Guide to anticoagulant therapy. Part 2: Oral anticoagulants. American Heart Association

Comparison of Two Different Techniques Of Warfarin Dosing Determination - A Chemometrics Study

A high prevalence of genetic polymorphisms increases sensitivity to warfarin therapy. In this study, we investigated 47 patients with effective long-term therapy by warfarin well-controlled by monitoring of International Normalised Ratio (INR). All patients were tested for gene polymorphisms VKORC1, CYP2C9*C2, and CYP2C9*C3, which were used for a dose calculation employing a program www.WarfarinDosing.org. The main goal was to investigate whether the warfarin doses determined by INR are in accordance with the doses calculated according to the pharmacogenetic algorithm. For this purpose, several chemometric tools, namely principal component analysis, cluster analysis, correlation analysis, correspondence analysis, Passing-Bablock regression, Bland-Altman method, descriptive statistics, and ANOVA were used. We also analysed the relationship between the dose of warfarin determined by INR and several constitutional and genetic factors. Statistically significant association between clinically optimized warfarin dose and indication for the treatment, age, and warfarin sensitivity determined by VKORC1, CYP2C9 gene polymorphisms were confirmed. Finally, we confirmed a good concordance between the INR determined warfarin doses and pharmacogenetic approach.

Systemic Disease and Bleeding Disorders for the Oral and Maxillofacial Surgeon

There are multiple systemic diseases that have an impact on coagulation, of which oral and maxillofacial surgeons must be cognizant. Recent evidence has supported the potential for both hypocoagulable and hypercoagulable states in patients with liver and kidney disease with an even less understood impact on prolonged bleeding in the oral cavity. These systemic diseases are not limited to diseases affecting the liver, kidney, and bone marrow; however, these diseases are common among the patient population and surgeons must be capable of making appropriate judgment and modifying care appropriately.

Evaluation of Anticoagulation Therapy in an Academic Nursing Home

Objective:

To evaluate the warfarin management patterns in an academic nursing home and evaluate what predetermined factors are associated with variability in the international normalized ratio (INR).

Setting:

A 566-bed academic nursing home.

Methods:

A retrospective chart review of all residents receiving warfarin therapy for >3 consecutive months in a calendar year was conducted. Data were collected regarding the number of times the INR fluctuated during the follow-up period and the degree of fluctuation between each blood sampling. An INR that changed by 0.5–0.99 between samplings was classified as a small fluctuation; a change >0.99 was defined as a large fluctuation. The sample was divided into 2 groups, easy management and difficult management, based on variability in the INR. The easy-management group consisted of residents who had small fluctuations in the INR and who had INRs outside of the therapeutic range ≤10% of the time. The difficult- management group had large fluctuations in the INR, with the ratio outside of the therapeutic range >10% of the time.

Results:

Thirty-seven patients were taking warfarin (mean ± SD age 71 ± 14 y; mean number of medical illnesses 7.6 ± 3). The mean length of time of warfarin therapy was 10.6 ± 3.2 months. The average dose and INR were 4.0 ± 1.9 mg and 2.0 ± 0.3, respectively. No statistically significant differences were found between age, dose, or INR. For patients who had INR values exceeding the therapeutic range, there was no significant difference between the management groups in length of treatment, age, number of medical illnesses, number of high-risk factors, dose, average monthly INR, number of medication adjustments per year, albumin and creatinine levels, total number of medications, or number of routine medications known to interact with warfarin. The difficult-management group received more medications known to interact with warfarin than the easy-management group. These medications may have caused the INR to increase above the normal range (p = 0.003), as well as producing a large (p = 0.001) or small fluctuation (p = 0.0007) in the INR. Of all the interacting medications, 55% were antibiotics and 28% were analgesics. No statistically significant differences in outcome were seen between groups.

Conclusions:

Results of this study indicate that large variations (>0.99) in the INR may be due to newly prescribed medications that enhance the anticoagulant effect of warfarin. These variations may be minimized by closely monitoring the INR when a drug known to interact with warfarin is prescribed.

