The pharmacodynamics and pharmacokinetics of the oral direct thrombin inhibitor ximelagatran and its active metabolite melagatran: a mini-review

Evaluation of amidoxime derivatives as prodrug candidates of potent bis-cationic antimalarials

Plasmodium falciparum is responsible for most of the cases of malaria and its resistance to established antimalarial drugs is a major issue. Thus, new chemotherapies are needed to fight the emerging multi-drug resistance of P. falciparum malaria, like choline analogues targeting plasmodial phospholipidic metabolism. Here we describe the synthesis of amidoxime derivatives as prodrug candidates of reverse-benzamidines and hybrid compounds able to mimic choline, as well as the design of a new series of asymmetrical bis-cationic compounds. Bioconversion studies were conducted on amidoximes in asymmetrical series and showed that amidoxime prodrug strategy could be applied on C-alkylamidine moieties, like benzamidines and that N-substituents did not alter the bioconversion of amidoximes. The antimalarial activity of the three series of compounds was evaluated in vitro against P. falciparum and in vivo against P. vinckei petteri in mice.

Pharmacokinetics and pharmacodynamics of oral anticoagulants used in atrial fibrillation

INTRODUCTION

The availability of non-vitamin K antagonist oral anti-coagulants alongside vitamin K antagonists has offered a variety of options for anti-coagulation, but has also necessitated a good understanding of the pharmacological properties of each of these drugs prior to their use, to maximise the therapeutic benefit and minimise patient harm Areas covered: This review article outlines the pharmacokinetic and pharmacodynamic profiles of the currently licensed VKAs and NOACs that are most commonly used in clinical practice, with the aim of demonstrating how variations in these characteristics influence their use in clinical practice. A literature search was conducted on PubMed using keywords and relevant articles published by the 31^st of December 2018 were included. Expert opinion: The effect of a drug is determined by a combination of elements which include patient characteristics and external factors, in addition to its pharmacokinetic and pharmacodynamic properties. A good understanding of these is essential. Despite the wealth of information available, particularly on VKAs, our knowledge on the pharmacology responsible for certain drug effects and inter-individual variations is still limited. Increasing efforts are being made to understand these and include focus on pharmacogenomics and drug transporter proteins.

From the Eukaryotic Molybdenum Cofactor Biosynthesis to the Moonlighting Enzyme mARC

All eukaryotic molybdenum (Mo) enzymes contain in their active site a Mo Cofactor (Moco), which is formed by a tricyclic pyranopterin with a dithiolene chelating the Mo atom. Here, the eukaryotic Moco biosynthetic pathway and the eukaryotic Moco enzymes are overviewed, including nitrate reductase (NR), sulfite oxidase, xanthine oxidoreductase, aldehyde oxidase, and the last one discovered, the moonlighting enzyme mitochondrial Amidoxime Reducing Component (mARC). The mARC enzymes catalyze the reduction of hydroxylated compounds, mostly N-hydroxylated (NHC), but as well of nitrite to nitric oxide, a second messenger. mARC shows a broad spectrum of NHC as substrates, some are prodrugs containing an amidoxime structure, some are mutagens, such as 6-hydroxylaminepurine and some others, which most probably will be discovered soon. Interestingly, all known mARC need the reducing power supplied by different partners. For the NHC reduction, mARC uses cytochrome b5 and cytochrome b5 reductase, however for the nitrite reduction, plant mARC uses NR. Despite the functional importance of mARC enzymatic reactions, the structural mechanism of its Moco-mediated catalysis is starting to be revealed. We propose and compare the mARC catalytic mechanism of nitrite versus NHC reduction. By using the recently resolved structure of a prokaryotic MOSC enzyme, from the mARC protein family, we have modeled an in silico three-dimensional structure of a eukaryotic homologue.

Hematoma Expansion Following Intracerebral Hemorrhage: Mechanisms Targeting the Coagulation Cascade and Platelet Activation

Hematoma expansion (HE), defined as a greater than 33% increase in intracerebral hemorrhage (ICH) volume within the first 24 hours, results in significant neurological deficits, and enhancement of ICH-induced primary and secondary brain injury. An escalation in the use of oral anticoagulants has led to a surge in the incidences of oral anticoagulation-associated ICH (OAT-ICH), which has been associated with a greater risk for HE and worse functional outcomes following ICH. The oral anticoagulants in use include vitamin K antagonists, and direct thrombin and factor Xa inhibitors. Fibrinolytic agents are also frequently administered. These all act via differing mechanisms and thus have varying degrees of impact on HE and ICH outcome. Additionally, antiplatelet medications have also been increasingly prescribed, and result in increased bleeding risks and worse outcomes after ICH. Aspirin, thienopyridines, and GPIIb/IIIa receptor blockers are some of the most common agents in use clinically, and also have different effects on ICH and hemorrhage growth, based on their mechanisms of action. Recent studies have found that reduced platelet activity may be more effective in predicting ICH risk, hemorrhage expansion, and outcomes, than antiplatelet agents, and activating platelets may thus be a novel target for ICH therapy. This review explores how dysfunctions or alterations in the coagulation and platelet cascades can lead to, and/or exacerbate, hematoma expansion following intracerebral hemorrhage, and describe the mechanisms behind these effects and the drugs that induce them. We also discuss potential future therapy aimed at increasing platelet activity after ICH.

The molybdenum cofactor enzyme mARC: Moonlighting or promiscuous enzyme?

