New pharmaceutical compositions containing N- {3- [3-cyclopropyl-5- (2-fluoro-4-iodo-phenylamino) -6,8-dimethyl-2,4,7-trioxo- dimethyl sulfoxide solvate are described 3,4,6,7-tetrahydro-2H-pyrido [4,3-d] pyrimidin-1-yl] phenyl} acetamide, methods for using the compositions in therapy and procedures for preparing them.