Thrombosis and the pharmacology of antithrombotic agents

Current and emerging drug strategies for the prevention of venous thromboembolism in acutely ill medical inpatients

INTRODUCTION

Venous thromboembolism (VTE) is a common complication in patients hospitalized for acute medical illnesses. Therefore, medical inpatients require a careful VTE and bleeding risk assessment to drive optimal strategies for VTE prevention. Low molecular weight heparin and fondaparinux have long been used for inhospital prophylaxis for patients at increased risk of VTE. The selection of patients who require post-discharge prophylaxis, and the role of direct oral anticoagulants remain debated. New molecules currently under development may contribute to improve the risk benefit of VTE prevention in this setting.

AREAS COVERED

This text summarizes the evidence on approved treatments and on other drugs for the prevention of VTE in acutely ill medical patients. The main focus is on their pharmacological proprieties, clinical efficacy and safety, and the current license approved by the FDA (Food and Drug Administration) and EMA (European Medicines Agency), giving the readers a way to compare available drugs to date. The trials presented consider both inhospital and extended prophylaxis.

EXPERT OPINION

Thanks to the potentially favorable safety profile, factor XI inhibitors may play a role in the prevention of VTE in this setting. The expert opinion section discusses pharmacological properties, prophylaxis trials, and potential clinical applications of this novel class of drugs.

Preparation of thermo-responsive polymer encapsulated exosomes and its role as a therapeutic agent for blood clot lysis

Tissue plasminogen activators induce enzymatic activation of plasminogen to plasmin that cleaves fibrin strands in blood clots. In the present study, extracellular vesicles such as exosomes from fibrosarcoma cell line HT1080 were utilized as clot-busting agents. These exosomes were being used for clot lysis of whole blood which showed 28% lysis within 10 h, which was comparable to that of the streptokinase (commercial plasmin activator) with no significant difference. These exosomes were able to facilitate the migration of endothelial cells in a scratch wound assay where normalized wound area remaining was 7.5% at 18 h. Also, exosomes aided in attenuation of oxidative stress generated on the cells, thereby maintaining cell viability. These exosomes were further encapsulated in a thermo-responsive polymer for better localized delivery that showed no cytotoxic effects, and sustained delivery was achieved up to a concentration of 117 µg/mL in 25 days, which corresponds to around 65% of the total amount of exosomes added. When a combination of exosomes and thermo-responsive polymer was utilized, the clot lysis activity reached to around 22% in 72 h. Thus, it proves the potential of this combinatorial approach which can be effectively used for thrombus degradation and healing of endothelium lining in damaged blood vessels.

Antidepressant, anxiolytic, antipyretic, and thrombolytic profiling of methanol extract of the aerial part of Piper nigrum: In vivo, in vitro, and in silico approaches

Piper nigrum L. also called black pepper is popular for its numerous uses. The present research is designed to investigate the pharmacological potential of methanol extract of Piper nigrum (MEPN). The antidepressant investigation was performed by using both in vivo forced swimming test (FST) and tail suspension test (TST) methods while the anxiolytic research by hole-board test (HBT) method. Again, the antipyretic analysis was conducted through yeast-induced pyrexia method, whereas clot lysis activity was employed by the thrombolytic method. Furthermore, in silico studies followed by molecular docking analysis of several secondary metabolites, pass prediction, and ADME/T were evaluated with AutoDock Vina, Discovery Studio 2020, UCSF Chimera software PASS online, and ADME/T online tools. The plant extract demonstrated dose-dependent potentiality in antidepressant, anxiolytic, antipyretic, and thrombolytic activities. Induction of MEPN produced a significant (p < .5, p < .001) increase of mobility in FST and TST, and increased the head dipping and decreased the latency of time (p < .01, p < .001) in HBT. MEPN 400 (mg/kg; b.w.; p.o.) lowered the rectal temperature of yeast-induced pyrexia substantially (p < .001). Besides, MEPN produced promising (p < .001) clot lysis activity. In the computational approach, among all the proteins, a docking score was found ranging from -1.0 to -7.90 kcal/mol. Besides, all the compounds were found safe in ADME/T study. The results of our scientific research validate the suitability of this plant as an alternative source of novel therapeutics.

Withametelin: a biologically active withanolide in cancer, inflammation, pain and depression