Molybdenum (Mo) is present in the active center of eukaryotic enzymes as a tricyclic pyranopterin chelate compound forming the Mo Cofactor (Moco). Four Moco containing enzymes are known in eukaryotes, nitrate reductase (NR), sulfite oxidase (SO), xanthine oxidoreductase (XOR), and aldehyde oxidase (AO). A fifth Moco enzyme has been recently identified. Because of the ability of this enzyme to convert by reduction several amidoximes prodrugs into their active amino forms, it was named mARC (mitochondrial Amidoxime Reducing Component). This enzyme is also able to catalyze the reduction of a broad range of N-hydroxylated compounds (NHC) as the base analogue 6-hydroxylaminopurine (HAP), as well as nitrite to nitric oxide (NO). All the mARC proteins need reducing power that is supplied by other proteins. The human and plants mARC proteins require a Cytochrome b5 (Cytb5) and a Cytochrome b5 reductase (Cytb5-R) to form an electron transfer chain from NADH to the NHC. Recently, plant mARC proteins were shown to be implicated in the reduction of nitrite to NO, and it was proposed that the electrons required for the reaction were supplied by NR instead of Cytochrome b5 components. This newly characterized mARC activity was termed NO Forming Nitrite Reductase (NOFNiR). Moonlighting proteins form a special class of multifunctional enzymes that can perform more than one function; if the extra function is not physiologically relevant, they are called promiscuous enzymes. In this review, we summarize the current knowledge on the mARC protein, and we propose that mARC is a new moonlighting enzyme. © 2017 BioFactors, 43(4):486-494, 2017.

Beyond warfarin: The advent of new oral anticoagulants

New oral anticoagulants (NOAC) are the latest addition to anticoagulant armamentarium. Unlike traditional anti-coagulants like warfarin, lab monitoring and management of bleeding complications secondary to these agents is different. As more and more patients are being switched to these drugs, interventional radiologists in particular will benefit from a clinical review of NOAC.

The mammalian molybdenum enzymes of mARC

The "mitochondrial amidoxime reducing component" (mARC) is the most recently discovered molybdenum-containing enzyme in mammals. All mammalian genomes studied to date contain two mARC genes: MARC1 and MARC2. The proteins encoded by these genes are mARC-1 and mARC-2 and represent the simplest form of eukaryotic molybdenum enzymes, only binding the molybdenum cofactor. In the presence of NADH, mARC proteins exert N-reductive activity together with the two electron transport proteins cytochrome b5 type B and NADH cytochrome b5 reductase. This enzyme system is capable of reducing a great variety of N-hydroxylated substrates. It plays a decisive role in the activation of prodrugs containing an amidoxime structure, and in detoxification pathways, e.g., of N-hydroxylated purine and pyrimidine bases. It belongs to a group of drug metabolism enzymes, in particular as a counterpart of P450 formed N-oxygenated metabolites. Its physiological relevance, on the other hand, is largely unknown. The aim of this article is to summarize our current knowledge of these proteins with a special focus on the mammalian enzymes and their N-reductive activity.

Ximelagatran for stroke prevention in atrial fibrillation

Atrial fibrillation is the most common sustained cardiac arrhythmia and the most frequently encountered cause of embolic stroke. Vitamin K antagonists (such as warfarin) have represented the cornerstone of anticoagulation practice for the last 60 years. Although highly effective in preventing thromboembolic events among patients with atrial fibrillation, warfarin therapy is limited by a multitude of potential problems. Hence, warfarin is significantly underused in clinical practice, with only half of warfarin-treated patients actually achieving therapeutic anticoagulation in routine clinical practice. Consequently, there is an overwhelming need for an alternative oral anticoagulant for patients with atrial fibrillation that is safer, more practical and effective. Ximelagatran (Exanta, AstraZeneca) is a novel oral direct thrombin inhibitor that is rapidly converted to the active compound melagatran after oral absorption. It has a low potential for drug interactions, anticoagulation monitoring is not required, and it is administered at a fixed twice-daily dose. The Stroke Prevention using the ORal Thrombin Inhibitor in patients with nonvalvular atrial Fibrillation (SPORTIF) III and V trials have together demonstrated the noninferiority of ximelagatran relative to warfarin for the prevention of stroke and embolic events in atrial fibrillation. Unfortunately, initial optimism has been tempered by serious concerns over its safety data in view of its propensity to cause elevation in liver enzymes.

Snake bites and hemostasis/thrombosis

Snake venom toxins have evolved to affect many prey physiological systems including hemostasis and thrombosis. These toxins belong to a diverse array of protein families and can initiate or inhibit multiple stages of the coagulation pathway or platelet aggregation with incredible specificity. Such specificity toward vertebrate molecular targets has made them extremely useful for diagnosis of human diseases or as molecular scalpels in physiological studies. The large number of yet-to-be characterized venoms provides a vast potential source of novel toxins and subsequent cardiovascular therapeutics and diagnostic agents.

No Pharmacokinetic or Pharmacodynamic Interaction Between Digoxin and the Oral Direct Thrombin Inhibitor Ximelagatran in Healthy Volunteers

The interaction potential of digoxin and ximelagatran, an oral direct thrombin inhibitor being developed for the prevention and treatment of thromboembolic disease, was investigated in this randomized, double-blind, 2-way crossover study. On 2 separate occasions, healthy female and male volunteers (n = 16) received ximelagatran 36 mg or placebo twice daily for 8 days separated by a 4- to 14-day washout period. All volunteers received a single oral dose of digoxin 0.5 mg on day 4 of both study periods. No interaction between ximelagatran and digoxin was detected in the pharmaco-kinetic parameters (using a 90% confidence interval [CI] of least squares mean estimate ratios), including melagatran (the active form of ximelagatran) AUC(tau) and C(max) and digoxin AUC(t) and C(max). Digoxin did not alter the melagatran-induced prolongation of the activated partial thromboplastin time, and both drugs were well tolerated when administered in combination. In conclusion, no pharmacokinetic or pharmacodynamic interaction between digoxin and ximelagatran was observed in this study.

