Characteristics of drug loading, drug release and degradation of chitosan microspheres prepared using the dry-in-oil method

Chitosan microspheres were prepared using the dry-in-oil method, in which silicone oil was used as a dispersion medium. Their drug loading, drug release and degradation properties were investigated using p-hydroxybenzoate esters (parabens) or 5-fluorouracil as model drugs. This preparation permitted good formation of microspheres with relatively high drug loading. The particle size was influenced by the viscosity of the silicone oil. The drug content was dependent on the physicochemical properties of the drugs and their added amounts in the preparations process of the microspheres. The drug release varied among the species of parabens and accelerated with the addition of lysozyme. The microspheres gradually degraded with the coexistence of lysozyme in vitro and when they were subcutaneously implanted into mice.