Formation and physical stability of the amorphous phase of ranitidine hydrochloride polymorphs prepared by cryo-milling

Abstract

The effect of cryo-milling on ranitidine hydrochloride polymorphs form 1 and 2 was investigated with particular interest in the formation and the stability of the amorphous phase. Cryo-milling was carried out using an oscillatory ball mill for periods up to 60 min, with re-cooling of the milling chamber with liquid nitrogen at 15 min intervals. Results showed that both ranitidine hydrochloride form 1 and form 2 could be fully converted to the amorphous form as determined by XRPD within 30 min. Upon 14 days storage, the amorphous samples crystallized back to their original forms. In the stability studies of amorphous drug with seeds, significant polymorphic transformation from form 1 to form 2 was not found when amorphous form prepared from form 1 was seeded with form 2 crystals by gentle physical mixing. In contrast, amorphous form prepared from form 1 seeded with form 2 crystals by ball milling for 1 min and simultaneous cryo-milling methods were found to transform amorphous form prepared from form 1 to crystalline form 2 under some storage conditions. The transformation was thought to be facilitated by interaction between seed crystals and amorphous drug and a storage temperature above the Tg. Amorphous form prepared from form 2 did not transform to crystalline form 1 under any conditions used in this study.