Acute thrombocytopenia after treatment with tirofiban or eptifibatide is associated with antibodies specific for ligand-occupied GPIIb/IIIa

Current and Future Roles of Glycoprotein IIb-IIIa Inhibitors in Primary Angioplasty for ST-Segment Elevation Myocardial Infarction

Acute myocardial infarction still represents the major cause of mortality in high-income countries. Therefore, considerable efforts have been focused on the treatment of myocardial infarctions in the acute and long-term phase, with special attention being paid to reperfusion strategies and adjunctive antithrombotic therapies. In fact, despite the successful mechanical recanalization of the epicardial conduit, a substantial percentage of patients still experience poor myocardial reperfusion or acute/subacute in-stent thrombosis. Due the delayed onset of action of currently available oral antiplatelet therapies, glycoprotein (GP) IIb-IIIa inhibitors could be expected to improve clinical outcomes, especially when administrated in the early phase of the infarction, due to the larger platelet composition of fresh thrombi, the dynamic nature of early thrombi, and the larger amount of viable myocardium existing in the early, as compared to a delayed, phase. Considerable evidence has accumulated regarding the benefits from GP IIb-IIIa inhibitors on mortality, especially among high-risk patients and when administered as an upstream strategy. Therefore, based on currently available data, GP IIb-IIIa inhibitors can be considered when the drug can be administered within the first 3 h of symptom onset and among high-risk patients (e.g., those with advanced Killip class or an anterior myocardial infarction). Even though it is not universally accepted, in our opinion, this strategy should be implemented in a pre-hospital setting (in an ambulance) or as soon as possible when arriving at the hospital (at the Emergency Room or Coronary Care Unit, irrespective of whether they are in spoke or hub hospitals). A new, second-generation GP IIb-IIIa inhibitor (zalunfiban) appears to be highly suitable as a pre-hospital pharmacological facilitation strategy at the time of first medical contact due to its favourable features, including its simple subcutaneous administration, rapid onset of action (15 min), and limited time of action (with a half-life of ~1 h), which is likely to minimize the risk of bleeding. The ongoing CELEBRATE trial, including 2499 STEMI patients, may potentially provide compelling data to support the upstream treatment of STEMI patients undergoing mechanical reperfusion. In fact, although the current therapeutic target of increased rates of timely reperfusion has been achieved, the future goal in myocardial infarction treatment should be to achieve the most rapid reperfusion prior to primary percutaneous coronary intervention, thus further minimizing myocardial damage, or, in some cases, even preventing it completely, and improving survival.

Application of Funnel Metadynamics to the Platelet Integrin αIIbβ3 in Complex with an RGD Peptide

Integrin αIIbβ3 mediates platelet aggregation by binding the Arginyl-Glycyl-Aspartic acid (RGD) sequence of fibrinogen. RGD binding occurs at a site topographically proximal to the αIIb and β3 subunits, promoting the conformational activation of the receptor from bent to extended states. While several experimental approaches have characterized RGD binding to αIIbβ3 integrin, applying computational methods has been significantly more challenging due to limited sampling and the need for a priori information regarding the interactions between the RGD peptide and integrin. In this study, we employed all-atom simulations using funnel metadynamics (FM) to evaluate the interactions of an RGD peptide with the αIIb and β3 subunits of integrin. FM incorporates an external history-dependent potential on selected degrees of freedom while applying a funnel-shaped restraint potential to limit RGD exploration of the unbound state. Furthermore, it does not require a priori information about the interactions, enhancing the sampling at a low computational cost. Our FM simulations reveal significant molecular changes in the β3 subunit of integrin upon RGD binding and provide a free-energy landscape with a low-energy binding mode surrounded by higher-energy prebinding states. The strong agreement between previous experimental and computational data and our results highlights the reliability of FM as a method for studying dynamic interactions of complex systems such as integrin.

Delayed-onset eptifibatide-induced thrombocytopenia

PURPOSE

We present a unique case of delayed-onset, profound eptifibatide-induced thrombocytopenia that occurred 5 days after initiation of the drug.

SUMMARY

Eptifibatide is a platelet glycoprotein IIb/IIIa receptor inhibitor with indications for use in patients with acute coronary syndromes. Eptifibatide-induced thrombocytopenia is uncommon but well studied and typically occurs within 24 hours of initiation of the drug. In the case described here, a 62-year-old male with a past history of coronary artery disease (including percutaneous coronary intervention within the past 12 months) was started on eptifibatide at a dosage of 2 µg/kg per minute for management of significant thrombus burden prior to a planned cardiac revascularization procedure; heparin for anticoagulation was also initiated. About 5 days after initiation of eptifibatide, the patient developed severe thrombocytopenia, with the platelet count dropping precipitously from 249 × 103/µL on admission to less than 1 × 103/µL. After eptifibatide and heparin therapy were discontinued and the patient was switched to argatroban, the platelet count recovered to 38 × 103/µL over the next 2 days. An eptifibatide platelet antibody assay was positive for IgG-mediated reactions consistent with eptifibatide-induced thrombocytopenia. Scoring of this case with the Naranjo scale yielded a score of 4, suggesting a possible adverse reaction to eptifibatide.

CONCLUSION

This is the first published case report of profound eptifibatide-induced thrombocytopenia occurring more than 24 hours after eptifibatide initiation and serves to bring awareness that a delayed reaction can occur.