Withanolides are natural medicinal agents whose safety and therapeutic profiles make them valuable to mankind. Among multiple withanolides, withametelin is underexplored. The present study was aimed to create a general biological profile of isolated withametelin from Datura innoxia Mill. targeting different biological models. In-silico studies include drug-likeliness, pharmacokinetics, toxicity, molecular targets and cytotoxicity to cancer cell lines predictions. In silico directed preliminary in-vitro evaluation comprised of cancer/normal cell cytotoxicity, DPPH and protein kinase inhibition assays while in-vivo bioactivities include antiinflammatory, analgesic, antidepressant and anticoagulant assays. Pharmacological findings were strengthened by molecular docking studies to check interactions with various proteins and to propose the future path of studies. Results indicated compliance with Lipinski drug-likeliness rule (score −0.55). ADMET prediction showed strong plasma protein binding, GI absorption (Caco-2 cells permeability = 46.74 nm/s), blood brain barrier penetration (Cbrain/Cblood = 0.31), efflux by P-glycoprotein, metabolism by CYP1A2, CYP2C19 and CYP3A4, medium hERG inhibition and non-carcinogenicity in rodents. Predicted molecular targets included mainly receptors (glucocorticoid, kappa opioid, delta opioid, adrenergic and dopamine), oxidoreductase (arachidonate 5-lipoxygenase and cyclooxygenase-2), enzymes (HMG-CoA reductase) and kinase (NFκb). Withametelin was more cytotoxic to cancer cells (DU145 IC₅₀ 7.67 ± 0.54 µM) than normal lymphocytes (IC₅₀ 33.55 ± 1.31 µM). It also showed good antioxidant and protein kinase inhibition potentials. Furthermore, withametelin (20 mg/kg) significantly reduced inflammatory paw edema (68.94 ± 5.55%), heat-induced pain (78.94 ± 6.87%) and immobility time (50%) in animals. Molecular docking showed hydrogen bonding interactions (binding energies: −11.3 to −7.8 kcal/mol) with arachidonate 5 lipoxygenase, NFκb and glucocorticoid receptor. Withametelin has potential for advance investigations for its cytotoxic, anti-inflammatory, analgesic and antidepressant activities.

In vivo neuroprotective, antinociceptive, anti-inflammatory potential in Swiss albino mice and in vitro antioxidant and clot lysis activities of fractionated Holigarna longifolia Roxb. bark extract

Background The study investigated the in vivo neuroprotective, antinociceptive, anti-inflammatory potential and in vitro antioxidant and clot lysis activities of crude methanol extract with its different solvent-soluble fractions like petroleum ether (PESF), carbon tetrachloride (CTSF), chloroform (CSF) and aqueous (AQSF) of Holigarna longifolia Roxb. Methods Phenobarbitone-induced sleeping time method was used for the neuroprotective activity, writhing response experimental model introduced by acetic acid was designed for antinociceptive efficacy, carrageenan-induced paw edema model was carried out for anti-inflammatory activity, DPPH free radical scavenging activity was assessed for antioxidant activity and clot lysis model was investigated for the thrombolytic potential of the plant. Results On investigation it was found that methanol extract and CS fraction revealed statistically meaningful (p<0.05) neuroprotective activity by increasing phenobarbitone-induced sleeping time of mice, produced substantial (p<0.05) inflammation inhibitory efficacy compared to standard diclofenac sodium and also exhibited statistically significant (p<0.01) oxidative stress inhibitory efficacy by inhibiting free radical formation compared to ascorbic acid as standard. Only methanol extract produced significant (p<0.05) antinociceptive activity by inhibiting abdominal writhes produced by acetic acid compared to standard analgesic drug diclofenac sodium. And only aqueous soluble fraction exhibited moderate clot lysis activity compared to streptokinase as standard. Conclusion The findings demonstrate that H. longifolia could be potential neuroprotective due to its justified antioxidative capacity as well as clot lysis properties.

Evaluation of analgesic, anti-inflammatory, thrombolytic and hepatoprotective activities of roots of Premna esculenta (Roxb)

BACKGROUND

The objective of this study was to investigate the antinociceptive, anti-inflammatory, thrombolytic and hepatoprotective activities of root extracts of Premna esculenta (family: Verbenaceae).

METHODS

The analgesic activity was evaluated using the acetic-acid-induced writhing test in mice and radiant heat tail-flick method in rats. The anti-inflammatory activity was investigated by carrageenan-induced rat's paw edema, while the thrombolytic activity was evaluated by in vitro clot lysis model. The hepatoprotective activity was investigated against carbon-tetrachloride-induced liver damage in rats.

RESULTS

In acetic-acid-induced writhing test, chloroform and ethyl acetate fraction of ethanolic extract at a dose of 200 mg/kg showed a significant (p<0.001) reduction in the number of writhes with 85.96% and 61.98% of inhibition, respectively. In radiant heat tail-flick method, the ethanolic extract produced 88.49% (p<0.001) elongation of tail-flicking time at 90 min after oral administration at same dose level. In the carrageenan-induced edema test, the ethanolic extract at a dose of 200 mg/kg showed a significant inhibition of paw edema with 22.68% and 17.24% inhibition after the first and third hours of the study period, respectively. In clot lysis model, the ethanolic extract at 5 mg/mL induced a significant clot lysis activity (37.69%, p<0.001). Oral administration of ethanolic extract at the dose of 400 mg/kg/day for 7 days significantly (p<0.001) reduced the elevated levels of serum glutamic pyruvic transaminase, serum glutamyl oxaloacetate transaminase and alkaline phosphatase compared to the CCl4-treated control group.

CONCLUSIONS

The results of the study demonstrated the antinociceptive, anti-inflammatory, thrombolytic and hepatoprotective activities of roots of P. esculenta.

