Efficacy, safety and tolerability of anagrelide in the treatment of essential thrombocythaemia

Ventricular tachyarrhythmia in a 78-year-old woman with essential thrombocythaemia

Anagrelide is a phosphodiesterase-3 inhibitor used in the treatment of essential thrombocythaemia. Cardiovascular side effects such as ventricular tachycardia and cardiomyopathy are rare but potentially fatal and should be made known to patients before starting the medication. It usually arises within the first 6 months after initiation of therapy and may be dose related. The elderly population are particularly susceptible. These cardiotoxicities result from an increase in cyclic AMP that induces positive inotropic and chronotropic effects and are often reversible with cessation of use. We report a case of a 78-year-old woman with essential thrombocythaemia and recently started on anagrelide who presented with syncope and multiple bruises and facial trauma and found to have developed ventricular tachyarrhythmia.

Advances and challenges in the management of essential thrombocythemia

The new World Health Organization (WHO) diagnostic criteria for essential thrombocythemia (ET) issued in 2008 made an important distinction between true ET and early myelofibrosis (MF), which has helped to identify a more homogenous population for the diagnosis with longer survival and much less transformation to overt MF. The recent finding of a new mutation (CALR), which is mutually exclusive with JAK2 and MPL mutations, adds to the characterization of ET patients, since there are important phenotypic differences between the mutation types. CALR patients are younger, have lower white blood cell counts (WBC) and a lower thrombosis incidence. A growing field of interest is the state of hypercoagulation due to dysfunction of hemostatic systems, cell-cell interaction and hereditary prothrombotic traits. Activation of platelets, WBC and endothelial cells has been found, making the whole intravascular milieu prothrombotic. Several risk score models, based on retrospective studies, have been developed lately, distinguishing patient groups with graded risk for complications and death. Even if these may be helpful in evaluating patients, they have not been validated in prospective studies and there are not enough data to support their use as a basis for treatment algorithms. The traditional risk factors age, previous thrombosis and platelets >1500 × 10(9)/l are still recommended for the distinction between high risk and low risk ET and the decision to give cytoreductive therapy. However, cardiovascular (CV) risk factors add to thrombosis risk and should be considered both for specific treatment in any risk group and for upgrading low risk patients with high CV risk to an intermediary group where active therapy with aspirin and cytoreduction may be considered. First-line cytoreductive therapy differs with age; in younger patients interferon (IFN) or anagrelide are preferable, in older patients hydroxycarbamide (HC). Second-line therapy for younger patients is HC, for older patients IFN or anagrelide (ANA). JAK2 inhibitors may be suitable in rare cases with symptoms not responding to other therapy.

Characterization of different regimens for initiating anagrelide in patients with essential thrombocythemia who are intolerant or refractory to their current cytoreductive therapy: results from the multicenter FOX study of 177 patients in France

OBJECTIVES

To identify switch modalities used when initiating second- or third-line anagrelide for essential thrombocythemia (ET), assess whether anagrelide is initiated consistently with Summary of Product Characteristics (SPC) recommendations, and determine whether different observed switch regimens have any relationship with maintenance, platelet response, or tolerability.

METHODS

This observational study was conducted across 43 centers in France. High-risk patients (>60 yr of age and/or history of thrombosis and/or platelet count >1000 × 10(9) /L) with ET starting second- or third-line anagrelide therapy were identified and monitored for 6 months.

RESULTS

A total of 177 patients were enrolled. The SPC-recommended starting dose (1 mg/d) was used in 52.6% of patients; 0.5 mg/d was used in 41.1%. 77.1% of patients underwent an anagrelide dose increase during the study. At 6-month follow-up, 84.7% of patients (n = 144/170) were still receiving anagrelide; 70.6% (n = 120/170) achieved a platelet response. A higher proportion of patients who discontinued previous cytoreductive therapy (CRT) after initiating anagrelide achieved a platelet response (n = 34/39, 87.2%) vs. patients who discontinued their previous CRT before anagrelide initiation (n = 77/115, 67.0%). Platelet response rates were higher in patients whose anagrelide initiation was consistent (n = 100/133, 75.2%) vs. inconsistent (n = 20/37, 54.1%) with the SPC. The incidence of adverse drug reactions was lower in patients whose anagrelide treatment was consistent (n = 52/133, 39.1%) vs. inconsistent (n = 25/37, 67.6%) with the SPC.

CONCLUSIONS

To our knowledge, the FOX study provides the first comprehensive real-world data on the modalities used when switching from previous CRT to anagrelide. Highest platelet responses were observed when previous CRT was discontinued after anagrelide initiation or when anagrelide was initiated consistently with the SPC. Safety data corresponded with the SPC.

