Anagrelide: new drug. Essential thrombocythaemia: further evaluation needed for this last-resort treatment

(1) For patients aged over 60 years who have essential thrombocythaemia, and are considered to be at increased risk of thromboembolism, the standard cytotoxic agent is hydroxycarbamide (hydroxyurea), which reduces the risk of thrombocytosis but adversely affects other blood cell lines. It may also increase the risk of progression to cancer. (2) Anagrelide, initially studied as an antiplatelet drug, was approved in Europe for the treatment of essential thrombocythaemia in high-risk patients when other treatments fail or are poorly tolerated. (3) Evaluation data includes a trial versus hydroxycarbamide that was prematurely halted because of an excess of cardiovascular events among patients on anagrelide. Among 809 patients who were also receiving aspirin as an antithrombotic (and who may not have met strict criteria for essential thrombocythaemia), arterial or venous thrombosis and haemorrhage were significantly more frequent with anagrelide, during a median follow-up of 39 months (55 versus 36 patients). (4) According to the results of 3 non comparative trials involving about 500 patients, and the European Medicines Agency report analysing these and other study populations, anagrelide reduces the platelet count to below 600 times 10 to the 9th power/litre in two-thirds of patients. No data are available on the clinical implications of this reduction in platelets. (5) Between 10% and 20% of patients treated with anagrelide experience cardiovascular adverse effects (palpitations, myocardial infarction, heart failure) or neurological adverse effects (headache, stroke, transient ischaemic attack). Gastrointestinal disturbances are also frequent (diarrhoea, nausea, abdominal pain, pancreatitis). Some of these adverse effects can be fatal. (6) Follow-up is too short to show whether anagrelide affects the risk of progression to cancer. (7) In practice, anagrelide has a less favourable risk-benefit balance than hydroxycarbamide, which remains the first-line cytotoxic agent in this setting. Anagrelide therapy can be considered if hydroxycarbamide fails or is poorly tolerated, provided patients are included in a long-term clinical trial.