A Comparative Bioavailability Study of Carbamazepine Tablets and a Chewable Tablet Formulation

Abstract

Differences in product formulations have been shown to affect the therapeutic response by altering the relative bioavailability and pharmacokinetics of a drug. The relative bioavailability and pharmacokinetics of carbamazepine tablets (CBZ) and a chewable tablet formulation were evaluated in 10 normal healthy subjects (five men and five women). The study utilized a randomized, crossover design with a 4-week washout period between doses. Blood samples were collected at 0, 1, 2, 3, 4, 6, 8, 10, 14, 24, 30, 36 and 48 h following a 200-mg dose. Plasma samples were assayed by fluorescence polarization immunoassay. Ke, Cmax, Tmax, area under the curve (AUC), and relative bioavailability were estimated using traditional pharmacokinetic methods and compared by paired t test. A statistically significant higher Cmax (3.81 .+-. 81 vs. 4.64 .+-. .80 mg/L) was observed with the chewable tablet formulation but was not thought to be clinically relevant. No significant differences between formulations for Ke (0.022 .+-. 0.007 vs. 0.025 .+-. 0.008h-1h), Tmax (7.49 .+-. 2.69 vs. 6.04 .+-. 2.7 h), AUC 48 h (119 .+-. 22 vs. 133 .+-. 13 mg/h/L), or AUCO-.infin. (221 .+-. 40 vs. 203 .+-. 41 mg/h/L) were noted. Absorption was variable for both preparations. The relative bioavailability using the tablet as the standard formulation was (0.92 .+-. 0.22). Transient, mild side effects were noted in three subjects with the chewable tablet alone, and one subject experienced side effects with both formulations. It was concluded that CBZ tablet and chewable tablets may be used interchangeably; however, considerable intra- and intersubject variability exists, and the need for patient monitoring is emphasized.