Alprazolam in the elderly: pharmacokinetics and pharmacodynamics during multiple dosing

Previous studies have suggested that elderly men eliminate alprazolam more slowly than young adults. This study in the elderly was designed to determine whether a change in pharmacokinetics influences the response to alprazolam during multiple dose regimens. In addition, the study was designed to determine alprazolam pharmacokinetics and the degree to which its hydroxymetabolites accumulate, the degree of psychomotor impairment, and whether tolerance to impairment and sedation develops during three different multiple dose regimens. Twenty-six subjects completed this study. The subjects were randomized into one of three treatment groups: 0.25 mg q8h, 0.5 mg q8h, and 2 mg q12h. Subjects remained in the clinic for 8 days (day -2-day 5). Day 0 was used as a drug free testing day to establish baseline scores for sedation, digit symbol substitution (DSS), card sorting (CS) tasks, and two computer tests. Subjects received the drug according to schedule on days 1 through 4, with day 5 as the washout day. Blood samples were assayed for alprazolam, alpha-hydroxyalprazolam and 4-hydroxyalprazolam. Alpha-hydroxyalprazolam concentrations were below assay detection limits in all subjects in the 0.25 and 0.5 mg q8h groups and less than or equal to 2.6 ng/ml in the 2 mg q12h group. When detectable, 4-hydroxyalprazolam concentrations were less than 10% of the corresponding alprazolam concentration. Mean alprazolam oral clearance values in the three treatment groups ranged between 0.54 and 0.62 ml/min/kg and half-lives were in excess of 21 h. Degree of sedation and impairment was dose related. Sedation and impairment was not higher on day 4 despite concentrations 2-3 times as great as on day 1, indicating development of tolerance. Subjects were not, however, back to baseline level of performance on day 4.