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O Iqbal

Publications and source records attributed to O Iqbal.

At least 19 recordsLinked to original sources
PubMed2005

Comparative tissue factor pathway inhibitor release potential of heparins.

Tissue factor pathway inhibitor (TFPI) is released following the administration of unfractionated heparin, low-molecular-weight heparins, defibrotide and PI-88. In this study, the comparative effects of heparin, a low-molecular-weight heparin-gammaparin and a heparin-derived oligosaccharide mixture-subeparin (C3) were studied on functional and immunologic tissue factor pathway inhibitor activity levels in a non-human primate (Macaca mulatta) model. The dose-dependent effect was studied following intravenous and subcutaneous administration. Following the administration of 1 mg/kg of heparin, gammaparin, and C3, the functional levels of TFPI at 5 minutes were 2.40, 2.56, and 1.08 U/mL and the corresponding TFPI immunologic levels were 4.3-, 4.0-, and 2.1-fold, increased, respectively, over the baseline value. From these results, it can be concluded that heparin and gammaparin produced similar levels of TFPI release. Hence, gammaparin and heparin have similar TFPI release potential despite their differences in molecular weight. The influence of molecular weight, charge density, and interactions with heparin cofactor II on TFPI release are also discussed.

Animals↗
PubMed2004

Blood levels of nitric oxide, C-reactive protein, and tumor necrosis factor-alpha are upregulated in patients with malignancy-associated hypercoagulable state: pathophysiologic implications.

Endogenous generation of nitric oxide (NO) plays an important role in the regulation of cardiovascular and inflammatory responses. This mediator is synthesized by a family of enzymes collectively known as NO synthase. Several isoforms of this enzyme have been identified and can be grouped as constitutive or inducible. Increased production of NO is reported in several inflammatory disorders, such as sepsis, arthritis, thrombotic thrombocytopenic purpura (TTP), and antiphospholipid syndrome. In addition, NO upregulates cyclo-oxygenase-2 and synthesis of several other inflammatory cytokines. Inflammation and thrombotic complications are usually associated with malignancy. Earlier reports indicate the upregulation of tumor necrosis factor-alpha (TNF-alpha), C-reactive protein (CRP), and tissue factor (TF) in patients with malignancy. To determine the relationship between inflammatory cytokines and NO in cancer patients with hypercoagulable states, baseline plasma samples from 160 patients with confirmed malignancy and hypercoagulable state were analyzed for NO levels. A chemical method based on a chemiluminescent reaction between NO and ozone using a highly sensitive gas phase NO analyzer was used. CRP, TF, and TNF-alpha were measured using enzyme-linked immunosorbent assay methods. Of the 160 patients who were plasma tested, the baseline NO levels ranged from 13.7 to 98.6 microM (63.1+/-15.9 microM, mean+/-SD) in contrast to age-matched control, which ranged from 9.1 to 34.6 microM (19.8+/-6.2 microM, mean+/-SD, n=138). Cancer patients also showed marked variations in the NO levels. Eighteen of 60 cancer patients exhibited greater than 60 microM NO levels. The CRP, TNF-alpha and TF were also significantly elevated. A correlation between CRP (r(2)=0.73) and NO levels was noted in cancer patients with hypercoagulable state. These data suggest that the pathogenesis associated with malignancy/hypercoagulable state is associated with an inflammatory component. In addition, the observed hemodynamic changes in some of the cancer patients may be due to increased NO production.

Biomarkers↗
PubMed2003

Influence of different anticoagulant agents on fibrinopeptide a generation.

