In vitro delivery of dexamethasone using hydroxyapatite reservoirs

Dexamethasone has been shown to stimulate bone nodule formation in vitro. A hydroxyapatite (HA) reservoir drug release device was designed to release dexamethasone in vitro. Two HA particle sizes (< 38 microns or 63-75 microns) were used to fabricate the reservoirs. Each HA reservoir was loaded with 2 mg of dexamethasone and suspended in 100 ml of 50% aqueous ethanol at 37 degrees C for a period of 28 days. The positive controls indicated a limited solubility of dexamethasone of 1.18 mg per 100 ml of 50% aqueous ethanol. Dexamethasone was not released from any of the HA reservoirs for the first 24 hours. The largest amount of dexamethasone (0.0137 microgram/microliter) was released from the 63-75 microns particle HA reservoirs. A significantly lesser amount (0.00855 microgram/microliter) of dexamethasone was released from the < 38 microns particle HA reservoirs. The results of this study suggest that a HA ceramic reservoir loaded with dexamethasone can be used to deliver dexamethasone over long periods of time.