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.