The purpose of this study was to determine the in vitro effects of different anticoagulant drugs on fibrinopeptide A (FPA) generation inhibition and to identify whether there is any correlation between FPA generation, Hemochron ACT, global clotting assays, and chromogenic assays. Unfractionated heparin is a conventionally used anticoagulant. New anticoagulant drugs such as low molecular weight heparins (LMWHs), pentasaccharide, and antithrombin drugs are now approved for various indications. Anti-Xa drugs are in various phases of clinical development. The influence of different anticoagulant agents has been studied on fibrinopeptide A generation, Hemochron celite ACT, global clotting assays, and chromogenic anti-Xa and anti-IIa assays. Different LMWHs (Clivarin, Dalteparin, Enoxaparin, and Tinzaparin), anti-Xa agents (Pentasaccharide, DX-9065a and unfractionated heparin), and anti-IIa agents (PEG-Hirudin, Hirudin, Efegatran and Argatroban) were studied. The blood from healthy volunteers (n=4) was drawn for each drug. Imuclone FPA enzyme-linked immunosorbent kit assay, Hemochron celite ACT assay, global clotting assays (PT, APTT, Heptest-HI, thrombin time), and Loyola chromogenic anti-Xa and anti-IIIa assays were studied. Pentasaccharide demonstrated minimal effects on the whole blood clotting time such as ACT and on inhibition of FPA generation (IC50 > 25 microg/mL). DX-9065a exhibited a significant prolongation of ACT and marked inhibition of FPA generation (IC50 = 4.12 microg/mL). Unfractionated heparin showed a marked inhibition of FPA generation (IC50 = 5.16 microg/mL). Pentasaccharide, DX-9065a and UFH showed a marked correlation between ACT and inhibition of FPA generation. LMWHs demonstrated concentration-dependent inhibition of FPA generation. LMWHs studied showed good correlation between FPA generation inhibition and ACT test. Similar correlation was seen between FPA generation inhibition and the APTT, anti Xa (heptest-HI assay) and anti-IIa activity. Anti-IIa drugs demonstrated concentration-dependent inhibition of FPA generation. Their FPA generation inhibition potency is correlated with the ACT assay. A strong correlation between Hemochron ACT and FPA generation inhibition was observed. Based on this significant correlation, the FPA generation inhibition can be predicted by point-of-care ACT assay.

Anticoagulants↗
PubMed2001

Ecarin clotting time is sensitive to heparinoids: comparison of two different techniques.

Ecarin clotting time (ECT) is currently developed for the specific monitoring of antithrombin drugs, such as hirudin, argatroban, and hirulog. Aqueous reagent and dry chemistry technology have become available for ECT monitoring of antithrombin agents. Currently, many heparinoids and heparinomimetic drugs are being developed. These agents activate heparin cofactor II (HCII) and primarily mediate their effects by inhibiting thrombin. Although the test is specific for antithrombin agents, heparin cofactor II-mediated thrombin inhibitors are capable of prolonging the ECT. In order to study the relative effects of some of these agents, ECT was measured in human plasma supplemented with Pl-88 (a sulfated pentomanose; Progen Industries Limited, Sydney, Australia), aprosulate, pentosan polysulfate, dermatan sulfate, unfractionated heparin (UFH), and recombinant hirudin (r-hirudin). All agents were supplemented to the citrated-pooled plasma prepared from 10 healthy volunteers at a graded dosage of 0 to 100 microg/ml. These techniques gave comparable results for all of the agents used (PI-88, r2 = 0.99; r-hirudin, r2 = 0.98; UFH, r2 = 0.98; dermatan sulfate, r2 = 0.95; aprosulate, r2 = 0.95; pentosan polysulfate, r2 = 0.94). The relative anticoagulant effects of various agents used on ECT varied widely, exhibiting their potency in the following order: r-hirudin = pentosan polysulfate > dermatan sulfate > PI-88 > aprosulate > UFH. The sensitivity of ECT was adjusted by varying the concentration of the ecarin reagent. The results suggest that HCII-mediated inhibition of thrombin can be detected by using ECT reagents.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

Anticoagulant and antiprotease effects of a novel heparinlike compound from shrimp (Penaeus brasiliensis) and its neutralization by heparinase I.

Heparin is usually obtained from mammalian organs, such as beef lung, beef mucosa, porcine mucosa, and sheep intestinal mucosa. Because of the increased use of heparin in the production of low-molecular-weight heparin (LMWH), there is a growing shortage of the raw material needed to produce LMWHs. A previous report described the structural features of a novel LMWH from the shrimp (Penaeus brasiliensis). In order to compare anticoagulant and antiprotease effects of this heparin, global anticoagulant tests, such as the prothrombin time, activated partial thromboplastin time, thrombin time, and Heptest, were used. Amidolytic anti-Xa and anti-IIa activities were also measured. The relative susceptibility of this heparin to flavobacterial heparinase was also evaluated. The United States Pharmacopeia (USP) potency of shrimp heparin (SH) was found to be 28 U/mg. SH produced a concentration-dependent prolongation of all of the clotting tests and exhibited marked inhibition of FXa and FIIa. Heparinase treatment resulted in a marked decrease of the anticoagulant effects and neutralized the in vitro anti-IIa actions. However, the anti-Xa activities were only partially neutralized. Protamine sulfate was only partially effective in neutralizing the anticoagulant and antithrombin effects of SH. SH also produced marked prolongation of activated clotting time, which was neutralized by heparinase but not by protamine sulfate. These results suggest that SH is a strong anticoagulant with comparable properties to mammalian heparins and can be used in the development of clinically useful antithrombotic-anticoagulant drugs.

