Phase II study of avatrombopag in thrombocytopenic patients with cirrhosis undergoing an elective procedure

Thrombocytopenia in chronic liver disease

Thrombocytopenia is a common haematological disorder in patients with chronic liver disease. It is multifactorial and severity of liver disease is the most influential factor. As a result of the increased risk of bleeding, thrombocytopenia may impact upon medical procedures, such as surgery or liver biopsy. The pathophysiology of thrombocytopenia in chronic liver disease has long been associated with the hypothesis of hypersplenism, where portal hypertension causes pooling and sequestration of all corpuscular elements of the blood, predominantly thrombocytes, in the enlarged and congested spleen. Other mechanisms of importance include bone marrow suppression by toxic substances, such as alcohol or viral infection, and immunological removal of platelets from the circulation. However, insufficient platelet recovery after relief of portal hypertension by shunt procedures or minor and transient recovery after splenic artery embolization have caused many to question the importance and relative contribution of this mechanism to thrombocytopenia. The discovery of the cytokine thrombopoietin has led to the elucidation of a central mechanism. Thrombopoietin is predominantly produced by the liver and is reduced when liver cell mass is severely damaged. This leads to reduced thrombopoiesis in the bone marrow and consequently to thrombocytopenia in the peripheral blood of patients with advanced-stage liver disease. Restoration of adequate thrombopoietin production post-liver transplantation leads to prompt restoration of platelet production. A number of new treatments that substitute thrombopoietin activity are available or in development.

Pharmacokinetics, Pharmacodynamics, Pharmacogenomics, Safety, and Tolerability of Avatrombopag in Healthy Japanese and White Subjects

Avatrombopag, an orally administered, small-molecule thrombopoietin receptor (c-Mpl) agonist, is currently in clinical development for the potential treatment of severe thrombocytopenia in patients with chronic liver disease undergoing an elective procedure. The objectives of this study were to characterize and compare the pharmacokinetics (including the food effect) and pharmacodynamics (platelet count) of avatrombopag following single doses in Japanese and white subjects. Following single dosing under fasted and fed conditions, mean peak concentrations occurred at 5 to 8 hours and subsequently declined with a half-life of 16 to 18 hours in Japanese and white subjects. Administration with food did not alter the rate or extent of avatrombopag absorption but substantially reduced pharmacokinetic variability relative to the fasted state. CYP2C9 polymorphism (*2, *3) was associated with higher pharmacokinetic variability but not with any clinically important effect on variability in platelet response. Plasma exposures of avatrombopag increased in a dose-proportional manner over the dose range tested. After a single dose, platelet count increased in a dose-related manner, reaching a maximum by day 11 and returning to baseline levels by day 27. No clinically important differences were found when avatrombopag pharmacokinetics and pharmacodynamics were compared between Japanese and white subjects. Administration of avatrombopag was generally well tolerated.

Platelets in liver and renal disease

This review will discuss how 2 common and morbid conditions, renal disease and liver disease, alter platelet number and function. It will review the impact of thrombocytopenia on bleeding complications in patients with these disorders and whether the low platelet count actually correlates with bleeding risk. Emerging data also suggest that platelets are much more than bystanders in both renal and liver disease, but instead play an active role in the pathobiology of these disorders. This review will briefly cover the emerging information on novel roles of platelets in the biology of renal and liver disease.