No Pharmacokinetic or Pharmacodynamic Interaction Between Atorvastatin and the Oral Direct Thrombin Inhibitor Ximelagatran

In this randomized, 2-way crossover study, the potential for interaction was investigated between atorvastatin and ximelagatran, an oral direct thrombin inhibitor. Healthy female and male volunteers (n = 16) received atorvastatin 40 mg as a single oral dose and, in a separate study period, ximelagatran 36 mg twice daily for 5 days plus a 40-mg oral dose of atorvastatin on the morning of day 4. In the 15 subjects completing the study, no pharmacokinetic interaction was detected between atorvastatin and ximelagatran for all parameters investigated, including melagatran (the active form of ximelagatran) area under the plasma concentration versus time curve (AUC) and maximum plasma concentration, atorvastatin acid AUC, and AUC of active 3-hydroxy-3-methyl-glutaryl-coenzyme-A (HMG-CoA) reductase inhibitors. Atorvastatin did not alter the melagatran-induced prolongation of the activated partial thromboplastin time, and both drugs were well tolerated when administered in combination. In conclusion, no pharmacokinetic or pharmacodynamic interaction between atorvastatin and ximelagatran was observed in this study.

The role of structural information in the discovery of direct thrombin and factor Xa inhibitors

The quest for novel medications to treat thromboembolic disorders such as venous thrombosis, pulmonary embolism and stroke received a boost when the 3D structures of two major players in the blood coagulation cascade were determined in 1989 and 1993. Structure-guided design of inhibitors of thrombin (factor IIa, fIIa) and factor Xa (fXa) eventually led to the discovery of potent, selective, efficacious, orally active and safe compounds that proved successful in clinical studies. In 2008, the direct thrombin inhibitor dabigatran etexilate developed by Boehringer Ingelheim became the first novel antithrombotic molecular entity to enter the market in 50 years. Additional compounds targeting factor Xa were subsequently granted marketing authorization or are in late-stage clinical studies. In this review, I use selected case studies to describe the discovery of novel fIIa and fXa inhibitors, with a particular emphasis on the pre-eminent role that structural information played in this process.

New anticoagulants - promising and failed developments

New direct and indirect acting factor Xa (FXa) and thrombin inhibitors are being developed to overcome the downsides of the conventional anticoagulants - unfractionated and low molecular weight heparins and vitamin K antagonists. Ximelagatran and idraparinux failed to demonstrate an acceptable safety profile. Rivaroxaban and dabigatran are approved for the post-operative prevention of thromboembolic complications after elective hip or knee replacement surgery; dabigatran is approved for the prevention of embolism in patients with atrial fibrillation in an increasing number of countries. Several novel indirect antithrombin-dependent anticoagulants as well as antithrombin-independent oral direct FXa and thrombin inhibitors are investigated in multiple indications for the prophylaxis and treatment of venous thromboembolism and the prophylaxis of arterial thrombotic disorders. Quality-adjusted life years costs and incremental cost-effectiveness ratios are relatively high at present, but may decrease after approval of more new anticoagulants for additional indications.

Looking at the proteases from a simple perspective

Proteases have received enormous interest from the research and medical communities because of their significant roles in several human diseases. Some examples include the involvement of thrombin in thrombosis, HIV-1 protease in Acquired Immune Deficiency Syndrome, cruzain in Trypanosoma cruzi infection, and membrane-type 1 matrix metalloproteinase in tumor invasion and metastasis. Many efforts has been undertaken to design effective inhibitors featuring potent inhibitory activity, specificity, and metabolic stability to those proteases involved in such pathologies. Protease inhibitors usually target the active site, but some of them act by other inhibitory mechanisms. The understanding of the structure-function relationships of proteases and inhibitors has an impact on new inhibitor drugs designing. In this paper, the structures of four proteases (thrombin, HIV-protease, cruzain, and a matrix metalloproteinase) are briefly reviewed, and used as examples of the importance of proteases for the development of new treatment strategies, leading to a longer and healthier life.

Serine proteases mediate inflammatory pain in acute pancreatitis

Acute pancreatitis is a life-threatening inflammatory disease characterized by abdominal pain of unknown etiology. Trypsin, a key mediator of pancreatitis, causes inflammation and pain by activating protease-activated receptor 2 (PAR(2)), but the isoforms of trypsin that cause pancreatitis and pancreatic pain are unknown. We hypothesized that human trypsin IV and rat P23, which activate PAR(2) and are resistant to pancreatic trypsin inhibitors, contribute to pancreatic inflammation and pain. Injections of a subinflammatory dose of exogenous trypsin increased c-Fos immunoreactivity, indicative of spinal nociceptive activation, but did not cause inflammation, as assessed by measuring serum amylase and myeloperoxidase activity and by histology. The same dose of trypsin IV and P23 increased some inflammatory end points and caused a more robust effect on nociception, which was blocked by melagatran, a trypsin inhibitor that also inhibits polypeptide-resistant trypsin isoforms. To determine the contribution of endogenous activation of trypsin and its minor isoforms, recombinant enterokinase (ENK), which activates trypsins in the duodenum, was administered into the pancreas. Intraductal ENK caused nociception and inflammation that were diminished by polypeptide inhibitors, including soybean trypsin inhibitor and a specific trypsin inhibitor (type I-P), and by melagatran. Finally, the secretagogue cerulein induced pancreatic nociceptive activation and nocifensive behavior that were reversed by melagatran. Thus trypsin and its minor isoforms mediate pancreatic pain and inflammation. In particular, the inhibitor-resistant isoforms trypsin IV and P23 may be important in mediating prolonged pancreatic inflammatory pain in pancreatitis. Our results suggest that inhibitors of these isoforms could be novel therapies for pancreatitis pain.

