Use of hydroxyapatite small crystals as drug carrier

Hydroxyapatite small crystals(HAp-sol) applied as a drug carrier are being developed. The HAp-sol was synthesized by a wet method and amounts of drug adsorbed onto the hydroxyapatite small crystals were measured. The HAp-sol was characterized by X-ray powder diffraction, transmission electron microscopy, and infrared absorption. From the TEM observation, the crystal had a stick-like shape (average length was 730 Å and width was 140 Å). The amount of drug adsorbed onto the crystals was measured by an ultraviolet-visible radiation spectrophotometer. The drugs used were doxorubicin hydrochloride, mitomycin C, and fluorouracil (Kyowa Hakkou) which are glycoside antibiotics. An adsorption curve as a function of time, adsorption isotherm, and eluted amount of adsorbed drug were measured. Investigation of the adsorption was carried out at pH 7.50 (1.0 mmol/1 phosphoric buffer solution) and incubated at 37°C. The concentration of HAp-sol was 5 mg/ml. The saturation time of doxorubicin-hydrochloride-adsorption onto HAp-sol required 2 hours. The amount of doxorubicin hydrochloride saturated adsorption was 0.2 mg per 1 mg HAp-sol. In the measurement of the eluted amount of doxorubicin hydrochloride, half of the saturated adsorbed drug was eluted into the phosphoric buffer solution. This result indicates that HAp-sol adsorbed with doxorubicin hydrochloride is useful as a drug delivery system.