Long-term influence of anticonvulsant agents on calcitonin, parathyroid hormone and osteocalcin

It has been reported that anticonvulsant drugs decrease serum calcitonin; this effect may be dose dependent and/or hypocalcemia dependent. The objective of the present study is to assess such a dependence and to evaluate other parameters in relation to calcitonin. Serum calcitonin, parathyroid hormone and osteocalcin were determined through RIA, and serum calcium, total protein and alkaline phosphatase through an autoanalyzer in 17 patients undergoing long-term treatment with phenytoin and phenobarbital. At the same time, 20 normal subjects were studied and served as controls. In the patients, no changes were observed in calcitonin, parathormone, osteocalcin and calcemia corrected for protein, and there was a statistically significant increase in alkaline phosphatase values (p < 0.001). Calcemia correlated positively with calcitonin (p < 0.01) and negatively with parathormone (p < 0.05). There was no calcitonin correlation with the anticonvulsant dosage or with the total doses ingested. Increased alkaline phosphatase levels in the presence of normal osteocalcin figures suggest a hepatic origin of the former. The fact that there were no calcitonin level changes but a correlation did exist between calcitonin and calcemia leads us to think that any hormonal changes induced by anticonvulsant agents may act indirectly through changes induced in serum calcium.