Real-world characteristics of hospitalized frail elderly patients with atrial fibrillation: can we improve the current prescription of anticoagulants?

BACKGROUND

In elderly patients, especially those older than 80 years, atrial fibrillation (AF) is associated with an almost 25% increased risk of stroke. Stroke prophylaxis with anticoagulants is therefore highly recommended. The prevalence of factors that have been associated with a lower rate of prescription and adherence to anticoagulant therapy in these patients is little known. The objective of this study was to explore the clinical characteristics of elderly subjects, with and without AF, consecutively admitted to an acute geriatric unit, discussing factors that may decrease the persistence on stroke prophylaxis therapy. We also highlight possible strategies to overcome the barriers conditioning the current underuse of oral anticoagulants in this segment of the population.

METHODS

A retrospective observational study was performed on a cohort of elderly patients with and without AF admitted to the Acute Geriatric Unit of San Gerardo Hospital (Monza, Italy).

RESULTS

Compared to patients without AF (n = 1216), those with AF (n = 403) had a higher Charlson Comorbidity Index (3 vs. 2, P < 0.001), number of administered drugs (4 vs. 3, P < 0.001), rate of heart failure (36.5% vs. 12%, P < 0.001) and chronic kidney disease (20.6 vs. 13.2, P < 0.001). Many patients with AF were frail (54%) or pre-frail (29%).

CONCLUSIONS

Elderly patients with AF have higher rates of conditions that affect adherence to traditional anticoagulant therapy (vitamin K antagonists, VKA). New direct oral anticoagulants (DOAs) can help overcome this problem. In order to prescribe the most appropriate VKA or DOAs, with the best efficacy/safety profile and the highest compliance, a comprehensive geriatric assessment should always accompany the scores for thrombotic and hemorrhagic risk stratification.

Molecular modeling studies, synthesis and biological evaluation of dabigatran analogues as thrombin inhibitors

In this work, 48 thrombin inhibitors based on the structural scaffold of dabigatran were analyzed using a combination of molecular modeling techniques. We generated three-dimensional quantitative structure-activity relationship (3D-QSAR) models based on three alignments for both comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) to highlight the structural requirements for thrombin protein inhibition. In addition to the 3D-QSAR study, Topomer CoMFA model also was established with a higher leave-one-out cross-validation q(2) and a non-cross-validation r(2), which suggest that the three models have good predictive ability. The results indicated that the steric, hydrophobic and electrostatic fields play key roles in QSAR model. Furthermore, we employed molecular docking and re-docking simulation explored the binding relationship of the ligand and the receptor protein in detail. Molecular docking simulations identified several key interactions that were also indicated through 3D-QSAR analysis. On the basis of the obtained results, two compounds were designed and predicted by three models, the biological evaluation in vitro (IC50) demonstrated that these molecular models were effective for the development of novel potent thrombin inhibitors.

Development of Orally Active Thrombin Inhibitors for the Treatment of Thrombotic Disorder Diseases

Thrombotic disorders represent the major share of the various cardiovascular diseases, and significant progress has been made in the development of synthetic thrombin inhibitors as new anticoagulants. In addition to the development of highly potent and selective inhibitors with improved safety and suitable half-life, several allosteric inhibitors have been designed and synthesized, that did not fully nullify the procoagulant signal and thus could result in reduced bleeding complications. Furthermore, natural products with thrombin inhibitory activity have been isolated, and some natural products have been modified in order to improve their inhibitory activity and metabolic stability. This review summarizes the development of orally active thrombin inhibitors for the treatment of thrombotic disorder diseases, which could serve as a reference for the interested researchers.

Prolinamide derivatives as thrombin inhibitors for the treatment of thrombin-mediated diseases: a patent evaluation of US2013296245

INTRODUCTION

Thrombotic disorders can lead to deep vein thrombosis, myocardial infarction and stroke. Thrombin plays a vital role in cascade reaction of blood coagulation, inhibition of the activity of thrombin can block the formation of thrombus and direct thrombin inhibitor has a prospect to overcome the limitations in application of the traditional anticoagulant drugs.