Critical Analysis of Thrombocytopenia Associated With Glycoprotein IIb/IIIa Inhibitors and Potential Role of Zalunfiban, a Novel Small Molecule Glycoprotein Inhibitor, in Understanding the Mechanism(s)

Thrombocytopenia is a rare but serious complication of the intravenous glycoprotein IIb/IIIa (GPIIb/IIIa; integrin αIIbβ3) receptor inhibitors (GPIs), abciximab, eptifibatide, and tirofiban. The thrombocytopenia ranges from mild (50 000-100 000 platelets/μL), to severe (20 000 to <50 000/μL), to profound (<20 000/μL). Profound thrombocytopenia appears to occur in <1% of patients receiving their first course of therapy. Thrombocytopenia can be either acute (<24 hours) or delayed (up to ~14 days). Both hemorrhagic and thrombotic complications have been reported in association with thrombocytopenia. Diagnosis requires exclusion of pseudothrombocytopenia and heparin-induced thrombocytopenia. Therapy based on the severity of thrombocytopenia and symptoms may include drug withdrawals and treatment with steroids, intravenous IgG, and platelet transfusions. Abciximab-associated thrombocytopenia is most common and due to either preformed antibodies or antibodies induced in response to abciximab (delayed). Readministration of abciximab is associated with increased risk of thrombocytopenia. Evidence also supports an immune basis for thrombocytopenia associated with the 2 small molecule GPIs. The latter bind αIIbβ3 like the natural ligands and thus induce the receptor to undergo major conformational changes that potentially create neoepitopes. Thrombocytopenia associated with these drugs is also immune-mediated, with antibodies recognizing the αIIbβ3 receptor only in the presence of the drug. It is unclear whether the antibody binding depends on the conformational change and whether the drug contributes directly to the epitope. Zalunfiban, a second-generation subcutaneous small molecule GPI, does not induce the conformational changes; therefore, data from studies of zalunfiban will provide information on the contribution of the conformational changes to the development of GPI-associated thrombocytopenia.

Novel strategies in antithrombotic therapy: targeting thrombosis while preserving hemostasis

Antithrombotic therapy is a delicate balance between the benefits of preventing a thrombotic event and the risks of inducing a major bleed. Traditional approaches have included antiplatelet and anticoagulant medications, require careful dosing and monitoring, and all carry some risk of bleeding. In recent years, several new targets have been identified, both in the platelet and coagulation systems, which may mitigate this bleeding risk. In this review, we briefly describe the current state of antithrombotic therapy, and then present a detailed discussion of the new generation of drugs that are being developed to target more safely existing or newly identified pathways, alongside the strategies to reverse direct oral anticoagulants, showcasing the breadth of approaches. Combined, these exciting advances in antithrombotic therapy bring us closer than we have ever been to the "holy grail" of the field, a treatment that separates the hemostatic and thrombotic systems, preventing clots without any concurrent bleeding risk.

Case report: reuse of tirofiban leads to very severe thrombocytopenia

Background

Telofiban is a class of small molecule non-peptide tyrosine derivatives containing RGD sequences. It is the only platelet surface glycoprotein (GP) IIb/IIIa receptor antagonist (GPI) currently marketed in China. In patients with ST-segment elevation myocardial infarction(STEMI) who receive percutaneous coronary intervention (PCI) with a heavy thrombotic load, postoperative intravenous tirofiban can prevent complications of myocardial ischemia due to sudden coronary artery occlusion. With the increase in the clinical use of tirofiban, the number of adverse reactions related to thrombocytopenia induced by tirofiban has gradually increased. Still, most of them have thrombocytopenia after the first use. We report one case of very severe thrombocytopenia following the reuse of tirofiban.

Case summary

A 65-year-old man of Han nationality, 170 cm in height, 85 kg in weight, and 29.4 BMI, suffered from cerebral infarction 13 years ago and left with right limb movement disorder. Five days before this hospitalization, the patient underwent PCI, and three stents were implanted. After the operation, anti-platelet tirofiban and nadroparin calcium were given, and no thrombocytopenia was found. The patient still retains 80% stenosis due to anterior descending branches and plans to undergo PCI again half a month later. The patient with a history of hypertension, type 2 diabetes, diabetic nephropathy, and cerebral infarction usually took 100 mg of aspirin and 75 mg of clopidogrel, antiplatelet therapy, and had no history of food and drug allergy. One day after discharge, the patient suddenly felt chest tightness and wheezing. The laboratory showed hypersensitivity troponin 2.85 ng/ml (normal 0-0.0268 ng/ml), and the admission ECG showed ST-T changes in leads I, aVL, V5-V6. On the 6th day of hospitalization, PCI was performed, a stent was implanted in the proximal section of the anterior descending branch opening, and tirofiban(10 ug/kg, 3 min bolus, then 0.1 ug/kg/min) antiplatelet therapy was given after surgery. About 10 min after the tirofiban infusion, the patient suddenly shivered, accompanied by convulsions, accompanied by elevated body temperature (up to 39.4°C), accompanied by epistaxis and microscopic hematuria. An urgent blood test showed that the platelets dropped to 1 × 109/L, tirofiban and aspirin stopped immediately, and the antiplatelet therapy of clopidogrel was retained. After infusion of methylprednisolone sodium succinate and gamma globulin, the patient's platelets gradually recovered, and the patient was successfully discharged seven days later in stable condition.

Conclusion

This case is typical of severe thrombocytopenia caused by reusing tirofiban. This case may provide new insights into: 1. Patients who did not have thrombocytopenia after the first use of tirofiban may still have extremely severe thrombocytopenia after re-exposure to tirofiban. Routine platelet count monitoring and early identification of thrombocytopenia are the essential links. 2. Thrombocytopenia caused by re-exposure to tirofiban may have a faster onset, deeper degree, and slower recovery due to antibodies retained after the first exposure to tirofiban; 3. Platelet transfusions may not be necessary for patients with severe thrombocytopenia; 4. Immunosuppressants help suppress the body's immune response, promote platelet recovery, and can be reduced or discontinued when platelets rise and may be safe; 5. After tirofiban for PCI, continuing the maintenance dose of clopidogrel may be safe if the patient has no significant bleeding events.

RGD and Scutellarin Conjugate (WK001) Targeting Platelet Glycoprotein IIb/IIIa Receptor Protects from Myocardial Ischemia/Reperfusion Injury: Synthesis, Characterization, and Bioactivity Evaluation

Myocardial ischemia/reperfusion (MI/R) injury is an unresolved clinical challenge. The blockade of binding fibrinogen by glycoprotein IIb/IIIa (GPIIb-IIIa) inhibitors has become a new therapeutic approach against MI/R injury. In this study, we modified the RGD structure to combine with scutellarin and synthesized a novel peptide, scutellarin-HomoArg-Gly-Asp-Trp-NH₂ (WK001). Herein, reported experimental and docking evidence indicates that WK001 provides immediate and potent platelet inhibition, with stronger inhibition of platelet aggregation than eptifibatide and scutellarin. In particular, it is administered intravenously to prevent thrombus formation and attenuate myocardial fibrosis progression in vivo. Therefore, WK001 could be developed as an antiplatelet drug to treat thrombosis-associated diseases, such as stroke and myocardial infarction.

