Background : Thrombocytosis can result in life-threatening thrombotic or hemorrhagic events. Anagrelide acts exclusively on megakaryocytes and has been reported as an useful agent in controlling thrombocytosis associated with chronic myeloproliferative disorders.
Methods: Seven patients with essential thrombocythemia and three with chronic myelogenous leukemia were enrolled and early responses and adverse effects of anagrelide were retrospectively analyzed. The drug was started with a dose of 2 mg/day with increases of 0.5 mg/day every 5~7 days as needed.
Results : Anagrelide in starting doses of 2 mg/day reduced the platelet count by 50%, or to less than 600,000/㎣, for at least 28 days in 7 of the 9 (78%) evaulable patients. Adverse effects of the drug were observed in 5 patients and generally well tolerated; headache in 4, gastrointestinal troubles in 2, palpitations and chest tightness in 1, and tinnitus in 1. Changes in hemoglobin or white blood cell counts in peripheral blood were minimal and tolerable.
Conclusion : The present study shows that anagrelide is a useful platelet-lowering agent in whom hydroxyurea or interferon has failed. Long-term efficacy and adverse effects of the drug remain to be determined.

Keywords: Anagrelide, Thrombocytosis, Essential thrombocythemia, Chronic myeloenous leukemia,