Bioequivalence studies of a new valproic acid delayed-release capsule and divalproex sodium delayed-release tablet

ABSTRACT

Objective: The study examined relative bioavailability of a novel valproic acid (VPA) delayed-release (DR) soft gelatin capsule formulation to divalproex sodium DR tablet under fasting conditions and the effect of food on the bioavailability of the VPA DR soft gelatin capsule.

Method: This open-label, randomized three-way crossover study enrolled 36 healthy non-smoking adult volunteers. Treatments included a single 500 mg divalproex sodium DR tablet, fasting; a single 500 mg VPA DR soft gelatin capsule, fasting; and, a single 500 mg VPA DR soft gelatin capsule 500 mg, non-fasting. Analysis of variance was performed on the pharmacokinetic parameters. The ratio of geometric means and corresponding 90% confidence intervals (CI) were calculated on ln-transformed data for the area under the serum concentration-time curve (µg-hr/mL) from time zero to the time of the last quantifiable concentration (t) (AUC_0–t), AUC_0–∞ and maximum plasma concentration (C_max). Bioequivalence was shown when 90% CIs were within the 80–125% range.

Results: All subjects completed the study. The 90% CIs of VPA DR soft gelatin capsules compared to divalproex sodium DR tablets were within the 80–125% limits for AUC_0–t, AUC_0–∞, and C_max. The time of maximum or peak concentration (T_max) of VPA DR soft gelatin capsules was 2.3 hours versus 3.7 hours with divalproex sodium DR tablets. AUC_0–t and AUC_0–∞ of VPA soft gelatin capsules were not affected in the non-fasting condition, but T_max occurred at 6.1 hours compared to 2.3 hours fasting. Eight subjects experienced a total of 10 adverse events; none were serious.

Conclusion: The VPA DR soft gelatin capsule formulation was shown to be bioequivalent to divalproex sodium DR tablet and no serious adverse events occurred. Because this was not a multiple-dose study, however, direct comparisons in chronic dosing were not possible. Administration with food affected rate but not extent of absorption of the VPA DR soft gelatin capsules, but comparisons with the reference product were not conducted under non-fasting conditions.