Eutectics and Salt of Dapsone With Hydroxybenzoic Acids: Binary Phase Diagrams, Characterization and Evaluation

Poor solubility and low dissolution rate of pharmaceuticals in many cases largely limit their bioavailability and efficacy. One of the promising approaches to improve dissolution behavior is to develop new multicomponent solid forms. Herein we use this strategy to synthesize new multicomponent solids of dapsone (DAP), which belongs to BCS class IV, with a series of hydroxybenzoic acid coformers. A new salt of DAP with 2,6-dihydroxybenzoic acid (26DHBA) and 4 eutectics with other hydroxybenzoic acids were reported through comprehensive characterizations using powder X-ray diffraction DSC, and vibrational spectroscopy techniques. The salt formation was evidenced by the presence of ionic interactions detected using FT-IR and Raman spectroscopy, and the stoichiometric ratio was determined to be 1:1. Binary phase diagrams were established to determine the composition of eutectics. The cause for salt and eutectic selection was further understood by computing molecular electrostatic potential (MEP) surface where 26DHBA shows the greatest acidity. Moreover, the powder dissolution study and microenvironment pH measurement reveal that both salt and eutectics of DAP display improvements on the dissolution rate and equilibrium concentration in which the acidity of coformers plays a dominant role. Our findings provide a direction for future coformer screening of multicomponent solids with improved pharmaceutical properties.