Bromhexine and its fumarate salt: Crystal structures, Hirshfeld surfaces and dissolution study

•Multicomponent crystallization was used to improve the solubility of bromhexine.•A new bromhexine crystal and its fumarate salt crystal have been synthesized.•The crystal structure and Hirshfeld analyses of the two crystals were investigated.•The multicomponent crystal shows higher thermal stability and improved solubility. Bromhexine is an expectorant drug repurposing as a TMPRSS2 inhibitor, which has also been proposed for potential treatment in COVID-19 infection. Multicomponent crystal strategy has been applied in bromhexine to improve its poor solubility, which limits its bioavailability and efficacy. A new bromhexine crystal and its fumarate salt crystal have been successfully obtained by slow evaporation technique. Both compounds have been characterized by X-ray single-crystal diffraction, TGA and FT-IR spectroscopy. Hirshfeld surface analysis has been carried out to further quantify the patterns of intermolecular interactions. Compared with bromhexine, the multicomponent crystal with pharmaceutically acceptable conformer of fumaric acid shows improved thermal stability and solubility in water.