Abstract
The flowability and dispersion behavior are two important physicochemical properties of pharmaceutical formulations for dry powder inhalers (DPIs). They are usually affected by the environmental conditions, such as temperature and relative humidity (RH). However, very few studies have been focused on the relationship between the two properties and their dependence on RH during storage. In this research, model pharmaceutical formulations were prepared using mixtures of coarse and fine lactose. The fractions of fines in the mixtures were 0%, 5%, 10%, and 20%, respectively. These blends were stored at four different RH levels, 0%, 30%, 58%, and 85%, for 48 h. The FT4 Powder Rheometer was used to evaluate the powder flowability, and the Malvern Spraytec® laser diffraction system was employed to assess the powder dispersion performance. The results indicated that both the flow and dispersion properties of lactose blends deteriorate after being stored at 85% RH, but improved after being conditioned at 58% RH. The fine particle fractions (FPFs) of the blends with 5% and 10% fine fractions and the as-received coarse lactose decreased when they were conditioned at 30% RH. For the blend with 20% fine fraction, a high RH during storage (i.e., 85% RH) affected the dispersion property, but had a limited influence on its flowability, while, for the coarse lactose powder, the different RH conditions affected its flowability, but not the dispersion results. A strong correlation between the powder flowability and its dispersion performance was found.
Highlights
The flowability of powder materials is important for their handling and processing [1]
The innovative dynamic flowability testing methods based on the FT4 Powder Rheometer were proved to correlate well with other measurement methods [5] and be able to characterise the different fine powder flow properties [6]
The lactose blends with fine lactose fractions of 0, 5, 10 and 20 wt. % were prepared by sandwiching the fine lactose between the coarse one and mixing manually at a constant room of 22 ± 2 ◦ C and an relative humidity (RH) of 50% ± 10%
Summary
The flowability of powder materials is important for their handling and processing [1]. Several characterisation methods for the flow properties of bulk solids, e.g., the angle of repose, the determination of densities (for compressibility index and Hausner ratio), the mass flow rate, through orifice and shear cell tests, have often been used [3,4]. For cohesive powders, the flowability are often difficult to be differentiated by the methods above. The innovative dynamic flowability testing methods based on the FT4 Powder Rheometer were proved to correlate well with other measurement methods [5] and be able to characterise the different fine powder flow properties [6].
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