Platelet activation and function during eltrombopag treatment in immune thrombocytopenia

The immune thrombocytopenia paradox: Should we be concerned about thrombosis in ITP?

Despite the predisposition to bleeding, patients with immune thrombocytopenia (ITP) may also have an increased risk of arterial and venous thrombosis, which can contribute to significant morbidity. The risk of thrombosis increases with age and the presence of cardiovascular risk factors. This narrative review explores the multifactorial nature of thrombosis in ITP, focusing on new pathological mechanisms, emerging evidence on the association between established treatments and thrombotic risk, the role of novel treatment approaches, and the challenges in assessing the balance between bleeding and thrombosis in ITP. The review also explores the challenges in managing acute thrombotic events in ITP, since the platelet count does not always reliably predict either the risk of bleeding or thrombosis and antithrombotic strategies lack specific guidelines for ITP. Notably, second-line therapeutic options, such as splenectomy and thrombopoietin receptor agonists (TPO-RAs), exhibit an increased risk of thrombosis especially in older individuals or those with multiple thrombotic risk factors or previous thrombosis, emphasizing the importance of careful risk assessment before treatment selection. In this context, it is important to consider second-line therapies such as rituximab and other immunosuppressive agents, dapsone and fostamatinib, which are not associated with increased thrombotic risk. In particular, fostamatinib, an oral spleen tyrosine kinase inhibitor, has promisingly low thrombotic risk. During the current era of the emergence of several novel ITP therapies that do not pose additional risks for thrombosis, it is critical to outline evidence-based strategies for the prevention and treatment of thrombosis in ITP patients.

Aplastic Anemia With Thrombosis Following the Administration of Immunosuppressant and Thrombopoietin Receptor Agonist (TPO-RA)

Thrombopoietin receptor agonist (TPO-RA) is effective for aplastic anemia (AA) and idiopathic thrombocytopenic purpura (ITP). However, the risk of thrombosis during ITP treatment with TPO-RA is higher than without TPO-RA. It is unclear whether TPO-RA increases the risk of thrombosis in patients with AA. We report a case of a 66-year-old female with severe AA having paroxysmal nocturnal hemoglobinuria (PNH) clones in the peripheral blood who developed ischemic colitis after three days of starting eltrombopag. Contrast-enhanced computed tomography showed ischemic colitis and contrast enhancement defect in the left atrial appendage, which indicated a thrombus in the heart. Stopping eltrombopag and providing supportive care improved her symptoms, and her blood cell counts gradually increased. Thrombosis should be considered when TPO-RA is administered during the immunosuppressive treatment of AA.

Association of thrombopoietin-related drugs with thromboembolic events: Mendelian randomization and a real-world study

Background

Studies have shown conflicting results when using thrombopoietin-related drugs (TPORD) for thromboembolic events (TEEs). Our study aimed to explore the correlation between TPORDs and TEEs.

Method

Drug-targeted Mendelian randomization (MR) and multivariate MR (MVMR) analysis were used to explore the causal relationship between TPORDs and TEEs such as venous thromboembolism (VTE), deep vein thrombosis (DVT), pulmonary embolism (PE), myocardial infarction (MI) and ischemic stroke (STR). At the same time, a real-world study was conducted by extracting adverse events (AEs) from the FDA Adverse Event Reporting System database included in AERSMine to further validate our findings.

Outcome

In drug-target MR, TPORDs were associated with VTE (OR = 1.193, 95% confidence interval (CI): 1.001-1.423, p = 0.049], DVT (OR = 1.321, 95% CI: 1.027-1.700, p = 0.030), MI (OR = 1.216, 95% CI: 1.010-1.464, p = 0.039), STR (OR = 1.224, 95% CI: 1.021-1.468, p = 0.029). VTE/DVT/STR remained stable in MVMR (VTE: OR = 1.3, 95% CI: 1.187-1.422, p < 0.001; DVT: OR = 1.465,95% CI:1.285-1.671, p < 0.001; STR: OR = 1.119, 95% CI: 1.018-1.229, p = 0.019) and real-world studies [lower bound of proportional reporting ratio (ROR) greater than 1]. The significance of myocardial infarction disappeared in MVMR (OR = 0.996, 95% CI: 0.894-1.109, p = 0.942) and in real-world studies (lower ROR lower than 1). There was no evidence of a causal relationship between TPORD and PE (OR = 1.244, 95% CI: 0.969-1.597, p = 0.087), but it generated a signal from a real-world study (lower bound of ROR greater than 1).

