Biological activity of 24,24-difluoro-1,25-dihydroxyvitamin D3.

The biological activity of 24,24-difluoro-1,25-dihydroxyvitamin D3 was compared with 1,25-dihydroxyvitamin D3 in the rat. The 24,24-difluoro-1,25-dihydroxyvitamin D3 has a potency of approximately 5-10 times that of 1,25-dihydroxyvitamin D3 in the known in vivo vitamin D responsive systems. These systems include intestinal calcium transport, bone calcium mobilization, calcification of epiphyseal plate cartilage, and elevation of plasma calcium and phosphorus concentrations. Thus, 24,24-difluoro-1,25-dihydroxyvitamin D3 is the first known analogue with higher potency than 1,25-dihydroxyvitamin D3 in vivo.