Psychomotor performance: investigating the dose-response relationship for caffeine and theophylline in elderly volunteers

Objective: The aim of this study was to investigate the dose-response relationship for psychomotor performance, caffeine and theophylline in healthy elderly volunteers. Methods: In a randomized, double-blind, placebo-controlled, six-period cross-over study we compared the effect of three doses of theophylline (predicted peak concentrations of 3, 6 mg · l⁻¹ and 12 mg · l⁻¹), two doses of caffeine (predicted peak concentrations of 4.5 mg · l⁻¹ and 9 mg · l⁻¹) and placebo on ten healthy elderly volunteers. Psychomotor performance was measured using a continuous attention task, symbol digit substitution test and choice reaction time. Subjective effects were assessed using visual analogue scales. Following drug administration, subjects received the test battery at 30-min intervals, up to 150 min. Maximum and mean effects from baseline on each variable were included in the analysis. Results: Significant improvement on the continuous attention task was seen at the lowest concentration of caffeine and theophylline used, while at higher concentrations there was a non-significant trend towards placebo scores. There was little effect of either drug on the subjective effects measured by visual analogue scales. Conclusion: Caffeine and theophylline increase psychomotor performance measures of attention at low plasma concentrations in healthy elderly volunteers. This effect is not increased by higher drug concentrations and there is trend towards a return to placebo scores. The lack of effect of both caffeine and theophylline on subjective measures is consistent with previous studies of caffeine in the elderly. Received: 11 December 1997 / Accepted in revised form: 18 March 1998