The effect of formulation variables and breathing patterns on the site of nasal deposition in an anatomically correct model. 
This study was conducted to evaluate the effect of formulation variables and breathing patterns on aerosol distribution in the nasal cavity.  Placebo nasal spray formulations containing 0.25% w/v Avicel CL611 (viscosity = 4 cP) and 2% w/v methylcellulose (MC; viscosity = 18.2 cP) were radiolabeled with (99m)Technicium.  Following spraying into a silicone nose model, through which air was drawn at one of three constant rates (0, 10, and 20 L/min) or one of two breathing profiles (representing fast and slow inhalations), aerosol deposition in the model was quantified by gamma scintigraphy.  Regional deposition was expressed as horizontal[inner, middle (h), outer] and vertical distribution [upper, middle (v), lower] in the nose model.  Compared to 2% MC, Avicel CL611 significantly increased aerosol deposition in the middle (h) region of the nasal cavity under all breathing conditions, and in the inner region at 0 and 20 L/min and with a slow inhalation.  The different breathing rates showed no effect on deposition of 2% MC.  However, 10 L/min significantly increased the upper deposition of Avicel compared to 0 and 20 L/min.  Nasal sprays with a low viscosity provided greater surface coverage of the nasal mucosa than higher viscosity formulations.  Changes in breathing profiles did not affect aerosol deposition in this nose model.