Eptifibatide-Induced Severe Thrombocytopenia After ST-Elevation Myocardial Infarction (STEMI): A Case Report

Eptifibatide is a platelet glycoprotein (GP) IIb/IIIa inhibitor that is used in certain cases of acute coronary syndrome, including those with high thrombus burden or with no-reflow. It can rarely be associated with severe thrombocytopenia, which brings up a dilemma in managing those patients who require antiplatelet therapy. We discuss a patient who had ST-elevation myocardial infarction (STEMI) and developed severe thrombocytopenia after eptifibatide infusion. He was managed with platelet transfusion, stopping eptifibatide, and interrupting dual antiplatelet therapy (DAPT).

Clinical pharmacology of antiplatelet drugs

INTRODUCTION

Platelets play a key role in arterial thrombosis and antiplatelet therapy is pivotal in the treatment of cardiovascular disease. Current antiplatelet drugs target different pathways of platelet activation and show specific pharmacodynamic and pharmacokinetic characteristics, implicating clinically relevant drug-drug interactions.

AREAS COVERED

This article reviews the role of platelets in hemostasis and cardiovascular thrombosis, and discusses the key pharmacodynamics, drug-drug interactions and reversal strategies of clinically used antiplatelet drugs.

EXPERT OPINION

Antiplatelet therapies target distinct pathways of platelet activation: thromboxane A₂ synthesis, adenosine diphosphate-mediated signaling, integrin α_IIbβ₃ (GPIIb/IIIa), thrombin-mediated platelet activation via the PAR1 receptor and phosphodiesterases. Key clinical drug-drug interactions of antiplatelet agents involve acetylsalicylic acid - ibuprofen, clopidogrel - omeprazole, and morphine - oral P2Y₁₂ inhibitors, all of which lead to an attenuated antiplatelet effect. Platelet function and genetic testing and the use of scores (ARC-HBR, PRECISE-DAPT, ESC ischemic risk definition) may contribute to a more tailored antiplatelet therapy. High on-treatment platelet reactivity presents a key problem in the acute management of ST-elevation myocardial infarction (STEMI). A treatment strategy involving early initiation of an intravenous antiplatelet agent may be able to bridge the gap of insufficient platelet inhibition in high ischemic risk patients with STEMI.

Acute Profound Thrombocytopenia Induced by Eptifibatide Causing Diffuse Alveolar Hemorrhage

Background

Eptifibatide is a glycoprotein IIb/IIIa (GP IIb/IIIa) receptor inhibitor which prevents platelet activation. The mechanism in which eptifibatide causes profound thrombocytopenia is poorly understood. One hypothesis suggests antibody-dependent pathways which cause thrombocytopenia upon subsequent reexposure to eptifibatide. This case reports acute profound thrombocytopenia (platelets < 20 × 10³/mm³) within 24 hours of administration. Alveolar hemorrhage occurred during a second eptifibatide infusion 5 days after initial asymptomatic eptifibatide treatment. Case Presentation. A 50-year-old male presenting with a STEMI was treated with eptifibatide during cardiac catheterization. Twelve hours posttreatment, the patient encountered profound thrombocytopenia and hemoptysis. The patient was briefly intubated for airway protection. The patient was stabilized after receiving platelet transfusion and fully recovered.

Conclusion

This is one of several cases reported on eptifibatide causing acute profound thrombocytopenia and subsequent alveolar hemorrhage. This case supports the theory in which antibodies contribute to eptifibatide-induced thrombocytopenia.

Complications and Management of Eptifibatide-Induced Thrombocytopenia

BACKGROUND

Eptifibatide is used in acute coronary syndromes to reversibly block platelet aggregation by inhibiting the platelet glycoprotein IIb/IIIa receptor. A serious adverse effect of eptifibatide is a profound drop in platelet count, termed eptifibatide-induced thrombocytopenia (EIT).

OBJECTIVE

To provide insight into the types of complications and management of EIT.

METHODS

Cases of EIT submitted to the Food and Drug Administration adverse event reporting system were evaluated. Data analyses included management of EIT, complications of thrombocytopenia, initial platelets, and platelet nadir following eptifibatide.

RESULTS

103 cases of EIT were reported from January 2010 to 2019; 57 cases met the Naranjo scale and were included. Only 37 of those cases contained information on how EIT was managed. Eptifibatide administration was withheld in all 37 of those cases. Platelet transfusions were administered in 20 cases (54%). Two cases were managed with steroids (5.4%), and 1 case used intravenous immunoglobulin G to reverse EIT (2%). The median initial platelet count prior to administration of eptifibatide was 207 000 cells/mm³ (SD = 69 000; n = 27), and median platelet nadir was 9000 cells/mm³ (SD = 19 000; n = 35) The majority of complications of EIT included bleeding events (16/28, 57%). Delayed procedures, prolonged stay, allergic reactions, and thrombosis were each reported in 3 patients (10.75%).

CONCLUSION AND RELEVANCE

Most cases of EIT were managed by withholding eptifibatide with platelet transfusion if necessary. The majority of complications included bleeding. However, significant procedure delays, prolonged hospital stay, thrombosis, and allergic reactions were also reported.

A rare case of eptifibatide-induced thrombocytopenia

Eptifibatide is a glycoprotein (GP) IIb/IIIa receptor antagonist, used for the treatment of acute coronary syndrome with high-risk features or ongoing ischemia. Several case reports have described thrombocytopenia as a rare side effect of eptifibatide administration. The exact mechanism remains unclear but may be due to immune destruction of circulating platelets in the peripheral blood. We present the case of acute-onset severe thrombocytopenia in a 76-year-old female undergoing percutaneous coronary intervention.

