Concentrations Of Eptifibatide Research Articles

Spectrofluorimetric determination of eptifibatide in human plasma and dosage form.

A spectrofluorimetric method for the determination of eptifibatide is presented based on its native fluorescence. The type of solvent and the wavelength of maximum excitation and emission were carefully selected to optimize the experimental conditions. Under the specified experimental conditions, the linearities obtained between the emission intensity and the corresponding concentrations of eptifibatide were in the range 0.1-2.5μg/ml for the calibration curve constructed for direct determination of eptifibatide in dosage form and 0.05-2.2μg/ml for the calibration curve constructed in spiked human plasma with a good correlation coefficient (r>0.99). The lower limit of quantification for the calibration curve constructed in human plasma was 0.05μg/ml. Recovery results for eptifibatide in spiked plasma samples and in dosage form, represented as mean±% RSD, were 95.17±1.94 and 100.29±1.33 respectively. The suggested procedures were validated according to the International Conference on Harmonization (ICH) guidelines for the direct determination of eptifibatide in its pure form and dosage form and United States Food and Drug Administration (US FDA) Guidance for Industry, Bioanalytical Method Validation for the assay of eptifibatide in human plasma.

The Kinetics of Integrilin Limited by Obesity: A multicenter randomized pharmacokinetic and pharmacodynamic clinical trial

KILO tested 2 novel weight-based eptifibatide dosing strategies compared with standard dosing in obese patients undergoing elective percutaneous coronary intervention (PCI). Eptifibatide dosing is weight adjusted for patients up to 121 kg. Patients above this weight receive the same maximal dose, although it is unknown if this provides adequate eptifibatide concentration or platelet inhibition. Sixty-seven patients weighing ≥125 kg undergoing elective PCI were randomized to 1 of 3 eptifibatide dosing regimens: standard dosing using a weight of 121 kg, actual body weight (ABW)-based dosing with no upper limit, or ideal body weight (IBW)-based dosing. Boluses of 180 μg/kg were given 10 minutes apart, followed by a 2.0 μg/kg per minute infusion. Plasma eptifibatide concentrations were drawn at 12 to 18 hours after initiating the infusion. Platelet aggregation was assessed at baseline and 10 minutes after the second bolus. Sixty-seven patients were randomized to standard (n = 22), ABW (n = 23), or IBW (n = 22) dosing. The median (25th, 75th) steady-state plasma eptifibatide concentrations were 1,740 ng/mL (1,350, 2,350), 1,780 ng/mL (1,510, 2,350), and 1,055 ng/mL (738, 1,405), respectively (P < .001). Ten-minute median (25th, 75th) platelet aggregation units were 7 (0, 21), 2 (0, 8), and 14 (8, 20), respectively (P = .001). Actual body weight eptifibatide dosing leads to higher plasma concentrations and greater platelet inhibition than standard or IBW dosing in obese patients undergoing PCI. Current recommendations for eptifibatide dosing may be inadequate in patients >121 kg. Further study is warranted to define the optimal dosing of eptifibatide and other medications in obese patients.

Making the right choice: Optimizing rt-PA and eptifibatide lysis, an in vitro study

Introduction Recombinant tissue plasminogen activator (rt-PA) is the only FDA approved lytic therapy for acute ischemic stroke. However, there can be complications such as intra-cerebral hemorrhage. This has led to interest in adjuncts such as GP IIb-IIIa inhibitors. However, there is little data on combined therapies. Here, we measure clot lysis for rt-PA and eptifibatide in an in vitro human clot model, and determine the drug concentrations maximizing lysis. A pharmacokinetic model is used to compare drug concentrations expected in clinical trials with those used here. The hypothesis is that there is a range of rt-PA and eptifibatide concentrations that maximize in vitro clot lysis. Materials and Methods Whole blood clots were made from blood obtained from 28 volunteers, after appropriate institutional approval. Sample clots were exposed to rt-PA and eptifibatide in human fresh-frozen plasma; rt-PA concentrations were 0, 0.5, 1, and 3.15 μg/ml, and eptifibatide concentrations were 0, 0.63, 1.05, 1.26 and 2.31 μg/ml. All exposures were for 30 minutes at 37 C. Clot width was measured using a microscopic imaging technique and mean fractional clot loss (FCL) at 30 minutes was used to determine lytic efficacy. On average, 28 clots (range: 6-148) from 6 subjects (3-24) were used in each group. Results and Conclusions FCL for control clots was 14% (95% Confidence Interval: 13-15%). FCL was 58% (55-61%) for clots exposed to both drugs at all concentrations, except those at an rt-PA concentration of 3.15 μg/ml, and eptifibatide concentrations of 1.26 μg/ml (Epf) or 2.31 μg/ml. Here, FCL was 43% (36-51) and 35% (32-38) respectively. FCL is maximized at moderate rt-PA and eptifibatide concentration; these values may approximate the average concentrations used in some rt-PA and eptifibatide treatments.