Animals↗
PubMed2001

Synthetic heparin pentasaccharide depolymerization by heparinase I: molecular and biological implications.

A synthetic pentasaccharide (SR90107/ ORG31540) representing the antithrombin III (ATIII) binding sequence in heparin is under clinical development for the prophylaxis and management of venous thromboembolism. This pentasaccharide exhibits potent anti-factor Xa (AXa) effects (>750 IU/mg) and does not exhibit any anti-factor IIa (AIIa) activity. Previous reports have suggested that synthetic heparin pentasaccharides are resistant to the digestive effects of heparinase I. To investigate the effect of heparinase I on the AXa activity of pentasaccharide SR90107/ORG31540, graded concentrations (1.25-100 microg/ml) were incubated with a fixed amount of heparinase I (0.1 U/ml). Heparinase I produced a strong neutralizing effect on this pentasaccharide, as measured by AXa activity. This observation led to further studies where high performance liquid chromatography (HPLC) analysis was employed to determine the potential breakdown products of the pentasaccharide. The experiment with the pentasaccharide included incubation (37 degrees C) at 1 mg/ml and exposure to graded concentrations of heparinase I (0.125-1 U/ml). After 30 min of incubation, the enzymatic activity was stopped by heat treatment and the mixture was analyzed using high performance size exclusion chromatography (HPSEC). Heparinase I concentration-dependent cleavage of the pentasaccharide was evident. The breakdown products exhibited a mass of 1,034 d and 743 d, respectively, suggesting the generation of a trisaccharide and a disaccharide moiety. The extinction of a disaccharide moiety in the UV region was high, indicating the presence of a double bond in this molecule. These data clearly suggest that pentasaccharide SR90107/ORG31540 is digestible by heparinase I into its two components. Furthermore, these data support the hypothesis that heparinase I can be used as a neutralizing agent for pentasaccharide overdose. Additionally, a highly methylated analog of the previously mentioned synthetic pentasaccharide. SanOrg34006, which has also been subjected to similar experiments, has shown complete resistance to the depolymerizing function of heparinase I; therefore, its use may be appropriate in chronic situations as a long-acting form of the pentasaccharide.

Antithrombin III↗
PubMed2001

Anticoagulant and antiprotease profiles of a novel natural heparinomimetic mannopentaose phosphate sulfate (PI-88).

Heparinomimetic mannopentaose phosphate sulfate (PI-88) (Progen Industries Ltd. Brisbane, Australia), currently developed as an anticoagulant and antiproliferative agent, mainly is composed of a pentomannan. However, tetrasaccharide and disaccharide components are also present. The molecular profile and the anticoagulant potency of PI-88 are investigated in this study. Gel permeation chromatography and polyacrylamide gel electrophoresis analyses were carried out to determine the molecular profile and separation of components of PI-88, respectively. Potentiation of antithrombin III (ATIII) and heparin cofactor-II (HC-II) activity were measured using chromogenic substrate assay. In order to determine anticoagulant and antiprotease effects of PI-88, various global anticoagulant tests, such as the prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), Hep-test (Haemachem Inc., St. Louis), ecarin clotting time (ECT), activated clotting time (ACT), and thromboelastography (TEG) were used. Anti-Xa and anti-IIa activities also were measured. The effect of PI-88 on the release of tissue factor pathway inhibitor (TFPI) was performed in nonhuman primates who received PI-88 and in endothelial cell culture systems. The relative susceptibility of PI-88 to heparinase I, protamine sulfate (PS), and platelet factor 4 (PF4) also was evaluated. The high-performance liquid chromatography profiles of PI-88 showed that its average molecular weight is approximately 2300 Da. Separation and gradient electrophoretic patterns of PI-88 showed that it is composed of five different fractions. This agent activates HC-II through inhibiting the thrombin generation but not inhibiting ATIII. Although PI-88 produced a concentration-dependent prolongation of all of the clotting tests, ECT gave the best correlation in the dose-response curve (ECT, r2 = 0.94; TT, r2 = 0.84; APTT, r2 = 0.69). Heparinomimetic mannopentaose phosphate sulfate (PI-88) exhibited marked inhibition of FIIa, but not of FXa. Heparinase I failed to produce significant neutralization of PI-88 in all the assays used, whereas PS and PF4 partially neutralized the effects of this compound. Heparinomimetic mannopentaose phosphate sulfate (PI-88) produced fivefold increase in the TFPI levels at 15 minutes after intravenous (IV) injection to primates. The incubation of PI-88 in endothelial cell culture system also showed a strong effect on TFPI release. These results suggest that PI-88 exhibited strong antithrombotic and anticoagulant activity in addition to its known antiproliferative properties. Because of the molecular characteristics and the dual nature of the pharmacologic action of PI-88, this agent represents an attractive pharmacologic agent for the control of thrombotic and proliferative disorders.