First Human Use of RUC-4: A Nonactivating Second-Generation Small-Molecule Platelet Glycoprotein IIb/IIIa (Integrin αIIbβ3) Inhibitor Designed for Subcutaneous Point-of-Care Treatment of ST-Segment-Elevation Myocardial Infarction

Background Despite reductions in door-to-balloon times for primary coronary intervention, mortality from ST-segment-elevation myocardial infarction has plateaued. Early pre-primary coronary intervention treatment of ST-segment-elevation myocardial infarction with glycoprotein IIb/IIIa inhibitors improves pre-primary coronary intervention coronary flow, limits infarct size, and improves survival. We report the first human use of a novel glycoprotein IIb/IIIa inhibitor designed for subcutaneous first point-of-care ST-segment-elevation myocardial infarction treatment. Methods and Results Healthy volunteers and patients with stable coronary artery disease receiving aspirin received escalating doses of RUC-4 or placebo in a sentinel-dose, randomized, blinded fashion. Inhibition of platelet aggregation (IPA) to ADP (20 μmol/L), RUC-4 blood levels, laboratory evaluations, and clinical assessments were made through 24 hours and at 7 days. Doses were increased until reaching the biologically effective dose (the dose producing ≥80% IPA within 15 minutes, with return toward baseline within 4 hours). In healthy volunteers, 15 minutes after subcutaneous injection, mean±SD IPA was 6.9%+7.1% after placebo and 71.8%±15.0% at 0.05 mg/kg (n=6) and 84.7%±16.7% at 0.075 mg/kg (n=6) after RUC-4. IPA diminished over 90 to 120 minutes. In patients with coronary artery disease, 15 minutes after subcutaneous injection of placebo or 0.04 mg/kg (n=2), 0.05 mg/kg (n=6), and 0.075 mg/kg (n=18) of RUC-4, IPA was 14.6%±11.7%, 53.6%±17.0%, 76.9%±10.6%, and 88.9%±12.7%, respectively. RUC-4 blood levels correlated with IPA. Aspirin did not affect IPA or RUC-4 blood levels. Platelet counts were stable and no serious adverse events, bleeding, or injection site reactions were observed. Conclusions RUC-4 provides rapid, high-grade, limited-duration platelet inhibition following subcutaneous administration that appears to be safe and well tolerated. Registration URL: https://www.clini​caltr​ials.gov; Unique identifier: NTC03844191.

Heparin Induced Thrombocytopenia for the Perioperative and Critical Care Clinician

Purpose of Review

This review will illustrate the importance of heparin-induced thrombocytopenia in the intraoperative and critical care settings.

Recent Findings

Heparin-induced thrombocytopenia (HIT) occurs more frequently in surgical patients compared with medical patients due to the inflammatory release of platelet factor 4 and perioperative heparin exposure. Recognition of this disease requires a high index of suspicion. Diagnostic tools and therapeutic strategies have been expanded and refined in recent years.

Summary

HIT is a condition where antibodies against the heparin/platelet factor 4 complex interact with platelet receptors to promote platelet activation, aggregation, and thrombus formation. Our review will focus on intraoperative and postoperative considerations related to HIT to help the clinician better manage this rare but often devastating hypercoagulable disease process.

Pathophysiology and Diagnosis of Drug-Induced Immune Thrombocytopenia

Drug-induced immune thrombocytopenia (DITP) is a life-threatening clinical syndrome that is under-recognized and difficult to diagnose. Many drugs can cause immune-mediated thrombocytopenia, but the most commonly implicated are abciximab, carbamazepine, ceftriaxone, eptifibatide, heparin, ibuprofen, mirtazapine, oxaliplatin, penicillin, quinine, quinidine, rifampicin, suramin, tirofiban, trimethoprim-sulfamethoxazole, and vancomycin. Several different mechanisms have been identified in typical DITP, which is most commonly characterized by severe thrombocytopenia due to clearance and/or destruction of platelets sensitized by a drug-dependent antibody. Patients with typical DITP usually bleed when symptomatic, and biological confirmation of the diagnosis is often difficult because detection of drug-dependent antibodies (DDabs) in the patient's serum or plasma is frequently not possible. This is in contrast to heparin-induced thrombocytopenia (HIT), which is a particular DITP caused in most cases by heparin-dependent antibodies specific for platelet factor 4, which can strongly activate platelets in vitro and in vivo, explaining why affected patients usually have thrombotic complications but do not bleed. In addition, laboratory tests are readily available to diagnose HIT, unlike the methods used to detect DDabs associated with other DITP that are mostly reserved for laboratories specialized in platelet immunology.

Structure-guided design of pure orthosteric inhibitors of αIIbβ3 that prevent thrombosis but preserve hemostasis

A prevailing dogma is that inhibition of vascular thrombosis by antagonizing platelet integrin αIIbβ3 cannot be achieved without compromising hemostasis, thus causing serious bleeding and increased morbidity and mortality. It is speculated that these adverse outcomes result from drug-induced activating conformational changes in αIIbβ3 but direct proof is lacking. Here, we report the structure-guided design of peptide Hr10 and a modified form of the partial agonist drug tirofiban that act as "pure" antagonists of αIIbβ3, i.e., they no longer induce the conformational changes in αIIbβ3. Both agents inhibit human platelet aggregation but preserve clot retraction. Hr10 and modified tirofiban are as effective as partial agonist drugs in inhibiting vascular thrombosis in humanized mice, but neither causes serious bleeding, establishing a causal link between partial agonism and impaired hemostasis. Pure orthosteric inhibitors of αIIbβ3 may thus provide safer alternatives for human therapy, and valuable tools to probe structure-activity relationships in integrins.

