Impact of drug particle shape on permeability and cellular uptake in the lung

The generation of inhalable sized particles (1–5 μm) usually involves a particle-processing step; most commonly milling but spray drying has shown to be a suitable alternative. Besides particle size, processing may affect other particle properties, like shape and solid-state. For example, spray drying of salbutamol sulphate leads to spherical shaped predominantly amorphous particles whereas jet milling frequently maintains the irregular shape and the crystallinity of the raw material. The aim of the present study was to investigate whether particle properties, especially shape, change the biological action of the inhaled particles as well. Therefore, highly water soluble salbutamol sulphate and poorly water soluble budesonide were compared regarding dissolution, permeation and preferential uptake by epithelial cells compared to macrophages after jet milling and spray drying. For both drugs the spray dried, predominantly amorphous, particles resulted in lower respirable fractions, but higher permeability and cell uptake rates compared to the needle shaped, predominantly crystalline particles. The distinct particle properties did not affect the dissolution behaviour of salbutamol sulphate. In turn for drugs with lower solubility (budesonide), spray dried particles dissolved slower compared to jet milled particles. Preferential uptake by macrophages was higher for spray dried particles, suggesting that processing may improve targeted delivery. The comparison between murine cell lines and human monocyte derived macrophages primary cells showed similar trends in rate and preference of particle uptake.