Investigation of L-leucine in reducing the moisture-induced deterioration of spray-dried salbutamol sulfate power for inhalation

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The aim of this study was to investigate the ability of L-leucine (LL) in preventing moisture-induced deterioration in the in vitro aerosolization performance of spray-dried (SD) salbutamol sulfate (SS). Increasing mass fraction of LL (5–80%) were co-spray dried with SS, and the physicochemical properties of the powders were characterized by laser diffraction, X-ray powder diffraction (XRD) and dynamic vapour sorption (DVS). Furthermore, the surface morphology and chemistry of fine particles was analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The in vitro aerosolization performance of powders stored at different relative humidity (RH) was evaluated by a next generation impactor (NGI). The SD SS powders were moderately hygroscopic and amorphous, of which the uptake of moisture upon storage caused a drop in the aerosolization performance. The results showed that 40% (w/w) LL was sufficient to eliminate the effect of moisture on the aerosolization performance at 60% RH. The formulation containing 40% (w/w) LL also maximized the aerosolization performance of SD SS powders (stored in desiccator) with the emitted fraction being 90.0 ± 1.8%, and the fine particle fraction based on the recovered dose (FPFrecovered) and emitted dose (FPFemitted) being 78.0 ± 3.7% and 86.6 ± 2.9%, respectively. The underlying mechanisms were that the crystalline LL increased the degree of particle surface corrugation, and reduced particle fusion and cohesiveness to facilitate dispersion. However, there is still a great challenge to prevent the moisture-induced deterioration in the aerosolization performance at 75% RH due to the recrystallization of SD SS. In conclusion, LL is a potential excipient for reducing moisture-induced deterioration in the aerosolization performance of SD amorphous powders, but still has drawbacks in preventing the recrystallization-induced deterioration.

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