Pharmacological management of essential thrombocythemia

INTRODUCTION

Two factors have deeply influenced the area of essential thrombocythemia (ET). A gain-of-function mutation in the pseudokinase region of the JAK2 gene, which partly explains the pathophysiology of myeloproliferative neoplasms (MPNs), was discovered in 2005 and is present in 50 - 60% of ET patients. Furthermore, the 2008 WHO MPN classification outlined criteria for the separation of ET and early or prefibrotic primary myelofibrosis (PMF). However, these and other new findings have not yet changed the pharmacotherapy of ET, which is based on risk stratification for thrombohemorrhagic risk and aims to reduce thrombosis and bleeding.

AREAS COVERED

Studies on the basis for and the validation of the WHO classification as well as studies on possible new risk factors are covered. The most important drugs for ET treatment and consensus recommendations for management of ET are also presented.

EXPERT OPINION

The new WHO classification should be used for both ET studies and clinical practice, since true ET has a different prognosis than early PMF. The management of patients should be based on risk stratification. Age > 60 years or previous throbosis (high risk) and platelet counts > 1500 × 10(9)/l warrant cytoreductive treatment, and high risk patients and selected low risk patients should be given anti-aggregation therapy.

Current treatment practices for essential thrombocythemia: survey results from European hematologists/oncologists

Physicians from nine European countries were asked to complete a survey, which was conducted in two waves (Wave II, October 2009; Wave III, May 2010), based on their current treatment practices for essential thrombocythemia (ET). The aim of the study was to gain insight into physicians' criteria for treatment initiation and reasons for switching from one therapy option to another. The majority of patients receiving first-line cytoreductive therapy for ET were treated with hydroxycarbamide (HC; 63 and 71% in Waves II and III, respectively), while the majority of patients on second-line therapy received anagrelide (51 and 60% in Waves II and III, respectively). Efficacy was the main factor cited for switching therapies (cited by 47 and 58% of physicians in Waves II and III, respectively). Further studies are needed to determine whether current practices used by physicians for the treatment of ET are consistent with consensus guidelines.

A critical review of anagrelide therapy in essential thrombocythemia and related disorders

Thrombocytosis is a common clinical problem and it represents either a primary myeloid disorder (a clonal process) or a reactive phenomenon. While reactive thrombocytosis is often inconsequential, clonal thrombocytosis may require cytoreductive therapy to prevent thrombohemorrhagic complications. In this regard, a controlled clinical trial has previously demonstrated the efficacy of hydroxyurea in reducing the risk of thrombosis in high-risk patients with essential thrombocythemia (ET). Despite the absence of similar evidence for clinical benefit, the platelet-lowering agent anagrelide has been widely used in both ET and polycythemia vera (PV) and recent reports of serious side-effects suggest that such practice might be detrimental to patients. In the current review we provide basic drug information as well as a critical assessment of anagrelide treatment in ET and related disorders.

[Retrospective analysis of the efficacy and tolerability of anagrelide in patients with essential thrombocytemia: Spanish registry of essential thrombocytemia]

BACKGROUND AND OBJECTIVE

A retrospective analysis of a registration database was used to assess the efficacy and tolerability of anagrelide for treating essential thrombocythemia (ET). The study was conducted by analysing information on response to treatment, time to response and tolerability.

PATIENTS AND METHOD

A total of 411 patients with ET from 54 centres in Spain were included in a retrospective chart review. Patients who had started treatment with anagrelide as a first- or second-line therapy before December 31, 2004 were included.

RESULTS

Of 411 patients, anagrelide was given as a first-line therapy in 110 patients, following hydroxyurea in 280 patients, and following other drugs in 21 patients. Overall response (OR) with anagrelide was 81.2% (77,0-84,9; p=0,05). Complete response (platelets <400x10(9)/L) was observed in 53.6% (48,6-58,5; p=0,05) and partial response (<600x10(9)/L) in 27.6% (23,4-32,2; p=0,05) of patients. There was no significant correlation of previous treatment with OR rate (p=0.103) despite a higher OR for previously untreated patients (86.4%) than for previously treated patients (79.3%). The most frequent treatment-related adverse reactions were headache (13.1%), palpitations (10.2%) and tachycardia (7.5%).

CONCLUSIONS

The observed response rates and tolerability profile are similar to those reported previously. Anagrelide is well tolerated and effective in reducing platelets to target levels in patients with ET.

