Disclosed are novel pharmaceutical compositions containing N-{3-[3-cyclopropyl-5-(2-fluoro-4-iodo-phenylamino)-6,8-dimethyl-2,4,7-trioxo-3,4,6,7-tetrahydro-2H-pyrido[4,3-d]pyrimidin-1-yl]phenyl}acetamide dimethyl sulfoxide solvate, methods of using the compositions in therapy and processes for preparing the same.L'invention concerne de nouvelles compositions pharmaceutiques contenant un N-{3-[3-cyclopropyl-5-(2-fluoro-4-iodo-phénylamino)-6,8-diméthyl-2,4,7-trioxo-3,4,6,7-tétrahydro-2H-pyrido[4,3-d]pyrimidin-1-yl]phényl}acétamide diméthyl sulfoxyde solvate, des procédés d'utilisation des compositions en thérapie et leurs procédés de préparation.