Objective: the aim of the present study was to assess the effects of a single dose of risperidone (0.25 or 0.5 mg) on psychomotor performances and cognitive functions compared to a placebo and to a positive control, lorazepam 1 mg, in 12 healthy elderly subjects.
Design: this study was a randomized, double-blind, four-way crossover clinical trial involving four eight hour-long treatment periods.
Materials and Methods: the pharmacodynamic assessment criteria included a battery of psychomotor tests, a subjective evaluation and an electroencephalogram. Safety was evaluated by clinical laboratory tests, electrocardiogram and recording of adverse events. Concentrations of risperidone, 9-hydroxy-risperidone and lorazepam were determined before and 2 hours after dosing.
Results: few significant effects were observed on psychomotor tests with risperidone at all dosages. Risperidone was devoid of any deleterious effects on speed of reaction, vigilance and sustained attention, working and long-term memory and increased cortical arousal. Risperidone demonstrated minor impairment on motor activity (decreased finger taping), postural stability, and information processing (impaired digit symbol substitution). Contentedness subjective evaluation was decreased with risperidone 0.5 mg, 6 hours after dosing. No significant difference was observed on EEG frequencies and no sedative activity was detected with risperidone. At 2 hours after dosing, risperidone plasma concentrations were 1.54 ± 0.99 ng/ml and 2.80 ± 1.41 ng/ml; 9-hydroxy-risperidone concentrations were 0.77 ± 0.46 ng/ml and 1.54 ± 0.85 ng/ml after intake of 0.25 mg and 0.5 mg doses, respectively. Well-known detrimental effects of lorazepam on psychomotor performances were observed and sedative effects were confirmed by the EEG findings. At 2 hours following lorazepam 1 mg administration, plasma concentrations were 13.40 ± 2.17 ng/ml. None of both compounds have induced serious adverse events.
Conclusion: the results of this clinical trial conducted on healthy subjects demonstrated that low doses of risperidone, but not low doses of lorazepam, did not disturb the cognitive functions in the elderly.
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