Elimination kinetics of desmethyldiazepam in two young and two elderly subjects.

Pinazepam (P) (10 mg) was orally administered to two young (22-23 years) and two elderly (74-80 years) healthy volunteers. Also, desmethyldiazepam (DD) (10 mg) was orally administered to the same young volunteers on a separate occasion. P was almost completely converted into DD 24 h after administration. Plasma levels of DD were measured in all subjects. In all cases, the DD concentration-time curve showed a biphasic decay (a first slow decay was followed by a fast one) which closely fitted by a Michaelis-Menten equation. Vmax and km constant were computed for all subjects. The kinetic analysis relative to the young subjects showed that T 1/2 of both the slow and fast decay as well as the area under the curve (AUC) were reduced when P was administered instead of DD. Comparison of DD kinetics between young and elderly subjects showed an increase of half-life in the elderly, while AUC was found unchanged.