Implications of the consensus definition of clinical resistance and intolerance to hydroxyurea for clinical practice.

The consensus-based definition for clinical resistance and intolerance to hydroxyurea (HU) (1) is intended to facilitate a more consistent approach to the management of essential thrombocythaemia (ET). In particular, the definition is designed to aid clinical decision-making regarding whether treatment with HU should be stopped or switched to an alternative agent such as anagrelide or a-interferon. However, incorporation of the definitions into clinical practice may vary between clinicians working in different countries, for example, due to differences in national treatment guidelines, patient populations, and the regulatory and reimbursement status of different medications. The implications of the consensus definition for clinical practice in different regions of the world were examined at the 2007 ‘New Horizons in Haematology’ meeting within country-based workshops. Discussions were framed around key topics including the importance of the definition in clinical practice, the use of platelet counts for defining treatment targets and HU resistance and the importance of muco-cutaneous side effects as a criterion for HU intolerance. The workshops were chaired by experts from each region who had been involved in the development of the consensus. The panel of experts then assessed the anticipated impact of the consensus definition on clinical practice and identified the areas of agreement and differences between countries. In this article, I will summarise the key issues identified during the country workshops as chairperson of the expert panel. Importance of the definition in clinical practice