Pharmacokinetics of loprazolam and its principal metabolite in young subjects and elderly hospital patients

1. The pharmacokinetics of loprazolam and its principal pharmacologically active metabolite, the piperazine N-oxide, were compared in young subjects (aged 21–25 years) and elderly patients (aged 63–86 years) following single oral evening doses (0.5 mg and 1 mg).2. Plasma loprazolam was assayed by a specific h.p.l.c./g.c. method. The N-oxide metabolite was assayed by gas chromography.3. Mean times to peak plasma concentration of loprazolam did not differ significantly between young and elderly subjects and ranged from 1.6–2.7 h. There was, however, a longer mean time to peak concentration of the N-oxide metabolite in the elderly but this was only statistically different after the 0.5 mg dose (4.5 mg young, 6.4 h elderly).4. Mean peak plasma concentrations of loprazolam did not differ significantly between young and elderly nor did plasma concentrations of the N-oxide metabolite.5. Although the mean elimination half-life of loprazolam was not statistically signiticantly different between young and elderly s...