Efficacy of Anagrelide Compared with Hydroxyurea in Patients with Essential Thrombocythemia.

The essential thrombocythemia (ET) is characterized by thrombohemorrhagic risk. ET patients receiving HU and anti-aggregants show normal platelets but present platelet coagulant and endothelial aggregation. Anagrelide (ANA) is a platelet-lowering drug that inhibits platelet aggregation. Therefore, we evaluated platelets, platelet factor 4 (PF4), prothrombin fragment 1+2 (F1+2), thrombin antithrombin complex (TAT) and d-dimer (DD) and von Willebrand factor (vWF) as markers of platelet coagulant and endothelial aggregation, respectively, in ET patients treated either with HU or ANA. All measurements were performed before treatment and when complete response, defined as platelet < 400 x10⁹/L for more than 1 month, was achieved. Prolonged thrombocytosis causes thrombohemorrhagic risk. Hence, we investigated the cytoreduction time. The study comprised 36 patients (19 men, 17 women; mean age 65 years) who fulfilled PVSG and WHO. The mean duration of disease was 6 years. 17 patients received HU and 19 patients were on ANA. The average dose of HU was 0.5 g/d. ANA was initially administered at a dose of 0.5 mg/d. The dose was increased by 0.5 mg/d every week until the platelets had decreased to below 400 x 10⁹/L. The average maintenance was 1.7 mg/d. All patients were on aspirin at dose of 100 mg/d and 50 mg/d in HU and ANA group, respectively. None of the patients had acquired or inherited thrombotic risk factors or had inherited coagulopathy. Eleven out of 17 HU patients (5 men, 6 women; mean age 68.6 years) developed thrombosis including six transient ischemic attack (TIA), three myocardial infarct (MI) and two deep venous thrombosis (DVT). The thrombosis occurred at a median time from diagnosis of 2 years. The ANA group did not experience thrombosis. Platelets were determined by automated analyser. PF4, F1+2, TAT and DD and vWF were assayed by ELISA and immunoturbidimetric assay, respectively. Before treatment, all patients had high platelets (1027±297 x 10⁹/L) and elevated PF4, F1+2, TAT and DD (134±48 IU/mL vs 6±2 IU/mL, 3±2 nmol/L vs 0.6±0.2 nmol/L, 25±34 μg/L vs 2.7±1 μg/L, 224±172 μg/L vs 197±43 μg/L, respectively) (p< 0.0001, p<0.0001, p<0.0001 and p<0.0001, respectively) and low vWF (23±9% vs 102±30%) (p<0.0001). After treatment all patients had platelets <400 x 10⁹/L (364 ±77 x 10⁹/L), whereas PF4, F1+2, TAT and DD were higher (147±45 IU/mL, 3±2 nmol/L, 24±41 μg/L and 264±291 μg/L, respectively) and vWF was lower (34±9.9%) in HU group than controls (p<0.0001, p<0.0001, p<0.0001, p=0.001 and p<0.0001, respectively) and normal in ANA group (7±3 IU/mL, 1.1±0.8 nmol/L, 2.4±1.1 μg/L, 121±84 μg/L and 95±37%, respectively). The mean cytoreduction time was 3.2 and 1.8 months in HU and ANA group, respectively. A correlation there was between PF4 and F1+2 and TAT and DD and vWF (p=0.004, p=0.005, p=0.022 and p<0.0001, respectively). vWF did not correlate with F1+2, TAT and DD. Platelets did not correlate with thrombosis, whereas a correlation there was between PF4, F1+2, TAT and DD and thrombosis (p<0.0001, p=0.015, p=0.005 and p=0.034, respectively). A difference was observed in cytoreduction time between HU and ANA (p<0.0001). These results might support the superiority of ANA as antithrombotic drug besides its platelet-lowering effect.