Kinetics of carbamazepine and its 10,11-epoxide metabolite in children.

The plasma steady-state concentration of carbamazepine (CBZ) and its metabolite (carbamazepine-10,11-epoxide, CBZ-epoxide) was assessed in 43 children (2-15 yr) on CBZ (Tegretol) treatment. Twenty of the children received combined treatment with other anticonvulsant drugs simultaneously. The plasma concentrations were in the same range as had been found in adult patients on corresponding doses. Only a weak correlation was noted between dose and plasma CBZ concentration in the group of children on single-drug treatment, and there was no correlation in the group of children on combined drug regimen. Plasma levels of CBZ correlated with those of the metabolite. Children on combined treatment had lower CBZ concentration and, expressed as percent of the parent drug, the metabolite concentration was significantly higher than in children treated only with CBZ. In 2 children the plasma half-life of CBZ was estimated and found to be slightly shorter than has previously been reported in adults. In evaluating the plasma level-effect relationship of CBZ, the plasma concentration of the CBZ-epoxide should be measured simultaneously because of its anticonvulsant effect and interindividual variability.