Drug Class, Renal Elimination, and Outcomes of Direct Oral Anticoagulants in Asian Patients: A Meta-Analysis.

BACKGROUND: Direct oral anticoagulants (DOACs) have a better risk benefit profile in Asian patients with atrial fibrillation (AF). Whether treatment effects could be modified by drug class and dependency on renal elimination of studied agents has not yet been explored. METHODS: We searched PubMed, CENTRAL, and CINAHL databases through November 2016 for phase III randomized controlled trials comparing DOACs with warfarin in patients with AF. Efficacy and safety outcomes were pooled according to drug class and dependency on renal elimination of DOACs and were compared with the Mantel-Haenszel fixed-effects model. Effect differences were assessed with Bucher's indirect comparisons using common estimates, once heterogeneity was low, and with the Bayesian method. RESULTS: Among 6496 Asian patients from 6 trials, both direct thrombin inhibitors and factor Xa inhibitors, compared with warfarin, were associated with lower risks of stroke or systemic embolism and major bleeding (risk ratio [95% confidence interval], 0.51 [0.33-0.78], 0.74 ([0.58-0.96], 0.60 [0.41-0.86], and 0.59 [0.47-0.76], respectively). There was no between-group difference in direct thrombin inhibitors and factor Xa inhibitors or in DOACs with renal elimination less than 50% and 50% or greater (all I2 < 25% and interaction P > .05). Indirect comparisons within strata of drug class and dependency on renal elimination showed no preferential effect of any given regimen over another. There was no difference in effects on ischemic and hemorrhagic stroke, intracranial hemorrhage, myocardial infarction, and all-cause mortality between DOACs stratified by pharmacologic characteristics. CONCLUSIONS: DOACs, as a therapeutic class, outperform warfarin in efficacy and safety in Asian patients with AF.

Tolerability and Acceptability of Non-Vitamin K Antagonist Oral Anticoagulants in Atrial Fibrillation: Systematic Review and Meta-Analysis.

BACKGROUND: The non-vitamin K antagonist oral anticoagulants (NOACs) overcame some limitations of vitamin K antagonists (VKAs), and are at least as effective in stroke prevention, with an additional decrease of intracranial bleeding risk. The transferability of these benefits to the real world requires tolerability (related to adverse events) and acceptability (drug discontinuation) profiles at least similar to VKAs. METHODS: We performed a systematic review with meta-analysis of randomized controlled trials (RCTs) evaluating NOACs versus VKAs in patients with non-valvular atrial fibrillation (AF). Studies were searched in April 2015 through MEDLINE, the Cochrane Collaboration's Database, Health Technology Assessment (HTA), Web of Science, and regulatory agencies' documents. Serious adverse events (SAEs) as well as drug-related and patient-related discontinuation rates were the outcomes of interest. Random-effects meta-analysis was performed, and the results expressed as risk ratios (RRs) and 95 % confidence intervals (CIs). Heterogeneity was evaluated with I (2) test. RESULTS: Five RCTs evaluating four NOACs (apixaban, dabigatran, edoxaban, and rivaroxaban) and 72,720 patients were included. Overall, NOACs were associated with a 4 % risk reduction of SAEs (95 % CI 2-6; I (2) = 0 %). Drug-related and patient-related discontinuation rates were similar between NOACs and VKAs (RR 1.03 [0.88-1.21] and RR 0.99 [0.89-1.10], respectively). Significant heterogeneity (I (2) ≥ 75 %) was found among studies results, which could be, at least partially, explained by the findings of the open-label dabigatran trial. CONCLUSIONS: NOACs were associated with a small, yet significant, risk reduction of SAEs in patients with AF. NOACs' drug-related and patient-related acceptability profiles were similar to those for VKAs. The results were heterogeneous mainly because of the increased rate of discontinuation associated with dabigatran. Pragmatic trials and cohort studies should be conducted to further address these important clinical questions.

A new method to quantify ß-antithrombin glycoform in plasma reveals increased levels during the acute stroke event.

