The kinetics of pentoxifylline release from drug-loaded hydroxyapatite implants

Hydroxyapatite (HAP) was synthesized by the aqueous precipitation method from CaO and H3PO4 as the reagents. The HAP powders, either subjected or not subjected to preliminary calcination, were mixed with a pore-creating medium and isostatically shaped at a pressure of 350 MPa to form cylindrical samples. A natural product such as flour served as a pore-creating medium. Sintering was performed in the air, at 1200 or 1250°C. The employed procedure allowed for achieving microporous materials of pore sizes ranging from 0.1 to 15 μm and with open porosity values of 23–44%. It was demonstrated that the porosity of the obtained materials depended mainly on the amount of the added pore-creating medium and the temperature of sintering. The implants, shaped as hollow cylinders, were filled with 50 mg of pentoxifylline (PTX) as a model drug. Internal wells for drug placement were drilled in the samples using a high precision drill. The drug release study was performed in pH=7.35 phosphate buffer, at 37°C. The results showed that the amount and time of PTX release, as well as the lag time were mainly controlled by the open porosity of the carriers.