Spotlight on anagrelide hydrochloride for the treatment of essential thrombocythemia

Anita Sarma,1 Donal P Mclornan,1,2 Claire N Harrison2 1Department of Haematology, King’s College Hospital NHS Foundation Trust, 2Department of Haematology, Guy’s and St Thomas’ NHS Foundation Trust, London, UK Abstract: Anagrelide (ANA) hydrochloride is an oral imidazoquinazoline registered as an orphan drug in Europe. It is indicated as a second-line agent for the reduction of thrombocytosis in high-risk essential thrombocythemia (ET) in Europe and in any myeloproliferative neoplasm-associated thrombocytosis and for the amelioration of thrombo-hemorrhagic events in the context of myeloproliferative neoplasm in the USA and Japan. The compound has been in clinical use for almost two decades with approval in the European Union (EU) for over a decade. The licensed indication encompasses the apparently specific action of the drug to reduce the platelet count; however, the precise mode of action of ANA remains unclear. Here, we review the current data from two large phase 3 studies, PT-1 and ANAHDRET, and a phase 4 post-approval observational study EXELS. All of these studies were conducted in the EU and therefore pertain to ET as the only licensed indication. Data from these studies suggest that ANA is on the whole as effective as the most commonly used agent hydroxycarbamide (HC). Although ANA, when compared to HC, appears to be slightly less effective in preventing arterial thrombosis and myelofibrotic transformation, it is associated with lower risk of venous thrombosis. Since the initial data from the PT-1 study, a caution has been recommended for the combined use of ANA and aspirin as this may provoke excess hemorrhage. ET is a clinically and biologically heterogeneous condition, and these biological variations may in part explain some of the clinical differences observed in various studies in response to specific treatments. No new toxicities of ANA have emerged in the past decade, which means that clinicians and patients can be reassured about the efficacy and safety of this agent, which is of particular importance in a chronic condition such as ET. Keywords: anagrelide, essential thrombocythemia, PT-1, ANAHYDRET, EXEL