Conclusion

This study suggests that TPORDs may be associated with an increased risk of TEEs, particularly AEs leading to VTE/DVT/STR. In addition, the relationship between TPORDs and PE/MI is debatable and requires more research.

Immunomodulation with romiplostim as a second-line strategy in primary immune thrombocytopenia: The iROM study

Thrombopoietin receptor agonists (TPO-RAs) stimulate platelet production, which might restore immunological tolerance in primary immune thrombocytopenia (ITP). The iROM study investigated romiplostim's immunomodulatory effects. Thirteen patients (median age, 31 years) who previously received first-line treatment received romiplostim for 22 weeks, followed by monitoring until week 52. In addition to immunological data, secondary end-points included the sustained remission off-treatment (SROT) rate at 1 year, romiplostim dose, platelet count and bleedings. Scheduled discontinuation of romiplostim and SROT were achieved in six patients with newly diagnosed ITP, whereas the remaining seven patients relapsed. Romiplostim dose titration was lower and platelet count response was stronger in patients with SROT than in relapsed patients. In all patients, regulatory T lymphocyte (Treg) counts increased until study completion and the counts were higher in patients with SROT. Interleukin (IL)-4, IL-9 and IL-17F levels decreased significantly in all patients. FOXP3 (Treg), GATA3 (Th2) mRNA expression and transforming growth factor-β levels increased in patients with SROT. Treatment with romiplostim modulates the immune system and possibly influences ITP prognosis. A rapid increase in platelet counts is likely important for inducing immune tolerance. Better outcomes might be achieved at an early stage of autoimmunity, but clinical studies are needed for confirmation.

Platelet function and soluble P-selectin in patients with primary immune thrombocytopenia

BACKGROUND

The bleeding phenotype in immune thrombocytopenia (ITP) is heterogeneous, but usually mild and only partly dependent on the severity of thrombocytopenia. Platelet reactivity has previously been suggested to underly the mild phenotype.

METHODS

Platelet function was assessed as basal and agonist-induced surface expression of P-selectin and activation of GPIIb/IIIa via flow cytometry, and soluble (s)P-selectin levels were assessed in plasma of 77 patients with primary ITP, 19 hemato-oncologic thrombocytopenic controls (TC) and 20 healthy controls (HC). The association of platelet function with laboratory and clinical parameters such as bleeding manifestations at inclusion and previous thrombosis was analyzed.

RESULTS

ITP patients showed tendency towards increased surface P-selectin and elevated levels of activated GPIIb/IIIa. Platelet activation after stimulation with all agonists including TRAP-6, ADP, arachidonic acid and CRP was decreased compared to HC. Compared to TC, only GPIIb/IIIa activation but not surface P-selectin was higher in ITP. Levels of soluble (s)P-selectin were significantly higher in ITP patients compared to TC, but similar to HC. Higher sP-selectin levels were associated with blood group O and current therapy, with highest levels in TPO-RA treated patients. Platelet reactivity was not associated with platelet count or size, platelet antibodies, treatment regime, or blood group. No correlation between platelet activation with the bleeding phenotype or previous thrombotic events could be observed.

CONCLUSION

ITP patients did not have hyper-reactive platelets compared to HC, but partly higher reactivity compared to TC. Further studies are needed to understand the underlying mechanism behind the bleeding and pro-thrombotic phenotype in ITP. 250/250.

Evaluation of the effect of eltrombopag therapy on the platelet collagen receptor glycoprotein VI (GPVI) expression and soluble GPVI levels in young patients with immune thrombocytopenia

BACKGROUND

Platelet glycoprotein VI (GPVI) receptor is essential for platelet adhesion and aggregation. Eltrombopag is as an effective treatment for chronic immune thrombocytopenia (ITP); yet, its effect on platelet function is not fully characterized.

AIM

This prospective study investigated the effect of eltrombopag therapy on platelet function through assessment of GPVI receptor expression and soluble GPVI levels among pediatric patients with persistent or chronic ITP.