Effects of Policosanol and Ticlopidine in Patients with Intermittent Claudication: A Double-Blinded Pilot Comparative Study

Policosanol is a cholesterol-lowering drug with concomitant antiplatelet effects. The present study was undertaken to compare the effects of policosanol and ticlopidine in patients with moderately severe intermittent claudication (IC). The study had a 4-week baseline step, followed by a 20-week double-blinded, randomized treatment period. Twenty-eight eligible patients were randomized to policosanol 10 mg or ticlopidine 250 mg tablets twice daily (bid). Walking distances in a treadmill (constant speed 3.2 km/hr, slope 10°, temperature 25°C) were assessed before and after 20 weeks of treatment. Both groups were similar at baseline. Compared with baseline, policosanol significantly increased (p<0.01) mean values of initial (ICD) and absolute (ACD) claudication distances from 162.1 to 273.2 m and from 255.8 to 401.0 m, respectively. Ticlopidine also raised significantly (p<0.01) ICD (166.2 to 266.3 m) and ACD (252.9 to 386.4 m). Comparisons between groups did not show significant differences. Policosanol, but not ticlopidine, significantly (p<0.05), but modestly, increased the ankle/arm pressure ratio. After 10 weeks, policosanol significantly (p<0.001) lowered low-density lipoprotein-cholesterol (LDL-C), total cholesterol (TC) (p<0.01), and TC/HDL-C and raised (p<0.05) high-density lipoprotein-cholesterol (HDL-C). At study completion, policosanol lowered (p<0.001) LDL-C (30.2%), TC (16.9%), and TC/HDL-C (33.9%), increased (p<0.01) HDL-C (+31.7%), and left triglycerides unchanged. Ticlopidine did not affect the lipid profile variable. Policosanol induced modest, but significant, reductions (p<0.01) of fibrinogen levels compared with baseline and ticlopidine. Treatments were well tolerated and did not impair safety indicators. Three ticlopidine patients (21.4%) withdrew from the trial, only 1 owing to a serious adverse experience (AE) (unstable angina). Three other ticlopidine patients experienced mild AE (headache, diarrhea, and acidity). It is concluded that policosanol (10 mg bid) can be as effective as ticlopidine (250 mg bid) for improving walking distances of claudicant patients, and it could be advantageous for the global risk of these individuals owing to its cholesterol-lowering effects. This study is, however, just a pilot comparison, so that further studies in larger sample sizes are needed for definitive conclusions of the comparative effects of both drugs on patients with IC.

Efficient Double Suzuki Cross-Coupling Reactions of 2,5-Dibromo-3-hexylthiophene: Anti-Tumor, Haemolytic, Anti-Thrombolytic and Biofilm Inhibition Studies

The present study describes several novel 2,5-biaryl-3-hexylthiophene derivatives (3a–i) synthesized via a Pd(0)-catalyzed Suzuki cross-coupling reaction in moderate to good yields. The novel compounds were also analyzed for their anti-thrombolytic, haemolytic, and biofilm inhibition activities. In addition, the anti-tumor activity was also evaluated in vitro for newly-synthesized compounds, where 3-hexyl-2,5-bis(4-(methylthio)phenyl)thiophene exhibited the best anti-tumor activity against 4T1 cells with IC₅₀ value of 16 μM. Moreover, 2,5-bis(4-methylphenyl)-3-hexylthiophene showed the highest activity against MCF-7 cells with an IC₅₀ value of 26.2 μM. On the other hand, the compound 2,5-bis(4-chloropheny)-3-hexylthiophene exhibited excellent biofilm inhibition activity. Furthermore, the compound 2,5-bis(3-chloro-4-fluorophenyl)-3-hexylthiophene also exhibited better anti-thrombolytic and hemolytic activity results as compared to the other newly-synthesized compounds.

Selective C-arylation of 2,5-dibromo-3-hexylthiophene via Suzuki cross coupling reaction and their pharmacological aspects

The present study reports the synthesis of various new derivatives based on 5-aryl-2-bromo-3-hexylthiophene with moderate-to-good yields via a palladium-catalyzed Suzuki cross-coupling reaction. This coupling method involved the reaction of 2,5-dibromo-3-hexylthiophene with several arylboronic acids in order to synthesize corresponding thiophene derivatives under controlled and optimal reaction conditions. The different substituents (CH₃, OCH₃, Cl, F etc.) present on arylboronic acids are found to have significant electronic effects on the overall properties of new products. The synthesized thiophene molecules were studied for their haemolytic, biofilm inhibition and anti-thrombolytic activities, and almost all products showed potentially good properties. The compound 2-bromo-5-(3-chloro-4-fluorophenyl)-3-hexylthiophenein particular exhibited the highest values for haemolytic and bio-film inhibition activities among all newly synthesized derivatives. In addition, the compound 2-bromo-3-hexyl-5-(4-iodophenyl)thiophene also showed high anti-thrombolytic activity, suggesting the potential medicinal applications of these newly synthesized compounds.

