Collagen microparticles: carriers for glucocorticosteroids.

Collagen microparticles were evaluated as a carrier system for glucocorticoids, and their physicochemical characteristics were determined. The particles were prepared by emulsifying and cross-linking native collagen. Particles in a size range of about 10 microns were obtained. The particle charge was dependent on the pH. A positive charge resulted when the surrounding medium had a pH below 4.5 and a negative charge with a pH above 4.5. This charge determined the magnitude of the interaction with dissolved charged drugs. The positively charged drug, prednylidene diethylaminoacetate, bound significantly to the particles above pH 4.5, whereas the negatively charged prednisolone sodium phosphate was bound below this pH. Adsorption of uncharged lipophilic drugs such as hydrocortisone was largely independent of the pH. The adsorption isotherm for this drug was determined and found to follow a Langmuir adsorption isotherm. The release and stability of the microparticle system was tested with hydrocortisone only, because of its pH-independent binding properties to the particles. The liberation of this drug was not influenced by the pH of the release medium. Binding to the particles did not effect the stability of hydrocortisone. The results of this study demonstrate that collagen microparticles can be successfully used as a carrier system for lipophilic steroids.