Disclosed is a crystalline salt form which is the sulfate salt of 3-endo-(8-{ 2- [cyclohexylmethyl-((S)-2,3-dihydroxy-propionyl)amino]ethyl} -8-aza-bicyclo[3.2.1]oct-3-yl)benzamide or a solvate thereof. Also disclosed is a process for preparing a crystalline sulfate salt of 3-endo-(8-{ 2-[cyclohexylmethyl-((S)-2,3-dihydroxy-propionyl)amino]ethyl} -8-aza-bicyclo[3.2.1]oct-3-yl)benzamide. Also disclosed is the bisulfite adduct of N-cyclohexylmethyl-(2-oxoethyl)-carbamic acid benzyl ester. Also disclosed is the use of the crystalline salt for the manufacture of a medicament for the treatment of a disease or medical condition in a mammal ameliorated by treatment with a mu opioid receptor antagonist, wherein the disease or condition is opioid-induced bowel dysfunction or post-operative ileus.
