Spray Pattern and Droplet Size Analyses for High-Shear Viscosity Determination of Aqueous Suspension Corticosteroid Nasal Sprays

Abstract

Aqueous suspension corticosteroid nasal sprays exhibit the rheological property of shear thinning, meaning they exhibit a decrease in viscosity upon application of shear. Most rheological methods are limited in the amount of shear that can be applied to samples (∼1,000 s⁻¹) and thus can only approximate the viscosities at the high-shear conditions of nasal spray devices (∼10⁵–10⁶ s⁻¹). In the current work, spray area and droplet size were shown to demonstrate viscosity dependence. Three Newtonian fluids were used to determine equations to approximate viscosity at the spray nozzle from correlations to spray area and droplet size using a standard 100 μL Pfeiffer® nasal spray pump. Several shear-thinning solutions, including four commercial aqueous suspension corticosteroid nasal sprays and three aqueous Avicel® (1, 2, and 3%, wt/wt) samples, were analyzed to demonstrate the ability of spray area and droplet size analysis to estimate high-shear viscosities. The calculated viscosity values trend in accordance with the rheometer data along with the ability to distinguish differences between all samples analyzed.

Keywords:

• rheology
• Avicel
• spray area
• droplet size
• viscosity
• shear thinning

ACKNOWLEDGMENTS

The authors are thankful to Dr. Gary D. Ewing and Christopher George from Schering-Plough Research Institute for their help with this study, Malvern Instruments for their help with the high-shear data, and TA Instruments for the technical support with the AR-2000 rheometer.