The described invention provides a biodegradable, biocompatible delivery system of flowable sustained release microparticulate composition of a substantially pure crystalline form of a bioactive agent such as, for example, nimodipine, a process of preparing a therapeutic form of a substantially pure crystalline form of the bioactive agent and a method for treating an interruption of a cerebral artery in a subarachnoid space at risk of interruption caused by brain injury in a mammal, which reduces signs or symptoms of at least one delayed complication associated with brain injury.