Management of Thrombocytopenia in Chronic Liver Disease: Focus on Pharmacotherapeutic Strategies

Thrombocytopenia (platelet count <150 × 10⁹/L) often complicates chronic liver disease, impeding optimal management of these patients. The prevalence of this manifestation ranges from 6 % among non-cirrhotic patients with chronic liver disease to 70 % among patients with liver cirrhosis. It has also been shown that the severity of liver disease is associated with both prevalence and level of thrombocytopenia. Its development is often multifactorial, although thrombopoietin is thought to be a major factor. The discovery of and ability to clone thrombopoietin led to new treatment opportunities for this clinical manifestation. This review discusses data on the three most important thrombopoietin receptor agonists: eltrombopag, avatrombopag, and romiplostim. Currently, only eltrombopag is approved for usage among patients with thrombocytopenia and chronic hepatitis C virus infection in order to initiate and maintain interferon-based antiviral treatment. Nevertheless, the optimal management of hematologic abnormalities among patients with chronic liver disease, and its risk for bleeding complications, is still a matter of discussion. Thrombocytopenia definitely contributes to hemostatic defects but is often counterbalanced by the enhanced presence of procoagulant factors. Therefore, a thorough assessment of the patient’s risk for thrombotic events is essential when the use of thrombopoietin receptor agonists is considered among patients with chronic liver disease and thrombocytopenia.

Determinants of platelet count are different in patients with compensated and decompensated cirrhosis

BACKGROUND & AIMS

Different mechanisms including portal hypertension and hypersplenism have been involved in the development of thrombocytopenia in cirrhosis. However, the relative contribution of each one is unknown. The aim was to evaluate simultaneously different mechanisms that determine platelet count in cirrhosis.

METHODS

Cross-sectional study including cirrhotics (n = 120) with hepatic venous pressure gradient (HVPG) measurement. Samples were obtained from peripheral (P) veins to evaluate thrombopoietin (TPO), stem cell factor, hepatocyte growth factor (HGF), tumour necrosis factor, interleukin-(IL6) and (IL11) and from hepatic (H) veins to evaluate TPO. A subgroup (n = 72) had spleen volume estimation. H and P-TPO were also measured in non-cirrhotic patients (n = 15).

RESULTS

Patients (Child A: 55, B: 43, C: 22) had a median platelet count of 81 000/mm(3) (IQR 60 500, 110 750), which correlated with spleen volume (r = -0.38, P < 0.001). Platelets were associated also to HVPG (r = -0.47, P = 0.004) and P-TPO (r = 0.31, P = 0.050) only in compensated patients. H-TPO decreased, and the proportion of patients with P-TPO > H-TPO increased, with the presence and the severity of liver disease. H-TPO was correlated with liver function (bilirubin r = -0.350, P < 0.001 and international normalized ratio r = -0.227, P = 0.011). Patients with H-TPO < P-TPO had higher levels of IL-11 and HGF.

CONCLUSION

Platelet count in cirrhosis is associated mainly to spleen volume, although portal hypertension as estimated by HVPG and liver function plays a significant role in compensated patients. H-TPO and the proportion of patients with P-TPO > H-TPO were associated to the presence and severity of liver disease.

The Use of Thrombopoietin Receptor Agonists for Correction of Thrombocytopenia prior to Elective Procedures in Chronic Liver Diseases: Review of Current Evidence

Patients with chronic liver diseases (CLD) undergo a range of invasive procedures during their clinical lifetime. Various hemostatic abnormalities are frequently identified during the periprocedural work-up; including thrombocytopenia. Thrombocytopenia of cirrhosis is multifactorial in origin, and decreased activity of thrombopoietin has been identified to be a major cause. Liver is an important site of thrombopoietin production and its levels are decreased in patients with cirrhosis. Severe thrombocytopenia (platelet counts < 60-75,000/µL) is associated with increased risk of bleeding with invasive procedures. In recent years, compounds with thrombopoietin receptor agonist activity have been studied as therapeutic options to raise platelet counts in CLD. We reviewed the use of Eltrombopag, Romiplostim, and Avatrombopag prior to various invasive procedures in patients with CLD. These agents seem promising in raising platelet counts before elective procedures resulting in reduction in platelet transfusions, and they also enabled more patients to undergo the procedures. However, these studies were not primarily aimed at comparing bleeding episodes among groups. Use of these agents had some adverse consequences, importantly being the occurrence of portal vein thrombosis. This review highlights the need of further studies to identify reliable methods of safely reducing the provoked bleeding risk linked to thrombocytopenia in CLD.