METHODS

Thirty-six children and adolescents with persistent or chronic ITP were divided equally into two groups either to receive eltrombopag therapy or the standard of care. All patients were followed-up for 12 months with assessment of bleeding score and complete blood count (CBC). Evaluation of GPVI expression using flow cytometry and measurement of its soluble form by ELISA was done at baseline and at 6 months.

RESULTS

ITP patients on eltrombopag had significantly lower bleeding score after 6 months of therapy while the quality of life has significantly improved. Platelet count was significantly increased throughout the study. GPVI expression by flow cytometry and soluble GPVI levels were significantly increased after eltrombopag therapy. After 12 months, ITP patients on eltrombopag were able to maintain a good quality of life and low bleeding score.

CONCLUSION

Our data suggest that eltrombopag, through its effect on the GPVI receptor expression and its soluble form, might reduce bleeding manifestations and improve the quality of life of chronic and persistent ITP children independent of its effect on the platelet count.

Cerebral venous sinus thrombosis in immune thrombocytopenia patients treated with thrombopoietin receptor agonist: Case reports and literature review

Introduction and importance

Cerebral venous sinus thrombosis is an uncommon adverse event in immune thrombocytopenia (ITP) patients treated with thrombopoietin receptor agonists (TPO-RAs).

Case presentation

We reported two cases of cerebral venous sinus thrombosis after eltrombopag administration. The first case is a 29-year-old ITP woman who recently initiated eltrombopag one month before admission. She presented with progressive headache, visual disturbance, and nausea for six days with unremarkable physical examination except for bilateral optic disc edema. She was treated with enoxaparin and switched to edoxaban when discharged. The second case is a 75-year-old man with a history of vaccine-induced ITP. He was initially treated with dexamethasone and eltrombopag. One month later, he developed acute cerebral venous thrombosis with hemorrhagic infarction in the bilateral frontal lobes. Even though he was treated with intravenous heparin, his status was not improved. He received the best supportive care.

Discussion

The pathophysiology of TPO-RAs-associated cerebral venous sinus thrombosis remained unclear but might associate with platelet activation. Most cases of cerebral venous sinus thrombosis occur within two months, thus closed platelet monitoring is important.

Conclusion

Careful use and closed monitoring might prevent this event. Indications of initiation and tapering must be considered before TPO-RAs administration. Off-label use may enhance TPO-RA side effects.

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The rate of TPO-RA-associated CVT is increasing after the widespread use of TPO-RAs.

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Abnormal platelet activation may be the crucial factor for TPO-RA-associated CVT.

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Most cases of CVT occur within two months, thus closed monitoring is important.

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Before giving TPO-RAs, consider initiation and tapering indications.

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Off-label usage may unnecessarily increase the incidence of TPO-RAs adverse events.

Zusanli (ST36) Acupoint Injection With Dexamethasone for Chemotherapy-Induced Myelosuppression: A Systematic Review and Meta-Analysis

Objective

Myelosuppression is the most common adverse reaction of chemotherapy, which seriously affects the course of treatment. Zusanli (ST36) acupoint injection with dexamethasone has achieved good clinical efficacy in China. This study aimed to systematically evaluate the efficacy of ST36 acupoint injection with dexamethasone in the treatment of chemotherapy-induced myelosuppression (CIM).

Methods

Randomized controlled trials of CIM treated with ST36 acupoint injection with dexamethasone were retrieved from eight electronic databases. We used the Cochrane Collaboration tool to assess the risk of bias. Excel 2010 was used to establish a database for information extraction, and RevMan 5.3.0 software was used to analyze the included test data. GRADE profiler 3.6 software was used to grade the quality of evidence for the outcome indicators of the study.

Results

A total of 17 studies involving 1177 patients were included in this meta-analysis. The results showed that, compared with conventional western medicine (CWM), ST36 acupoint injection with dexamethasone could significantly improve the clinical total effective rate [RR=1.95, 95% CI (1.53, 2.49), P <0.00001] and increase white blood cell (WBC) (MD=1.38, 95% CI (0.74, 2.01), P<0.0001) and hemoglobin (Hb) levels [MD=3.89, 95% CI (1.57, 6.20), P=0.001]. In addition, ST36 acupoint injection with dexamethasone can shorten recovery time of myelosuppression [MD=-3.94, 95% CI (-4.97 to -2.91), P<0.00001] and improve Karnofsky performance status [MD=10.7, 95% CI (1.36, 20.05), P=0.02<0.05]. However, there was no significant difference among ST36 acupoint injection with dexamethasone and CWM in platelet (PLT) elevation [MD=4.61, 95% CI (-10.14, 19.35), P=0.54].

