Lubiprostone is a pharmaceutical that is sold under the trademark Amitiza™. Methods for stabilizing a lubiprostone by dissolving lubiprostone in a glyceride are known in the art. Also known are a method of stabilizing lubiprostone by admixing lubiprostone with a polyol and/or fatty acid ester other than glyceride and a composition obtained by the method. In addition a soft gelatin capsule formulation of lubiprostone obtained by incorporating lubiprostone in a soft gelatin capsule shell comprising gelatin and a polyol plasticizer is also known.
Also known in the art is a soft gelatin capsule formulation of lubiprostone, which comprises: a soft gelatin capsule shell comprising gelatin and sugar alcohol as a plasticizer, and a mixture comprising a 15-keto-prostaglandin compound and a pharmaceutically acceptable vehicle which is filled in the shell. By encapsulating the lubiprostone in the specified soft gelatin capsule shell, stability of the compound is significantly improved.