The PFA-100® cannot detect blood group-dependent inhibition of platelet function by eptifibatide or abciximab at therapeutic plasma concentrations

Previous investigations revealed that AB0 blood groups are associated with divergent concentrations of several coagulation factors. Concentrations of von Willebrand factor (vWF) and factor VIII are lower in individuals with blood group 0 compared to subjects with blood group A, B or AB, which might in turn result in a reduced inhibition of platelet aggregation in individuals with blood group 0. The aim of the present in vitro investigation was to elucidate the impact of AB0 blood group-dependent vWF concentrations on eptifibatide and abciximab mediated inhibition of GPIIb/IIIa function. Platelet function was measured with the platelet function analyzer PFA-100® at baseline and at increasing concentrations of eptifibatide and abciximab. It was stratified for blood group 0 vs A. If measured with the collagen/ADP cartridge, blood group 0 was associated with a prolonged mean baseline closure time in comparison with blood group A (94.3 ± 14.6 s vs. 74.6 ± 9.9 s, p = 0.007) which was paralleled by reduced concentrations of vWF and factor VIII. In contrast, no statistically significant differences in closure times (167.4 ± 83.9 s vs. 140.1 ± 99.0 s, p = 0.562) could be found in the presence of eptifibatide (0.1 µg/ml). Higher concentrations of abciximab (1 µg/ml) than those of eptifibatide were needed to increase the closure times in both cartridges of the PFA-100, but at this concentration of abciximab differences in closure times could not be detected most probably due to higher variability at these drug concentrations. The PFA-100® is not suitable for monitoring abciximab or eptifibatide within the therapeutic concentration range because the highest concentrations where the PFA-100® had measurable closure times of below 300 s is much too low to lead to the necessary platelet inhibition and, consequently, does not resemble the in vivo situation.

Regulation of CD40L (CD154) and CD62P (p-selectin) Surface Expression upon GPIIb-IIIa Blockade of Platelets from Stable Coronary Artery Disease Patients

Introduction The aim of this study was to further characterize the effect of the antiplatelet agents, aspirin and eptifibatide, on the surface expression of CD40L and CD62P on platelets from patients with stable coronary artery disease. Materials and methods Platelet function was evaluated using standard light transmission aggregometry. Measurements of CD62P and CD40L were carried out by flow cytometry and ELISA assays. Results All patients had the expected level of platelet aggregation inhibition in response to 20 μM ADP in the presence of increasing eptifibatide concentrations. Platelet activation by adenosine diphosphate (ADP) or thrombin agonist peptide (TRAP) increased CD62P and CD40L surface density in the presence of aspirin by 1.9 – 2.8 -fold. Aspirin treatment did not prevent either CD62P or CD40L expression. Eptifibatide pretreatment at pharmacologically relevant concentrations blocked agonist-induced increases in CD62P platelet surface density. A marked percentage of platelets still expressed low levels of surface CD62P suggesting slight platelet activation even with potent platelet inhibition. Eptifibatide also blocked agonist-induced increases in CD40L surface expression and decreased the percent of platelets positive for surface CD40L. Decreased expression of CD40L was due to an inhibition of CD40L translocation and not caused by enhanced shedding from the surface, as soluble CD40L (sCD40L). Eptifibatide concentrations that effectively blocked platelet aggregation correlated with total inhibition of increased CD62P and CD40L surface density. Conclusion Blockade of the GPIIb-IIIa receptor on platelets from coronary artery disease patients may have significant bearing on reducing proinflammatory and procoagulant events mediated by CD62P and sCD40L.

Determination of eptifibatide concentration in human plasma utilizing the liquid chromatography–tandem mass spectrometry method

A sensitive and selective liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed to determine the concentration of eptifibatide in human plasma. Following protein precipitation, the analyte was separated on a reversed-phase C 18 column. Acetonitrile:5 mM ammonium acetate:acetic acid (30:70:0.1, v/v/v) was used at a flow-rate of 0.5 mL/min with the isocratic mobile phase. An API 4000 tandem mass spectrometer equipped with a Turbo IonSpray ionization source was used as the detector and was operated in the positive ion mode. “Truncated” multiple reaction monitoring using the transition of m/ z 832.6 → m/ z 832.6 and m/ z 931.3 → m/ z 931.3 was performed to quantify eptifibatide and the internal standard (EPM-05), respectively. The method had a lower limit of quantification of 4.61 ng/mL for eptifibatide. The calibration curve was demonstrated to be linear over the concentration range of 4.61 − 2770 ng/mL. The intra- and inter-day precisions were less than 10.5% for each QC level, and the inter-day relative errors were 2.0%, 5.6%, and 2.8% for 9.22, 184, and 2490 ng/mL, respectively. The validated method was successfully applied to the quantification of eptifibatide concentration in human plasma after intravenous (i.v.) administration of a 270-μg/kg bolus of eptifibatide and i.v. administration of eptifibatide at a constant rate of infusion of 2 μg/(kg min) for 18 h in order to evaluate the pharmacokinetics.

