Influence of dosing regimen on alprazolam and metabolite serum concentrations and tolerance to sedative and psychomotor effects |
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Authors: | R B Smith P D Kroboth |
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Institution: | (1) Pharmacokinetic and Pharmacodynamic Research Unit, The Upjohn Company, Kalamazoo, MI, USA;(2) Pharmacodynamic Research Center, School of Pharmacy and Department of Medicine, University of Pittsburgh, 527 Salk Hall, 15261 Pittsburg, PA, USA |
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Abstract: | The relationships between alprazolam and metabolite concentrations and CNS effects were determined in a double-blind placebo
controlled four-way crossover trial in 16 normal male volunteers. Active drug treatments consisted of 4-day regimens of 4
mg alprazolam PO daily as 2 mg bid., 1 mg qid, and 0.25 mg each hour. On days 1 and 4, the kinetics, sedative and psychomotor
effects were evaluated. Plasma concentrations of the 4- and α-hydroxy metabolites of alprazolam were less than 10% of unchanged
alprazolam levels on both days. Accumulation of these metabolites and alprazolam was dependent on alprazolam half-life (11.6
h). Acute and chronic tolerance to the sedative and psychomotor effects was observed with all active drug treatments. All
alprazolam treatments resulted in significantly greater sedation than placebo on days 1 and 4. However, on day 4, sedation
was 16–36% less than observed on day 1, despite plasma concentrations 1.4–2.76 times the day 1 concentrations. Sedation from
alprazolam was reduced in each successive study phase, suggesting a tolerance which was sustained during the 10-day washout
between phases. By day 4, psychomotor performance was not different from placebo, indicating more complete development of
tolerance than occurred for the sedative effect. Sedation and psychomotor impairment on day 1 were greatest with 2 mg alprazolam
bid. During the initiation of therapy, the patient will likely experience less sedation and psychomotor impairment with smaller,
more frequent doses. Since tolerance develops to these effects, the advantage of more frequent dosing regimen dissipates by
the 4th day. |
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Keywords: | Alprazolam 4-Hydroxyalprazolam α -Hydroxyalprazolam Pharmacodynamics Pharmacokinetics Tolerance Dosing regimen Psychomotor effects Sedation |
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