Effects of parathyroid hormone dosage and schedule on bone regeneration.

This study investigated the effects of administration of parathyroid hormone (PTH) at different dosages and schedules on bone regeneration in critical-size bone defects in rat calvariae. After calvarial defects had been prepared in 50 rats, they were divided into five treatment groups: 15 µg/kg PTH daily (PTH-15), 35 µg/kg PTH three times per week (PTH-35), 105 µg/kg once per week (PTH-105-1), 105 µg/kg three times per week (PTH-105-3), and controls given vehicle alone. Bone regeneration was evaluated radiographically using micro-computed tomography (micro-CT) or histologically. The amount of newly generated bone in the calvarial defects was found to be significantly greater in the PTH groups than in the control group, and did not differ significantly among the PTH-15, PTH-35, and PTH-105-1 groups, whereas the PTH-105-3 group showed a significantly greater degree of new bone formation than the other PTH groups. It appeared that a higher dose of PTH stimulated a greater degree of bone regeneration in this experimental setting. The present results also suggest that the total dose of PTH administered is significantly related to the amount of bone regenerated within a defined period, indicating that less frequent administration of PTH might be a feasible protocol for bone regeneration therapy.