PRECIPITOUS FALL IN PLATELET COUNT WITH ANAGRELIDE - CASE-REPORT AND CRITIQUE OF DOSING RECOMMENDATIONS

Thrombotic and hemorrhagic events may result from high circulating con centrations of platelets (> 1,000,000/mm(3)), and measures to reduce t he platelet count are indicated in symptomatic or extreme thrombocytos is. The platelet count can be decreased quickly by plasmapheresis, but the effect is transient. Patients with thrombocytosis secondary to a myeloproliferative disease, such as chronic myelogenous leukemia (CML) , frequently require more sustained suppression of the platelet count. Hydroxyurea, busulfan, and interferon are used to maintain a lower pl atelet count but are occasionally ineffective or intolerable. An alter native to these therapies is anagrelide, a quinazolin derivative that was approved by the Food and Drug Administration in March 1997. Becaus e current dosing guidelines for anagrelide are scarce, the dosing meth od of the Anagrelide Study Group that published the largest study to d ate on the drug's efficacy in thrombocytosis was followed. Two unexpec ted episodes of anagrelide-induced thrombocytopenia occurred despite f ollowing these dosing methods. This prompted a critical evaluation of the pharmacodynamic response and the appropriateness of anagrelide dos age recommendations. A case of thrombocytosis treated with anagrelide in a patient with CML is described.