AREAS COVERED

The current patent US2013296245 describes a series of prolinamide derivatives with formula (I) as thrombin inhibitors. These new compounds are defined to be pharmaceutically acceptable salts derived from pharmaceutically acceptable inorganic acid and organic acid, and pharmaceutically acceptable prodrug where N-alkoxycarbonyl is protected or carboxylic acid is protected by ester.

EXPERT OPINION

The patent used formamidine and its N-alkoxycarbonyl-protected derivatives as the P1 group; these groups were less basic compared with the traditional guanidine group, so their lipophilicity could be optimized to achieve oral absorption. Furthermore, these pharmaceutically acceptable prodrugs where N-alkoxycarbonyl is protected or carboxylic acid is protected by ester could achieve prolonged half-life for a convenient once- or twice-daily oral dosing. These efforts gave a new hope and confidence to treat thrombotic disorders with selective and orally active thrombin inhibitors.

Management of portal vein thrombosis in liver cirrhosis

Portal vein thrombosis (PVT) is a fairly common complication of liver cirrhosis. Importantly, occlusive PVT might influence the prognosis of patients with cirrhosis. Evidence from a randomized controlled trial has shown that anticoagulation can prevent the occurrence of PVT in patients with cirrhosis without prior PVT. Evidence from several case series has also demonstrated that anticoagulation can achieve portal vein recanalization in patients with cirrhosis and PVT. Early initiation of anticoagulation therapy and absence of previous portal hypertensive bleeding might be positively associated with a high rate of portal vein recanalization after anticoagulation. However, the possibility of spontaneous resolution of partial PVT questions the necessity of anticoagulation for the treatment of partial PVT. In addition, a relatively low recanalization rate of complete PVT after anticoagulation therapy suggests its limited usefulness in patients with complete PVT. Successful insertion of a transjugular intrahepatic portosystemic shunt (TIPS) not only recanalizes the thrombosed portal vein, but also relieves the symptomatic portal hypertension. However, the technical difficulty of TIPS potentially limits its widespread application, and the risk and benefits should be fully balanced. Notably, current recommendations regarding the management of PVT in liver cirrhosis are insufficient owing to low-quality evidence.

Review of stroke thrombolytics

The cornerstone of acute ischemic stroke treatment relies on rapid clearance of an offending thrombus in the cerebrovascular system. There are various drugs and different methods of assessment to select patients more likely to respond to treatment. Current clinical guidelines recommend the administration of intravenous alteplase (following a brain noncontract CT to exclude hemorrhage) within 4.5 hours of stroke onset. Because of the short therapeutic time window, the risk of hemorrhage, and relatively limited efficacy of alteplase for large clot burden, research is ongoing to find more effective and safer reperfusion therapy, as well as focussing on refinement of patient selection for acute reperfusion treatment. Studies using advanced imaging (incorporating perfusion CT or diffusion/perfusion MRI) may allow us to use thrombolytics, or possibly endovascular therapy, in an extended time window. Recent clinical trials have suggested that Tenecteplase, used in conjunction with advanced imaging selection, resulted in more effective reperfusion than alteplase, which translated into increased clinical benefit. Studies using Desmoteplase have suggested its potential benefit in a sub-group of patients with large artery occlusion and salveageable tissue, in an extended time window. Other ways to improve acute reperfusion approaches are being actively explored, including endovascular therapy, and the enhancement of thrombolysis by ultrasound insonation of the clot (sono-thrombolysis).

Benchmark for time in therapeutic range in venous thromboembolism: a systematic review and meta-analysis

INTRODUCTION

The percentage of time within the target INR range 2.0 to 3.0 (TTR) in patients treated with vitamin K antagonists varies considerably among efficacy-studies of novel anticoagulants. In order to properly asses the quality of anticoagulant control in upcoming cost-effectiveness studies and real life registries this systematic review reports a benchmark of TTR for different treatment durations in patients with venous thromboembolism and discusses ways to calculate TTR.