Evaluation of the efficacy and safety of rivaroxaban using a computer model for blood coagulation

Rivaroxaban is an oral, direct Factor Xa inhibitor approved in the European Union and several other countries for the prevention of venous thromboembolism in adult patients undergoing elective hip or knee replacement surgery and is in advanced clinical development for the treatment of thromboembolic disorders. Its mechanism of action is antithrombin independent and differs from that of other anticoagulants, such as warfarin (a vitamin K antagonist), enoxaparin (an indirect thrombin/Factor Xa inhibitor) and dabigatran (a direct thrombin inhibitor). A blood coagulation computer model has been developed, based on several published models and preclinical and clinical data. Unlike previous models, the current model takes into account both the intrinsic and extrinsic pathways of the coagulation cascade, and possesses some unique features, including a blood flow component and a portfolio of drug action mechanisms. This study aimed to use the model to compare the mechanism of action of rivaroxaban with that of warfarin, and to evaluate the efficacy and safety of different rivaroxaban doses with other anticoagulants included in the model. Rather than reproducing known standard clinical measurements, such as the prothrombin time and activated partial thromboplastin time clotting tests, the anticoagulant benchmarking was based on a simulation of physiologically plausible clotting scenarios. Compared with warfarin, rivaroxaban showed a favourable sensitivity for tissue factor concentration inducing clotting, and a steep concentration–effect relationship, rapidly flattening towards higher inhibitor concentrations, both suggesting a broad therapeutic window. The predicted dosing window is highly accordant with the final dose recommendation based upon extensive clinical studies.

Will warfarin ever be replaced?

Arterial and venous thromboembolism account for significant morbidity and mortality worldwide. Warfarin, and other vitamin K antagonists (VKAs), have been the only class of oral anticoagulants currently in clinical use and have been so for over 50 years. Although warfarin is effective in preventing thromboembolism, its use is limited by its narrow therapeutic index that necessitates frequent monitoring and dose adjustments resulting in considerable inconvenience to patients and clinicians. There are now several orally administered anticoagulants in late stages of clinical development that may offer effective, safer, and more convenient anticoagulation. This review summarizes and compares data on novel anticoagulants in the prophylaxis and treatment of venous thromboembolism, acute coronary syndromes, and the prevention of stroke in patients with atrial fibrillation.

New direct thrombin inhibitors

Direct thrombin inhibitors (DTIs) are a class of anticoagulants that bind selectively to thrombin and block its interaction with its substrates. Dabigatran etexilate and AZD0837, the new generation of DTIs, are now under intense development, and are potentially of great interest for internists. Dabigatran etexilate is a potent, non-peptidic small molecule that specifically and reversibly inhibits both free and clot-bound thrombin by binding to the active site of thrombin molecule. It has been already licensed in the European Union and in Canada for the prevention of VTE in patients undergoing hip- and knee-replacement surgery. Ongoing trials are evaluating its efficacy and safety for the treatment of deep venous thrombosis and pulmonary embolism, primary and secondary prevention of VTE, prevention of systemic embolism in patients with non-valvular atrial fibrillation, and prevention of cardiac events in patients with acute coronary syndromes. AZD0837 is the prodrug of ARH06737, a potent, competitive, reversible inhibitor of free and fibrin-bound thrombin. At present, only limited, preclinical, phase I and phase II clinical data have been presented. The drug has now entered a phase III clinical program in the population of patients with atrial fibrillation. Their properties and the oral administration render these compounds, theoretically, more convenient than both vitamin K antagonist and low molecular weight heparins. However, only reports from clinical practice patterns over the next months and years will tell us how and when to use the new DTIs.

Lessons from ximelagatran: issues for future studies evaluating new oral direct thrombin inhibitors for venous thromboembolism prophylaxis in orthopedic surgery

Venous thromboembolism is a frequent complication of total hip and knee replacement requiring prophylaxis with anticoagulants. A direct thrombin inhibitor-ximelagatran-did not show advantages over other anticoagulants and it was withdrawn from the market; however, new drugs are being developed. We conducted a systematic review and meta-analysis to identify conditions under which ximelagatran might potentially be superior to current standards. Medline, EMBASE, the Cochrane Library, and grey literature were screened for randomized trials comparing ximelagatran with warfarin or low-molecular-weight heparin for thromboprophylaxis in total hip or knee replacement. Two reviewers independently assessed and extracted data. A meta-analysis with especial attention to statistical heterogeneity was conducted. This study suggested that the risk-benefit profile of ximelagatran-and probably other similar agents-depends on the type of surgery, the initial timing of administration, and probably the dose. These issues should be explicitly explored in future trials evaluating new direct thrombin inhibitors.

New anticoagulants for atrial fibrillation

Although warfarin and other vitamin K antagonists have clearly the greatest efficacy among treatments commonly available in preventing stroke in atrial fibrillation, their use is associated with a substantial risk of major bleedings and are unpractical and difficult to use because of their narrow therapeutic window, their interaction with drugs and foods, and the need of frequent coagulation monitoring. Several new anticoagulants are now undergoing phase III clinical trials in atrial fibrillation with the aim of demonstrating noninferiority compared with vitamin K antagonists or superiority compared with aspirin in patients in whom vitamin K antagonists are contraindicated or not tolerated. These drugs fall in different pharmacological categories of oral direct thrombin inhibitors, parenteral long-lived indirect factor Xa inhibitors, and oral direct factor Xa inhibitors. Cardiologists need to be aware of the explosive pharmacological literature being accrued with these new drugs, as most of these will likely enter the clinical arena in the near future.

Anticoagulant activity of original synthetic peptide derivatives

Original synthetic peptide derivatives exhibit anticoagulant activity in vitro and in vivo. They delayed fibrin clot formation from human blood plasma in tests for the intrinsic coagulation pathway (activated partial thromboplastin time) and final stage of plasma coagulation (thrombin time) and inhibited amidolytic activity of thrombin. We determined the minimum effective dose of the most active compound providing a 2-fold lengthening of blood clotting time (activated partial thromboplastin time test and thrombin time test), which persisted for 2-3 h.

