Pharmacokinetic and pharmacodynamic effects of a single nocturnal dose of alprazolam

Six healthy volunteers participated in a study of the pharmacokinetic and psychomotor effects of a single dose of 2 mg of alprazolam compared to placebo when given at night. Alprazolam reached a maximum concentration in the plasma between 0.5 and 2.5 h after the dose. It was extensively distributed to the tissues as shown by the large apparent volume of distribution (1.42 l/kg) and slowly eliminated (t1/2 = 13.7 h). Significant impairment of choice reaction time occurred 1 and 11 h after the dose of alprazolam compared to placebo. Critical flicker fusion was also impaired after alprazolam but the difference from the placebo administration did not reach significance.