Preoperative Platelet Inhibition With Eptifibatide During Coronary Artery Bypass Grafting With Cardiopulmonary Bypass

Platelet glycoprotein IIb-IIIa antagonists reduce cardiac events in acute coronary syndromes (ACSs), but their use is limited during coronary artery bypass grafting (CABG) because of bleeding concerns. Patients with ACS, however, are at increased risk for cardiac events after CABG. The use of short-acting glycoprotein IIbIIIa inhibitor eptifibatide in patients with ACS undergoing CABG was investigated. Fifteen patients with ACS and undergoing CABG with cardiopulmonary bypass were enrolled. One withdrew before surgery. Patients received heparin and eptifibatide preoperatively. Eptifibatide concentration and receptor occupancy (RO) at termination of infusion were similar in the two groups. Immediately before surgery, eptifibatide levels in the 2-hour group were twice that in the 4-hour group, and platelet RO was higher. Cessation of eptifibatide 4 hours before surgery results in less bleeding and transfusions than 2 hours before surgery. The optimal balance between bleeding and platelet inhibition is approximately 60% platelet RO. Further investigation of upstream therapy should target this threshold.

In vitro effect of the potent poly(ADP-ribose) polymerase (PARP) inhibitor INO-1001 alone and in combination with aspirin, eptifibatide, tirofiban, enoxaparin or alteplase on haemostatic parameters

It has been shown that PARP inhibition is protective in several models of ischemia–reperfusion injury including cardiac, cerebral and renal ones. Due to their ability to reduce myocardial necrosis and to improve myocardial function PARP inhibitors emerged as candidates for treating various cardiovascular diseases including acute myocardial ischemia. Since the pathophysiology of acute ischemic cardiac diseases involves haemostatic impairment and the therapeutic regimen includes antithrombotic drugs, we investigated the effect of the potent poly(ADP-ribose) polymerase (PARP) inhibitor INO-1001 alone and in combination with platelet aggregation inhibitors (aspirin, eptifibatide and tirofiban), unfractionated heparin, low molecular weight heparin (enoxaparin) or the recombinant fibrinolytic drug (alteplase), on various haemostatic parameters in vitro. ADP- and epinephrine-induced platelet aggregation was evaluated by optical aggregometry in the presence or absence of different concentrations of INO-1001, in combination with aspirin, tirofiban, eptifibatide or saline on ten healthy volunteers' platelet rich plasma (PRP). Activated partial thromboplastin time, Anti-Xa activity and euglobulin lysis time were determined in the presence or absence of different concentrations of INO-1001, in combination with sodium heparin, enoxaparin or alteplase, respectively. INO-1001, on its own does not affect the measured platelet, and haemostatic functions, i.e. does not reduce the respective anti-platelet, anti-coagulant and thrombolytic activity of therapeutically relevant concentrations of aspirin, tirofiban, eptifibatide, enoxaparin and alteplase in vitro. INO-1001 enhanced the effects of heparins above therapeutic ranges; the magnitude of this effect was negligible. Consequently, the PARP inhibitor INO-1001 can be safely applied together with the drugs tested.

Detection and Mechanisms of GPIIb-IIIa Antagonist Induced Thrombocytopenia: Role for Antibody Induced Platelet Activation.

After the administration of GPIIb-IIIa antagonists, 1 – 3% of patients become thrombocytopenic, and 0.5 – 1% of patients develop profound thrombocytopenia. This GPIIb-IIIa antagonist-induced thrombocytopenia may be antibody mediated. In this study we demonstrated that GPIIb-specific monoclonal antibody 5B12 augmented platelet activation, as determined by platelet surface P-selectin and leukocyte-platelet aggregation) in the presence of therapeutic concentrations of abciximab, but not epitifibatide or tirofiban. Furthermore, the GPIIIa-specific monoclonal antibody Y2/51 augmented platelet activation in the presence of therapeutic concentrations of eptifibatide or tirofiban, but not abciximab. This activation was abolished by an FcγRII receptor (CD32)-specific antibody and was absent when Fab fragments 5B12 or Y2/51 were used. These results suggest that (i) GPIIb-IIIa antagonists cause conformational changes in GPIIb-IIIa; resulting in (ii) antibody binding to GPIIb-IIIa; and, consequently (iii) platelet activation via the FcγRII receptor. To determine whether this mechanism is operative in vivo, plasma from patients who developed abciximab-induced thrombocytopenia (n=2), eptifibatide-induced thrombocytopenia (n=5) and normal donors (n=7) was incubated with ABO Rh matched donor whole blood with and without therapeutic concentrations of GPIIb-IIIa antagonists. Platelet activation was assessed by flow cytometric measurement of platelet surface P-selectin. Abciximab, but not eptifibatide or tirofiban, increased platelet surface P-selectin in patients who developed abciximab-induced thrombocytopenia. Eptifibatide, but not abciximab or tirofiban, increased platelet surface P-selectin in patients who developed eptifibatide-induced thrombocytopenia. Platelet surface P-selectin in normal donors was not changed by abciximab, tirofiban or eptifibatide. These data (i) provide novel insight into the mechanisms of GPIIb-IIIa antagonist induced thrombocytopenia; and (ii) suggest a possible assay for the clinical diagnosis and prediction of this phenomenon.Platelet surface P-selectin after addition of a GPIIb-IIIa antagonist (% baseline fluorescence). *p<0.05AbciximabEptifibatideTirofibanNormal donors10310599Eptifibatide-induced thrombocytopenia103170 *104Abciximab-induced thrombocytopenia1571 *108105

