Ruxolitinib is a pyrazole substituted at position 1 with a 2-cyano-1-cyclopentylethyl group and at position 3 with a pyrrolo[2,3-d]pyrimidin-4-yl group. It is used as the phosphate salt in the treatment of intermediate or high-risk myelofibrosis, including primary myelofibrosis, post-polycythemia vera myelofibrosis, and post-essential thrombocythemia myelofibrosis. It functions as an antineoplastic agent and a non-specific protein-tyrosine kinase inhibitor (EC 2.7.10.2). It is a nitrile, a pyrrolopyrimidine, and a member of pyrazoles.