Clinical pharmacokinetics and pharmacodynamics of the oral direct thrombin inhibitor dabigatran etexilate

The direct thrombin inhibitor dabigatran etexilate is currently in phase III of development for the prophylaxis and treatment of thromboembolic disorders, with three trials completed in primary venous thromboembolism (VTE) prevention. Dabigatran etexilate is an orally administered prodrug, which is rapidly absorbed and converted to the active form, dabigatran. Dabigatran has been shown to specifically and reversibly inhibit thrombin, the key enzyme in the coagulation cascade. Studies in healthy volunteers and in patients undergoing orthopaedic surgery have indicated that dabigatran has a predictable pharmacokinetic/pharmacodynamic profile, allowing for a fixed-dose regimen. Peak plasma concentrations of dabigatran are reached approximately 2 hours after oral administration in healthy volunteers, with no unexpected accumulation of drug concentrations upon multiple dosing. Excretion is predominantly via the renal route as unchanged drug. Dabigatran is not metabolized by cytochrome P450 isoenzymes. The small differences in dabigatran pharmacokinetics associated with age and gender are attributed to variations in renal function. Additional studies have shown that the pharmacokinetic/pharmacodynamic profile of dabigatran is consistent across a range of patient populations, with no effect of moderate hepatic impairment being observed. Drug-drug interactions are not observed with concomitant administration of atorvastatin, diclofenac or digoxin. The pharmacodynamic profile of dabigatran demonstrates effective anticoagulation combined with a low risk of bleeding. Further phase III studies are ongoing, including acute VTE treatment and stroke prevention in atrial fibrillation; the results obtained so far show that dabigatran etexilate is well tolerated and effective in the treatment and prevention of thromboembolic events.

Preparation of methyl ester precursors of biologically active agents

This method enables scientists to easily convert biologically active carboxylic acids into their methyl esters ("pro-drugs" generally having improved ability to penetrate cell membranes) using only equipment commonly found in a biology laboratory. An ion-exchange resin is used to convert the acid into its salt, which is thereby sequestered on the resin. The addition of methyl iodide converts the salt to the ester, which has no affinity for the resin and is readily eluted. Evaporation of the liquid phase provides the pure methyl ester. The preparation in good chemical yields of methyl esters of bioactive agents in excellent purity and 10-20 mg quantities can be achieved using this method. The method can be completed in 1 day.

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.

Pharmacokinetic properties of TDP4815 after single intravenous and oral administrations to rat, rabbit, monkey, dog and in vitro drug metabolism

The pharmacokinetics of TDP4815 was evaluated in rats, rabbits, dogs and monkeys. After intravenous administration, TDP4815 achieved C(O) of 3255 ng/ml in rats at 5 mg/kg, 9066 ng/ml in rabbits and 7858 ng/ml in monkeys at 6 mg/kg, and 4457 ng/ml in dogs at 3 mg/kg. The clearance (C(L)) was 3105, 1692, 835 and 640 ml/h/kg in rats, rabbits, monkeys and dogs, respectively. The volume of distribution (V(Z)) was more than 3861 ml/kg in all species, except 1915 ml/kg in monkeys. The oral bioavailability was rabbit >rat> monkey compared at 100 mg/kg, but it was much higher in dogs (>64%) after oral administrations. The calculated intrinsic clearance data suggested that the clearance of dog and human was restricted by binding to the plasma protein, and the clearance of rat and monkey was dependent on both the free fraction of plasma protein binding and the liver blood flow rate. The unbound hepatic intrinsic clearance of monkey was close to its C(L) suggesting that the hepatic clearance was an important excretion in monkeys. The poor oral bioavailability in the monkey may be related to the extensive glucuronidation. The V(Z).kg and C(L).kg in test species showed good correlation with the animal body weights (R(2)=0.87 and 0.96).

Inhibitors of Factor VIIa/tissue factor

The formation of the proteolytic complex composed of the serine protease Factor VIIa and the cell-associated glycoprotein tissue factor (FVIIa/TF) initiates a cascade of amplified zymogen activation reactions leading to thrombus formation. The critical role of the coagulation cascade in pathological thrombosis has been the basis for significant efforts to design selective inhibitors of the protease components as new anticoagulant alternatives for the treatment of thrombotic diseases. However, for the new generation of anticoagulant drugs in development that primarily target protease complexes distal from FVIIa/TF, the differential between efficacy and safety as defined by bleeding is unresolved. Targeting the FVIIa/TF complex has several theoretical advantages that exploit the amplified nature of the coagulation cascade. However, progress on the development of clinical-stage FVIIa/TF-based anticoagulants has not been as successful to date. This review summarizes recent efforts in the discovery of synthetic inhibitors of FVIIa/TF.

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.

Pharmacokinetics and Pharmacodynamics of the Dual FII/FX Inhibitor BIBT 986 in Endotoxin-induced Coagulation

BIBT986 is a dual inhibitor of factors Xa and IIa. The aim of this study was to compare with placebo the effect of three doses of BIBT986 on coagulation, platelet activation, and inflammation. This was a prospective, randomized, double-blind, placebo-controlled, parallel-group dose escalation trial in 48 healthy male volunteers. Participants received one of three doses of BIBT986 or placebo intravenously together with a bolus infusion of 2 ng/kg lipopolysaccharide (LPS). BIBT986 dose-dependently changed global coagulation parameters and in vivo markers of thrombin generation and action: BIBT986 doses, which prolonged activated partial thromboplastin time by 100%, completely suppressed the LPS-induced increases in prothrombin fragment, thrombin-antithrombin complexes, and D-dimer, which were 6.1-, 14.5, and 3.5-fold in the placebo group, respectively. BIBT986 did not influence inflammation, fibrinolysis, or platelet activation. Therefore, BIBT986 is a potent anticoagulant in the human endotoxemia model.

