Autoinduction of carbamazepine metabolism in children examined by a stable isotope technique.

Autoinduction of carbamazepine (CBZ) metabolism was investigated in 3 children (10 to 13 yr old) using tetradeuterium-labeled CBZ (CBZ-D4). Prior to treatment, CBZ and CBZ-D4 given as a mixture had almost identical kinetics in each patient. During maintenance therapy with CBZ, part of the CBZ was exchanged for CBZ-D4 on 3 occasions. The clearance of CBZ-D4 given on the second day of therapy was 0.036 +/- 0.003 1 . kg-1 . hr-1, whereas it had been 0.028 +/- 0.003 before treatment. After 17 to 32 days of treatment, clearance doubled (0.056 +/- 0.010) but during the next 4 mo there was no further increase, indicating that the autoinduction was complete within 1 mo. As a corollary there was a decrease in steady-state plasma levels.