Quazepam kinetics in the elderly.

The kinetics of quazepam, a benzodiazepine hypnotic, was studied in 10 geriatric subjects. Each received one 15-mg tablet of quazepam. Blood samples were collected before and at specified times (up to 672 hr) after dosing. Plasma concentrations of quazepam and its two major active plasma metabolites, 2-oxoquazepam and N-desalkyl-2-oxoquazepam (N-desalkylflurazepam), were determined by specific GLC methods. Kinetics were best described by a two-compartment open model with first-order absorption/formation kinetics and standard equations. Quazepam was rapidly absorbed, with a t1/2 of 0.8 hr. The mean maximum plasma level (Cmax) was 29.3 ng/ml. The disposition t1/2s in the distribution (t1/2 alpha) and elimination (t1/2 beta) phases were 3.5 and 53.3 hr. 2-Oxoquazepam was rapidly formed with quazepam, with an apparent formation t1/2 of 0.8 hr. Mean Cmax was 14.5 ng/ml. The t1/2 alpha and t1/2 beta of 2-oxoquazepam were 4.2 and 43.1 hr, of the order of those of quazepam. The t1/2 beta of N-desalkyl-2-oxoquazepam, formed from 2-oxoquazepam, was 189.7 hr, much longer than that of its precursor. Comparison of these data with reported kinetic data in young subjects shows that t 1/2 betas of quazepam and 2-oxoquazepam increased only slightly or not at all with age, but that the t 1/2 beta of N-desalkyl-2-oxoquazepam in the elderly was more than twice that in young subjects.