FACTORS INFLUENCING PLASMA-LEVEL DOSE RATIOS OF CARBAMAZEPINE AND ITS MAJOR METABOLITES IN EPILEPTIC CHILDREN

The relationship between daily dose and plasma concentrations of carbamazepine (CBZ), CBZ-10,11-epoxide (CBZ-EP), and 10,11-dihydro-10,11 -trans-dihydroxy-CBZ (CBZ-DIOL) was investigatedin 21 children aged 7–16 years who received CBZ monotherapy, twice daily in equally divided doses. Significant linear correlations between CBZ dose and plasma levels were obtained for CBZ and its metabolites (p < 0.01). In addition, the effects of daily dose and patients' age on the plasma level/dose ratios for CBZ, CBZ-EP, and CBZ-DIOL were evaluated. A significantnegative correlation was observed between the daily dose of CBZand the CBZ plasma level/dose ratio (p < 0.01). By contrast, plasma level/dose ratios for CBZ-EP and CBZ-DIOL were independent of dose (p > 0.1). On the basis of these observations,we consider that the decrease in CBZ plasma level/dose ratio withincreasing CBZ dose appears to be due to dose-dependent metabolicclearance of CBZ. The influence of age on plasma level/doseratiosfor CBZ and its metabolites was not significant (p > 0.05). However, there was considerable interdose and diurnal variation in the plasma level/dose ratios, particularly for CBZ (28–41%); this must be taken into account when making dose adjustments based on plasma level/dose ratios. © 1990 Raven Press, Ltd., New York.