Hydrogen Bond Synthons in the Interplay of Solubility and Membrane Permeability/Diffusion in Variable Stoichiometry Drug Cocrystals

The bronchodilator drug theophylline (THP), though a BCS class-I drug, is considered as a representative compound to prepare variable stoichiometry cocrystals with isomeric aminobenzoic acids (o-ABA, m-ABA, and p-ABA) as coformers. Cocrystals are synthesized using crystal engineering principles through liquid-assisted mechanochemical grinding. Four different stoichiometry cocrystals of THP are isolated with o-ABA. Coformers m-ABA and p-ABA afforded only 1:1 cocrystals irrespective of crystallization media and different starting materials ratios. All cocrystal materials were subjected to aqueous solubility and diffusion/membrane permeability to examine drug biopharmaceutic properties to predict the in vivo performance of the drug. They exhibited different but improved solubility and modulated diffusion/membrane permeability when compared with pure THP. The interplay of drug solubility and membrane permeability that predicts the overall bioavailability is emphasized based on hydrogen bond synthons and solute···solvent interactions. Hirshfeld surface analysis was carried out in all cases to determine whether a correlation exists between permeability and drug–coformer interactions.