Anticoagulants↗
PubMed2001

Global anticoagulant effects of a novel sulfated pentomanan oligosaccharide mixture.

PI-88 is a potent antiproliferative agent, which is developed for various indications in cancer. This agent is obtained from yeast fermentation and is primarily composed of pentamannose and tetramannose oligosaccharide units. PI-88 is capable of producing anticoagulant effects, which are mediated by heparin cofactor II. The purpose of this study was to determine the anticoagulant properties of PI-88 in native whole blood, freshly drawn from human volunteers, supplemented with PI-88 at various concentrations (0-100 microg/mL). Whole blood activated clotting time (ACT) was measured using Hemochron instruments. PI-88 produced a strong anticoagulant effect at 100 microg/mL (479.0+/-59.5 sec). This anticoagulant effect was comparable to that observed in interventional cardiology and open-heart surgery. At the lower level, PI-88 produced concentration-dependent effects on ACT. Using thromboelastographic techniques (TEG), the effect of PI-88 was measured in terms of various parameters. PI-88 produced potent anticoagulant effects in the TEG studies. At the concentration of 25 microg/mL, it produced a complete anticoagulant effect in whole blood. Whole blood samples supplemented with PI-88 showed a concentration-dependent decrease in the generation of various markers of clotting activation. These results clearly suggest that PI-88 exerts an anticoagulant effect in whole blood. Because of the low-molecular-weight nature and a novel mechanism of action, this new drug may be considered for further development, particularly in cancer patients.

Anticoagulants↗
PubMed2001

Emerging anticoagulant and thrombolytic drugs.

Since its discovery, heparin has been used intensely as an anticoagulant for several medical and surgical indications. However, efforts are in progress to replace heparin because of its serious complications, such as intraoperative and postoperative bleeding, osteoporosis, alopecia, heparin resistance, heparin rebound, heparin-induced thrombocytopenia (HIT) and thrombosis syndrome (HITTS), and other disadvantages. Significant developments in the field of new anticoagulants have resulted in the evaluation and introduction of low molecular weight heparins (LMWHs) and heparinoids, hirudin, ancrod, synthetic peptides and peptidomimetics. However, despite significant progress in the development of these new anticoagulants, a better or an ideal anticoagulant for cardiovascular patients is not yet available and heparin still continues to amaze both basic scientists and the clinicians. To minimise the adverse effects of heparin, newer approaches to optimise its use in combination with the new anticoagulants may provide better clinical outcome. In our experience, the off-label use of argatroban at a dose of 300 microg/kg iv. bolus followed by 10 microg/kg/minute infusion in combination with aggrastat (a glycoprotein [GP] IIb/IIIa inhibitor) at a dose of 10 microg/kg iv. bolus followed by an infusion of 0.15 microg/kg/minute in patients with HIT undergoing percutaneous coronary interventions resulted in elevation of celite activated clotting time (ACT) to 300 seconds followed by a gradual decline and the ACT remained above 200 seconds even after 200 min of drug administration. A bewildering array of newer anticoagulants now exist, such as LMWHs and heparinoids, indirect or direct thrombin inhibitors, oral thrombin inhibitors, such as melagatran (AstraZeneca) and HC-977 (Mitsubishi Pharmaceuticals), Factor IXa inhibitors, indirect or direct Factor Xa inhibitors, Factor VIIa/tissue factor (TF) pathway inhibitor, newer antiplatelet agents, such as GPIIb/IIIa inhibitors, fibrin specific thrombolytic agent, such as tenecteplase and modulation of the endogenous fibrinolytic activity by thrombin activatable fibrinolytic inhibitor (TAFI), Factor XIIIa inhibitors and PAI-1 inhibitors. The quest for newer anticoagulant, antiplatelet and fibrinolytic agents will continue until ideal agents are found.