Conclusion

This study found that ST36 acupoint injection with dexamethasone had a positive effect on CIM. However, more studies with well-designed, large sample size, strict randomization, and clear descriptions about detection and reporting processes are needed in the future to further confirm the efficacy of ST36 acupoint injection with dexamethasone in the treatment of CIM.

Systematic Review Registration

https://www.crd.york.ac.uk/, identifier CRD42021223979.

Hemostatic changes by thrombopoietin-receptor agonists in immune thrombocytopenia patients

Thrombopoietin receptor agonist (TPO-RA) treatment increases the thrombosis rate in immune thrombocytopenia (ITP). We hypothesize that TPO-RAs influence platelet function, global and secondary hemostasis and/or fibrinolysis. A systematic review was performed. If possible, data were compared between responders (relevant increase in platelet count), and non-responders. Twelve observational studies with 305 patients were included (responders (127/150 (85%))). There were indications that TPO-RA treatment enhanced platelet function, with respect to platelet-monocyte aggregates, soluble P-selectin, GPVI expression, and adhesion under flow. Studies addressing global and secondary hemostasis and fibrinolysis were scarce. Overall, no changes were found during TPO-RA treatment, apart from an accelerated clot formation and conflicting data on levels of plasminogen activator inhibitor (PAI)-1. The parameters that increased have previously been associated with thrombosis in other patient groups, and might contribute to the increased rate of thrombosis observed in TPO-RA-treated ITP patients.

Mechanisms and therapeutic prospects of thrombopoietin receptor agonists

The second-generation thrombopoietin (TPO) receptor agonists eltrombopag and romiplostim are potent activators of megakaryopoiesis and represent a growing treatment option for patients with thrombocytopenic hematological disorders. Both TPO receptor agonists have been approved worldwide for the treatment of children and adults with chronic immune thrombocytopenia. In the EU and USA, eltrombopag is approved for the treatment of patients with severe aplastic anemia who have had an insufficient response to immunosuppressive therapy and in the USA for the first-line treatment of severe aplastic anemia in combination with immunosuppressive therapy. Eltrombopag has also shown efficacy in several other disease settings, for example, chemotherapy-induced thrombocytopenia, selected inherited thrombocytopenias, and myelodysplastic syndromes. While both TPO receptor agonists stimulate TPO receptor signaling and enhance megakaryopoiesis, their vastly different biochemical structures bestow upon them markedly different molecular and functional properties. Here, we review and discuss results from preclinical and clinical studies on the functional and molecular mechanisms of action of this new class of drug.

A sticky situation: myocardial infarction in a young woman with immune thrombocytopenia on eltrombopag and a history of mediastinal radiation

More recent immune thrombocytopenia (ITP) treatment strategies enhance platelet production with the use of thrombopoietin receptor agonists (TPO-RA) such as eltrombopag. Patients receiving TPO-RA agents may be at an increased risk of thromboembolism, however the pathophysiology and common underlying risk factors are not well understood. We present the case of a young asplenic woman on eltrombopag for chronic ITP with acute myocardial infarction involving the right coronary artery. Past medical history was significant for remote mediastinal radiation for lymphoma and splenectomy for ITP. She had no other risk factors for coronary artery disease. She underwent coronary catheterization and balloon angioplasty to the culprit lesion, although stenting was deferred due to concerns with dual antiplatelet therapy. She was discharged from hospital on single antiplatelet therapy with acetylsalicylic acid. We believe that the patient's ITP, recent eltrombopag use, surgical asplenia and history of mediastinal radiation synergistically contributed to her myocardial infarction. The risks of bleeding and thromboembolism must be carefully weighed in patients receiving TPO-RA therapy.