METHODS

Medline and Embase were searched for studies published between January 1990 and May 2012. Randomized controlled trials and cohort studies reporting the TTR in patients with objectively confirmed venous thromboembolism treated with vitamin K antagonists (VKA) were eligible. Duplicate reports, studies only reporting INR during initial treatment or with VKA treatment less than 3 months were excluded. Three authors assessed trials for inclusion and extracted data independently. Discrepancies were resolved by discussion between the reviewers. A meta-analysis was performed by calculating a weighted mean, based on the number of participants in each included study, for each time-period in which the TTR was measured since the confirmation of the diagnosis of VTE.

RESULTS

Forty studies were included (26064 patients). The weighted means of TTR were 54.0% in the first month since the start of treatment, 55.6% in months 1 to 3, 60.0% in months 2 to 3, 60.0% in the months 1 to 6+ and 75.2% in months 4 to 12+. Five studies reported TTR in classes. The INR in these studies was ≥ 67% of time in therapeutic range in 72.0% of the patients.

CONCLUSION

Reported quality of VKA treatment is highly dependent on the time-period since the start of treatment, with TTR ranging from approximately 56% in studies including the 1(st) month to 75% in studies excluding the first 3 months.

Novel incentive-based approaches to adherence

BACKGROUND

Adherence to medications for chronic conditions is often very low, limiting the benefit to patients, even when the medications are effective and have favorable side effect profiles.

PURPOSE

This article reviews some of the prior work on treatment adherence, introduces novel concepts from behavioral economics that can be used to design interventions to improve adherence, and proposes new approaches for clinical trials.

METHODS

Relevant experience of the authors and insights from the literature were combined to identify key issues and propose methodological improvements. Specific examples regarding adherence to warfarin are provided.

RESULTS

Several new approaches to trial design can be effectively applied in the context of medication adherence. These include tailored intervention strategies and sequential multiple assignment randomized trial (SMART) designs.

LIMITATIONS

While we have proposed to use these new approaches for ongoing studies of adherence in behavioral health, practical experience with their application is still somewhat limited.

CONCLUSIONS

Behavioral economics offer a variety of concepts that, when used in the design of interventions to improve adherence, may be more successful than traditional approaches. New clinical trial designs can also be adopted to improve the efficiency of studies that assess these approaches.

Surgical management of severe spontaneous hemorrhage of the abdominal wall complicating acenocoumarol treatment

Acenocoumarol is a vitamin K antagonist that is used for the treatment of acquired and congenital, both arterial and venous, thrombotic diseases. Its use is complicated by the narrow therapeutic range. Bleeding following oral anticoagulation, despite rare, remains the major complication. Most cases of hemorrhagic episodes usually require short hospitalization and transfusion, while surgical drainage of the hematoma is not recommended. However, in cases that conservative treatment isn't successful, surgical intervention remains an option. We present a case of severe spontaneous bleeding of the rectus abdominis muscle which was successfully managed surgically.

Bleeding incidence after oral surgery with continued oral anticoagulation

OBJECTIVES

The aim of this retrospective study was to assess the incidence of postoperative hemorrhage in patients treated with coumarins without interruption of the anticoagulant treatment undergoing oral surgical procedures, mostly osteotomies for tooth removal, when compared with patients who had never been anticoagulated.

MATERIAL AND METHODS

Six hundred thirty-seven patients underwent 934 oral surgical procedures on an outpatient basis. The INR was measured preoperatively being 2.44 in the mean SD 0.61. Local hemostasis was carried out routinely (80%) with collagen fleece, local flap, and acrylic splint.

RESULTS

Of these 637 patients, 47 presented with a postoperative hemorrhage (7.4%), 15 of these 47 cases had to be treated in hospital (2.4%). All patients showed up finally with a good wound healing, no administration of blood was necessary, and local measures revealed to be sufficient in all cases except for two patients, where the preoperative anticoagulant treatment had to be changed for 6 days. The bleeding incidence in 285 patients with comparable oral surgical procedures, who had never been anticoagulated, was 0.7%.

