Pharmacokinetics and pharmacodynamics of adinazolam and N-desmethyladinazolam after oral and intravenous dosing in healthy young and elderly volunteers.

The pharmacokinetics and pharmacodynamics of adinazolam and N-desmethyladinazolam were studied in 18 young subjects, from 21 to 36 years of age, and 18 elderly subjects, ranging in age from 65 to 76 years. Nine men and 9 women per age group were studied in a randomized three-way crossover design. Single doses of one 30-mg adinazolam mesylate sustained release tablet, one 30-mg immediate release tablet, and 15 mg of intravenous adinazolam mesylate were administered. Plasma adinazolam and N-desmethyladinazolam were determined by high-performance liquid chromatography, and psychomotor performance tests, including digit-symbol substitution and two card-sorting tasks, were performed. An effect index, defined as the maximal performance decrement divided by N-desmethyladinazolam maximum plasma concentration was calculated as a measure of sensitivity to these effects. Adinazolam oral and systemic clearances were reduced approximately 30% and 25%, respectively, in elderly volunteers. Adinazolam half-life was prolonged approximately 40% in the elderly after oral dosing. N-Desmethyladinazolam plasma concentrations and half-life were increased approximately 40% in elderly volunteers. Psychomotor performance decrements were observed following all treatments; decrements were lowest following sustained release tablets and intravenous adinazolam. Maximal performance decrements in elderly subjects were approximately twice those observed in young subjects. No significant influence of age on the effect index for digit-symbol substitution was evident. Effect indices for card-sorting tests were significantly higher in the elderly. Lower clearances of adinazolam and N-desmethyladinazolam are observed in elderly volunteers, and increased N-desmethyladinazolam levels contribute to increased psychomotor performance decrements in elderly subjects. Results also suggest that elderly subjects may be more sensitive to certain cognitive effects of N-desmethyladinazolam.