A Novel αIIbβ3 Antagonist from Snake Venom Prevents Thrombosis without Causing Bleeding

Life-threatening thrombocytopenia and bleeding, common side effects of clinically available α_IIbβ₃ antagonists, are associated with the induction of ligand-induced integrin conformational changes and exposure of ligand-induced binding sites (LIBSs). To address this issue, we examined intrinsic mechanisms and structure–activity relationships of purified disintegrins, from Protobothrops flavoviridis venom (i.e., Trimeresurus flavoviridis), TFV-1 and TFV-3 with distinctly different pro-hemorrhagic tendencies. TFV-1 with a different α_IIbβ₃ binding epitope from that of TFV-3 and chimeric 7E3 Fab, i.e., Abciximab, decelerates α_IIbβ₃ ligation without causing a conformational change in α_IIbβ₃, as determined with the LIBS antibody, AP5, and the mimetic, drug-dependent antibody (DDAb), AP2, an inhibitory monoclonal antibody raised against α_IIbβ₃. Consistent with their different binding epitopes, a combination of TFV-1 and AP2 did not induce FcγRIIa-mediated activation of the ITAM–Syk–PLCγ2 pathway and platelet aggregation, in contrast to the clinical antithrombotics, abciximab, eptifibatide, and disintegrin TFV-3. Furthermore, TFV-1 selectively inhibits Gα₁₃-mediated platelet aggregation without affecting talin-driven clot firmness, which is responsible for physiological hemostatic processes. At equally efficacious antithrombotic dosages, TFV-1 caused neither severe thrombocytopenia nor bleeding in FcγRIIa-transgenic mice. Likewise, it did not induce hypocoagulation in human whole blood in the rotational thromboelastometry (ROTEM) assay used in perioperative situations. In contrast, TFV-3 and eptifibatide exhibited all of these hemostatic effects. Thus, the α_IIbβ₃ antagonist, TFV-1, efficaciously prevents arterial thrombosis without adversely affecting hemostasis.

Safety of tirofiban and dual antiplatelet therapy in treating intracranial aneurysms

Background

Endovascular treatment of intracranial aneurysms usually involves stent-assisted coiling (SAC) and flow diverters. Glycoprotein IIb/IIIa inhibitors such as tirofiban and dual antiplatelet therapy (DAPT) are required to prevent thromboembolic complications afterwards. We sought to determine the safety of tirofiban and DAPT in these cases.

Methods

We conducted a retrospective analysis of our database for patients with intracranial aneurysms who underwent SAC or flow diversion. The tirofiban-DAPT protocol used is described. Data regarding duration of infusion, placement of external ventricular devices (EVDs), complications, haemoglobin levels and platelet count before and 24 hours after antiplatelet therapy were collected and analysed.

Results

One-hundred and forty-one patients with 148 aneurysms/procedures were included. 110 aneurysms were treated acutely and 38 electively. Minor and major haemorrhagic events were recognised in 20% (30/148) aneurysms. Only 5 (3.4%) intracerebral haemorrhages were symptomatic: 3 cortical/SAH and 2 EVD-related. The average blood volume in symptomatic haemorrhages was 24.8 cc versus 5.42 cc in asymptomatic haemorrhages (p=0.002). The rate of EVD-related haemorrhages was 15.7% (19/121) and only 2 (1.7%) were symptomatic. Most haemorrhagic events occurred in ruptured aneurysms (90.1%, p=0.01). No significant change in platelet count or haemoglobin levels before and 24 hours after administration of tirofiban and DAPT was documented. Concomitant administration of heparin did not increase haemorrhagic events.

Conclusion

The use of the GP IIb/IIIa inhibitors tirofiban and DAPT in this series was safe. Tirofiban and DAPT did not affect platelet count or haemoglobin levels and did not increase rate of symptomatic haemorrhages or thromboembolic complications.

A Simple Clinical Pre-procedure Risk Model for Predicting Thrombocytopenia Associated With Periprocedural Use of Tirofiban in Patients Undergoing Percutaneous Coronary Intervention

Background: No risk model for predicting thrombocytopenia associated with periprocedural tirofiban exposure is available. The purpose of this study was to develop a simple clinical pre-procedure risk model based on pre-procedural characteristics for early prediction of thrombocytopenia before patients were exposed to tirofiban. Methods: The series included 1862 patients who underwent percutaneous coronary intervention with tirofiban exposure. Baseline demographic and clinical characteristics were collected from the hospital information system on admission. The earliest pro-procedural platelets within 72 h were used to evaluate the thrombocytopenia incidence. Risk factors associated with thrombocytopenia in patients with tirofiban exposure were investigated by univariable and multivariable analyses. Locally weighted scatterplot smoothing procedure was used to identify the cut points for the numeric variables. The discriminatory power of the scoring system was assessed with the receiver operating characteristic (ROC) curve analysis. Results: The occurrence of thrombocytopenia was 4.02% (75 of 1862), 4.01% (56 of 1396), and 4.08% (19 of 466) in the overall, developmental, and validation data sets, respectively. The risk score was developed based on five independent predictors: age ≥65y, white blood cell ≥12 × 10⁹/L, diabetes mellitus, congestive heart failure, and chronic kidney disease. This tool was well calibrated (Hosmer Lemeshow χ² = 6.914; P = 0.546) and good discrimination was well obtained in validation data set (C-statistic, 0.82). Conclusion: The clinical pre-procedure risk model is a simple and accurate tool for early identification of high-risk patients of thrombocytopenia before tirofiban exposure, allowing for timely and appropriate intervention.

A Case of Hyperacute Severe Thrombocytopenia Occurring Less than 24 Hours after Intravenous Tirofiban Infusion

Thrombocytopenia is defined as a condition where the platelet count is below the lower limit of normal (<150 G/L), and it is categorized as mild (100–149 G/L), moderate (50–99 G/L), and severe (<50 G/L). We present here a 79-year-old man who developed severe thrombocytopenia with a platelet count of 6 G/L, less than 24 hours after intravenous tirofiban infusion that was given to the patient during a percutaneous transluminal coronary angioplasty procedure with placement of 3 drug-eluting stents. The patient's baseline platelet count was 233 G/L before the procedure. Based on the timeline of events during hospitalization and laboratory evidence, it was highly likely that the patient's thrombocytopenia was the result of tirofiban-induced immune thrombocytopenia, a type of drug-induced immune thrombocytopenia (DITP) which occurs due to drug-dependent antibody-mediated platelet destruction. Anticoagulant-mediated artefactual pseudothrombocytopenia was ruled out as no platelet clumping was seen on the peripheral blood smears. The treatment of DITP includes discontinuation of the causative drug; monitoring of platelet count recovery; or treatment of severe thrombocytopenia with glucocorticoids, IVIG, or platelet transfusions depending on the clinical presentation. The most likely causative agent of this patient's thrombocytopenia—tirofiban—was discontinued, and the patient did not develop any signs of bleeding during the remainder of his hospital stay. His platelet count gradually improved to 24 G/L, and he was discharged on the sixth hospital day.