CONCLUSIONS

The results suggest that oral surgical procedures can be performed safely without alteration of the oral anticoagulant treatment. CINICAL RELEVANCE: Local hemostasis with collagen fleece, local flap, and acrylic splint seems to be sufficient to prevent postoperative bleeding.

Vitamin K antagonists--current concepts and challenges

Vitamin K antagtonists (VKAs) have, for decades, been the corner-stone of anticoagulation in the outpatient setting. While the long half life makes once daily administration practical, close monitoring of VKA effect is necessary because these medicines have a narrow therapeutic index. Despite inter-individual variations in response to VKA doses, the increasing availability of specialized anticoagulation monitoring systems, along with a better understanding of potential drug and dietary interactions, has made the use of VKAs safer and less burdensome. In the future, newer classes of oral anticoagulants and genomic-based dosing strategies may further expand or improve the management options for many patients at risk for thromboembolism.

Randomized clinical trial comparing percutaneous closure of patent foramen ovale (PFO) using the Amplatzer PFO Occluder with medical treatment in patients with cryptogenic embolism (PC-Trial): rationale and design

Background

Several studies have shown an association of cryptogenic stroke and embolism with patent foramen ovale (PFO), but the question how to prevent further events in such patients is unresolved. Options include antithrombotic treatment with warfarin or antiplatelet agents or surgical or endovascular closure of the PFO. The PC-Trial was set up to compare endovascular closure and best medical treatment for prevention of recurrent events.

Methods

The PC-Trial is a randomized clinical trial comparing the efficacy of percutaneous closure of the PFO using the Amplatzer PFO occluder with best medical treatment in patients with cryptogenic embolism, i.e. mostly cryptogenic stroke. Warfarin for 6 months followed by antiplatelet agents is recommended as medical treatment. Randomization is stratified according to patients age (<45 versus ≥45 years), presence of atrial septal aneurysm (ASA yes or no) and number of embolic events before randomization (one versus more than one event). Primary endpoints are death, nonfatal stroke and peripheral embolism.

Discussion

patients were randomized in 29 centers of Europe, Canada, and Australia. Randomization started February 2000. Enrollment of 414 patients was completed in February 2009. All patients will be followed-up longitudinally. Follow-up is maintained until the last enrolled patient is beyond 2.5 years of follow-up (expected in 2011).

Trial Registration

Trial listed in ClinicalTrials.gov as NCT00166257 and sponsored by AGA Medical, Plymouth, MN, USA

The dental patient on oral anticoagulant medication: a literature review

Specific diseases and medications may considerably influence the delivery of oral care and the course of dental therapy. The purpose of this literature review is to examine the relationship between oral anticoagulant medication and dental treatment. Electronic and manual searches were conducted for clinical studies in the English literature for the years 1988-2010. The review process provided a total of 110 pertinent literature references, out of which 38 studies dealt with oral anticoagulants and dental treatment. Different treatment strategies relative to dental periprocedural anticoagulation regimens have been identified, and their accompanying thromboembolic and bleeding risks are being presented and discussed. Regarding to what extent a safe and successful dental treatment in patients on anticoagulant medication is feasible, the level of evidence is lacking. Until high-level data are provided, an individualised treatment approach after consultation with the physician of the patient is highly recommended.

Prospective alpha allocation in the Clarification of Optimal Anticoagulation through Genetics (COAG) trial

BACKGROUND

The Clarification of Optimal Anticoagulation through Genetics (COAG) trial is a large, multicenter, double-blinded, randomized trial to determine whether use of a genotype-guided dosing algorithm (using clinical and genetic information) to initiate warfarin treatment will improve anticoagulation status when compared to a dosing algorithm using only clinical information.

PURPOSE

This article describes prospective alpha allocation and balanced alpha allocation for the design of the COAG trial.