Silver nano particles prevent platelet adhesion on immobilized fibrinogen

Vascular thrombotic disorders have emerged as a serious threat to our society. Platelet adhesion to fibrinogen, collagen and other platelet activators exposed over the atherosclerotic plaques can trigger platelet signaling events, activate platelets and lead to thrombotic events. Since anticoagulant and thrombolytic treatment strategies are usually associated with serious bleeding complications, preventing platelets adhesion may help to maintain platelets in an inactive state. In this study we tried to find out the effect of Silver nanoparticles, through their interaction with various platelet surface integrins on platelet adhesion on immobilized fibrinogen. Platelets, isolated from anti-coagulated human whole blood sample from healthy donors, were suspended in physiological buffer and each sample was divided into four tubes. In three of them 0.05, 0.5, and 5 μM concentrations of Silver nanoparticles were added, fourth tube served as control. Platelet adhesion on immobilized fibrinogen matrices and integrin mediated cell signaling events were studied in all the four samples. In the present study we show that nanosilver prevent platelet adhesion without conferring any lytic effect on them and effectively prevents integrin-mediated platelet responses in a concentration-dependent manner.

Anticoagulation Review

Anticoagulants, also known as antithrombotics, are among the most commonly prescribed medications in the United States. Understanding how these medications work, the propensity for interactions with other drugs, dietary factors, and disease states is important for clinicians assessing and providing care to patients in all environments. In this review, we seek to provide essential information for the home health care provider for evaluating patients receiving anticoagulants commonly prescribed in the home health care setting. The low-molecular-weight heparins and vitamin K antagonists are the most commonly used agents for outpatient anticoagulation. New agents, such as the direct factor Xa inhibitors and direct thrombin inhibitors have recently been approved with additional new agents in the approval process and development pipeline. We seek to review the most pertinent information for each of these classes of medications providing information on pharmacology, interactions with other drugs, diet, and diseases and important clinical information.

Enoxaparin: a pharmacologic and clinical review

INTRODUCTION

Both arterial and venous thromboembolism constitute a significant disease burden worldwide, leading to major use of healthcare resources. As anticoagulants play a pivotal role in the treatment of these disorders, it is vital for healthcare providers to have sufficient knowledge of their biochemical and clinical attributes.

AREAS COVERED

Enoxaparin is one of the most commonly used low-molecular-weight heparins in a wide variety of thromboembolic disorders and has several advantages over unfractionated heparin. An analysis of its biophysical profile, with special emphasis on pharmacokinetic and pharmacodynamic properties, is undertaken in this article. In addition, most recent major clinical studies elucidating its role in common thromboembolic conditions are discussed, while keeping the historical perspective at hand. Readers will be able to understand the pharmacologic properties of enoxaparin with their clinical relevance for day-to-day use and critically analyze the amount and weight of scientific evidence behind its use in various disorders.

EXPERT OPINION

In summary, enoxaparin has been shown, by a vast amount of scientific data, to be a safe and effective agent in the treatment of a whole spectrum of acute coronary syndromes, with similar efficacy and safety in the prevention and treatment of venous thromboembolism.

Characterization of antiplatelet properties of silver nanoparticles

Thrombotic disorders have emerged as serious threat to society. As anticoagulant and thrombolytic therapies are usually associated with serious bleeding complications, the focus has now shifted to regulating and maintaining platelets in an inactive state. In the present study we show that nanosilver has an innate antiplatelet property and effectively prevents integrin-mediated platelet responses, both in vivo and in vitro, in a concentration-dependent manner. Ultrastructural studies show that nanosilver accumulates within platelet granules and reduces interplatelet proximity. Our findings further suggest that these nanoparticles do not confer any lytic effect on platelets and thus hold potential to be promoted as antiplatelet/antithrombotic agents after careful evaluation of toxic effects.

Management of prehospital antiplatelet and anticoagulant therapy in traumatic head injury: a review

Trauma and emergency department clinicians encounter a growing number of patients admitted with traumatic head injury on prehospital antithrombotic therapies. These patients appear to be at increased risk of developing life-threatening intracranial hemorrhage. It is imperative that trauma clinicians understand the mechanism and duration of commonly prescribed outpatient antithrombotics in order to appropriately assess and treat patients who develop intracranial hemorrhage. This review summarizes current literature on the morbidity and mortality associated with premorbid non-steroidal anti-inflammatory drugs, aspirin, clopidogrel, warfarin, and heparinoids in the setting of traumatic head injury, and also examines the current strategies for reversal of these therapies.

Future directions in thrombolysis

An extensive body of research conducted in the past 25 years has helped foster understanding of the mechanisms and pathogenesis of the acute coronary syndromes and occlusive disease. Thus, it is well established that thrombosis is caused by vascular injury and that immediate lysis of the arterial thrombus and subsequent prevention of thrombotic reocclusion are critical to the treatment of these disorders. Remarkable progress in the understanding of the biological and molecular mechanisms involved in vascular-wall-platelet interactions, platelet-platelet interactions, and coagulation has led to the identification of multiple targets for drug discovery and the development of numerous antithrombotic drugs. The purpose of this article is to review emerging antithrombotic therapies, introduce potential future molecular targets for drug discovery efforts, and discuss novel strategies for managing patients with coronary disease.