Changing common sense: Anti-platelet/coagulation therapy against cirrhosis

Until recently, anti-platelet/coagulation therapy had not been recommended for patients with cirrhosis. Although venous thrombosis is one of the representative complications of cirrhosis and ischemic disorders associated with atherosclerosis are not infrequent in cirrhotic patients, many clinicians have tended to hesitate to introduce anti-platelet/coagulation therapy to their patients. Undoubtedly, this is due to the increased risk of hemorrhagic diathesis in cirrhotic patients. However, accumulating evidence has revealed the benefits of anti-platelet/coagulation therapy for cirrhotic patients. In addition to the safety of the therapy carried out against cardiovascular diseases in cirrhotic patients, some clinical data have indicated its preventive effect on venous thrombosis. Moreover, the efficacy of anti-platelet/coagulation therapy against cirrhosis itself has been demonstrated both clinically and experimentally. The conceptual basis for application of anti-platelet/coagulation therapy against cirrhosis was constructed through two pathologic studies on intrahepatic thrombosis in cirrhotic livers. It may be better to use thrombopoietin-receptor agonists, which have been tested as a treatment for cirrhosis-related thrombocytopenia, in combination with anti-platelet drugs to reduce the risk of venous thrombosis. During the last decade, the World Journal of Gastroenterology, a sister journal of World Journal of Hepatology, has been one of the main platforms of active discussion of this theme.

Novel insights into the development of portal vein thrombosis in cirrhosis patients

The prognostic impact of portal vein thrombosis (PVT) in liver cirrhosis remains controversial among studies, primarily because the risk stratification of PVT is often lacking. A definition of clinically significant PVT should be proposed and actively improved. Moreover, the risk factors for the development of PVT in liver cirrhosis should be fully recognized to screen and identify high-risk patients. Currently, well-recognized risk factors include a reduced portal vein flow velocity, a worse liver function, splenectomy, liver transplantation, and factor V Leiden and prothrombin G20210A mutations. Novel risk factors include an increased flow volume of portosystemic collateral vessel, thrombopoietin receptor agnonists, and non-selective beta-blockers. In contrast to the traditional perspectives, the abnormalities of procoagulant and anticoagulant factors may not contribute to the development of PVT in liver cirrhosis. Further studies should explore the role of other risk factors, such as antiphospholipid antibodies, methylenetetrahydrofolate reductase C677T gene mutation, hyperhomocysteinemia, and myeloproliferative neoplasms.

Coagulopathy in liver disease: a balancing act

Liver disease results in complex alterations of all 3 phases of hemostasis. It is now recognized that hemostasis is rebalanced in chronic liver disease. The fall in clotting factor levels is accompanied by a parallel fall in anticoagulant proteins. High von Willebrand factor levels counteract defects in primary hemostasis. Conventional coagulation tests do not fully reflect the derangement in hemostasis and do not accurately predict the risk of bleeding. Global coagulation assays (thrombin generation, thromboelastography) reflect the interaction between procoagulant factors, anticoagulant factors, platelets, and the fibrinolytic system and show promise for assessing bleeding risk and guiding therapy. These assays are not yet commercially approved or validated. Prevention of bleeding should not be aimed at correcting conventional coagulation tests. Thrombopoietin receptor agonists were shown to increase the platelet count in cirrhotic patients undergoing invasive procedures but may increase the risk of thrombosis. Rebalanced hemostasis in liver disease is precarious and may be tipped toward hemorrhage or thrombosis depending on coexisting circumstantial risk factors. Bacterial infection may impair hemostasis in cirrhosis by triggering the release of endogenous heparinoids. There are no evidence-based guidelines for hemostatic therapy of acute hemorrhage in liver disease. There is currently inadequate evidence to support the use of recombinant FVIIa, prothrombin complex concentrates, or tranexamic acid in acute variceal or other hemorrhage.