Conversion of nanosuspensions into dry powders by spray drying: a case study

Drying of nanosuspensions can cause destabilization of the particles, leading to irreversible aggregation. In order to prepare an effective solid dosage form for a nanosuspension, it is imperative that the spray-dried nanoparticles should go back to their original particle size when reconstituted in an aqueous system. This case study examines impact of various formulation and processing parameters on redispersibility of the spray dried nanoparticles.

Nanosuspensions were prepared using the microprecipitation-homogenization process. Spray drying of nanosuspensions was achieved using a lab-scale Buchi spray dryer.

Formulation components appeared to have the most significant impact on redispersibility of spray dried particles. Absence of surface charge led to particles that could not be redispersed. On the other hand, charged particles stabilized with an appropriate sugar led to spray dried powders that were flowable and easily redispersible. Dissolution testing showed the presence of two phases--a lag phase that represented dispersion of the loose aggregates, and dissolution of the dispersed nanoparticles.

Nanosuspensions of a poorly soluble drug could be spray dried to obtain flowable powders that could be easily redispersed. These optimized powders also showed significantly improved dissolution rates as compared to the micronized drug, or unoptimized nanosuspensions.