Crystalline forms, including salts and polymorphs, of a compound useful in the treatment of tetracycline compound-responsive states are provided herein. The crystalline compounds are useful for the treatment or prevention of conditions and disorders such as bacterial infections and neoplasms, as well as other known applications for tetracycline compounds in general.本發明提出可用於治療對四環素化合物有反應狀態之化合物的結晶形,包括其鹽類與同素異形體。該結晶化合物可用於治療或預防諸如細菌感染與腫瘤之狀態與病症,以及四環素化合物一般之習知應用。