Sprayable Intranasal Powder Formulation of Ionic Liquid-Associated Mesoporous Silica

Ionic liquids (ILs) have garnered significant attention in pharmaceutical development because of their diverse applications in improving drug absorption across the nasal mucosa. However, because ILs typically exhibit high viscosity, their poor spray characteristics through intranasal devices pose a challenge for their intranasal administration. To address this issue, we designed an intranasal powder formulation that can be applied using an intranasal powder device by loading an IL within the pores of mesoporous silica (MPS). MPS was added to an IL composed of choline and L-malic acid, and the mixture was stirred. Over time, IR spectroscopy measurements revealed a reduction in the intensity of the IL-derived peaks, suggesting that most ILs were associated with MPS pores. This loading process proceeded more rapidly at higher mixing temperatures owing to the reduced IL viscosity. Furthermore, specific surface area measurements and scanning electron microscopy (SEM) observations demonstrated that the IL was successfully encapsulated within the pores with minimal residue on the MPS surface at an MPS:IL mixing ratio of 1 : 0.4. The IL-MPS prepared from MPS with different physical properties tended to exhibit improved flowability compared to the original MPS, suggesting that the amount of IL retained may vary with the MPS pore volume. The spray characteristics of the IL-MPSs prepared using an intranasal powder device were superior to those of lactose hydrate, a commonly used excipient. Thus, the IL-MPS powder formulation can be a suitable candidate for intranasal administration.