Influence of solid phase and formulation processing on stability of Abbott-232 tablet formulations

Abbott-232 is a chemically stable, highly water soluble non-hygroscopic compound selected for development as a potent uroselective alpha(1A) agonist. An anhydrate, a monohydrate, and an amorphous phase were isolated. The anhydrate was chosen for formulation development based on solid-state characterization. Excipients for immediate release (IR) tablet formulations were selected according to compatibility studies. However, the prototype IR tablets designed for clinical trials were found to be chemically unstable. Thus, process-induced phase transformation was investigated as the likely cause of the observed instability. Since the drug loading in the formulations was low (1%), model granulations containing 30% drug were evaluated to test this hypothesis. Investigation using a variety of analytical techniques indicated that the observed degradation was, indeed, a result of a solution-mediated phase transformation from anhydrate to amorphous Abbott-232 during wet granulation. A new direct compression formulation was, therefore, developed to prevent the solution-mediated process induced phase transition. Since the drug loading was low, a polarized light microscope (PLM) method was used to evaluate the solid phase in the new formulation. PLM confirmed that the original anhydrate form remained unchanged in tablets manufactured by the dry process. Stability studies confirmed that both IR and extended release (ER) tablets of Abbott-232 were successfully developed for clinical trials using direct compression.