[maryz]

You might as well be taking prednisone, it's chemical structure is very close to that of vitamin D,

Are you sure about this? If it's true, it seems odd that they would use prednisone to treat vitamin D toxicity.

[slowhandluke]

Quite sure. Vitamin D,25 and prednisone tend to deactivate the nuclear receptors that D,1,25 activate. However, D,25 is also quickly converted to D,1,25 so while it cools things in the short run, it feeds the fire in the long run.