New anticoagulants for venous thromboembolic disease

PURPOSE OF REVIEW

In this paper, recent advances in new anticoagulants with the potential to be used for prevention or treatment of venous thrombosis are reviewed.

RECENT FINDINGS

Numerous novel anticoagulants targeting specific stages of the coagulant pathway are in various stages of development. Fondaparinux, an indirect activated factor VII inhibitor, has been shown to be effective for initial treatment and prevention of venous thromboembolism, but still requires parenteral administration. Ximelagatran, an oral direct thrombin inhibitor, has also been shown to effective for treatment and prevention of venous thrombosis. Both agents are associated with bleeding, however, and ximelagatran is associated with hepatic toxicity with long-term use. Direct activated factor X inhibitors, orally available forms of heparin, and other direct thrombin inhibitors remain in early stages of development. Further data on the clinical utility of these agents are likely to emerge in the next few years, and uptake of their use will be affected by the cost considerations.

SUMMARY

Numerous alternative anticoagulants are in varying stages of development. Clinical data have yet to show that these agents have a clearly superior risk-benefit ratio compared with currently used antithrombotics. Many drugs remain in initial stages of development. The ideal anticoagulant agent is being sought but has yet to be discovered.

Pharmacokinetics and pharmacodynamics of the oral direct thrombin inhibitor ximelagatran co-administered with different classes of antibiotics in healthy volunteers

OBJECTIVE

To study the effects of amoxicillin, doxycycline, ciprofloxacin, azithromycin, and cefuroxime on the pharmacokinetics and pharmacodynamics of melagatran, the active form of the oral direct thrombin inhibitor ximelagatran, which is a substrate for the P-glycoprotein pump (P-gp) transporter but is not metabolized by the cytochrome P450 (CYP450) enzyme system.

METHODS

Five parallel groups of 16 healthy volunteers received two sequential treatments. The first treatment was a single 36-mg dose of ximelagatran. During the second treatment period, one of the above antibiotics was given on days 1-5 after a washout of at least 2 days. A single 36-mg oral dose of ximelagatran was given on the mornings of days 1 and 5 of the second treatment period.

RESULTS

No pharmacokinetic interactions were detected between ximelagatran and amoxicillin, doxycycline, or ciprofloxacin as the least-squares geometric mean treatment ratio of ximelagatran with-to-without antibiotic fell within the intervals of 0.80-1.25 for the area under the curve (AUC) and 0.7-1.43 for C(max). After co-administration with azithromycin, the least square mean ratio with-to-without antibiotic for AUC of melagatran was 1.60 (90% CI, 1.40-1.82) on day 1 and 1.41 (90% CI, 1.24-1.61) on day 5. For melagatran C(max), the corresponding ratios were 1.63 (90% CI, 1.38-1.92) and 1.40 (90% CI, 1.18-1.66). After co-administration with cefuroxime, the ratios were 1.23 (90% CI, 1.07-1.42) and 1.16 (90% CI, 0.972-1.38) for AUC and 1.33 (90% CI, 1.07-1.66) and 1.19 (90%CI, 0.888-1.58) for C(max) of melagatran. Co-administration with the antibiotics did not change mean time to C(max), half-life, or renal clearance of melagatran. The melagatran plasma concentration-response relationship for activated partial thromboplastin time (APTT) prolongation was not altered by any of the studied antibiotics, but the increased plasma concentrations of melagatran after co-administration of ximelagatran with azithromycin resulted in a minor increase in the mean maximum APTT of about 15%.

CONCLUSION

The pharmacokinetics of ximelagatran were not affected by amoxicillin, doxycycline, or ciprofloxacin. Melagatran exposure was increased when ximelagatran was co-administered with azithromycin and, to a lesser extent, with cefuroxime. APTT was not significantly altered by any of the antibiotics.

New anticoagulants for the prevention and treatment of venous thromboembolism

Anticoagulant therapy is effective at preventing the development of venous thromboembolism in high-risk patients, and reduces morbidity and mortality in individuals with established thromboembolic disease. Vitamin K antagonists and heparins are currently the most commonly used anticoagulant drugs, but they have practical limitations. Therefore, new antithrombotic agents with predictable dose-responses (thereby decreasing the need for monitoring without compromising efficacy or safety), ideally available in an oral formulation and with a rapidly reversible anticoagulant effect, are needed. New drugs fulfilling some of the above criteria have been developed and have proven to be effective agents for the treatment and prevention of venous thromboembolism.

Ximelagatran versus warfarin for prophylaxis of venous thromboembolism in major orthopedic surgery: systematic review of randomized controlled trials

BACKGROUND

Ximelagatran has been recently studied for prophylaxis in surgical orthopedic cases.

PURPOSE

We proposed to establish whether interventions involving ximelagatran, as compared with warfarin, would increase thromboembolic prophylaxis in patients undergoing major orthopedic knee surgery.

DATA SOURCE

Studies with random assignment were identified by an electronic search of the medical literature up to 2006. Data were double-entered into the Review Manager software, version 4.2.5.