The Use of the Point of Care Helena ICHOR/Plateletworks® and the Accumetrics Ultegra® RPFA for Assessment of Platelet Function with GPIIb-IIIa Antagonists

To evaluate a newly modified rapid platelet function analysis system (ICHOR/ Plateletworks) and to compare the results obtained with those of traditional light transmission aggregometry (LTA), and the Ultegra/RPFA system. Anti-platelet therapy is standard of care for patients as an adjunct to percutaneous coronary intervention (PCI) or for medical management of non-ST elevation acute coronary syndromes (NSTE ACS). Recent clinical trial results suggest that the three currently approved platelet GPIIb-IIIa receptor antagonists, eptifibatide, tirofiban and abciximab, may vary in extent of inhibition of platelet aggregation (IPA) at the approved doses. Thus, pharmacodynamic evaluations of these agents to determine the extent of platelet function inhibition, especially during the periprocedural time of a cardiac intervention, are necessary. A rapid measurement method as a surrogate for LTA, the current gold standard, would be ideal in order to have the option for dose monitoring or adjustment prior to or during an intervention. The Helena ICHOR/ Plateletworks may be useful for point of care testing. Blood samples collected in D-Phe-Pro-Arg-chloromethyl ketone dihydrochloride (PPACK) anticoagulant were treated with increasing concentrations of eptifibatide, tirofiban or abciximab. LTA was carried out in conjunction with the ICHOR/Plateletworks, using a modified method, and Accumetrics Ultegra with RPFA cartridges. This study demonstrated that platelet inhibition measured by the ICHOR/Plateletworks mirrored the level of IPA obtained with LTA. In contrast, the Ultegra system had less correlation when compared to LTA at inhibition levels < 90%. Based on these data, the ICHOR/ Plateletworks utilized under modified guidelines may serve as a surrogate for LTA when rapid measurements are necessary.A rapid platelet function measurement method as a surrogate for light transmission aggregometry (LTA), the current gold standard, is ideal in order to have the option for GPIIb-IIIa antagonist dose monitoring or adjustment prior to or during a coronary intervention. A newly modified rapid platelet function analysis system (ICHOR/Plateletworks was evaluated and compared to the results obtained with traditional light transmission aggregometry (LTA), and the Ultegra/RPFA system. Blood samples collected in D-Phe-Pro-Arg-chloromethyl ketone dihydrochloride (PPACK) anticoagulant were treated with increasing concentrations of eptifibatide, tirofiban or abciximab. LTA was carried out in conjunction with the ICHOR/Plateletworks, using a modified method, and Accumetrics Ultegra with RPFA cartridges. Based on these data, the ICHOR/Plateletworks utilized under modified guidelines may serve as a surrogate for LTA when rapid measurements are necessary.

A Novel Method to Assess Platelet Inhibition by Eptifibatide with Thrombelastograph??

We examined a novel method to detect platelet inhibition with thrombelastography (TEG). We hypothesized that this method would be suitable for monitoring the antiplatelet effects of eptifibatide (Integrilin). Whole blood from healthy volunteers was anticoagulated with 3.2% citrate or unfractionated heparin (7 IU/mL). For the platelet aggregation test, both citrate and heparinized samples were spiked with increasing concentrations of eptifibatide (0, 0.2, 0.4, 0.8, 1.6, and 4 microg/mL). Conventional kaolin TEG was performed with citrated samples, and batroxobin-modified TEG was performed with heparinized samples, which were spiked with eptifibatide at concentrations of 0, 0.4, 0.8, 1.6, 4, 8, and 24 microg/mL. Adenosine 5'-diphosphate-induced platelet aggregation was reduced to 6.4% +/- 2.9% (citrate) and 10.3% +/- 4.8% (heparin) with eptifibatide at the concentration of 4 mug/mL. The kaolin TEG showed a decrease in maximum amplitude (MA) only at the eptifibatide concentration of 24 mug/mL and no change in alpha angle, whereas with the batroxobin-based TEG, the difference in MA and alpha angle was observed at concentrations >/=0.8 microg/mL. Additionally, the time to achieve maximum MA was much shorter for batroxobin TEG than for kaolin TEG. We conclude that the batroxobin-modified TEG is a sensitive method that detects platelet inhibition induced by eptifibatide.