My patient is thrombocytopenic! Is (s)he? Why? And what shall I do?

Solving the riddle of a thrombocytopenic patient is a difficult and fascinating task. The spectrum of possible aetiologies is wide, ranging from an in vitro artefact to severe treatment-resistant thrombocytopenic bleeding conditions, or even life-threatening prothrombotic states. Moreover, thrombocytopenia by itself does not protect from thrombosis and sometimes a patient with a low platelet count requires concomitant antithrombotic treatment as well. In order to identify and treat the cause and the effects of the thrombocytopenia, you have to put together several pieces of information, solving a unique jig-jaw puzzle.

The present work is not a textbook article about thrombocytopenia, rather a collection of differential diagnostic thoughts, treatment concepts, and some basic knowledge, that you can retrieve when facing your next thrombocytopenic patient. Enjoy reading it, but most importantly enjoy taking care of patients with a low platelet count. I bet the present work will assist you in this challenging and rewarding clinical task.

Indication for allogeneic stem cell transplantation in Glanzmann’s thrombasthenia

Glanzmann’s thrombasthenia (GT) is an autosomal recessive disorder characterized by a lack of thrombocyte aggregation due to the absence of thrombocyte glycoproteins IIb and αIIbβ3. The role of haematopoietic stem cell transplantation (HSCT) in GT remains controversial. However, HSCT offers the only curative approach for patients with a severe clinical phenotype.

In this review, we will discuss the limitation of current status evidence and the specific risk of GT, in particular the alloimmunization and refractoriness to thrombocyte infusions. 19 successful HSCT in 18 GT type I patients have been reported. Mean age at transplantation was 5 years. All patients are still alive. The majority received sibling bone marrow transplant with busulfan and cyclophosphamid conditioning. GvHD incidence was within the normal range, but 10 patients showed alloimmunization of thrombocytes. Median follow up is 25 months.

An αIIb β3 antagonist prevents thrombosis without causing Fc receptor γ-chain IIa-mediated thrombocytopenia

Essentials FcγRIIa-mediated thrombocytopenia is associated with drug-dependent antibodies (DDAbs). We investigated the correlation between αIIb β3 binding epitopes and induction of DDAbs. An FcγRIIa-transgenic mouse model was used to evaluate thrombocytopenia among anti-thrombotics. An antithrombotic with binding motif toward αIIb β-propeller domain has less bleeding tendency.

SUMMARY

Background Thrombocytopenia, a common side effect of Arg-Gly-Asp-mimetic antiplatelet drugs, is associated with drug-dependent antibodies (DDAbs) that recognize conformation-altered integrin αIIb β3 . Objective To explore the correlation between αIIb β3 binding epitopes and induction of DDAb binding to conformation-altered αIIb β3 , we examined whether two purified disintegrins, TMV-2 and TMV-7, with distinct binding motifs have different effects on induction of αIIb β3 conformational change and platelet aggregation in the presence of AP2, an IgG1 inhibitory mAb raised against αIIb β3 . Methods We investigated the possible mechanisms of intrinsic platelet activation of TMV-2 and TMV-7 in the presence of AP2 by examining the signal cascade, tail bleeding time and immune thrombocytopenia in Fc receptor γ-chain IIa (FcγRIIa) transgenic mice. Results TMV-7 has a binding motif that recognizes the αIIb β-propeller domain of αIIb β3 , unlike that of TMV-2. TMV-7 neither primed the platelets to bind ligand, nor caused a conformational change of αIIb β3 as identified with the ligand-induced binding site mAb AP5. In contrast to eptifibatide and TMV-2, cotreatment of TMV-7 with AP2 did not induce FcγRIIa-mediated platelet aggregation and the downstream activation cascade. Both TMV-2 and TMV-7 efficaciously prevented occlusive thrombosis in vivo. Notably, both eptifibatide and TMV-2 caused severe thrombocytopenia mediated by FcγRIIa, prolonged tail bleeding time in vivo, and repressed human whole blood coagulation indexes, whereas TMV-7 did not impair hemostatic capacity. Conclusions TMV-7 shows antiplatelet and antithrombotic activities resulting from a mechanism different from that of all other tested αIIb β3 antagonists, and may offer advantages as a therapeutic agent with a better safety profile.

Integrins as Therapeutic Targets: Successes and Cancers

Integrins are transmembrane receptors that are central to the biology of many human pathologies. Classically mediating cell-extracellular matrix and cell-cell interaction, and with an emerging role as local activators of TGFβ, they influence cancer, fibrosis, thrombosis and inflammation. Their ligand binding and some regulatory sites are extracellular and sensitive to pharmacological intervention, as proven by the clinical success of seven drugs targeting them. The six drugs on the market in 2016 generated revenues of some US$3.5 billion, mainly from inhibitors of α4-series integrins. In this review we examine the current developments in integrin therapeutics, especially in cancer, and comment on the health economic implications of these developments.

Management of antithrombotic agents in patients undergoing flexible bronchoscopy

Bleeding is one of the most feared complications of flexible bronchoscopy. Although infrequent, it can be catastrophic and result in fatal outcomes. Compared to other endoscopic procedures, the risk of morbidity and mortality from the bleeding is increased, as even a small amount of blood can fill the tracheobronchial tree and lead to respiratory failure. Patients using antithrombotic agents (ATAs) have higher bleeding risk. A thorough understanding of the different ATAs is critical to manage patients during the peri-procedural period. A decision to stop an ATA before bronchoscopy should take into account a variety of factors, including indication for its use and the type of procedure. This article serves as a detailed review on the different ATAs, their pharmacokinetics and the pre- and post-bronchoscopy management of patients receiving these medications.

[Long-lasting thrombocytopenia induced by glycoprotein IIb/IIIa inhibitor]

INTRODUCTION

Glycoprotein IIb/IIIa inhibitors (anti-GPIIbIIIa) prevent platelet binding to fibrinogen. Transient sometimes-severe thrombocytopenia is a well-known side effect.

