Effects of tacrolimus (FK506) on the development of osteonecrosis in a rabbit model.

The present study examined the effects of tacrolimus (FK506) on the development of osteonecrosis in rabbits. In Experiment A, rabbits were given FK506, and also given a single dose of steroid. Control rabbits were given the same dose of steroid only. In Experiment B, rabbits were given FK506 and a reduced dose of steroid. The results showed that addition of FK506 did not change the number of rabbits with osteonecrosis when an identical steroid dose was given. When the steroid dose was reduced, the osteonecrosis incidence significantly decreased (p < 0.01). These results suggest that the clinically reported decrease in the osteonecrosis incidence following the introduction of FK506 is most likely attributable to the lower doses of steroids.