Changes in the mucoadhesion of powder formulations after drug application investigated with a simplified method.

The residence time in the nasal cavity can be prolonged by dry particles that absorb water and subsequently increase the viscosity of the mucus layer. A novel nasal drug delivery system based on interactive mixtures has previously been developed, where fine particles of the active component are adhered to the surface of mucoadhesive carrier particles by dry mixing. The surface coverage may alter the original mucoadhesiveness of the carrier particles and to investigate this, a simplified tensile strength method was developed and evaluated. Reliable results were obtained with a plastic coated absorbent paper covered by a mucin solution as a substitution for porcine nasal mucosa and should also be applicable to other dry particle systems. The method showed that the swelling of sodium starch glycolate particles was slightly delayed, corresponding to the degree of hydrophobic surface coverage. Carrier particles of partly pregelatinized maize starch were not influenced by the addition of a hydrophobic substance, probably because of the rough particle shape that inhibited a complete surface coverage. It was concluded that the surface coverage of carrier particles in interactive mixtures only could cause a short delay in water absorption that should not affect their mucoadhesive characteristics in vivo.