Journal Article↗
PubMed2000

Human anti-heparin-platelet factor 4 antibodies are capable of activating primate platelets: towards the development of a HIT model in primates.

In the first step to establish an animal model of heparin-induced thrombocytopenia (HIT) that is physiologically relevant to humans, studies were undertaken to determine the similarities or differences between human and non-human primate (Macaca mulatta) platelets in HIT assay systems. The collagen-, ADP-, and TRAP-induced platelet aggregation, and flow cytometric analysis of P-selectin expression and microparticle formation were similar for both species platelets (p>0.1, n=18 each). The classical HIT assays using platelet-rich plasma (PRP) as well as a flow cytometric assay revealed the activation/aggregation and serotonin release assay (SRA) profiles for both primate and human platelets were similar in response to human HIT positive sera. All assays were heparin concentration-dependent; heparin, at 0.1 U/mL, produced maximum and similar platelet activation/aggregation and SRA responses with both primate (76+/-7%, n=18) and human (68+/-11%, n=20; p>0.1) platelets. At concentrations > or =10 U/mL, heparin suppressed the platelet aggregation and SRA responses in both systems. Primate and human platelets displayed similar behavior to low molecular weight heparin and pentasaccahride in HIT assay systems. Immunoglobulins isolated from serum of patients with HIT caused activation/aggregation of human (65+/-18%, n=10 donors) and primate (79+/-12%, n=6 monkeys, p>0.08) platelets. Unlike human platelets, the primate platelets exhibited a more consistent aggregation/release response (15 out of 18 primate platelets reactive). In contrast, human donors showed wide variations in the activation/release response (4 out of 10 reactive). These observations suggest that primate platelets are activatable by anti-H-PF4 antibodies, and support the hypothesis that primates can be used to develop an animal model to study the pathogenesis of HIT.

Animals↗
PubMed2000

Differential effects of unfractionated heparin and low-molecular-weight heparins on tissue thromboplastin inhibition test.

Circulating anticoagulants are endogenously produced substances that interfere with in vitro tests of coagulation like activated partial thromboplastin time (APTT), and cause prolongation of the clotting times. Evaluation of the abnormal APTT involving various factor assays and mixing studies may provide inconclusive and ambiguous results. Tissue thromboplastin inhibition test (TTIT) is one of the screening assays for detection of circulating anticoagulants. However, this test is influenced by the presence of unfractionated heparin (UFH) from concentrations 0.2 U/mL and higher. Since low-molecular-weight heparins (LMWHs) are increasingly used for the prevention of thrombotic disorders and may replace UFH in the future, in this study the authors studied the influence of LMWHs on the performance of TTIT and compared the results with UFH. UFH and LMWHs showed a prolongation of TTIT in the concentration range of 0.25-1.0 U/mL. The marked prolongation of the TTIT with UFH and different LMWHs is in decreasing order of UFH > ardeparin > tinzaparin > dalteparin > enoxaparin. Patients with circulating anticoagulants who are given LMWHs may have false-positive results of TTIT and this influence should be kept in mind during patient management.

Anticoagulants↗
PubMed2000

Bleeding complications with glycoprotein IIb/IIIa inhibitors.