Development of an in vitro model to study clot lysis activity of thrombolytic drugs

Background

Thrombolytic drugs are widely used for the management of cerebral venous sinus thrombosis patients. Several in vitro models have been developed to study clot lytic activity of thrombolytic drugs, but all of these have certain limitations. There is need of an appropriate model to check the clot lytic efficacy of thrombolytic drugs. In the present study, an attempt has been made to design and develop a new model system to study clot lysis in a simplified and easy way using a thrombolytic drug, streptokinase.

Methods

Whole blood from healthy individuals (n = 20) was allowed to form clots in a pre-weighed sterile microcentrifuge tubes; serum was removed and clot was weighed. After lysis by streptokinase fluid was removed and remnants of clot were again weighed along with the tube. Percentage of Clot lysis was calculated on the basis of the weight difference of microcentrifuge tubes obtained before and after clot lysis.

Results

There was a significant percentage of clot lysis observed when streptokinase was used. On the other hand with water (negative control), minimal (2.5%) clot lysis was observed. There was a significant difference between clot lysis done by streptokinase and water.

Conclusion

Our study could be a rapid and effective methodology to study clot-lytic effect of newly developed drugs as well as known drugs.

Anticoagulant and antiplatelet agents: their clinical and device application(s) together with usages to engineer surfaces

An essential aspect of the treatment of patients with cardiovascular disease is the use of anticoagulant and antiplatelet agents for the prevention of further ischaemic events and vascular death resulting from thrombosis. Aspirin and heparin have been the standard therapy for the management of such conditions to date. Recently, numerous more potent platelet inhibitors together with anticoagulant agents have been developed and tested in randomized clinical trials. This article reviews the current state of the art of antiplatelet and anticoagulant therapy in light of its potential clinical efficacy. It then focuses on the usages of these agents in order to improve the performance of clinical devices such as balloon catheters, coronary stents, and femoropopliteal bypass grafting and extra corporeal circuits for cardiopulmonary bypass. The article then goes on to look at the usage of these agents more specifically heparin, heparan, hirudin, and coumarin in the development of more biocompatible scaffolds for tissue engineering.

Fondaparinux: a new antithrombotic agent

BACKGROUND

Venous thrombosis is usually triggered by a low-flow state, as in prolonged periods of bed rest after hip or knee surgery. Antithrombotic agents are the drugs of choice in such circumstances. The new factor Xa inhibitor fondaparinux has been approved by the US Food and Drug Administration for the prevention of venous thromboembolism in patients undergoing hip fracture surgery, hip replacement surgery, or knee replacement surgery.

OBJECTIVE

The aim of this article was to review the clinical pharmacology of fondaparinux and summarize the data from available clinical trials of this agent.

METHODS

The terms fondaparinux, SR90107A/ORG31540, and factor Xa were used to search MEDLINE and Current Contents/Clinical Medicine for English-language studies in humans published between 1996 and May 2002. Unpublished data were provided by the manufacturer of fondaparinux, and additional information was obtained from abstracts presented at the 2001 congress of the International Society on Thrombosis and Haemostasis in Paris.

RESULTS

Fondaparinux is a synthetic pentasaccharide that selectively binds to antithrombin III, inducing a conformational change that increases anti-factor Xa activity. Phase III studies to date have reported that fondaparinux had greater efficacy compared with enoxaparin in terms of prevention of venous thromboembolism after hip or knee replacement surgery. Preliminary studies have suggested that this agent may have efficacy in the treatment of deep vein thrombosis, as well as in the management of acute coronary syndromes. However, 1 study reported a significant increase in the risk of major bleeding with fondaparinux compared with enoxaparin (2.1% vs 0.2%, respectively; P = 0.006), and another reported a significant increase in the risk of minor bleeding (4.1% vs 2.1%; P = 0.02).

CONCLUSIONS

Fondaparinux has shown efficacy in the prevention of venous thromboembolism in patients undergoing hip or knee replacement surgery. Large-scale clinical trials of its potential efficacy in deep vein thrombosis and acute coronary syndromes are ongoing. Use of fondaparinux may be associated with an increased bleeding risk, and patients should be assessed individually to ensure that the possible benefits outweigh the risks. Routine use of fondaparinux as a replacement for low-molecular-weight heparin is not recommended at this time.

Enoxaparin: an update of its clinical use in the management of acute coronary syndromes