DATA SYNTHESIS

We included three well-conducted clinical trials involving 4,914 participants. Sub-groups with two dosages of ximelagatran (24 mg and 36 mg, b.i.d.), were defined. Ximelagatran showed significantly lower frequency of total venous thromboembolism (VTE) than warfarin, but only with the 36-mg dosage (risk relative, RR: 0.72; 95% confidence interval, CI: 0.64-0.81; p < 0.00001). For the 24-mg subgroup, total VTE frequency was similar (RR: 0.86; 95% CI: 0.73-1.01; p = 0.06). No significant differences were shown with either ximelagatran dosage for deep vein thrombosis (DVT), pulmonary embolism, any bleeding or severe bleeding. At the end of the treatment, alanine aminotransferase (ALT) elevation was less frequent in the 24-mg ximelagatran sub-group (RR: 0.33; 95% CI: 0.12-0.91; p = 0.03], but during the follow-up period, the ALT elevation rate was greater in the 36-mg ximelagatran group (RR: 6.97; 95% CI: 1.26-38.50; p = 0.03].

CONCLUSIONS

Ximelagatran appears to be more effective than warfarin when used in higher dosages (36 mg b.i.d.), but at the expense of increased frequency of ALT elevation during the follow-up period.

Acute anticoagulation adjustment in patients with atrial fibrillation at risk for stroke: approaches, strategies, risks and benefits

The acute management of anticoagulation in patients with atrial fibrillation to prevent stroke and other thromboembolic complications includes the use of individualized strategies tailored to the patient and based on the situation (cardioversion, surgeries, dental procedures, cardiac interventions, other invasive procedures and initiation of, or adjustment to, warfarin dosing). The vast range of choices can cause confusion and few randomized controlled clinical trials in this area provide adequate guidance. Chronic anticoagulation management is more straightforward since clinical evidence is ample, randomized clinical trial data provides cogent informaiton and guidelines have been established. Acute management of anticoagulation in patients with atrial fibrillation to prevent thromboembolic complications is often unrecognized but is emerging as a crucial, but challenging, and increasingly complex aspect of the care of patients with atrial fibrillation. This review addresses issues regarding such patients who may be at risk for stroke and require acute adjustments of anticoagulation (in light of, or in lieu of, chronic anticoagulation). Several promising new strategies are considered in light of established medical care. This analysis provides practical recommendations based on available data and presents results from recent investigations that may provide insight into future strategies.

Pharmacokinetics and pharmacodynamics of BIBT 986, a novel small molecule dual inhibitor of thrombin and factor Xa

BACKGROUND

Current anticoagulant development focuses on agents with predictable pharmacokinetic and pharmacodynamic (PD) properties. BIBT 986 is a novel potent anticoagulant with a dual mechanism of action: it competitively inhibits factor (F) Xa and FIIa.

AIMS

To determine the safety, tolerability, pharmacokinetics (PK) and PD of BIBT 986 following intravenous infusion in healthy male volunteers.

METHODS

In three randomized, double-blind, placebo-controlled trials, subjects were administered by intravenous infusion escalating doses of BIBT 986 for up to 32 h. BIBT 986 concentrations were determined in plasma and urine samples by high pressure liquid chromatography tandem mass spectrometry. Pharmacodynamic response was assessed by measuring the changes in blood coagulation times. Activated partial thromboplastin time, International Normalized Ratio, thrombin time and ecarin clotting time were determined and compared with baseline results.

RESULTS

In all three studies, intravenous infusion of BIBT 986 was safe and well tolerated. BIBT 986 exhibited linear PK over the dose range tested. Clearance was about 8 L h(-1) and V(ss) about 50 L. Apparent steady state concentrations were reached within 24 h, indicating a dominant half-life of about 6 h. The terminal half-life of BIBT 986 was approximately 12 h. Renal excretion contributes approximately 50% to total elimination. Overall interindividual variability in pharmacokinetic and PD parameters was < 40%. There was a linear correlation between plasma concentrations and PD responses, suggesting excellent predictability.

CONCLUSION

BIBT 986 is the first small molecule of a novel class of anticoagulants that potently and directly inhibits both coagulation FXa and thrombin. It has predictable pharmacokinetic and PD characteristics.

Risk of recurrent venous thromboembolism or bleeding in relation to thrombophilic risk factors in patients receiving ximelagatran or placebo for long-term secondary prevention of venous thromboembolism

The impact of prothrombotic abnormalities on the risk of recurrent venous thromboembolism (VTE) and bleeding in patients receiving long-term anticoagulation remains unclear. This analysis evaluated the influence of potential prothrombotic risk factors (antithrombin, protein C, protein S, factor V Leiden mutation, prothrombin gene G20210A mutation, cardiolipin antibodies, number of risk factors) on the risk of recurrent VTE or bleeding during treatment with oral ximelagatran (24 mg twice daily) or placebo for 18 months [THRombin Inhibitor in Venous thromboEmbolism (THRIVE) III trial]. Of the 1223 patients in the intention-to-treat population, prothrombotic state was analysed in 559 patients receiving ximelagatran and 540 patients receiving placebo. It is possible that patients at a high risk of recurrent VTE were poorly represented in this analysis because of selection bias. Prothrombotic risk factors were reported in 41% of patients (8% had > or = 2 factors). No significant interactions were found between ximelagatran treatment and potential prothrombotic risk factors for the risk of recurrent VTE or bleeding by Cox proportionate hazard modelling. There was no clear evidence for a higher risk of recurrent VTE or bleeding across subgroups according to the potential prothrombotic factors analysed in this study.