Eltrombopag enhances platelet adhesion by upregulating the expression of glycoprotein VI in patients with chronic immune thrombocytopenic purpura

Eltrombopag, a thrombopoietin receptor agonist, has been approved for the treatment of patients with immune thrombocytopenia because of its abilities to enhance platelet production and reduce hemorrhage. Both platelet count and platelet adhesion are crucial to stop bleeding. Although eltrombopag is known to improve platelet counts, its effects on platelet adhesion are not yet known. This study aimed to assess the efficacy of eltrombopag on platelet production and platelet adhesive affinity. To evaluate the efficacy of low-dose eltrombopag (25 mg) for patients with chronic refractory immune thrombocytopenic purpura (ITP) and to determine the ex vivo platelet adhesion ability before and after treatment with eltrombopag, we conducted an open-label, multicenter study in which 25 Taiwanese patients with chronic ITP were enrolled. During the 6-month evaluation, the starting and maximum doses of eltrombopag were 25 and 50 mg, respectively, to maintain the platelet count of ≥50,000 per μL. Flow-based adhesion assay was used to detect the percentage of platelets adhering to immobilized von Willebrand factor-collagen on microslides. Of the enrolled patients, 48% achieved a platelet count of ≥50,000 per μL. Interestingly, 83% of all responders required 25 mg of eltrombopag daily to achieve the target platelet count. In addition, the percentage of bleeding patients was significantly reduced in both responders and nonresponders by 50% from the baseline level throughout the treatment period. The ex vivo platelet adhesion capacity was elevated after the 6-month eltrombopag treatment in both responders and nonresponders. Furthermore, glycoprotein VI (GPVI) expression was significantly upregulated after treatment with eltrombopag. Low-to-intermediate dose of eltrombopag showed good efficacy to expedite platelet production and augment platelet adhesion. These 2 factors might explain the efficacy of eltrombopag in ameliorating hemorrhage in patients with ITP.

Thrombosis Associated with Viral Hepatitis

Viral hepatitis may promote the development of venous thromboembolism (VTE) and, more specifically, portal vein thrombosis (PVT). In this narrative review, we summarize the clinical data and discuss the possible pathogenetic roles of cytomegalovirus (CMV), Epstein-Barr virus (EBV), and hepatitis A, B, and C viruses (HAV, HBV, HCV) in the occurrence of VTE. CMV is the first qualified candidate to enter the list of VTE minor risk factors, and in the rare case of fulminant infection, both EBV and CMV, like any severe infection or inflammatory disease, increase risk for thrombosis. In chronic hepatitis B and C, it remains controversial whether antiphospholipid antibodies are important for thrombotic complications or merely an epiphenomenon. Retinal vein occlusion described in chronic hepatitis C is usually attributed to the treatment with interferon. Eltrombopag, used for HCV-related thrombocytopenia, has been associated with increased thrombotic risk. The imbalance between procoagulant and anticoagulant factors associated with chronic liver disease may have clinical implications. This may help to explain why these patients are not protected from clinical events such as VTE, PVT, and the progression of liver fibrosis.

First report of elevated monocyte-platelet aggregates in healthy children

Platelets are subcellular fragments which circulate in blood and have well established roles in thrombosis and haemostasis in adults. Upon activation, platelets undergo granule exocytosis and express P-Selectin on the cell membrane which binds a ligand on monocytes, leading to monocyte-platelet aggregation. Elevated circulating monocyte-platelet aggregates in adults are linked to atherothrombosis, but have not been investigated in children where thrombosis is less common. This study aimed to measure monocyte-platelet aggregate formation in children using whole blood flow cytometry. Monocyte-platelet aggregates as well as activation and granule exocytosis of platelets were measured in healthy adults (n = 15, median age 28 years) and healthy children (n = 28, median age 7 years). Monocyte-platelet aggregates in healthy children were elevated compared to healthy adults (37.8±4.4% vs 15.5±1.9% respectively, p<0.01). However, this was not accompanied by any difference in platelet activation (PAC-1 binding 6.8±1.5% vs 6.3±2.0% respectively, p = ns) or granule exocytosis (P-selectin expression 4.4±0.5% vs 3.1±0.5% respectively, p = ns). Despite comparable numbers of platelets bound per monocyte (GPIb MFI 117.3±13.7 vs 130.9±28.6 respectively, p = ns), surface P-selectin expression per platelet-bound monocyte was lower in children compared to adults. We therefore provide the first data of elevated monocyte-platelet aggregates in healthy children.