Anagrelide: a review of its use in the management of essential thrombocythaemia

Anagrelide (Agrylin, Xagrid) is an oral imidazoquinazoline agent which is indicated in Europe for the reduction of elevated platelet counts in at-risk patients with essential thrombocythaemia who are intolerant of or refractory to their current therapy, and in the US for the reduction of elevated platelet counts and the amelioration of thrombohaemorrhagic events in patients with thrombocythaemia associated with myeloproliferative disorders. Anagrelide is well established as an effective platelet-lowering agent in most patients with essential thrombocythaemia, including both treatment-naive patients and those refractory to other cytoreductive therapy. Results of the only randomised trial to date (the Primary Thrombocythaemia 1 [PT1] study) indicated that the composite primary endpoint (arterial or venous thrombosis, serious haemorrhage or death from vascular causes) occurred more often in recipients of anagrelide plus aspirin than in those receiving hydroxycarbamide (hydroxyurea) plus aspirin. This trial also indicated that the incidence of the secondary endpoints transient ischaemic attack and gastrointestinal bleeding favoured hydroxycarbamide plus aspirin, while the incidence of venous thrombosis favoured anagrelide plus aspirin. There were no differences between the groups in the incidence of secondary endpoints myocardial infarction, stroke, unstable angina, pulmonary embolism, hepatic-vein thrombosis, other serious haemorrhage or related deaths. The design of the PT1 study has been queried with respect to the heterogeneous nature of the study population (possible inclusion of patients with early myelofibrotic disease) and the concomitant use of aspirin (interaction with anagrelide causing increased bleeding events). Further data are therefore required before the role of anagrelide in essential thrombocythaemia can be finalized. In the meantime, when considering treatment options for patients with this disorder, anagrelide's positive effects on platelet function, lack of mutagenicity and lack of association with leukaemia or angiogenesis must be balanced against its comparative expense and positive inotropic effects. Thus, the role of anagrelide in the management of high-risk patients with essential thrombocythaemia will ultimately depend on individual patient assessment and future clarification of the potential leukaemogenicity of hydroxycarbamide.

Anagrelide for control of thrombocytosis due to myeloproliferative disorders

Myeloproliferative disorders are characterized by overproduction of one or more blood lineages. The clinical course of the Philadelphia-negative myeloproliferative disorders, particularly essential thrombocythemia and polycythemia vera, are characterized by vascular symptoms and in the long-term, transformation to myelofibrosis and leukemia may occur. Control of myeloproliferation has traditionally been achieved using cytotoxic agents but many of these have a documented ability to increase the risk of leukemia. Anagrelide, initially developed as an antiaggregant, is an attractive alternative to these agents as it appears to be relatively selective in reducing the platelet count and is unlikely to be leukemogenic. This article reviews clinical studies in these patients and discusses the future scope for anagrelide.

Anagrelide for thrombocytosis in myeloproliferative disorders: a prospective study to assess efficacy and adverse event profile

BACKGROUND

Although the platelet count does not correlate with the rate of thrombosis, there is evidence that a strict control of the platelet count decreases the incidence of thromboembolic complications in essential thrombocythemia. In the current study, the authors evaluated the efficacy and tolerability of anagrelide in thrombocytosis associated with myeloproliferative disorders.

METHODS

The study cohort comprised 97 patients (n = 69 females, n = 28 males) with a median age of 59 years (range, 21-80 years). Patients with essential thrombocythemia (n = 79) or with thrombocytosis due to polycythemia vera (n = 16) or to chronic idiopathic myelofibrosis (n = 2) were enrolled in the multicenter, prospective study. Patients received anagrelide at a starting dose of 0.5 mg twice per day, which was then adjusted for each patient.

RESULTS

Treatment with anagrelide resulted in a rapid decrease in the platelet count, from a median baseline platelet count of 743 x 10(9)/L to a median platelet count of 441 x 10(9)/L after 6 months (P < 0.0001). The proportion of patients with a platelet count < 600 x 10(9)/L increased from 30% at baseline to 77% after the 6-month study period. The rate of major thrombotic complications significantly decreased from 5% to 2% (P = 0.2568). For patients with essential thrombocythemia, the reduction of major thromboembolic complications was significant (P = 0.0455). The rate of minor thromboembolic complications decreased from 25% before anagrelide treatment to 14% during anagrelide treatment (P = 0.0278). No severe side effects were observed during the study period. There was, however, evidence that concomitant administration of acetylsalicylic acid may increase bleeding tendency.

CONCLUSIONS

Anagrelide was an effective and well tolerated treatment modality for reducing platelet counts in both newly diagnosed and pretreated patients with thrombocytosis due to myeloproliferative disorders.

