Studies of platelet volume, chemistry and function in patients with essential thrombocythaemia treated with Anagrelide

Anagrelide (imidazoquinazolin derivative) is a new compound proposed for the treatment of myeloproliferative disorders. In this study, Anagrelide was given to patients with essential thrombocythaemia (ET) in a compassionate-use protocol. The aim of this study was to test the effect of this drug not only on the platelet count but also on platelet volume, chemistry and function, which has not previously been reported. Thus, in ET, different functional or structural platelet abnormalities were reported: a shortening of the bleeding time, hypoaggregation to several agonists, and in particular a lack of response to adrenalin, an increase in the amount of total platelet glycoprotein IV (or CD36), and an abnormal migration of thrombospondin on electrophoresis. These different parameters were studied before and during therapy with Anagrelide. Although the platelet count was corrected, no functional or chemical abnormality was improved. Furthermore, platelet volume was shown to be constantly increased under Anagrelide. Thus, Anagrelide, in reducing the platelet count, may possibly decrease the risk of thrombosis and haemorrhage. Nevertheless, if the risk of thromboses and/or myelofibrosis is related not only to the platelet count but also to the platelet abnormalities, the persistence of a thrombocytopathy in patients treated with Anagrelide must be taken in consideration. Our data suggest that thromboses and myelofibrosis are clinical end-points which should be included in future large-scale use of Anagrelide.