Augmentation of inhibitory effects of glycoprotein IIb-IIIa antagonists in patients with diabetes

Background: Patients with diabetes mellitus and acute coronary syndromes (ACS) derive enhanced benefit from treatment with glycoprotein (GP) IIb-IIIa inhibitors. To determine mechanisms potentially responsible we characterized the binding of fibrinogen to platelets from patients with and without diabetes in the presence and absence of GP IIb-IIIa antagonists. Methods: GP IIb-IIIa antagonists (tirofiban, eptifibatide, and abciximab) were added in vitro to blood from patients with and without diabetes. Binding of fibrinogen to activated GP IIb-IIIa was assessed with the use of flow cytometry. The kinetics of binding of I 125-abciximab and I 125-fibrinogen to washed platelets from subjects with and without diabetes mellitus were determined. Glycation of platelet membrane proteins was measured with the fructosamine assay. Results: In the presence of GP IIb-IIIa antagonists, activation-induced binding of fibrinogen to platelets was reduced to a greater extent ( p<0.02) in blood from patients with diabetes. The greater inhibition in blood from patients with diabetes was seen with pharmacologic concentrations of tirofiban (50 ng/ml, by 27%), eptifibatide (1.5 μg/ml, by 24%), and abciximab (2 mg/ml, by 12%). Whereas the binding of I 125-abciximab was similar to platelets from patients with diabetes and those without, the rate of binding of I 125-fibrinogen was decreased with platelets from patients with diabetes. Binding after 5 min was reduced by 46% in those with diabetes ( p<0.05). Platelet membrane proteins from patients with diabetes were glycated to a greater extent compared with those without diabetes. Conclusion: GP IIb-IIIa antagonists inhibit platelet activation to a greater extent in blood from patients with diabetes. The decreased rate of binding of fibrinogen early after activation of platelets appears to be a consequence of glycation and may promote inhibition by GP IIb-IIIa antagonists.

Pharmacokinetic and pharmacodynamic properties of eptifibatide in subjects with normal or impaired renal function

Backgroud: Previous studies of the glycoprotein IIb-IIIa inhibitor eptifibatide have included patients with moderate renal impairment (serum creatinine concentrations, 2.0–4.0 mg/dL). In these patients, adjustment of the standard infusion dose (2.0 μg/kg·min) to 1.0 μg/kg·min was recommended on empiric grounds because ∼50% of eptifibatide is cleared renally. Objective: The present study was designed to assess teh pharmacokinetic and pharmacodynamic properties of eptifibatide in subjects with various levels of creatinine clearance (CrCl), a parameter that is a more accurate indicator of renal function than serum creatinine concentration to determine the appropriate dose adjustment in patients with reduced renal function. A secondary objective was to determine the tolerability of eptifibatide when administered to patients with decreased renal function. Methods: This open-label study was concluded at 3 US sites experienced in conducting similar studies. Subjects with differing renal function (normal [group 1, CrCl > 80 mL/min], mild renal impairment [group 2, CrCl 51–80 mL/min], moderate renal impairment [group 3, CrCl 30–50 mL/min], or severe renal impairment [group 4, CrCl <30 mL/min]) received a 24-hour eptifibatide infusion of 2.0 μg/kg·min (groups 1, 2, and 3) or 1.0 μg/kg·min (group 4). The primary end point was the eptifibatide steady-state plasma concentration; the secondary end points included inhibition of platelet aggregation and eptifibatide clearance, terminal plasma half-life, and area under the plasma concentration-time curve. In addition to analyses performed for each group, pharmacokinetic models were estimated and eptifibatide clearance was related to CrCl as a continuous variable by linear regression. All adverse events were recorded, with particular attention to bleeding. Results: Thirty-one subjects (21 men, 10 women; mean age, 58.5 years [range, 44–73 years]; mean body weight, 81.6 kg [range, 51.5–105.1 kg]; mean height, 162.9 cm [range, 150–183 cm]) were included in the study. A strong correlation was found between eptifibatide clearance and CrCl. A tree-based analytic model indicated that the optimal discrete break point for the purpose of dose adjustment was a CrCl of 55.85 mL/min, which was rounded to 50 mL/min for practical clinical reasons. In patients with moderate or severe renal impairment (CrCl ≤ 50 mL/min), clearance rates and steady-state concentrations of eptifibatide were ∼50% lower and almost 2-fold higher, respectively, than in patients with normal renal function or mild renal impairment (CrCl > 50 mL/min). Inhibition of platelet aggregation exceeded the clinically significant threshold of 80% in all groups. Five subjects had a mild bleeding event and 4 subjects experienced mild to moderate nonbleeding events, 2 of which were considered drug-related by the investigator. None of the events required intervention. Conclusions: In this study, moderate to severe renal impairment was associated with an ∼50% reduction in total eptifibatide clearance and a corresponding doubling of plasma eptifibatide concentration. Based on these findings, in patients with moderately or severely impaired renal function (calculated CrCl ≤50 mL/min) who are scheduled for percutaneous coronary intervention or who have non-ST-segment elevation acute coronary syndromes, it is appropriate to reduce the infusion dose of eptifibatide by 50% (from 2 to 1 μg/kg·min). Because the bolus dose(s) is (are) used to establish the initial targeted plasma eptifibatide concentrations, which are independent of clearance, and given that the volume of distribution did not correlate with renal function, no adjustment of the bolus dose(s) is required.