METHODS

The trial involves two possibly heterogeneous populations, which can be distinguished by the difference in warfarin dose as predicted by the two algorithms. A statistical approach is detailed, which allows an overall comparison as well as a comparison of the primary endpoint in the subgroup for which sufficiently different doses are predicted by the two algorithms. Methods of allocating alpha for these analyses are given - a prospective alpha allocation and allocating alpha so that the two analyses have equal power, which we call a 'balanced alpha allocation.'

RESULTS

We show how to include an analysis of the primary endpoint in a subgroup as a co-primary analysis. Power can be improved by incorporating the correlation between the overall and subgroup analyses in a prospective alpha allocation approach. Balanced alpha allocation for the full cohort and subgroup tests to achieve the same desired power for both of the primary analyses is discussed in detail.

LIMITATIONS

In the COAG trial, it is impractical to stratify the randomization on subgroup membership because genetic information may not be available at the time of randomization. If imbalances in the treatment arms in the subgroup are found, they will need to be addressed.

CONCLUSIONS

The design of the COAG trial assures that the subgroup in which the largest treatment difference is expected is elevated to a co-primary analysis. Incorporating the correlation between the full cohort and the subgroup analyses provides an improvement in power for the subgroup comparison, and further improvement may be achieved via a balanced alpha allocation approach when the parameters involved in the sample size calculation are reasonably well estimated.

Discovery of a tetrahydropyrimidin-2(1H)-one derivative (TAK-442) as a potent, selective, and orally active factor Xa inhibitor

Coagulation enzyme factor Xa (FXa) is a particularly promising target for the development of new anticoagulant agents. We previously reported the imidazo[1,5-c]imidazol-3-one derivative 1 as a potent and orally active FXa inhibitor. However, it was found that 1 predominantly undergoes hydrolysis upon incubation with human liver microsomes, and the human specific metabolic pathway made it difficult to predict the human pharmacokinetics. To address this issue, our synthetic efforts were focused on modification of the imidazo[1,5-c]imidazol-3-one moiety of the active metabolite 3a, derived from 1, which resulted in the discovery of the tetrahydropyrimidin-2(1H)-one derivative 5k as a highly potent and selective FXa inhibitor. Compound 5k showed no detectable amide bond cleavage in human liver microsomes, exhibited a good pharmacokinetic profile in monkeys, and had a potent antithrombotic efficacy in a rabbit model without prolongation of bleeding time. Compound 5k is currently under clinical development with the code name TAK-442.

Thrombosis of mechanical valve prosthesis in patient with recent Caesarean delivery

We present a case of a mechanical mitral valve thrombosis in a 37-year-old woman occurred 2 days after a Caesarean delivery. The patient stopped warfarin and initiated low-molecular-weight heparin 1 week before the programmed delivery. Subsequently the diagnosis of thrombosis, heparin infusion was started however unsuccessfully and eventually patient was referred for cardiac surgery.

Ethnic differences in the VKORC1 gene polymorphism and an association with warfarin dosage requirements in cardiovascular surgery patients

OBJECTIVES

Vitamin K epoxide reductase (VKORC1) is the drug target for inhibition by coumarin-based anticoagulant drugs such as warfarin. Warfarin therapy has been reported as a leading cause of drug-related hospitalization and there is therefore an urgent need to develop tests for better warfarin prescription. We report here the distribution of the intron 1 -136 T>C (1173 T>C intron) polymorphism of VKORC1, previously reported to be associated with warfarin maintenance dose in Caucasians and Japanese, in several ethnic populations from Japan and Israel, and describe its significance for warfarin dosage in Japanese cardiovascular surgery patients.

METHODS

Subjects consisted of 132 Japanese individuals and 341 Israeli individuals from four Jewish ethnic groups (86 Ashkenazi Jews, 95 Yemenite Jews, 73 Moroccan Jews and 87 Libyan Jews). In addition, 31 Japanese patients receiving warfarin therapy after cardiovascular surgery, maintained with a target International Normalized Ratio, were studied. The genotyping for the 1173 T>C intron polymorphism of VKORC1 was determined using rapid real-time PCR.

