The aim of this study was to investigate influencing factors on the dissolution test for powders for pulmonary delivery with USP apparatus 2 (paddle apparatus). We investigated the influence of dose collection method, membrane holder type and the presence of surfactants on the dissolution process. Furthermore, we modeled the in vitro dissolution process to identify influencing factors on the dissolution process of inhaled formulations based on the Nernst-Brunner equation. A homogenous distribution of the powder was required to eliminate mass dependent dissolution profiles. This was also found by modeling the dissolution process under ideal conditions. Additionally, it could be shown that influence on the diffusion pathway depends on the solubility of the substance. We demonstrated that the use of 0.02% DPPC in the dissolution media results in the most discriminating and reproducible dissolution profiles. In the model section we demonstrated that the dissolution process depends strongly on saturation solubility and particle size. Under defined assumptions we were able show that the model is predicting the experimental dissolution profiles.
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