The invention relates to sulfonamide derivatives, to their use in medicine, to compositions containing them, to processes for their preparation and to intermediates used in such processes. More particularly the invention relates to a new sulfonamide Nav1.7 inhibitors of formula (I): or a pharmaceutically acceptable salt thereof, wherein X, Ar 1 , R 1 , R 2 , R 3 , R 4 and R 5 are as defined in the description. Nav 1.7 inhibitors are potentially useful in the treatment of a wide range of disorders, particularly pain.