INTRODUCTION: ß-antithrombin, the minor antithrombin glycoform in plasma, is probably the major thrombin inhibitor in vivo because of its high heparin affinity. The levels and variability of this glycoform in general population and its relevance in thromboembolic diseases is unknown since there is no specific method to measure this glycoform in clinical samples. METHODS: Plasma and recombinant α- and ß-antithrombins were purified by heparin affinity chromatography. An anti-FXa chromogenic method in presence of pentassacharide was used with two NaCl concentrations (15mM and 1.1M). This method was applied to plasma samples from 97 healthy subjects and 117 consecutive patients with ischemic cerebrovascular disease during the acute event and one year later. SERPINC1 sequencing was done in cases with antithrombin deficiency. RESULTS: High salt concentrations specifically restricted the pentassacharide-induced activation of antithrombin to the ß glycoform. ß-antithrombin displayed a normal distribution in the general population (89.5%-103.5%), with no significant variations according to age or sex. In patients, whole antithrombin values remained within the normal range. Only five cases had antithrombin deficiency during the thrombotic event, one carrying the L99F mutation in SERPINC1. Interestingly, both ß-antithrombin and the ß/whole antithrombin ratio were significantly higher in patients during the acute event but normalized after one year. CONCLUSIONS: We have developed a rapid, simple, sensitive and specific method to quantify ß-antithrombin activity using 1µL of plasma. ß-antithrombin significantly increases in patients with ischemic cerebrovascular disease during the acute event, probably by its release from the vasculature.

Antithrombin and its inherited deficiencies.

Human antithrombin is the major inhibitor of the coagulation serine proteases accounting for approximately 80% of the thrombin inhibitory activity of plasma. It is a member of the serpin family of serine protease inhibitors and in common with some other members of this family it undergoes a dramatic increase in its inhibitory activity in the presence of heparin and other sulphated glycosaminoglycans. Two functional domains in antithrombin are recognised, the reactive site domain which interacts with the active site serine residue of the protease and the heparin binding domain. The gene for antithrombin has been cloned and its entire nucleotide sequence determined. A deficiency or functional abnormality of antithrombin may result in an increased risk of thromboembolic disease. Such deficiencies are estimated to affect as many as 1:300 of the general population and 3 to 5% of patients with thrombotic disease. On the basis of functional and immunological antithrombin assays, antithrombin deficiency may be subdivided into Types I and II. Type I disease is due to a wide variety of heterogeneous DNA mutations whilst in Type II disease missense mutations leading to single amino acid substitutions have been identified in all cases. Clinically, Type I antithrombin deficiency is associated with recurrent thromboembolic disease whereas in Type II deficiency the risk of thrombosis is closely related to the position of the mutation within the protein. Thus, heterozygotes with mutations within the heparin binding domain of antithrombin have a relatively low risk of thrombosis compared to those with mutations at or close to the reactive site of the molecule.

Antithrombin Oslo: type Ib classification of the first reported antithrombin-deficient family, with a review of hereditary antithrombin variants.

Patients with classical antithrombin deficiency (Type I) from seven unrelated kindreds were studied by crossed immunoelectrophoresis of plasma in the presence and absence of heparin. The only abnormal pattern was found in the kindred first reported by Egeberg in 1965. An abnormal cathodal peak of antithrombin antigen was found in the presence, but not the absence, of heparin in the first dimension gel. We have named this variant antithrombin Oslo. Such evidence of an abnormal protein, despite equivalent low levels of antithrombin antigen and activity, has been denoted previously by Sas as Type Ib deficiency. In the context of this new report, we review the literature to date on 33 other variants of the Types Ib, II and III subclassifications with a discussion of the value of the classification scheme.

Comparative pharmacology of site directed antithrombin agents. Implication in drug development.

Beside the direct inhibition of thrombin and its regulatory functions, many of the newer antithrombin agents produce several additional effects, unrelated to their anticoagulant actions. Synthetic peptide inhibitors are capable of producing fibrinolytic compromise by virtue of their actions on fibrinolytic enzymes such as t-PA, plasmin, urokinase and protein Ca. In addition, the low molecular weight arginine-containing peptides are also known to produce hemodynamic and hemostatic deficits. The designs of the ongoing clinical trials are largely empirical because of the non-availability of valid pharmacologic and toxicologic data on thrombin inhibitors. In contrast to heparin, none of the thrombin inhibitors produce endogenous release of tissue factor pathway inhibitor (TFPI) in the experimental and clinical settings. These observations suggest that beside the direct inhibition of thrombin, these agents also produce multiple additional effects that can significantly contribute to their pharmacologic and toxicologic profile.

Insight into residues critical for antithrombin function from analysis of an expanded database of sequences that includes frog, turtle, and ostrich antithrombins.

Complete sequences were determined for frog, turtle, and ostrich antithrombins. Protein sequence comparisons with the other 10 known antithrombin sequences and with sequences of other serpins have provided striking evidence for the conservation of the heparin activation mechanism and new insight into those residues important for heparin binding, for heparin activation, and for reactive center loop function, as well as an indication of which glycosylation sites might be needed for function. Importantly, an understanding of, as yet, poorly understood antithrombin-protein interactions will be greatly aided by this expanded database and comparative analysis.