Enoxaparin (enoxaparin sodium) is a low molecular weight heparin (LMWH) indicated for use in the treatment of ischaemic complications of unstable angina and non-Q wave myocardial infarction (MI). Unfractionated heparin (UFH) has for many years represented the standard in anticoagulant therapy for patients with acute coronary syndromes; however, recent studies suggest that enoxaparin is also a viable option for anticoagulant therapy in these patients. The ESSENCE (Efficacy and Safety of Subcutaneous Enoxaparin in Non-Q wave Coronary Events) and the TIMI 11B (Thrombolysis in Myocardial Infarction) studies reported that twice daily enoxaparin was significantly more effective than a continuous infusion of UFH in reducing the composite triple endpoint of death, MI, or recurrent angina or urgent revascularisation. Follow-up of both patient populations showed continued benefit associated with enoxaparin. Enoxaparin has been compared with tinzaparin in the treatment of unstable coronary artery disease using a nonblind study design. There was no difference between treatment groups in the therapeutic endpoints. Three nonblind studies have also compared the effects of enoxaparin and UFH in patients receiving thrombolytic therapy following acute MI. The HART II (Heparin and Aspirin Reperfusion Therapy), the ASSENT 3 (Assessment of the Safety and Efficacy of a New Thrombolytic Regimen) and the ENTIRE-TIMI 23 (Enoxaparin and Tenecteplase with or without glycoprotein IIb/IIIa Inhibitor as Reperfusion strategy in ST Elevation MI - Thrombolysis in Myocardial Infarction) studies have revealed that enoxaparin in combination with alteplase or tenecteplase is at least equivalent (HART II and ENTIRE-TIMI 23), and possibly superior (ASSENT 3) to UFH. Enoxaparin is administered as a twice-daily subcutaneous injection. In contrast, UFH is administered as an intravenous infusion which requires routine monitoring of the activated partial thromboplastin time to ensure adequate levels of anticoagulation are maintained. During the acute phase of the the ESSENCE and TIMI 11B studies, the incidence of major bleeding was similar in patients receiving enoxaparin to that in patients receiving UFH. In contrast, the rates of minor bleeding were higher in patients receiving enoxaparin than in those receiving UFH throughout these studies.

CONCLUSIONS

Data from the ESSENCE, TIMI 11B and ASSENT 3 studies have prompted calls for those LMWHs which have been shown to be superior to UFH, to be considered as first choice treatment for anticoagulation in unstable coronary syndromes. To date, these suggestions are not reflected in current guidelines which consider UFH and LMWHs equally. Irrespective, the clinical data reported in this review support the use of enoxaparin in the treatment of acute coronary syndromes. These data suggest that enoxaparin shows certain clinical and practical advantages over standard treatment with UFH and represents an important development in the treatment of acute coronary syndromes.

Pharmacotherapeutic options for the management of myocardial infarction

The pharmacological treatment of acute coronary syndrome (ACS), including unstable angina, non-ST- and ST-segment elevation myocardial infarction (MI) is dynamic and continues to evolve. Expert guidelines based on the results of clinical trials for the management of different types of ACS have been published. In both ST-segment elevation and non-ST-segment elevation MI, aspirin/clopidogrel, heparin/low molecular weight heparin/direct thrombin inhibitors, beta-blockers and angiotensin converting enzyme inhibitors are part of the routine regimens. In patients with ST-segment elevation MI, eligibility for thrombolytic therapy needs to be determined and utilised as soon as possible. In patients with non-ST-segment elevation MI, the risks of thrombolytic therapy outweigh the benefits. The use of glycoprotein IIb/IIIa inhibitors has become increasingly important. The use of antihyperlipidaemic agents for the prevention of secondary events in both types of patients continue to be essential and the early aggressive use of lipid-lowering therapy also plays a role in improving endothelial function and stabilising atherosclerotic plaques.

Radiolabeled peptides in diagnosis and therapy

During the past few years, there has been exponential growth in the development of radiolabeled peptides for diagnosis and therapy. This is because the peptides can be synthesized easily and inexpensively, they have fast clearance and rapid tissue penetration, and they are less likely to be immunogenic. More importantly, most peptides have a high affinity for characteristic receptor molecules that are overexpressed on malignant mammalian cells. Peptides can be labeled with a variety of radionuclides intended for specific applications, diagnostic or therapeutic, by using both conventional and novel chelating moieties, many of which can be incorporated during the solid state synthesis of a chosen peptide. High specific-activity peptides can be prepared and used to minimize unwanted physiologic effects, and known sequences of amino acids can be modified to slow their in vivo catabolic rate. These characteristics have paved the way for the preparation of a large number of radiolabeled peptides for a variety of clinical and experimental applications. This article briefly discusses the peptide chemistry; it also summarizes the preparation of radiolabeled peptides and outlines their applications in imaging vascular thrombosis, detecting infection and inflammation, and localizing tumors. Their therapeutic applications in oncology are also presented and the future directions outlined. Peptides that have been approved for human use, such as AcuTect (Diatide, Londonderry, NH) or OctreoScan (Mallinckrodt, St. Louis, MO), or those that have made it to clinical trials, are emphasized. Also discussed are selected promising agents that are still in preclinical investigation.

Evaluation and survey of intravenous vitamin K1 for treatment of coagulopathy in critically ill patients

STUDY OBJECTIVES

To determine patient factors associated with coagulopathy, to assess variables affecting response to vitamin K1, to describe vitamin K1-associated adverse reactions, and to survey Canadian tertiary care hospitals about vitamin K1 practice patterns in their intensive care units (ICUs).

DESIGN

Retrospective chart audit and prospective survey.

SETTING

Medical-surgical ICU with a 23-bed complement in a tertiary care, university-affiliated hospital, and 47 Canadian tertiary care hospitals.

