Enhancing the Solubility of Isoconazole Nitrate Using Methyl-β-Cyclodextrin: Formulation and Characterization of Inclusion Complexes

Isoconazole nitrate (ISN) is a broad-spectrum antifungal agent whose therapeutic potential is limited by poor aqueous solubility and low bioavailability. This study aimed to enhance the solubility and physicochemical properties of ISN through the formation of inclusion complexes with methyl-β-cyclodextrin (M-β-CD) using freeze-drying (FD) and spray-drying (SD) methods. The prepared inclusion complexes were comprehensively characterized by high-performance liquid chromatography (HPLC), phase solubility analysis, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), and proton nuclear magnetic resonance (¹H-NMR). Phase solubility studies revealed an AL-type solubility diagram with a 1:1 molar ratio and an apparent stability constant (<i>K_S</i>) of 2711 M^-1. Structural and thermal analyses confirmed successful inclusion complex formation and reduced crystallinity. The solubility assessment showed that ISN/M-β-CD complexes prepared by SD exhibited an approximately seven-fold higher aqueous solubility than ISN and performed better than those prepared by FD. Moreover, SD complexes demonstrated a higher drug content. These findings highlight the potential of M-β-CD-based inclusion complexation, particularly via spray-drying, as an effective strategy to enhance the solubility and bioavailability of poorly water-soluble drugs, such as ISN.