A total of 809 patients with essential thrombocythaemia who were at high risk for vascular events (age at least 60 years, platelet count>1000, history of thrombosis, haemorrhage, hypertension, diabetes) were randomized to receive either hydroxyurea or anagrelide at a dose that maintained the platelet count under 400 1. All patients received aspirin 75-100mg/day. The risk of a composite primary end point (myocardial infarction, unstable angina, cerebral ischaemia, peripheral arterial trombosis, venous thrombosis, serious haemorrhage or death from thrombotic or haemorrhagic causes) was higher with anagrelide than with hydroxyurea (OR 1.57, 95% CI 1.04 to 2.37). Anagrelide was associated with increased rates of arterial thrombosis, serious haemorrhage, and transformation to myelofibrosis, but decreased rates of venous thombosis.
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