Antagonists of platelet fibrinogen receptor are less effective in carriers of Pl A2 polymorphism of β 3 integrin

The polymorphism Leu 33→Pro (platelet-specific antigen; Pl A1/A2) of platelet GPIIIa is a potential risk factor for arterial thrombosis. However, its influence on platelet function remains controversial and little is known about its impact on platelet sensitivity to GPIIb-IIIa antagonists. Our objective was to compare the effectiveness of various GPIIb-IIIa antagonists in Pl A2(+) and Pl A2(−) carriers. Platelet aggregation was monitored in healthy donors including Pl A2(−) ( N=31) and Pl A2(+) subjects ( N=27; 23 Pl A1/A2, 4 Pl A2/ A2) using the impedance and turbidimetric aggregation techniques. We evaluated the inhibition of ADP- and collagen-induced aggregation by disintegrins, kistrin and echistatin, and the low-molecular-weight blockers, GR144053F ((4-[4-[4-(aminoiminomethyl]-1-piperazinyl]-1-piperidineacetic acid, hydrochloride trihydrate) and eptifibatide ( N 6-(aminoiminomethyl)- N 2-(3-mercapto-1-oxopropyl- l-lysylglycyl- l-α-aspartyl- l-tryptophyl- l-propyl- l-cysteinamide, cyclic (1→6)-disulfide). Kistrin (10–30 nmol/l) inhibited ADP- and collagen-induced aggregation stronger in Pl A2(−) donors than in Pl A2(+) donors; there was a significant difference between 50% inhibitory concentrations (IC 50). The same tendency occurred with moderate concentrations of eptifibatide (40–100 nmol/l) and also at low concentrations of GR144053F (5–10 nmol/l) and high concentrations of echistatin (80–150 nmol/l), although in the case of the two latter inhibitors, the estimated IC 50 values were not significantly different. In conclusion, GPIIb-IIIa blockers representing various classes are less effective inhibitors of platelet aggregation in Pl A2(+) carriers; however, the effect of the genotype is both agonist- and antagonist-dependent.

Comparative efficacy of fibrinogen and platelet supplementation on the in vitro reversibility of competitive glycoprotein IIb/IIIa receptor-directed platelet inhibition

Background Platelet surface glycoprotein IIb/IIIa (αIIb/β 3) receptor inhibition, with prevention of fibrinogen binding and platelet aggregation, concomitantly attenuates arterial thrombotic capacity and impairs protective hemostasis, 2 divergent platelet-dependent processes. Purpose Because the currently available, Food and Drug Administration-approved small molecule glycoprotein IIb/IIIa receptor antagonists are considered “competitive” inhibitors and there is limited information on the reversibility of platelet inhibition with fibrinogen or platelet supplementation, the following series of in vitro experiments were performed. Methods and Results Washed platelets from 24 healthy volunteers were suspended in tyrodes buffer and incubated with achievable (in vivo) concentrations of either tirofiban or eptifibatide before activation with thrombin receptor agonist peptide (15 μmol/L). Platelet aggregation was inhibited by 40% to 50%, but reversal was achieved with fibrinogen supplementation in a concentration-dependent manner. In a separate series of in vitro experiments, platelet inhibition exceeding 90% was established with tirofiban (average concentration 9.28 μg/L) and eptifibatide (average concentration 95.4 μg/L). Recovery of platelet aggregation to at least 50% was achieved after the addition of fibrinogen (0.76-0.80 g/L), platelets (2.4 × 10 11/L), or their combination. There was an inverse relationship between plasma baseline fibrinogen and the amount of supplemental fibrinogen needed to restore platelet aggregability (r = −0.60; P <.01). Conclusion The reversibility of glycoprotein IIb/IIIa-directed platelet inhibition is influenced by cell surface receptor availability and intrinsic pharmacodynamic mechanism of action. Fibrinogen supplementation with fresh frozen plasma or cryoprecipitate either alone or in combination with platelet transfusion represents an important and readily available treatment consideration for restoring hemostatic potential and managing major hemorrhagic complications associated with the administration of small-molecule, competitive glycoprotein IIb/IIIa receptor antagonists. (Am Heart J 2002;143:725-32.)

