Solid State NMR Investigation for Molecular States of Specialized Formulation to Improve the Water Solubility of Poorly Water-soluble Drugs

Abstract

70-90% of recently developed new drug candidates are poorly soluble in water, which creates a series of thorny challenges in developing its oral dosage forms, resulting in low bioavailability. In pre-formulation study, various specialized formulations have been developed to improve drug solubility. Intermolecular interactions between drug and excipients in the formulations can modify the drug state and achieve the improvement of drug solubility. Therefore, the understanding of intermolecular interaction is essential to design formulations with higher quality and to assure the quality as a pharmaceutical product. Solid-state NMR has attracted much attention as a promising method to evaluate the molecular state of a drug and the interaction between a drug and excipient in its formulation. I have applied solid-state NMR and its characteristic technique, namely magic-angle spinning (MAS), for various specialized formulations including amorphous solid dispersion, supersaturated solution, drug-loaded organic nanotube, and drug nanosuspension. The intermolecular interactions of drug and excipient in amorphous solid dispersion have been identified by 13C and 15N solid-state NMR. High-resolution MAS determined the interaction modes of drug and excipient in a supersaturated solution. The two-step dissolution profile of drug from organic nanotube was understood, based on the molecular states revealed by the combination of various solid-state NMR techniques. A suspended-state NMR clarified the nanostructure of drug nanoparticles dispersed in water. It is expected that more qualified pharmaceutical formulations with improved drug solubility can be designed based on the remarkable development of recent solid-state NMR technology.