Study on the dose proportionality of the pharmacokinetics of sustained release sodium valproate

A bioavailability study using three different doses was designed to assess the dose proportionality of a new multiple-unit sustained release formulation of sodium valproate. SUBIECTS AND METHODS: The study was performed using an open, three-period, randomized, crossover design. Twelve healthy male volunteers received on three occasions single oral doses of either 100 mg, 150 mg and 300 mg of a sustained release sodium valproate formulation. A wash-out period of at least 7 days elapsed between the administrations. Valproic acid was determined in serum by gas chromatography with flame-ionization detector.

After administration of single doses of 100 mg, 150 mg and 300 mg sodium valproate the population mean curves reached their maxima of 4.3 microg/ml, 6.8 microg/ml and 12.8 microg/ml at 9 h, 9 h and 10 h, respectively. The geometric means of AUC0-tz and AUC0-infinity as well as Cmax related to each other approximately according to the expected ratios of 0.33:0.5:1. Point estimates and 90% confidence intervals for the ratios of geometric means of dose-normalized parameters (AUC0-tz, AUC0-infinity, Cmax) were included by the acceptance range of 80-125%. There were no differences in tmax as shown by the inclusion of zero in the 90% confidence interval for the median difference in tmax between the doses.

Parameters determining the extent and rate of absorption (AUC and Cmax) increased proportionally with the dose of the new sustained release sodium valproate formulation. This pharmacokinetic behavior offers easier treatment management as dose adjustment is facilitated.