RESULTS

The allele frequency of the combined VKORC1 1173 CT and CC genotypes varied among the four Israeli ethnic groups and was, on average, much higher in the Israeli (0.728) than in the Japanese population (0.152). For the Japanese cardiovascular surgery patients, the maintenance dose of warfarin was significantly larger in the combined VKORC1 1173 TC and CC genotype group than in the 1173 TT genotype group (3.6 +/- 0.5 mg vs 2.8 +/- 0.7 mg, respectively; p = 0.02).

CONCLUSION

The frequencies of the intron 1 VKORC1 1173 T>C SNP show significant differences between ethnic groups and are associated with warfarin dose requirements for achieving a recommended International Normalized Ratio range in Japanese cardiovascular surgery patients. This study supports the example of warfarin as an appropriate model for applying personalized medicine for anticoagulant drugs, and highlights the importance of ethnicity in pharmacogenetics.

Evaluation of coagulant activity after mechanical heart valve replacement

Long-term oral anticoagulant therapy is required for recipients of mechanical heart valves. In our hospital, the international normalized ratio of prothrombin time (PT-INR) has been set in the range 1.5-2.5 since October 2001. To evaluate whether coagulant activity is fully suppressed by this target range, coagulant activity was evaluated by measuring thrombin-antithrombin III complex (TAT) levels and valve-related complications were investigated retrospectively. Two hundred twenty-three patients who underwent mechanical valve replacement were enrolled in this study. PT-INR and TAT were measured at our outpatient clinic in March 2005 and valve-related complications since October 2001, when we started to control PT-INR in the range 1.5-2.5, were investigated. Under adequate warfarin control, there was no significant correlation between PT-INR and TAT, however nine patients who exhibited a PT-INR of less than 2.0 had high levels of TAT. And in atrial fibrillation (AF) patients after mitral valve replacement (MVR), the level of TAT was significantly high compared with sinus rhythm patients after atrial valve replacement. Valve-related complications were bleeding events at 2.75% per patient year and thromboembolism at 0.32% per patient year. Attention to complications of thromboembolism is necessary when the PT-INR is less than 2.0, especially in AF patients after MVR and in those with a thrombotic past history or high levels of TAT. The monitoring of TAT is useful in detecting potential coagulation factors and to determine the therapeutic range of warfarin that can normalize coagulant activity.

Appraisal of current vitamin K dosing algorithms for the reversal of over-anticoagulation with warfarin: the need for a more tailored dosing regimen

Warfarin is the most commonly prescribed oral anticoagulant in the UK for the treatment and prevention of thromboembolic disorders. Vitamin K administration is an effective way of reversing excessive anticoagulation. Over-anticoagulated patients present with a wide range of international normalized ratio (INR) values and may respond differently to a fixed dose of vitamin K. Current dosing algorithms for vitamin K administration in the non-urgent treatment of over-anticoagulation do not take this variability in response into account. Consequently, over a third of over-anticoagulated patients still remain outside their target INR 24 h after treatment. Such patients are therefore prone to either haemorrhage (if the patient is still over-anticoagulated) or thromboembolism (if the INR reversal is over-corrected). A number of factors such as patient age, body weight, co-morbidity, frailty, warfarin daily dose and CYP2C9 and VKORC1 polymorphism could affect response to vitamin K and thus the rate and extent of INR reversal. There is a need for a more individualized approach to the reversal of over-anticoagulation in asymptomatic or mildly haemorrhagic patients in order to improve the safety of warfarin therapy.

Potent and selective TF/FVIIa inhibitors containing a neutral P1 ligand

Inhibition of tissue factor/factor VIIa complex (TF/FVIIa) is an attractive strategy for antithrombotic therapies. We began with an investigation of a non-amidine TF/FVIIa inhibitor based on a modification of amidine compound 1. Optimization of the substituents on the P1 phenyl portion of the compound 1 led to a neutral or less basic alternative for the 4-amidinophenyl moiety. By further optimization of the substituents on the central phenyl ring, a highly potent and selective TF/FVIIa inhibitor 17d was discovered.

