Effect of Particle Size and Viscosity of Suspensions on Topical Ocular Bioavailability of Budesonide, a Corticosteroid.

Purpose: To determine the effect of particle size and viscosity of suspensions on topical ocular bioavailability of budesonide, a corticosteroid drug. Methods: Budesonide microparticle and nanoparticle (MP and NP) suspensions were prepared with or without homogenization and microfluidization. Using different grades of hydroxyl propyl methyl cellulose, low viscosity NP (NP-LV) and low and high viscosity MP (MP-LV and MP-HV) were prepared. Suspensions were characterized for particle size, viscosity, and osmolality. Budesonide suspensions were administered topically to rabbits and aqueous humor was collected and analyzed for budesonide. Budesonide Cmax, tmax, and the area under the concentration time curve (AUC (0-6h)) values were determined. The geometric mean ratio of AUC and bioequivalence was evaluated using a bootstrap method. Results: The particle sizes for NP and MP were ∼700 and 2,000 nm. The viscosities for low and HV formulations were ∼5 and 50 cP. The geometric mean budesonide Cmax values for the suspensions NP-LV, MP-LV, and MP-HV were 0.22, 0.22, and 0.31 µg/g, tmax values were 0.67, 0.60 and 0.53 h, and AUC0-6h values were 0.72, 0.53, and 0.95 µg h/g, respectively. Bootstrap analysis indicated that the 90% confidence intervals of the geometric mean ratio of AUC0-6h values were 1.00-1.74 (MP-HV vs. NP-LV), 0.57-0.96 (MP-LV vs. NP-LV), and 0.45-0.70 (MP-LV vs. MP-HV). Conclusions: The 3 budesonide suspensions assessed in this study were not bioequivalent. Results suggested that an increase in viscosity improves the bioavailability of budesonide from the microsuspension formulation.