Effect of phenytoin on rat bone resorption in vitro.

Effects of phenytoin (DPH) on parathyroid hormone (PTH)- and 1,25-dihydroxyvitamin D3(1,25DHCC)-mediated bone resorption in bone organ culture were evaluated: it markedly inhibited the actions of both. However, PTH tended to overcome the initial effects of DPH, whereas bone resorption due to 1,25DHCC remained depressed as if DPH treatment had continued. Thus DPH-induced bone abnormalities may involve a greater direct effect on 1,25DHCC regulation of bone homeostasis than on PTH.