Development of fine solid-crystal suspension with enhanced solubility, stability, and aerosolization performance for dry powder inhalation

Abstract

Dry powder for inhalation (DPI) is an attractive approach for the treatment of local lung diseases. However, the application of drugs with poor water solubility is often limited due to the dissolution obstacles in the fluid layer of the lung lining. In this study, fine solid-crystal suspension (FSCS) was proposed as a solvent-free method to improve the solubility of a drug with poor solubility (itraconazole) and achieve high deposition efficiency simultaneously. The FSCS, in which the crystalline drug particle was highly dispersed in the crystalline excipient, was initially prepared as drug-excipient extrudate by hot melt extrusion, followed by jet milling into fine particles. Unlike the amorphous solid dispersion in the high-energy state, which is liable to recrystallize and aggregate, the FSCS was expected not only to improve the solubility of itraconazole, but also to maintain excellent physical stability. As evidenced in the solubility and stability studies, the solubility of itraconazole in the FSCS was approximately 145-fold greater than that of the raw material, and the crystalline form of itraconazole in the FSCS was also unchanged after storage in the accelerated condition for 6 months (40°C and 75% relative humidity [RH]). The improved solubility might be ascribed to the reduced crystal size and increased wettability, as confirmed by the particle size and contact angle test. The FSCS also showed an encouragingly high fine-particle fraction of 50.59±0.67%, which might have benefited from the appropriate particle size. Therefore, the FSCS was suggested as a promising DPI for delivery of drugs with poor water solubility.