OBSERVATION

A 71-year-old patient presented severe thrombocytopenia after the administration of tirofiban (anti-GPIIbIIIa). Corticosteroid treatment was initiated at day 10 because of persistence of severe thrombocytopenia with poor platelet transfusion efficacy. Corticosteroid treatment led to platelet recovery evoking an immune mediated mechanism for thrombocytopenia.

CONCLUSION

Anti-GPIIbIIIa are associated with a risk of dramatic thrombocytopenia. The underlying mechanism is poorly understood. The management of these usually transient thrombocytopenias is based on platelet transfusion. As report here, in some cases persistent thrombocytopenia can respond to corticosteroids.

Acute Severe Thrombocytopenia Occurring After Administration of Eptifibatide Postpones Emergent Coronary Artery Surgery

Introduction

Eptifibatide is a platelet glycoprotein IIb/IIIa (GP IIb/IIIa) receptor antagonist that inhibits fibrinogen binding to the activated GP IIb/IIIa site and prevents platelet-platelet interaction and clot formation. GP IIb/IIIa inhibitors improve outcome in patients undergoing percutaneous coronary intervention for acute coronary syndrome. Thrombocytopenia is a complication of GP IIb/IIIa inhibitors, but severe thrombocytopenia is unusual. Most reported cases of severe thrombocytopenia after eptifibatide occurred in patients with acute coronary syndrome. The authors describe a patient who developed acute profound thrombocytopenia after receiving eptifibatide before emergent coronary artery bypass graft surgery.

Case Presentation

A 67-year-old man with a normal platelet count (220 K/uL) developed atrial fibrillation, left bundle branch block, and respiratory insufficiency consistent with acute coronary syndrome two days after colectomy. He received eptifibatide during cardiac catheterization, where three-vessel coronary artery disease was encountered. Emergent coronary artery surgery was planned, but the platelet count before surgery was 2 K/uL. Eptifibatide was discontinued, surgery was postponed, and acute coronary syndrome was treated with intraaortic balloon counterpulsation.

Conclusions

The authors describe the second reported case of eptifibatide-induced severe thrombocytopenia associated with cardiac surgery. In this case, discontinuation of eptifibatide and transfusion of apheresis platelets increased the platelet count (137 K/uL) the following day, and the patient subsequently underwent successful coronary artery surgery using cardiopulmonary bypass.

Integrin-based therapeutics: biological basis, clinical use and new drugs

Integrins are activatable molecules that are involved in adhesion and signalling. Of the 24 known human integrins, 3 are currently targeted therapeutically by monoclonal antibodies, peptides or small molecules: drugs targeting the platelet αIIbβ3 integrin are used to prevent thrombotic complications after percutaneous coronary interventions, and compounds targeting the lymphocyte α4β1 and α4β7 integrins have indications in multiple sclerosis and inflammatory bowel disease. New antibodies and small molecules targeting β7 integrins (α4β7 and αEβ7 integrins) and their ligands are in clinical development for the treatment of inflammatory bowel diseases. Integrin-based therapeutics have shown clinically significant benefits in many patients, leading to continued medical interest in the further development of novel integrin inhibitors. Of note, almost all integrin antagonists in use or in late-stage clinical trials target either the ligand-binding site or the ligand itself.

Design, Virtual Screening, and Synthesis of Antagonists of αIIbβ3 as Antiplatelet Agents

This article describes design, virtual screening, synthesis, and biological tests of novel αIIbβ3 antagonists, which inhibit platelet aggregation. Two types of αIIbβ3 antagonists were developed: those binding either closed or open form of the protein. At the first step, available experimental data were used to build QSAR models and ligand- and structure-based pharmacophore models and to select the most appropriate tool for ligand-to-protein docking. Virtual screening of publicly available databases (BioinfoDB, ZINC, Enamine data sets) with developed models resulted in no hits. Therefore, small focused libraries for two types of ligands were prepared on the basis of pharmacophore models. Their screening resulted in four potential ligands for open form of αIIbβ3 and four ligands for its closed form followed by their synthesis and in vitro tests. Experimental measurements of affinity for αIIbβ3 and ability to inhibit ADP-induced platelet aggregation (IC50) showed that two designed ligands for the open form 4c and 4d (IC50 = 6.2 nM and 25 nM, respectively) and one for the closed form 12b (IC50 = 11 nM) were more potent than commercial antithrombotic Tirofiban (IC50 = 32 nM).

Hospital-acquired thrombocytopenia

The development of thrombocytopenia is common in hospitalized patients and is associated with increased mortality. Frequent and important causes of thrombocytopenia in hospitalized patients include etiologies related to the underlying illness for which the patient is admitted, such as infection and disseminated intravascular coagulation, and iatrogenic etiologies such as drug-induced immune thrombocytopenia, heparin-induced thrombocytopenia, posttransfusion purpura, hemodilution, major surgery, and extracorporeal circuitry. This review presents a brief discussion of the pathophysiology, distinguishing clinical features, and management of these etiologies, and provides a diagnostic approach to hospital-acquired thrombocytopenia that considers the timing and severity of the platelet count fall, the presence of hemorrhage or thrombosis, the clinical context, and the peripheral blood smear. This approach may offer guidance to clinicians in distinguishing among the various causes of hospital-acquired thrombocytopenia and providing management appropriate to the etiology.

Contemporary antiplatelet therapy in patients undergoing percutaneous coronary intervention

The proper use of antiplatelet agents in the cardiac catheterization laboratory is important for ensuring optimal results in patients undergoing percutaneous revascularization. Understanding the mechanisms by which these drugs exerts their effects is important for both interventional and non-interventional cardiologists. The effects of these agents on platelet function can be assessed and monitored using a variety of commercially available laboratory assays but so far these tests have not been adopted in routine clinical practice. Currently, aspirin, thienopyridines and glycoprotein IIb/IIIa inhibitors are the primary types of antiplatelet drugs being utilized. The use of these drugs and of several newer antiplatelet drugs in the treatment of patients undergoing percutaneous revascularization in the cardiac catheterization laboratory will be discussed, especially in the light of the recently published guidelines.

