Objectives: Bisphosphonates have been used as inhibitors of osteoclastic bone resorption in the treatment of osteoporosis. It is generally accepted that the probable reason for this phenomenon is the marked affinity of the bisphosphonates to the hydroxyapatite (HA) of bone minerals. Consequently, we intended to develop composites of bisphosphonate and HA as a drug delivery system, and designed a method of evaluating the dissolution properties of calcium from calcined HA as well as the release properties of bisphosphonate from the bisphosphonate-HA composites. Methods: HA granules (300-500 mm in diameter) were calcined at 400, 800, or 1200°C. 10 mg of the HA granules were immersed in 1 mL bisphosphonate (Pamidronate) solution (10 mM) for 24 hours at room temperature to adsorb the bisphosphonate, and then gently rinsed with distilled water. The bisphosphonate-absorbed HAs were immersed in 1 mL of distilled water for 72 hours to evaluate the release properties of the bisphosphonate. Finally, the amounts of released bisphosphonates were measured using an LC mass spectrometer. To evaluate the solubility of HA, 100 mg of the HA granules of the different calcining temperatures were immersed in a 10 mL of distilled water for 24 and 72 hours. The amounts of calcium released from the HA granules were measured using an ICP spectrometer. Results: The amounts of bisphosphonates released from composites at 400, 800, and 1200°C were 0.293±0.057 mM, 0.173±0.023 mM, and 0.100±0.020 mM during 72 hours, respectively. Analysis of the data via one-way ANOVA revealed significant differences among the temperature (p<0.01). The amounts of calcium released from the HA granules decreased with an increase in the calcining temperature for both the 24- and 72-hour immersion periods. Conclusions: These results suggest that the release properties of bisphosphonates could be controlled by HA with various calcining temperatures, i.e., varying the solubility of HA.

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