Sulfamethoxazole:hydroxypropyl-β-cyclodextrin complex: preparation and characterization

A complex of sulfamethoxazole (SMX) and hydroxypropyl-β-cyclodextrin (HP-β-CD) was developed and characterized in order to investigate their interactions in aqueous solution and the solid state. The SMX solubility was significantly increased upon complexation with HP-β-CD, with the solubility isotherm being an AN type due to the presence of aggregates and the stability constant calculated for a 1:1 complex being 302 ± 3 M−1. Fourier-transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) experiments were used to compare the freeze-dried system with a physical mixture, and demonstrated the complex formation in the solid state. The differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the thermal stability of SMX was enhanced in the presence of HP-β-CD.