Serum vitamin D metabolites in epileptic patients treated with 2 different anti-convulsants

The serum concentrations of the vitamin D metabolites 25-hydroxy-vitamin D (25OHD), 24,25-dihydroxyvitamin D (24,25(OH)₂D), and 1,25-dihydroxyvitamin D (1,25(OH)₂D) were measured in 18 epileptic patients and 10 controls. The patients were divided according to the anti-convulsant treatment they had been receiving for at least 1 year: 9 patients had received phenytoin and 9 patients carbamazepine, as the sole anti-convulsant therapy.
The serum 25OHD was decreased in the patients on phenytoin ( P < 0.01). whereas the other serum vitamin D metabolites were normal. Moreover, serum alkaline phosphatase was increased ( P < 0.001) and serum calcium was decreased ( P < 0.001) in this patient group.
In the patient group treated with carbamazepine (a negligible liver inductor), changes in serum 25OHD and serum alkaline phosphatase were less pronounced ( P < 0.05), but the same degree of hypocalcaemia ( P < 0.001) was present.
Our data suggest that liver induction in epileptic patients on anti-convulsant drugs cannot explain the pathophysiology behind anti-convulsant osteomalacia.