PATIENTS

Forty-eight critically ill patients with nonconsumptive coagulopathies.

INTERVENTION

Intravenous vitamin K1 utilization over 4 months.

MEASUREMENTS AND MAIN RESULTS

The only independent risk factor for elevated baseline international normalized ratios (INRs) was Acute Physiologic and Chronic Health Evaluation (APACHE) II score (r2 = 0.51, p<0.05). The INR values decreased after two doses of vitamin K1 10 mg for patients grouped as a whole (2.14 +/- 0.96 to 1.61 +/- 0.62, p<0.0001) and when patients were stratified according to APACHE II scores below 23 (1.83 +/- 0.44 to 1.34 +/- 0.18, p<0.05). The INRs were not significantly reduced for patients with APACHE II scores of 23 or greater (2.44 +/- 1.23 to 1.82 +/- 0.66). No variables were associated with response, and adverse events were not observed. Of 47 Canadian tertiary care hospitals surveyed, 27 (55%) responded. Twenty-four (89%) indicated that vitamin K1 was administered intravenously, and no adverse events resembling anaphylaxis were reported.

CONCLUSION

Administration of two doses of intravenous vitamin K1 10 mg was associated with reversal of coagulopathies, but variable responses may be expected for patients with high APACHE II scores. Randomized, placebo-controlled studies are necessary to confirm the effectiveness of vitamin K1.

Enoxaparin: in the prevention of venous thromboembolism in medical patients

Enoxaparin (enoxaparin sodium) is a low-molecular-weight heparin that binds to and increases the activity of antithrombin III. The resulting complex inhibits prothrombinase-mediated thrombin generation and direct thrombin generation by binding to factor Xa and thrombin factor IIa. Enoxaparin, used as prophylaxis in medically ill patients at increased risk for thromboembolism, has shown significantly increased efficacy compared with placebo in reducing the incidence of deep vein thrombosis and pulmonary embolism. Indeed, 291 patients receiving subcutaneous enoxaparin 40 mg/day had a frequency of venous thromboembolism of 5.5% during 14 days of treatment, whereas 14.9% of the 288 placebo recipients experienced thromboemboli (p < 0.001). There was no reduction in the incidence of thromboembolism in the 287 recipients of enoxaparin 20 mg/day (15%). In other studies, prophylactic treatment for 7 days with subcutaneous enoxaparin 40 mg/day was at least as effective as unfractionated heparin in reducing the frequency of venous thromboembolism in 959 nonsurgical patients at increased risk for deep vein thrombosis and pulmonary embolism (total incidence = 0.2 and 1.4%, respectively). Moreover, enoxaparin recipients experienced fewer adverse events than did heparin recipients. The most frequent adverse events reported in medically ill and surgical patients receiving enoxaparin 40 mg/day were hemorrhage (17.4 vs 14.3% for placebo), hematoma at injection site, anemia, fever, peripheral edema, nausea, ecchymosis and edema (unspecified site).

Beneficial effects of statins in coronary artery disease--beyond lowering cholesterol

OBJECTIVE

To review the benefits of statins in coronary artery disease management beyond their cholesterol-lowering effects.

DATA SOURCES

A MEDLINE search (1966-May 2000) was conducted using the following terms: lovastatin, pravastatin, simvastatin, atorvastatin, fluvastatin, cerivastatin, endothelium, plaque stabilization, antithrombotic effects.

STUDY SELECTION

English-language human studies and case reports.

DATA EXTRACTION

Studies published demonstrating other mechanisms of statins' clinical beneficial effects were evaluated and reviewed.

DATA SYNTHESIS

The understanding of the pharmacologic effects of statins has led to the realization that the benefits of these agents extend beyond simply lowering cholesterol. These properties include beneficial effects on vessel endothelial tissue; decreased low-density lipoprotein oxidation and inflammation; ability to stabilize atherosclerotic plaques and perhaps promote regression; proliferative effects on smooth-muscle growths, possibly strengthening atherosclerotic plaques; antithrombotic effects by inhibiting platelet aggregation and stimulation of fibrinolytic factors; and improvement of blood viscosity and flow. With these actions, statins may benefit the situation of long-term atherosclerotic plaque formation and the setting of acute coronary syndrome.

CONCLUSIONS

Further large-scale studies are needed to determine the clinical importance and validity of these postulated beneficial effects of statins.

tPA, but not uPA, significantly affects antithrombotic therapy by a glycoprotein IIb/IIIa antagonist, but not by a factor Xa inhibitor

