reduction, p = 0.0007), and the heparin + eptifibatide group (35-minute reduction, p = 0.0005). Patients who received bivalirudin took significantly less time for the activated clotting time (ACT) to normalize despite significantly higher average ACTs and significantly fewer subtherapeutic ACTs.