Microencapsulation of antimicrobial ceftiofur drugs

Polymeric microparticles containing two ceftiofur salts as antimicrobial agents for intramammary application in dry cows were prepared by modified o/w-solvent evaporation methods (dispersion or cosolvent method) or by a w/o/w-multiple emulsion solvent evaporation method. The microspheres were characterized with respect to drug loading, drug release, and morphological properties. The three methods resulted in high encapsulation efficiencies. The choice of organic solvent/solvent mixture strongly affected the structure of the microparticles; both matrix and reservoir-type structures with different porosities were obtained. Scaling up to larger batch sizes resulted in microspheres with a faster drug release. The addition of water-miscible cosolvents to the water-immiscible polymer solution allowed the preparation of microparticles from a drug solution rather than a drug dispersion. Microparticles prepared by the cosolvent method could be separated after shorter time intervals from the aqueous phase; the microspheres had a denser matrix with finely dispersed drug crystals and a slower drug release when compared with microspheres prepared by the dispersion method, which had a more porous structure with larger embedded drug crystals. The cosolvent and dispersion methods present a simple alternative to the w/o/w-solvent evaporation method for the encapsulation of water-soluble drugs with an external water phase.