[Bioavailability of a valproic acid preparation. The relative bioavailability of enteric-resistant valproic acid preparations in tablet form with simultaneously administered tetradeuterated valproic acid as the bioavailability reference].

The relative bioavailability was measured for the 150-, 300-, and 600-mg enteric coated Leptilan tablets (valproic acid, sodium salt) using a new method. Simultaneously an equimolar amount of a tetradeuterated valproic acid - di-(2,3-dideutero-n-propyl)-acetic acid - was given as an aqueous solution of the sodium salt. This methodology excludes effects on the two partial pharmacokinetics caused by time-dependent intraindividual variations of the metabolising capacity or other biochemical or physiological changes in the body of the volunteer. Therefore, this methodology gives already reliable data for bioavailability when using only small numbers of volunteers. The relative bioavailability of the enteric coated Leptilan tablets was 95.5 +/- 0.6%, 104.4 +/- 7.6%, and 100.7 +/- 2.4% (mean from experiments with 3 volunteers each) for the 150-, 300-, and 600-mg tablets respectively.