Studies on the effects of anticonvulsant drugs on the activity of vitamin D in rats and dogs

An accelerated metabolism and consequent decreased activity of vitamin D 3 has been considered to be responsible for the osteomalacia associated with the use of anticonvulsant drugs. To investigate the effects of sodium phenobarbital and sodium diphenylhydantoin on the activity of vitamin D, rachitic rats were dosed daily for 9–10 days with the maximal tolerated doses of the drugs and twice during that time with graded doses of vitamin D 3. The healing of rickets in these rats was comparable to that in rats receiving only the vitamin. Adult Beagle dogs were given sodium phenobarbital, mixed in a normal diet, at a dose of 35 mg/kg/day for 20 months. Although liver microsomal enzyme induction developed, osteomalacia did not. The results show that the biologic activity of vitamin D was not affected by phenobarbital or diphenylhydantoin under the conditions of these studies.