Pharmacokinetics of valproic acid after administration of three oral formulations in healthy adults.

The pharmacokinetics and bioavailability of valproic acid was compared in six healthy volunteers after single dose oral administration of 400 mg of the drug in tablet, capsule and syrup form in a crossover manner. Blood samples were collected for 48 hours and valproic acid concentration analysed by enzymatic immunoassay. Following the administration of the three dosage forms, the absorption varied (Ka = Syrup K 2.64 +/- 0.5; tablet 1.57 +/- 0.22; and capsule 0.55 +/- 0.55 h-1). Valproic acid concentration reached a peak level of 102.3 micrograms.ml at 1.9 h after syrup administration, 73 micrograms/ml at 3.3 h after tablet and 44.8 micrograms/ml at 5.4 h after capsule. The bioavailability of tablet and syrup formulation was not significantly different from each other but it differed from capsule form in that the bioavailability was only 52%.