A structural and dynamic investigation of the facilitating effect of glycoprotein IIb/IIIa inhibitors in dissolving platelet-rich clots.

Glycoprotein IIb/IIIa (GP IIb/IIIa) inhibitors were shown recently to facilitate the rate and the extent of pharmacological thrombolysis. However, their synergistic potential with rtPA in dissolving thrombotic vaso-occlusions is not fully understood. We have therefore developed a dynamic and structural approach for analysis of fibrinolysis to assess the inhibiting effect of platelets and the facilitating effect of GPIIb/IIIa inhibitors in dissolving platelet-rich clots (PRCs). Fluorescent rtPA was used to study the architecture of PRCs, to follow the progression of the rtPA binding front, and to measure the lysis-front velocity using confocal microscopy. Fibrinolysis resistance of PRCs was related to a reduction of both rtPA binding and lysis-front velocities of platelet-rich areas compared with platelet-poor areas (2.4 +/- 0.2 versus 3.5 +/- 0.4 microm/min for rtPA binding velocity, P=0.04, and 1.2 +/- 0.6 versus 2.8 +/- 0.2 microm/min for lysis-front velocity, P=0.008, in platelet-rich and platelet-poor areas, respectively). Fibrinolysis appeared heterogeneous, leaving platelet-rich areas un-lysed. Adding pharmacological concentrations of abciximab (0.068 micromol/L) or eptifibatide (1 micromol/L) before clotting decreased the average surface of platelet-rich areas by 64% (P=0.0005) and 72% (P=0.0007), respectively. The resulting equalization of rtPA binding rate and rtPA binding-front velocity between platelet-rich and platelet-poor areas led to a 3-fold increase of the lysis-front velocity in platelet-rich areas of either abciximab-PRC (P=0.006) or eptifibatide-PRC (P=0.03). The overall lysis rate of treated-PRC was increased by 74% compared with control-PRC (P<0.01). These results demonstrate that fibrinolysis resistance of PRCs is related primarily to the heterogeneity in the clot structure between platelet-rich and platelet-poor areas. GP IIb/IIIa inhibitors facilitate the rate and the extent of fibrinolysis by improving rtPA binding velocity and, subsequently, the lysis rate in platelet-rich areas. These findings provide new insights on the synergistic potential of GP IIb/IIIa inhibitors and fibrinolytic agents.

Eptifibatide and 7E3, but Not Tirofiban, Inhibit α v β 3 Integrin–Mediated Binding of Smooth Muscle Cells to Thrombospondin and Prothrombin

To the Editor: The recent article in Circulation by Lele et al1 reports αvβ3 inhibitory activity of eptifibatide. Surprisingly, the authors contend that this is a novel observation. Lele et al1 demonstrate inhibition of αvβ3-mediated adhesion of human aortic smooth muscle cells (HASMCs) to thrombospondin (TSP) or prothrombin, human umbilical vein endothelial cell attachment to TSP or vitronectin, as well as the inhibition of TSP-induced proliferation of HASMCs mediated by αvβ3, with IC50 values of approximately 30 μmol/L in each assay. All of these data are consistent with the original publication on the αIIbβ3 antagonist, eptifibatide, by Scarborough et al.2 The authors reported that this agent is a highly selective integrin antagonist. They also showed that at higher concentrations, eptifibatide can …

Comparative efficacy of fibrinogen and platelet supplementation on the in vitro reversibility of competitive glycoprotein IIb/IIIa (αIIb/β3) receptor-directed platelet inhibition

Background Platelet surface glycoprotein (GP) IIb/IIIa (αIIb/β3) receptor inhibition, by preventing fibrinogen binding and platelet aggregation, concomitantly attenuates arterial thrombotic capacity and impairs protective hemostasis, 2 divergent platelet-dependent processes. Because the currently available Food and Drug Administration–approved small molecule GP IIb/IIIa receptor antagonists are considered “competitive” inhibitors and because there is limited information on the reversibility of platelet inhibition by fibrinogen or platelet supplementation, the following series of in vitro experiments were performed. Methods and Results Washed platelets from 24 healthy volunteers were suspended in Tyrodes buffer and incubated with achievable (in vivo) steady-state concentrations of either tirofiban or eptifibatide before activation with TRAP (thrombin receptor agonist peptide) (15 μmol/L). Platelet aggregation was inhibited by 40% to 50%, but reversal was achieved by fibrinogen supplementation in a concentration-dependent manner. In a separate series of in vitro experiments, platelet inhibition exceeding 90% was established with tirofiban (average concentration 9.28 μg/L) and eptifibatide (average concentration 95.4 μg/L). Recovery of platelet aggregation to at least 50% was achieved after the addition of fibrinogen (0.76-0.80 g/L), platelets (2.4 × 1011/L), or their combination. There was an inverse relationship between plasma baseline fibrinogen and the amount of supplemental fibrinogen required to restore platelet aggregability (r = –0.60, P <.01). Conclusions The reversibility of GP IIb/IIIa–directed platelet inhibition is influenced by cell surface receptor availability and the intrinsic pharmacodynamic mechanism of action. Fibrinogen supplementation with fresh frozen plasma or cryoprecipitate either alone or in combination with platelet transfusion, represents an important and readily available treatment consideration for restoring hemostatic potential and managing major hemorrhagic complications associated with the administration of small molecule competitive GP IIb/IIIa receptor antagonists. (Am Heart J 2001;142:204-10.)

