Cocrystal of metaxalone and succinic acid: Research on spectroscopic characterization, molecular vibration mode and dissolution performance optimization

• The prepared cocrystal was characterized by terahertz spectroscopy • The equilibrium solubility of cocrystal was detected in solutions of surfactants and polymers of different concentrations • The DFT was used to simulate the molecular vibration modes corresponding to each absorption peak in the terahertz spectrum Metaxalone is a muscle relaxant. However, its low solubility limits its bioavailability. Drug cocrystal technology can improve the physicochemical properties of the active pharmaceutical ingredient, achieving a synergistic effect without altering the mechanism of action of the drug. In this paper, a drug cocrystal composed of metaxalone and succinic acid in a stochemical ratio of 2:1 was prepared. Its formation was confirmed by characterization methods such as PXRD, DSC, THz-TDS and SEM. The vibration modes corresponding to each absorption peak in the terahertz spectrum of the cocrystal were studied in combination with the DFT method. In the simulated gastric juice and simulated intestinal fluid, the equilibrium solubility of the prepared cocrystal was significantly improved compared with the parent drug metaxalone. The addition of surfactants and polymers also had certain effects on the solubility of metaxalone and the cocrystal. This study provides a useful idea for understanding the solubility of cocrystal and researching cocrystal solubilization.