To define the interaction of fibrinolytic components with platelets or coagulation factors on thrombus formation, we investigated mouse deficient in tissue plasminogen activator (tPA -/-) or urokinase plasminogen activator (uPA -/-) and in their wild-type control (tPA +/+, uPA +/+). A thrombus was induced in the murine carotid artery using photochemical reaction. Blood flow was monitored and the time needed before the vessel became completely obstructed was within 12 min in all types of mice. When DX-9065a, a selective factor Xa inhibitor, or GR144053, a platelet glycoprotein (GP) complex IIb/IIIa antagonist was applied, the time required to occlusion was prolonged in a dose-dependent manner in all types of mice. When a factor Xa inhibitor was injected in tPA -/- mice, the estimated ED50 was not changed. However, when GR144053 was injected in tPA -/- mice, the most significant changes were observed: the estimated ED51 was 19.6 times higher than the one in tPA +/+ mice. Platelet aggregation, hemostasis tests, and bleeding times were not significantly different among the different types of mice. In conclusion, the antithrombotic effect of platelet inhibition by a GPIIb/IIIa antagonist, is severely affected by the absence or presence of tPA production. On the contrary, the inhibition of factor Xa shows a stable antithrombotic effect with or without tPA. Thus the lack of tPA, but not of uPA, significantly affects antithrombotic efficacy.

Effects of Intravenous Enoxaparin and Intravenous Inogatran in an Electrolytic Injury Model of Venous Thrombosis in the Dog

The objective of this study was to compare the effectiveness of the low molecular weight heparin, enoxaparin (Lovenox((R))), and inogatran (a direct thrombin inhibitor) in a canine electrolytic injury model of venous thrombosis. Effectiveness was defined as the ability of either drug to prolong the following parameters: activated partial thromboplastin time (aPTT), thrombin time (TT), prothrombin time (PT), and time to formation of an occlusive thrombus in the vein. There were 5 dogs and 10 vessels for each group (the right and left femoral veins were used in each dog to measure time to occlusion). Dogs were randomly assigned to one of six groups: (1) saline controls; (2) low-dose inogatran (0.075 mg/kg IV bolus followed by a 5 µg/kg/min infusion); (3) mid-dose inogatran (0.25 mg/kg IV bolus followed by a 20 µg/kg/min infusion); (4) high-dose inogatran (0.75 mg/kg IV bolus followed by a 50 µg/kg/min infusion); (5) low-dose enoxaparin (100 units/kg IV bolus followed by a 50 U/kg/h infusion); and (6) high-dose enoxaparin (200 U/kg IV bolus followed by a 100 U/kg/h infusion). Administration of inogatran resulted in dose-dependent increases in aPTT, TT, and PT, and administration of enoxaparin resulted in dose-dependent increases in aPTT and TT. There were no changes in hemodynamics. The time to occlusion in the control group averaged 81.7 +/- 9.9 minutes compared with 141.8 +/- 12.7, 185.8 +/- 17.6, and 226.9 +/- 8.8 minutes with the low, mid, and high doses of inogatran, and 131 +/- 20.3, and 183.0 +/- 19.0 minutes with the low and high doses of enoxaparin. Bleeding times were elevated by inogatran and enoxaparin, but no appreciable differences were detected between the two compounds. In summary, the direct thrombin inhibitor inogatran, administered intravenously, was as effective as the low molecular weight heparin enoxaparin in a canine model of venous thrombosis induced by electrolytic injury, supporting the conclusion that direct antithrombins may prove useful for prevention and treatment of deep venous thrombosis.

In vivo analysis of antithrombotic effectiveness of recombinant hirudin on microvascular thrombus formation and recanalization

PURPOSE

This study was undertaken to evaluate in vivo the effect of recombinant hirudin (r-hirudin [HBW 023]), a potent thrombin inhibitor, on the process of microvascular thrombus formation and recanalization.

METHODS

Thrombosis was induced photochemically in distinct arterioles (n = 25) and venules (n = 30) of the ear of 16 hairless hr/hr mice (8 to 10 weeks old, 25 to 30 g of body weight). r-Hirudin (1 mg/kg of body weight) was administered intravenously directly before thrombus induction; saline-treated animals served as controls. Thrombus formation (i.e., first platelet deposition at the endothelial lining [FPD]; inner luminal diameter reduction to 50% [D/2]; complete vessel occlusion [CVO]), vessel recanalization, microcirculatory parameters, and leukocyte-endothelial cell interaction were analyzed by means of intravital fluorescence microscopy.

RESULTS

Hirudin significantly delayed the process of thrombus formation compared with saline-treated controls in both arterioles (FPD: 381 +/- 80 vs 137 +/- 25 seconds, P < 0.05; D/2: 627 +/- 49 vs 501 +/- 71 seconds; CVO: 925 +/- 78 vs 854 +/- 60 seconds) and venules (FPD: 173 +/- 11 vs 59 +/- 4 seconds; D/2: 342 +/- 54 vs 228 +/- 27 seconds; CVO: 541 +/- 85 vs 344 +/- 43 seconds; P < 0.05). In addition, r-hirudin-treated animals showed an increased rate of vessel recanalization at 24 hours after thrombus induction (arterioles: 54% [7 of 13] vs 0% [0 of 12], P < 0.05; venules: 77% [10 of 13] vs 53% [9 of 17]), whereas microcirculatory parameters and leukocyte-endothelial cell interaction were not affected.

CONCLUSION

Our data indicate that r-hirudin not only counteracts the process of thrombus formation but also promotes vessel recanalization, thus supporting its use in clinical microvascular surgery.