Acute serious thrombocytopenia associated with intracoronary tirofiban use for primary angioplasty

Tirofiban, a specific glycoprotein IIb/IIIa inhibitor, may cause extensive thrombocytopenia with an incidence of 0.2% to 0.5%. We report the case of a 50-year-old man who developed thrombocytopenia after tirofiban use (both intracoronary and peripheral) over hours and the successful management of this complication after primary percutaneous coronary intervention for acute ST-segment elevation myocardial infarction.

Eptifibatide-induced acute profound thrombocytopenia: a case report

BACKGROUND

The interactions among cells or among cells and components of the extracellular matrix, is a crucial pathophysiological process involving some molecules collectively known as adhesion molecules (CAMs). Glycoprotein IIb / IIIa receptors are only restricted to blood platelets and they bind fibrinogen and adhesion proteins such as fibronectin, vitronectin, von Willebrand factor to form cross bridges between adjacent platelets. IIb/IIIa receptor antagonists are an object of intense research activity for target therapy worldwide during the last decades. Three GPIIb/IIIa inhibitors, abciximab, tirofiban, and eptifibatide, have been approved for clinical use. Profound thrombocytopenia is an uncommon but clinically important complication of glycoprotein IIb/IIIa inhibitors.

CASE PRESENTATION

This case report discusses a forty-four-year-old male patient with acute coronary syndrome who underwent percutaneous coronary intervention and developed profound thrombocytopenia within 4 hours of first administration of eptifibatide.

CONCLUSION

This report adds another case of eptifibatide-induced thrombocytopenia to the medical literature and endorses the importance of platelet count monitoring after initiating therapy with this agent.

Tirofiban in acute coronary syndromes

Acute coronary syndromes represent a major health problem in terms of incidence and mortality. Intracoronary platelet-rich thrombi may develop in response to plaque rupture, and are involved in the pathogenesis of all acute coronary syndromes. The glycoprotein IIb/IIIa receptor, a platelet surface integrin, plays a key role in platelet aggregation once it has been activated by specific ligands. The development of glycoprotein IIb/IIIa inhibitors has revolutionized the management of acute coronary syndromes. Tirofiban is one of three parenteral glycoprotein IIb/IIIa inhibitors in clinical use, and many trials have demonstrated its clinical efficacy and low rate of adverse effects in patients with non-ST-segment elevation acute coronary syndrome. This article reviews the data concerning its use in the clinical settings of acute coronary syndromes and percutaneous coronary angioplasty, and discusses its benefits in different treatment strategies and in association with other drugs. In particular, the role of early, upstream tirofiban coupled with early aggressive revascularization in the management of high-risk non-ST-segment elevation acute coronary syndromes is emphasized.

A novel class of ion displacement ligands as antagonists of the αIIbβ3 receptor that limit conformational reorganization of the receptor

A collection of αIIbβ3 integrin receptor antagonists possessing a unique MIDAS metal ion displacement mechanism of action is presented. Insight into these agents' structure-activity relationships, binding modality, and pharmacokinetic and pharmacodynamic profiles highlight the potential of these small molecule ion displacement ligands as attractive candidates for clinical development.

Approach to the diagnosis and management of drug-induced immune thrombocytopenia

Drug-induced immune thrombocytopenia (DITP) is a challenging clinical problem that is under-recognized, difficult to diagnose and associated with severe bleeding complications. DITP may be caused by classic drug-dependent platelet antibodies (eg, quinine); haptens (eg, penicillin); fiban-dependent antibodies (eg, tirofiban); monoclonal antibodies (eg, abciximab); autoantibody formation (eg, gold); and immune complex formation (eg, heparin). A thorough clinical history is essential in establishing the diagnosis of DITP and should include exposures to prescription medications, herbal preparations and even certain foods and beverages. Clinical and laboratory criteria have been established to determine the likelihood of a drug being the cause of thrombocytopenia, but these criteria can only be applied retrospectively. The most commonly implicated drugs include quinine, quinidine, trimethoprim/sulfamethoxazole and vancomycin. We propose a practical approach to the diagnosis of the patient with suspected DITP. Key features are: the presence of severe thrombocytopenia (platelet nadir <20×10(9)/L); bleeding complications; onset 5 to 10days after first drug exposure, or within hours of subsequent exposures or after first exposure to fibans or abciximab; and exposure to drugs that have been previously implicated in DITP reactions. Treatment involves stopping the drug(s), administering platelet transfusions or other therapies if bleeding is present and counselling on future drug avoidance. The diagnosis can be confirmed by a positive drug re-challenge, which is often impractical, or by demonstrating drug-dependent platelet reactive antibodies in vitro. Current test methods, which are mostly flow cytometry-based, must show drug-dependence, immunoglobulin binding, platelet specificity and ideally should be reproducible across laboratories. Improved standardization and accessibility of laboratory testing should be a focus of future research.

Small molecule agonist of very late antigen-4 (VLA-4) integrin induces progenitor cell adhesion

Activation of the integrin family of cell adhesion receptors on progenitor cells may be a viable approach to enhance the effects of stem cell-based therapies by improving cell retention and engraftment. Here, we describe the synthesis and characterization of the first small molecule agonist identified for the integrin α4β1 (also known as very late antigen-4 or VLA-4). The agonist, THI0019, was generated via two structural modifications to a previously identified α4β1 antagonist. THI0019 greatly enhanced the adhesion of cultured cell lines and primary progenitor cells to α4β1 ligands VCAM-1 and CS1 under both static and flow conditions. Furthermore, THI0019 facilitated the rolling and spreading of cells on VCAM-1 and the migration of cells toward SDF-1α. Molecular modeling predicted that the compound binds at the α/β subunit interface overlapping the ligand-binding site thus indicating that the compound must be displaced upon ligand binding. In support of this model, an analog of THI0019 modified to contain a photoreactive group was used to demonstrate that when cross-linked to the integrin, the compound behaves as an antagonist instead of an agonist. In addition, THI0019 showed cross-reactivity with the related integrin α4β7 as well as α5β1 and αLβ2. When cross-linked to αLβ2, the photoreactive analog of THI0019 remained an agonist, consistent with it binding at the α/β subunit interface and not at the ligand-binding site in the inserted ("I") domain of the αL subunit. Co-administering progenitor cells with a compound such as THI0019 may provide a mechanism for enhancing stem cell therapy.