The new class of antiplatelet drugs, the GPIIb/IIIa inhibitors, has proven to be effective in acute coronary syndromes including unstable angina and myocardial infarction as well as adjunct therapy for coronary interventions for preventing morbidity and mortality. As these drugs inhibit the final common pathway of platelet activation, effectively blocking the platelet aggregation response, potential bleeding is a concern with their use. The risk of bleeding has been demonstrated to be higher in patients treated with combination drug therapy (heparin, aspirin, thienopyridines, thrombolytics, oral anticoagulants), when antithrombotic drugs are not given on an individual weight basis and with late removal of vascular access sheaths. The early clinical trials have defined modifications in patient management that have effectively reduced bleeding. Pooled data from the more recent clinical trials, mostly in coronary intervention enrolling over 27,000 patients, show a bleeding rate of 3.6% in the drug group and 2.3% in the placebo group. Although this is acceptable, several unresolved issues remain to be addressed regarding the GPIIb/IIIa inhibitors. Thrombocytopenia occurs infrequently with all GPIIb/IIIa inhibitors but can be severe. The use of these drugs by oral administration presents new challenges with determining optimal dosing, drug-drug interactions and long-term effects. Incorporating point-of-care monitoring may enable better titration of these drugs to avoid bleeding complications. GPIIb/IIIa inhibitors are destined to become a mainstay therapy for cardiovascular treatment and over time these issues should be resolved.

Journal Article↗
PubMed2000

Pharmacokinetics of argatroban in primates: evidence on endogenous uptake.

BACKGROUND: Antithrombin agent, argatroban, is currently undergoing several clinical trials for cardiovascular indications. Because of its solubility, this drug is usually administered via an intravenous bolus followed by infusion. The purpose of this study was to determine the pharmacokinetics of argatroban after intravenous bolus injection in primates. METHODS: Parallel in vitro studies in primate whole blood were carried out to simulate a one-compartment system. Argatroban (range 1.0-7.5 mg/kg) was administered to four groups of primates and blood samples were drawn at various time periods. Argatroban measurements were made in plasma using functional (aPTT, Heptest, TT) and HPLC methods. RESULTS: In vitro, argatroban primarily distributed in the plasma in proportionate amounts. Relative uptake of argatroban to the blood cells (leukocytes and erythrocytes) was minimum. However, in vivo, argatroban followed a complex pharmacokinetics. Within 5 min after the bolus administration, only <20% of argatroban was recovered. The recovered amount was proportionate to the dosage and followed the expected kinetics with a half-life of <20 min. Simultaneous quantitation of M1-metabolite of argatroban revealed only a fraction of recovered argatroban (approximately 25%) converted into M1 in these experimental settings. Results obtained from the functional and absolute methods correlated well. HPLC profile did not reveal the presence of any other metabolite(s). CONCLUSIONS: These observations suggest that argatroban may be endogenously taken up by the vascular or other sites and may exhibit a complex kinetics. In acute settings, the metabolic transformation of argatroban to M1 is relatively low. To further clarify the pharmacokinetics/pharmacodynamics of this drug, additional studies are warranted.

Animals↗
PubMed1999

Simultaneous monitoring of argatroban and its major metabolite using an HPLC method: potential clinical applications.

Argatroban is a peptidomimetic inhibitor of thrombin that is currently undergoing extensive clinical trials as a heparin substitute for thrombotic complications. Argatroban is readily metabolized into a major derivative, M1, that has pharmacological characteristics distinct from its parent compound. The currently available clot-based assays measure the cumulative anticoagulant effect of argatroban and its metabolite(s). Available HPLC methods do not differentiate between argatroban and M1-metabolite. A modified method was developed to simultaneouly quantitate M1-metabolite and argatroban in biological fluids. Initial validation studies for the method included clinical trials of argatroban in patients with heparin-induced thrombocytopenia, (ARG 911 Study) and coronary interventional procedures (ARG 310 Study). Plasma samples were extracted with acetonitrile and reconstituted in a mobile phase. Calibration curves were prepared by running known standards of argatroban and M1-metabolite in normal human plasma. Ultraviolet detection was made at 320 nm. The retention times for argatroban and M1-metabolite peaks were found to be 10.5 +/- 0.3 minutes and 3.9 +/- 0.1 minutes, respectively. The extraction efficiency was > 95% (r2 = 0.99). In heparin-induced thrombocytopenia patients with major bleeding complications (n = 30), the relative increase in M1-metabolite compared to argatroban varied widely (two- to eight-fold). The mean concentration of argatroban during the steady infusion period was found to be 0.7 +/- 0.35 microgram/mL, and for M1-metabolite, it was 5.5 +/- 2.8 micrograms/mL. Proportionate results were not seen when higher dosages of argatroban were administered (coronary angioplasty studies). Argatroban and M1-metabolite levels also compared well with the results in global clotting assays. Owing to the simultaneous quantitation of argatroban and M1-metabolite, this method provides a rapid assessment of the pharmacokinetics and pharmacodynamics of argatroban. The differential quantitation may be useful in the assessment of relative metabolic turnover of argatroban that can be related to the hepatic and renal functions in a given patient.