Current opinion in essential thrombocythemia: pathogenesis, diagnosis, and management

A working diagnosis of essential thrombocythemia (ET) is made in the presence of nonreactive thrombocytosis and after the exclusion of another chronic myeloid disorder that may mimic ET in its presentation. Clinically, ET is characterized by vasomotor symptoms, thrombohemorrhagic complications, recurrent fetal loss, and transformation of the disease into either myelofibrosis with myeloid metaplasia or acute myeloid leukemia. Median survival in the majority of patients is close to that of an age-adjusted normal population, and current therapy has not been shown to either retard or hasten leukemic transformation, which is reported to occur in 1% to 20% of patients. The use of hydroxyurea in high-risk patients with ET has reduced the incidence of thrombosis, and recent studies have suggested the value of keeping the platelet count below 400 x 10(9)/L in such cases. The incidence of thrombosis in low-risk patients may not be high enough to warrant the use of cytoreductive therapy. Although effective in controlling vasomotor symptoms, aspirin therapy has not been shown to influence the risk of either recurrent thrombosis or first-trimester miscarriage in ET. Recent laboratory studies have suggested that hematopoiesis in ET may not always be clonal. Similarly, there is substantial heterogeneity in both megakaryocyte/platelet surface expression of the thrombopoietin receptor (c-Mpl) and bone marrow microvessel density. Clinicopathologic correlates to these biologic parameters are currently being defined.

Recent progress in the pathogenesis and management of essential thrombocythemia

In the last decade, the diagnosis of essential thrombocythemia (ET) has been refined by appreciation of the occurrence of karyotypically occult but molecularly evident chronic myelogenous leukemia and morphologically subtle myelodysplastic syndrome (MDS) and cellular-phase agnogenic myeloid metaplasia (AMM). Although ET continues to be defined by the presence of nonreactive thrombocythemia that is not accounted for by another chronic myeloid disorder, recent studies of clonality and other laboratory parameters have suggested clinically relevant biologic heterogeneity among affected patients. Furthermore, randomized, prospective, and controlled retrospective data have provided additional clinical information that has resulted in the development of risk categories and risk-adjusted treatment recommendations.

Long-term use of anagrelide in young patients with essential thrombocythemia

Anagrelide is a novel platelet-lowering agent that has recently been approved for use in essential thrombocythemia (ET) and related disorders. Short-term drug efficacy and toxicity data have previously been presented. The purpose of this study was to obtain additional information regarding long-term anagrelide use. This is a retrospective series of 35 young patients (17 to 48 years) with ET who received anagrelide treatment before 1992. Initial drug dosage ranged between 1 and 10 mg/d, and the median maintenance dosage was 2.5 mg/d. The overall initial response rate of 94% included 74% complete remissions and 20% partial remissions. Of the 33 responding patients, 27 (82%) remained on anagrelide therapy for a median of 10.8 years (range, 7 to 15.5). Of these, 66% maintained a complete and 34% a partial remission over the study period. In general, the reporting of somatic side effects decreased over time, and anemia was the only new side effect that emerged after long-term therapy. Eight patients (24%) experienced a more than 3 g/dL decrease in hemoglobin level. Despite active therapy, 20% of the patients experienced a total of 10 thrombotic episodes, and a similar proportion experienced major hemorrhagic events. All thrombohemorrhagic complications occurred at a platelet count of more than 400 x 10(9)/L. It is concluded that long-term treatment of ET with anagrelide is associated with decreased reporting of initial side effects and the development of mild-to-moderate anemia. Complete normalization of platelet counts may be needed to minimize residual thrombohemorrhagic risk during therapy. (Blood. 2001;97:863-866)

Anagrelide-induced cardiomyopathy

Anagrelide, a selective thrombocytopenic agent, is administered to treat a variety of hematologic disorders. Despite limited clinical experience with this drug, serious cardiovascular events, including congestive heart failure, have been reported. The proposed mechanism of cardiotoxicity is attributed to inhibition of phosphodiesterase, resulting in positive inotropic activity and vasodilation. A 48-year-old woman with polycythemia vera developed cardiotoxicity manifested by congestive heart failure and palpitations. It was suspected to be temporally related to titrating dosages of anagrelide.

Essential thrombocythaemia

Essential thrombocythaemia (ET) is a clonal stem cell disorder that frequently presents as an incidental finding of elevated platelet counts. Diagnosis depends on exclusion of other myeloproliferative disorders and reactive thrombocytosis. Patients with platelet counts above 1000 x 10(9)/L should receive platelet-lowering therapy, even if asymptomatic. Definitive recommendations cannot yet be made for asymptomatic patients with lower platelet counts. ET can be treated with alkylating agents, radioactive phosphorus or hydroxyurea, but there is evidence that these agents increase transformation to acute leukaemia. Interferon alfa-2a and anagrelide are useful treatment agents, particularly in younger patients.