More than 40 % of active pharmaceutical ingredients (APIs) discovered in last two decades are poorly soluble in water or body fluids. When developing a drug formulation, it is a great challenge to ensure concentration of API which is high enough, to furnish pharmacological activity. One of possible solutions to overcome this challenge are dry emulsions, which gained interest after scientists have discovered that adding certain lipophilic excipients to drug formulation enhances drug absorption in the gastrointestinal tract. Spray drying is a viable procedure for preparation of dry emulsions. It is the process which changes the emulsion into dry powder in one step, i.e. with drying the outer aqueous phase of emulsion. Changing the aggregate state of emulsion from liquid to solid state is a great way to avoid drawbacks of classic emulsions such as creaming, flocculation, droplet coalescence and potential drug instability. Solid carriers are often used, to ensure the proper oil droplet size distribution after the drying procedure. In our formulations we used macroporous silica as a highly porous carrier and nanocrystalline cellulose as a polymer carrier. Dried emulsion solid phase contained mannitol and hydroxypropyl methylcellulose as well. Experimental work began with screening (preliminary study), where the ranges of excipients in the formulation, that are still possible to spray dry, were identified. We entered those ranges in statistical software Minitab and used Design of Experiments (DoE) to generate 17 different experiments that were performed in random order. After spray drying formulations from experimental plan, we measured their properties – responses. We used lasser difraction to measure the emulsion droplet size distribution, particle size of solid carriers, that were not soluble in water/emusion, particle size of dry emulsion systems and size distribution of oil droplets in samples, after they were redispersed in water. Besides droplet and particle size, flow properties of dry emulsion powders were one of the observed attributes in our study. We analysed the responses data and figured out, that inclusion of porous silica improves product flow properties and process yield, but does not release all drug containing oil droplets into aqueous medium due to carrier particle high porosity. Addition of nanocrystalline cellulose in formulation improves the dissolution of the simvastatin but reduces process yields and flow properties, presumably due to pore surface coverage. Therefore we have to make a compromise between silica and nanocrystalline cellulose concentrations to get the formulation with desired properties.
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