INFLUENCE OF ERYTHROMYCIN ON THE PHARMACOKINETICS OF XIMELAGATRAN MAY INVOLVE INHIBITION OF P-GLYCOPROTEIN-MEDIATED EXCRETION

A pharmacokinetic interaction between erythromycin and ximelagatran, an oral direct thrombin inhibitor, was demonstrated in this study in healthy volunteers. To investigate possible interaction mechanisms, the effects of erythromycin on active transport mediated by P-glycoprotein (P-gp) in vitro in Caco-2 and P-gp-over-expressing Madin-Darby canine kidney-human multidrug resistance-1 cell preparations and on biliary excretion of melagatran in rats were studied. In healthy volunteers (seven males and nine females; mean age 24 years) receiving a single dose of ximelagatran 36 mg on day 1, erythromycin 500 mg t.i.d. on days 2 to 5, and a single dose of ximelagatran 36 mg plus erythromycin 500 mg on day 6, the least-squares mean estimates (90% confidence intervals) for the ratio of ximelagatran with erythromycin to ximelagatran given alone were 1.82 (1.64-2.01) for the area under the concentration-time curve and 1.74 (1.52-2.00) for the maximum plasma concentration of melagatran, the active form of ximelagatran. Neither the slope nor the intercept of the melagatran plasma concentration-effect relationship for activated partial thromboplastin time statistically significantly differed as a function of whether or not erythromycin was administered with ximelagatran. Ximelagatran was well tolerated regardless of whether it was administered with erythromycin. Erythromycin inhibited P-gp-mediated transport of both ximelagatran and melagatran in vitro and decreased the biliary excretion of melagatran in the rat. These results indicate that the mechanism of the pharmacokinetic interaction between oral ximelagatran and erythromycin may involve inhibition of transport proteins, possibly P-gp, resulting in decreased melagatran biliary excretion and increased bioavailability of melagatran.

New Anticoagulant Agents: Direct Thrombin Inhibitors

Decades of research have been devoted to developing effective, safe, and convenient anticoagulant agents. In recent years, much emphasis has been placed on the development of direct thrombin inhibitors (DTIs) that offer benefits over agents like heparin and warfarin including the inhibition of both circulating and clot-bound thrombin; a more predictable anticoagulant response, because they do not bind to plasma proteins and are not neutralized by platelet factor 4; lack of required cofactors, such as antithrombin or heparin cofactor II; inhibiting thrombin-induced platelet aggregation; and absence of induction of immune-mediated thrombocytopenia. Various injectable DTIs are currently available and used for many indications. In addition, research is now focusing on oral DTIs that seem promising and offer various advantages, such as oral administration, predictable pharmacokinetics and pharmacodynamics, a broad therapeutic window, no routine monitoring, no significant drug interactions, and fixed-dose administration.

Pharmacokinetics and Pharmacodynamics of the Oral Direct Thrombin Inhibitor Ximelagatran in Young Healthy Japanese Men

BACKGROUND AND OBJECTIVE

The direct thrombin inhibitor ximelagatran, which is rapidly bioconverted to its active form melagatran after oral administration, is being developed for the prevention and treatment of thromboembolism. This study assessed the effects of food and repeated dosing on the pharmacokinetics and pharmacodynamics of melagatran after oral administration of ximelagatran to young healthy Japanese males.

METHODS

In part one of the two-part study, volunteers (n = 24) were randomised to receive in a crossover fashion a single oral dose of ximelagatran 48mg with or without breakfast on 2 days separated by a 2- to 7-day washout period. In the second part of the study, all volunteers received oral doses of ximelagatran 48mg every 12 hours for 5 days followed by a single dose on the morning of day 6.

RESULTS

The area under the plasma concentration-time curve (AUC), peak plasma concentration (C(max)) and urinary excretion of melagatran did not differ as a function of whether ximelagatran was taken with or without food. The relationship between the melagatran plasma concentration and activated partial thromboplastin time (aPTT, which reflects the thrombin inhibitory effect of melagatran) was also independent of concomitant food intake. During repeated dosing, steady-state plasma concentrations of melagatran were achieved after the second dose of ximelagatran on day 1 and remained stable through the rest of the dosing period. The melagatran AUC and C(max) increased slightly (by 18% and 22%, respectively) on day 6 compared with day 1. The interindividual variability in the melagatran AUC and C(max) remained low, as reflected by coefficients of variation of <20% on both day 1 and day 6. The amount of melagatran excreted in urine remained stable over the 6 days of repeated dosing.

CONCLUSION

The pharmacokinetics, pharmacodynamics, safety and tolerability of melagatran after oral administration of ximelagatran were not affected by food or repeated dosing in healthy Japanese volunteers.

Ximelagatran, the Oral Anticoagulant of the Future An Evidence Based Review

This article presents the available data on Ximelagatran, a novel oral direct thrombin inhibitor and explores its therapeutic potential Recent large clinical trials have evaluated the efficacy and safety of this anticoagulant compared to the standard anticoagulation therapy with warfarin and heparins in several thrombotic disorders. These trials provide strong evidence for the efficacy and safety of ximelagatran in the following clinical indications; the prevention of venous thromboembolism after knee or hip replacement, the treatment of deep venous thrombosis, and prevention of stroke in patients with atrial fibrillation. Further evaluation of this promising oral anticoagulant is warranted in other thrombotic cardiovascular disorders requiring chronic oral anticoagulation therapy such as in patients with prosthetic heart valves, intracardiac thrombi, dilated cardiomyopathy, after myocardial infarction and post percutaneous coronary interventions.

New anticoagulants: a pediatric perspective

Unfractionated heparin and vitamin K antagonists such as warfarin have been used as the anticoagulants of choice for over five decades. Subsequently, low molecular weight heparins (LMWHs) became widely available and have provided several advantages, especially in infants and children. The field of anticoagulation, however, has undergone a major revolution with better understanding of the structure of coagulation proteins and the development of a host of new drugs with highly specific actions. Many of these drugs have undergone extensive clinical testing in adults and have been approved for specific indications in adults. Unfortunately, clinical data and the reported use of these drugs in children are extremely limited. A lack of familiarity with the actions and pharmacokinetic properties of these drugs could be a major contributing factor. This review focuses on several of the new anticoagulants, with a special emphasis on those that could be potentially beneficial in pediatric patients with thromboembolic disorders. The need for well-designed trials with large-scale participation by pediatric hematologists in order to improve the antithrombotic care of young infants and children is also emphasized.