Influence of neuroticism on oral absorption of diazepam

The subjects were 24 healthy males, 19 to 21 yr old. Twelve subjects had high neuroticism (HN) levels determined by Maudsley Personality Inventory, and 12 had low neuroticism (LN) levels. Subjects took a single 5-mg dose of diazepam (DZP) after a standardized breakfast. The mean plasma concentration for DZP was significantly higher in HN subjects at 1.5 hr after drug than in LN subjects. No difference was found in the DZP plasma levels of these 2 groups after administering the drug directly into the duodenum through a tube. No clear relationship between plasma DZP concentrations and DZP-induced sedative effects determined by Choice Reaction Time Test (CRTT) was demonstrated in the study. The results suggest that the absorption rate of DZP from the gastrointestinal tract is faster in HN subjects than in LN subjects due to the faster gastric emptying time in HN subjects in our experimental situation, which might have induced mild stress.