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A Comparison of the Deposition Patterns of Different Nasal Spray Formulations Using a Nasal Cast

For nasally delivered medications, it is quite a challenge in the formulation development to characterize the deposition pattern in vivo. An in vitro nose model has been developed recently and adopted in our study to compare the deposition pattern of different nasal solution formulations. One low-viscosity nasal solution and five other solutions containing either Avicel or hydroxypropyl methylcellulose (HPMC) as the viscosity enhancers were examined in this study. The viscosity, spray pattern, plume geometry, and droplet size were characterized. The in vitro deposition patterns were assessed using an anatomically correct silicone nasal cast combined with a color-based image-analysis method. The correlations between the formulation variables, the spray characteristics, and the deposition pattern were investigated. The addition of each viscosity enhancer resulted in increasing viscosity, larger droplet size, narrower plume angle, and lesser anterior deposition. However, it appears that the changes in spray characteristics and deposition pattern are influenced heavily by the identity of the viscosity enhancer, rather than merely by the formulation viscosity itself. Although the Avicel additions led to larger increases in the formulation viscosity, the HPMC additions had far greater impact on the spray characteristics and deposition pattern. The formulations with suboptimal deposition patterns, i.e., the formulations with ‘forward’ or ‘backward’ dripping, were successfully identified in this study. This in vitro method was able to discriminate between formulations, revealing differences in regional deposition and the tendency of formulations to drip. As such, the nasal cast method is recommended as a valuable tool for the development of nasal spray formulations.