Fine powder of lipid microparticles – spray drying process development and optimization

Performed studies were focused on developing spray drying technique for aqueous dispersion of solid lipid microparticles (SLM) by selecting appropriate process parameters and assessing their impact on the process and properties of the obtained dry SLM powders. Spray drying allows to obtain SLM in a dry powder form when the liquid form does not present sufficient long-term stability (e.g. due to degradation of the active substance or aggregation of particles) or when the dosage form is to be used in a fine powder form. In the first stage of research the experiments were designed to optimize process parameters during spray drying of the placebo SLM dispersions prepared with two lipids: Compritol or stearic acid. The inlet temperature and feed rate were process parameters selected for monitoring. As response values, yield and quality attributes of the final product, namely particle size, moisture content and powder flowability were chosen. The process parameters optimized in the first step were then used to dry the SLM with model active substances: cyclosporine and spironolactone. The use of 3D surface charts, developed on the basis of the results of the conducted experiments, allowed for the selection of optimal process conditions for obtaining final product with desired properties and satisfying yield. For SLM with Compritol these were: inlet temperature 90 °C and feed rate 2.4 ml/min; whereas for SLM with stearic acid 80 °C and 3 ml/min were optimal, respectively. Process parameters optimized for placebo formulations were found to be equally suitable for drying drug-loaded SLM. The spray drying was found to be an effective method of obtaining dry powders from aqueous SLM dispersions. The lipid forming the SLM matrix should be considered the most important factor on which the process parameters depend. The most appropriate drying conditions selected during drying placebo formulations proved to be equally effective when SLM with the same composition and with model active substance were subjected to drying.