Long-Term Experience with Anagrelide (Thromboreductin®) In the Treatment of Essential Thrombocythemia: Data from an International Registry

In 2001 Thromboreductin® was registered in Austria as the first EU country for the treatment of Essential Thrombocythemia (ET). Due to the low incidence of ET authorities demanded to establish a patient registry to evaluate safety and efficacy of anagrelide in the long-term treatment of ET. Following market authorization in several EU countries the patient registry is now being maintained in 10 Central European countries. Whereas most clinical trials have only a relatively short follow-up, a patient registry is able to provide long-term data.

This multinational, multi-center post-marketing observational registry is conducted to assess long-term efficacy and safety of anagrelide in patients with ET under “real-life” conditions. The clinical information is entered into the registry by the treating physicians. Besides relevant clinical data such as risk factors, past thrombotic as well as bleeding events, disease symptoms classified as “major” and “minor” events and previous ET therapies including anticoagulation, laboratory values including renal and liver function parameters as well as blood counts are monitored regularly.

This evaluation of the Thromboreductin® Patient Registry database includes 1572 ET patients (median age: 59 years), 1059 (67%) were women and 513 (33%) were male patients; 62% of patients were pretreated with cytoreductive agents, 38% were treatment naïve. The median observation period was 1.9 years (range: 7 days – 10 years), with 168 patients (11%) being followed for at least 5 years. Treatment with anagrelide lowered the platelet count from a median of 742 × 10⁹ /l (95%CI 717/757) to a median of 415 × 10⁹ /l (95%CI, 397/435). Eighty-four percent of patients achieved platelet counts < 450 × 10⁹ /l, no differences between pretreated (85%) and treatment-naïve /82%) patients were observed. During the 3464 patient years (PY) included in this evaluation a total of 338 ET-related events (including both thrombotic and bleeding events) were reported of which 102 (2,9% per PY) were considered as “major”. Of the 220 patients with a history of ET-related events, 178 patients (81%) have so far remained event-free under anagrelide therapy. Adverse effects were lower than those previously reported in clinical trials with headache, palpitations and diarrhea being the most frequent side effects (all < 3%) leading to treatment discontinuation in 43 patients (2,7%). No new toxicities have been observed.

We consider anagrelide to be safe and effective in terms of lowering platelet counts and reducing disease-related events in unselected ET patients treated outside clinical trials under “real-life” conditions. Based on our favourable long-term data we suggest that anagrelide may be considered a first-line agent in the management of ET.

Steurer:AOP Orphan Drugs: Honoraria. Petrides:AOP Orphan Drugs: Consultancy.