Effects of anticonvulsants and methotrexate on calcium disposition.

Administration of phenytoin for 5 days significantly reduced oral absorption and bone uptake of radiolabelled calcium in mice. Acute treatment with phenytoin had no effect on calcium disposition. Pretreatment (1--5 days) with phenobarbital also had no effect of calcium disposition. Methotrexate pretreatment for 5 days increased the bone uptake of radiolabelled calcium presumably by decreasing calcium renal clearance. It is concluded that phenytoin induced reduction in calcium metabolism is unrelated to a state of functional folate deficiency.