Alkaline phosphatase and its isoenzyme activity for the evaluation of bone metabolism in children receiving anticonvulsant monotherapy

This study aimed to investigate whether carbamazepine, sodium valproate or phenobarbital as monotherapy in ambulatory epileptic children with adequate sun exposure have some effect on their bone metabolism based on the determination of total serum alkaline phosphatase (AP) levels and its bone isoenzyme activity. Blood samples were obtained from 118 epileptic children (37 on carbamazepine, 47 on sodium valproate and 34 on phenobarbital) and from corresponding healthy controls matched for age, gender and anthropometric parameters. AP and its liver, bone and intestinal isoenzyme levels, other common biochemical markers of bone and liver metabolism and drug levels were measured in the study participants. Patients on carbamazepine or phenobarbital had significantly elevated AP levels accompanied by increased bone and liver isoenzyme activity compared to controls. An increase of bone AP isoenzyme values, correlated with the duration of treatment ( r= 0.49, P= 0.002), was found in children on sodium valproate without, however, a concomitant significant elevation of total AP values. We conclude that children who receive antiepileptic drugs as monotherapy, even when residing in a Mediterranean country with adequate sunlight, may have their bone metabolism affected as indicated by the elevated levels of bone AP isoenzyme. This isoenzyme, but not total AP values, could therefore be used as a marker for the selection of patients who would be benefited by a thorough evaluation of their bone metabolism profile.