Anagrelide, a therapy for thrombocythemic states: experience in 577 patients. Anagrelide Study Group.

PURPOSE: To evaluate the safety and efficacy of anagrelide when used to reduce platelet counts in patients with thrombocytosis.

PATIENTS AND METHODS: Five hundred seventy-seven patients were treated with anagrelide to control the thrombocytosis of chronic myeloproliferative diseases. Three hundred thirty-five patients had primary thrombocythemia, 114 chronic granulocytic leukemia, 68 polycythemia vera, and 60 undifferentiated myeloproliferative diseases. Of the 577 patients, 504 were known to have been previously treated unsuccessfully with other modalities.

RESULTS: Of the 577 patients treated, 424 were evaluable for response. Anagrelide in doses of 0.5 mg to 1.0 mg four times a day reduced the platelet count by 50%, or to less than 600,000/mm3, for at least 28 days in 396 of the 424 (93%) evaluable patients. Acquired resistance to the drug was not observed. Major side effects were neurologic, gastrointestinal, and cardiac. In more than 5 years, 16% of patients discontinued treatment because of side effects.

CONCLUSIONS: Our experience suggests that anagrelide should become a useful agent in controlling the thrombocythemia seen in chronic myeloproliferative diseases and can be effective in patients in whom treatment with currently available agents has failed.