The object of the present invention is to provide a pharmaceutical composition for the treatment of various diseases associated with renal dysfunction.The renal dysfunction is improved by the pharmaceutical composition comprising an optical isomer of a 1,4-benzothiazepine-1-oxide derivative represented by the following general formula [II] or a pharmaceutically acceptable salt thereof.(Wherein, R represents a hydrogen atom or a hydroxyl group. * Represents an optical isomer.)本發明之課題係提供一種用以治療伴隨腎功能障礙之各種疾病的醫藥組成物。藉由含有下述通式[II]所示之1,4-苯并硫氮呯-1-氧化物衍生物之光學異構物或其藥學上容許之鹽而構成之醫藥組成物，可改善腎功能障礙。(式中，R表示氫原子或羥基。＊表示光學異構物。)
