Hydroxyurea for Patients with Essential Thrombocythemia and a High Risk of Thrombosis

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Abstract
Abnormalities in the number and function of platelets may contribute to thromboembolic complications in patients with essential thrombocythemia. We assessed whether maintaining the platelet count below 600,000 per cubic millimeter with hydroxyurea reduces the incidence of thrombosis in patients with essential thrombocythemia and a high risk of thrombosis. A total of 114 patients with essential thrombocythemia (77 women and 37 men; median age, 68 years; range, 40 to 85) and a median platelet count of 788,000 per cubic millimeter (range, 533,000 to 1,240,000 per cubic millimeter) were randomly assigned to receive hydroxyurea (56 patients) or no myelosuppressive therapy (58 patients). Ninety-seven (85 percent) were over 60 years old, and 52 (46 percent) had had thrombosis. The two groups were matched for age, sex, and platelet count at randomization. Antiplatelet prophylaxis with aspirin or ticlopidine was not stopped. Follow-up lasted a median of 27 months in both groups. Two patients (3.6 percent) treated with hydroxyurea had thrombotic episodes (one stroke and one myocardial infarction), whereas 14 patients (24 percent) in the control group had thrombotic episodes (one stroke, five transient ischemic attacks, five peripheral arterial occlusions, one deep-vein thrombosis, and two cases of superficial thrombophlebitis). The difference (20.4 percentage points; 95 percent confidence interval, 8.5 to 32 percent) was statistically significant (chi-square with Yates' correction, 8.3; 1 df; P = 0.003). Hydroxyurea is effective in preventing thrombosis in high-risk patients with essential thrombocythemia.