Different actions of vitamin D2 and D3 on bone metabolism in patients treated with phenobarbitone/phenytoin

In 22 epileptic outpatients treated for at least 1 year with phenobarbitone/phenytoin the local and total bone mass, together with serum and urinary indices of calcium metabolism, were measured before and during treatment with either vitamin D2 or D3, 4,000 IU daily for 24 weeks. The results showed a distinct difference in the action of the two vitamins on bone metabolism during anti-convulsant treatment. The bone mass increased during treatment with vitamin D2, whereas the vitamin D3-treated patients showed unchanged values of bone mass, but an increased excretion rate of calcium, probably caused by increased intestinal calcium absorption. The data demonstrate that vitamins D2 and D3 (or their metabolites) have quantitative different effects in patients treated with phenobarbitone/phenytoin.