Binding of a fibrinogen mimetic stabilizes integrin αIIbβ3's open conformation

The platelet integrin alphaIIbbeta3 is representative of a class of heterodimeric receptors that upon activation bind extracellular macromolecular ligands and form signaling clusters. This study examined how occupancy of alphaIIbbeta3's fibrinogen binding site affected the receptor's solution structure and stability. Eptifibatide, an integrin antagonist developed to treat cardiovascular disease, served as a high-affinity, monovalent model ligand with fibrinogen-like selectivity for alphaIIbbeta3. Eptifibatide binding promptly and reversibly perturbed the conformation of the alphaIIbbeta3 complex. Ligand-specific decreases in its diffusion and sedimentation coefficient were observed at near-stoichiometric eptifibatide concentrations, in contrast to the receptor-perturbing effects of RGD ligands that we previously observed only at a 70-fold molar excess. Eptifibatide promoted alphaIIbbeta3 dimerization 10-fold more effectively than less selective RGD ligands, as determined by sedimentation equilibrium. Eptifibatide-bound integrin receptors displayed an ectodomain separation and enhanced assembly of dimers and larger oligomers linked through their stalk regions, as seen by transmission electron microscopy. Ligation with eptifibatide protected alphaIIbbeta3 from SDS-induced subunit dissociation, an effect on electrophoretic mobility not seen with RGD ligands. Despite its distinct cleft, the open conformer resisted guanidine unfolding as effectively as the ligand-free integrin. Thus, we provide the first demonstration that binding a monovalent ligand to alphaIIbbeta3's extracellular fibrinogen-recognition site stabilizes the receptor's open conformation and enhances self-association through its distant transmembrane and/or cytoplasmic domains. By showing how eptifibatide and RGD peptides, ligands with distinct binding sites, each affects alphaIIbbeta3's conformation, our findings provide new mechanistic insights into ligand-linked integrin activation, clustering and signaling.

In Vitro Dose Response to Different GPIIb/IIIa-Antagonists: Inter-Laboratory Comparison of Various Platelet Function Tests

Aims: The aim of this study was to assess the inter- and intra-laboratory variation of the concentration–response to the GPIIb/IIIa-antagonists abciximab and eptifibatide on platelet aggregometry and to compare results with flow cytometric tests as well as the rapid platelet function analyser (RPFA). Methods: In five different laboratory sites, blood from three to five healthy donors was spiked with abciximab or eptifibatide, followed by the assessment of: (1) aggregometry (anticoagulant: sodium citrate 3.18% or hirudin 5 μg/ml); (2) flow cytometry (fibrinogen binding or PAC1-expression), or (3) RPFA. Dose–response curves were established on the basis of a sigmoidal I max-model [ I=( I max* C γ )/(IC 50 γ + C γ )]. Results: For citrated blood, aggregation induced by 20 μM ADP was blocked up to 100% by both GPIIb/IIIa-antagonists, IC 50 values varied between 0.11–0.22 μg/ml for eptifibatide and 1.25–2.3 μg/ml for abciximab. I max of the response to 5 μg/ml collagen ranged from 46% to 100%, and IC 50 values varied between 0.28–0.34 μg/ml for eptifibatide and 2.3–3.8 μg/ml for abciximab. In hirudinized blood, IC 50 values for eptifibatide were 1.5- to 3-fold higher than those obtained with citrated plasma. Inhibition of PAC1-expression by abciximab (IC 50 0.84 μg/ml) showed results similar those of the RPFA (approx. 1.0 μg/ml); larger differences between PAC1 and RPFA results were observed for eptifibatide. Based on aggregometry, eptifibatide concentrations for 80% inhibition varied from 0.27 to 0.55 μg/ml, and were considerably less when the RPFA was taken as basis (0.15 or 0.22 μg/ml). A similar pattern was observed for abciximab. Conclusions: We found quite a low inter- and intra-laboratory variation in the in vitro pharmacodynamic characterization of GPIIb/IIIa-antagonists by aggregometry, making results of these tests obtained from different laboratories during clinical trials at least comparable. The RPFA exhibits a higher sensitivity to inhibitory GPIIb/IIIa-effects, in keeping with the “real” inhibition of the activated receptor (PAC1) as assessed with more elaborate flow cytometry.