Development and bioadhesive properties of chitosan-ethylcellulose microspheres for nasal delivery

Loratadine-loaded microspheres were prepared by spray-drying of dispersions, emulsions and suspensions differing in polymeric composition and solvents used. Conventional microspheres were obtained by spray-drying of dispersions composed of chitosan (CM) as only polymer, while composed microspheres were obtained by spray-drying of two-phase systems composed of chitosan and ethylcellulose (EC). Microspheres differed in EC/CM weight ratio (0:1, 1:2 and 1:3) and in loratadine/polymers weight ratio (1:6 and 1:8). The entrapment efficiencies were between 67.9 and 86.1%; less loratadine was entrapped as polymer/drug ratio decreased. In comparison to one-phase systems composed of CM as only polymer, spray-drying of two-phase systems composed of both, CM and EC resulted in improved loratadine entrapment (80.1-86.1%). All microspheres were positively charged, indicating the presence of chitosan at the surface, regardless of the drug content and the type of spray-dried system. The highest zeta-potential was measured for loratadine-free conventional microspheres, consisting of chitosan only (32.7+/-1.3 mV). Tensile studies showed that both, EC/CM ratio and the type of spray-dried system influenced the bioadhesive properties of the microspheres in a way that the microspheres with higher chitosan content were more bioadhesive and microspheres prepared from suspensions were more bioadhesive than those prepared from emulsions, regardless of the same polymeric composition. The results suggested that the spray-drying method is useful to produce bioadhesive loratadine-loaded microspheres.