Novel pharmaceutical salts of cephalexin with organic counterions: structural analysis and properties

Three novel pharmaceutical salts of cephalexin (CPX) with 2,6-dihydroxybenzoic acid (DHBA), 5-chlorosalicylic acid (CSA) and 5-sulfosalicylic acid (SSA), which were obtained and thoroughly explored by various analytical techniques, were found to be crystallized invariably in hydrated forms. It is the proton transfer from carboxylic or sulfonic counterions to the CPX molecules that results in the salt formation. Crystal structure analyses reveal that the N–H⋯O and O–H⋯O hydrogen bonding interactions among the CPX, acidic guest molecules and water molecules play a crucial role in the packing motifs of crystal stabilization. All the salts exhibit higher solubility compared with the parent drug. These salts offer an alternative way of increasing the number of solid forms for CPX, which facilitates selection of a suitable form in the context of drug formulation development for further repurposing investigations.