Anticoagulants↗
PubMed1999

Coagulation laboratory testing in patients treated with argatroban.

During clinical trials with the thrombin inhibitor argatroban, appropriate methods for drug monitoring were identified. Treated patients presented interesting challenges for coagulation laboratory parameter testing in the presence of argatroban. These issues are reported here. Regarding the monitoring of argatroban, the aPTT and ACT were effectively used clinically for low (0-2.5 microg/mL) or high (1-15 microg/mL) doses of argatroban. However, system (reagent and instrument) differences were noted in the time-to-clot values. A clot-based assay using Ecarin as the activator (ECT, Ecarin clotting time) appeared to be useful for monitoring both low and high drug levels with less interference from other drugs or coagulation defects. Also identified were the chromogenic antithrombin assay that could directly quantify argatroban and an HPLC based assay that could specifically quantify argatroban and its metabolites. With regard to assay interference by argatroban, several important effects were observed. The presence of argatroban synergistically interfered with the INR for those patients treated with oral anticoagulants. However, a chromogenic based method was able to determine factor X levels as a monitor of the oral anticoagulation without effect from argatroban. A similar synergistic response on the aPTT with heparin and argatroban was observed. Patients receiving argatroban evaluated for potential coagulation abnormalities could not be tested with the routine functional (clot based) assays for fibrinogen, factor levels or protein C. Argatroban acted as an inhibitor in these assays, causing a dose-dependent false decrease of fibrinogen and factor levels, and a false increase of protein C. Using a chromogenic assay for protein C, values equal to those obtained by an immunologic assay were achieved. These issues will most likely hold true for all thrombin inhibitors.

Antithrombins↗
PubMed1999

Clinical laboratory monitoring of a synthetic antithrombin agent, argatroban, using high performance liquid chromatography and functional methods.

BACKGROUND: Argatroban is a peptidomimetic inhibitor of thrombin which is in clinical trials for thrombotic complications. Clot-based assays measure the cumulative anticoagulant effect of argatroban and its metabolites(s). To monitor the absolute concentrations of argatroban, a specific HPLC method was developed. METHODS: Validation studies included normal volunteers administered with escalating doses of argatroban (ARG 102 Study), patients undergoing coronary interventional procedures (ARG 310), and patients receiving argatroban in conjuction with streptokinase for acute myocardial infarction (ARG 230). Plasma samples were extracted with acetonitrile and reconstituted in a mobile phase. UV detection was made at 333 nm. Calibratrion curves were prepared with known standards of argatroban in normal human plasma. RESULTS: The retention time for argaeroban was 6.0+/-0.5 min and the extraction efficiency was >98% (r2=0.99). In the ARG102 Study, argatroban levels were: 0.84+/-0.23 (day 1), 1.55+/-0.34 (day 2), 2.92+/-0.15 (day 3), and 3.04+/-0.49 (day 4). In the ARG310 trial, the mean argatroban levels were: 0.23+0.09 microg/ml (preinfusion), 5.77+/-0.92 microg/ml (postinfusion/intraprocedure), and 2.23+/-0.29 microg/ml (postprocedure). In the ARG 230 Study, the mean argatroban levels at 2-8 hrs were between 1.5-2.0 microg/ml. Upon completion of the infusion, a time-dependent clearance of argatroban was noted. CONCLUSIONS: Since heparinization, hemodilution and hypofibrinogenemia due to thrombolysis influence the clotting tests, absolute quantitation of argatroban by HPLC in these patients provides a more reliable means of monitoring this anticoagulant and helps in the dosage-optimization of this agent. The current HPLC method is of value in the monitoring of patients who are simultaneously administered with thrombolytic drugs.

Anticoagulants↗