A drug nanosuspension which consisted of phenytoin, polyvinylpirrolidone (PVP) and sodium lauryl sulfate (SLS) was prepared by a wet bead milling method. The drug nanosuspension was spray dried to yield products composed of nano-sized drug crystals, which were designated as a dry nanosuspension (DNS). It was revealed that the DNS was redispersed into a suspension corresponding to size distribution of the original nanosuspension and the drug was released immediately when placed in water. The contents of the dispersing agents and the spray-drying conditions were changed in this study to achieve rapid redispersion of the dried products in the aqueous phase. The redispersibility of the DNS was improved with increasing concentration of PVP and SLS, but was not improved with only increasing PVP content. Furthermore, it was found that a higher temperature or lower humidity of the supply air in the spray-drying process led to good redispersibility of the DNS. The results for water content in the DNS indicated the redispersibility increased significantly less than 1.7% of the residual water amount. The outcome of this research will be important to apply DNS to the pharmaceutical formulation of poorly water-soluble drugs.

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