Potential drug–herb interaction with antiplatelet/anticoagulant drugs

This is a cross-sectional survey evaluating the use of herbal medicines in medical wards patients that may interfere with the effect of antiplatelet or anticoagulant therapy. Among the 250 patients participated, 42.4% (n=106) were taking herbs with 76 patients (71.7%) using herbs for the past 12 months. Overall, almost 31% (n=23, N=76) of patients were taking one or more of the specified herbal medicines [ginseng (Panax ginseng), garlic (Allium sativum), ginkgo (Gingko biloba) thought to interact with antiplatelet or anticoagulant therapy. The study showed that 21% (n=16, N=76) of patients co-ingested specified herbs with antiplatelet or anticoagulant therapy, of which half of them were at risk of potential drug-herb interactions. A large proportion of respondents involved in potential drug-herb interaction were elderly people (62.5%, n=5). However, more than 90% of herbal users did not disclose the use of herbal medicine to their health professionals. It is thus prudent for all care givers to be aware of the possibility of drug-herb interaction and inquire about herbal use from patients.

Design, synthesis, and biological activity of non-basic compounds as factor Xa inhibitors: SAR study of S1 and aryl binding sites

Compound 7 was identified as the active metabolite of 6 by HPLC and mass spectral analysis. Modification of lead compound 7 by transformation of its N-oxide 6-6 biaryl ring system and fused aromatics produced a series of non-basic fXa inhibitors with excellent potency in anti-fXa and anticoagulant assays. The optimized compounds 73b and 75b showed sub to one digit micromolar anticoagulant activity (PTCT2). Particularly, anti-fXa activity was detected in plasma of rats orally administered with 1mg/kg of compound 75b.

Progress in the design of low molecular weight thrombin inhibitors

Intravascular thrombosis and its complication, embolism, is a leading cause of morbidity and mortality throughout the world. Past few decades have seen a great deal of progress in the development of antithrombotic agents, though the current treatment options are limited to heparin, LMW heparins, and warfarin. Detailed understanding of the biochemical and biophysical mechanisms of activation and regulation of blood coagulation have helped in developing specific inhibitors of enzymes, especially thrombin, within the coagulation cascade. Thrombin plays a central role in the coagulation cascade and so has become the primary target for the development of antithrombotic drugs. The review covers the main pharmacological aspects of haemostasis and thrombosis and provides an update on low molecular weight thrombin inhibitors along with the limitations of the prevalent antithrombotic agents. Recent developments in small molecule inhibitors of Protease Activated Receptor-1 (PAR-1) which can be helpful for the treatment of thrombotic and vascular proliferative disorders, have also been discussed.

Effect of vitamin K intake on the stability of oral anticoagulant treatment: dose-response relationships in healthy subjects

Oral anticoagulants exert their effect by blocking the utilization of vitamin K, yet little is known about competitive aspects of their interaction with dietary vitamin K. We carried out systematic dose-response studies in healthy volunteers who had been stably anticoagulated and maintained on their individualized doses for 13 weeks. First, we studied the response to weekly incremental doses (50 μg-500 μg) of vitamin K1 supplements (K1) taken daily for 7 days. The threshold K1 dose causing a statistically significant lowering of the INR was 150 μg/day. In 25% of the participants the INR change was regarded as clinically relevant at a vitamin K intake of 150 μg/day. Circulating undercarboxylated osteocalcin did not decrease until 300 μg K1/day compared with 100 μg K1/day for undercarboxylated FII, suggesting differential antidotal effects on bone and hepatic γ-carboxylation. Next, we tested the response to vitamin K-rich food items. The short-lived response after meals of spinach and broccoli suggested an inefficient bioavailability from these 2 sources. We conclude that short-term variability in intake of K1 is less important to fluctuations in the international normalized ratio (INR) than has been commonly assumed and that food supplements providing 100 μg/day of vitamin K1 do not significantly interfere with oral anticoagulant therapy. (Blood. 2004;104:2682-2689)