The role of eltrombopag in the management of hepatitis C virus-related thrombocytopenia

Eltrombopag is a 2nd generation thrombopoietin-receptor agonist. It binds with the thrombopoietin-receptors found on the surfaces of the megakaryocytes & increases platelet production. Many recent studies have suggested a potential role for this novel agent in the treatment of thrombocytopenia associated with hepatitis-C infection. Studies have shown that adjunct treatment with Eltrombopag can help avoid dose reductions/withdrawals of pegylated interferon secondary to thrombocytopenia. It may also have a role in priming up platelet levels to help initiate antiviral therapy. Similarly, chronic liver disease patients with thrombocytopenia who need to undergo an invasive procedure may be potential candidates for short two-week courses of eltrombopag in the periprocedural period to help reduce the risk of bleeding. Besides the price (deemed very expensive and probably not cost-effective), there are some legitimate concerns about the safety profile of this novel agent (most importantly, portal vein thrombosis, bone marrow fibrosis and hepatotoxicity). In this article, the potential role of eltrombopag in the context of hepatitis C virus (HCV)-related thrombocytopenia is reviewed. To write this article, a MEDLINE search was conducted (1990 to November 2012) using the search terms “eltrombopag,” “HCV,” and “thrombocytopenia.”

Function of eltrombopag-induced platelets compared to platelets from control patients with immune thrombocytopenia

Data on the in vivo function of platelets induced by the thrombopoietin receptor agonist eltrombopag are scarce. To assess a possible influence of eltrombopag we compared platelet function of eltrombopag-treated immune thrombocytopenia (ITP) patients (group 1; n=10) after treatment response to that from control ITP patients (group 2; n=12). We further analysed platelet function at baseline and after one, three, and four weeks of eltrombopag treatment and estimated daily changes of platelet function during the eltrombopag-induced platelet rise. The formation of platelet-monocyte aggregates (PMA), P-selectin expression [MFI], and platelet adhesion under high shear conditions (surface coverage, SC) in vivo and after in vitro addition of agonists (ADP, TRAP-6, Collagen) were similar between both groups after response to eltrombopag treatment. Only TRAP-6 induced a lower SC in the eltrombopag group (p=0.03). All platelet function parameters except for Collagen-induced P-selectin expression changed significantly during treatment with eltrombopag. PMA, naïve and after addition of ADP or TRAP-6 increased with increasing platelet counts. P-selectin expression decreased, when measured without and upon addition of ADP, increased in the presence of TRAP-6, and remained unchanged after addition of Collagen. SC increased during the eltrombopag-induced platelet rise. All significant changes of platelet function correlated to changes in platelet counts. Two patients developed venous thromboses during eltrombopag treatment, but no association with any distinct single platelet function parameter or combinations thereof was identifiable. Thus, eltrombopag-induced platelets function similar to those from control ITP patients without discernible increased hyper-reactivity.

Platelets and eltrombopag: a not-so-sticky situation

In this issue of Blood, Psaila and colleagues examine the in vivo effects of eltrombopag, a thrombopoietin receptor agonist (TPO-RA), on platelet function and reactivity.

In vivo effects of eltrombopag on platelet function in immune thrombocytopenia: no evidence of platelet activation

The effects of eltrombopag, a thrombopoietin-receptor agonist, on platelet function in immune thrombocytopenia (ITP) are not fully characterized. This study used whole blood flow cytometry to examine platelet function in 20 patients receiving eltrombopag treatment at days 0, 7, and 28. Platelet surface expression of activated GPIIb/IIIa, P-selectin, and GPIb was measured with and without low and high adenosine diphosphate (ADP) and thrombin receptor activating peptide (TRAP) concentrations. Before eltrombopag treatment with no ex vivo agonist, platelet activation was higher in ITP patients than controls. Platelet GPIb and activated GPIIb/IIIa expression without added agonist was unchanged following eltrombopag treatment, whereas a slight increase in P-selectin was observed. Expression of P-selectin and activated GPIIb/IIIa in response to high-dose ADP was lower during eltrombopag treatment than at baseline. Eltrombopag led to a slight increase in platelet reactivity to TRAP only in responders to eltrombopag but not to levels above those in controls; whole blood experiments demonstrated that this increase was probably because of higher platelet counts rather than higher platelet reactivity. In conclusion, although thrombocytopenic ITP patients have higher baseline platelet activation than controls, eltrombopag did not cause platelet activation or hyper-reactivity, irrespective of whether the platelet count increased.