Steady-state serum concentrations of carbamazepine and valproic acid in obese and lean patients with epilepsy.

Steady-state serum concentrations of carbamazepine (CBZ) and valproic acid (VPA) were investigated in normal weight (body mass index; BMI 20 to 25), lean (smaller than 20 BMI) and moderately obese subjects (greater than 25 BMI) who received either 400 mg/day of CBZ or 800 mg/day of VPA. The CBZ serum concentration in lean subjects was significantly higher than that in normal weight subjects. However, no significant differences in VPA serum concentration were found between the three groups. The CBZ serum concentration decreased with increases in total body weight, and the VPA serum concentration decreased with increases in ideal body weight. However, both serum concentrations were not correlated with BMI. These results suggest that VPA doses should be calculated using ideal body weight and that degree of obesity may affect CBZ serum concentration rather than VPA serum concentration.