MDM2 and neutropenia: However, interim data from the advanced solid tumour arm of the trial show that RO6839921 was generally well tolerated and main dose limiting toxicities observed were thrombocytopenia and neutropenia, in line with adult trial data for oral idasanutlin, as well as other MDM2 inhibitors.16, 41, 42, 43 Gastrointestinal toxicity was reported but not dose limiting as previously reported with oral Idasanutlin.15, 16 The current emphasis is on the development of the oral formulation of idasanutlin, which in comparison to the IV formulation, is at a later stage of development (Phase 3 in AML).