Effects of prolonged-release melatonin and zolpidem on postural stability in older adults

Objectives A prolonged-release formulation of melatonin (PR-M) is indicated for insomnia in patients aged 55years and older. Because hypnotics result in impairments of body sway, it was important to evaluate the effect of 2mg PR-M on postural stability in older adults at night. Methods Twenty-four healthy volunteers (12 women, 12 men, aged 55-64years) completed a randomized, double-blind, single-dose, three-way crossover study of postural stability of PR-M 2mg, zolpidem 10mg (active control) or placebo. Subjects were tested for body sway 30min before, 1.5 and 4h after dosing. Parameters tested were the area of the 95% confidence ellipse enclosing the center of pressure (COP; [A95]) and COP path length. Results Zolpidem significantly increased the A95 (both eyes conditions at all time points) and path length of COP. PR-M had no effect on A95 (both "eyes closed" and "eyes open" conditions at all time points) compared with placebo and increased COP path length by 10% at 4h post-dose in open but not closed eyes condition. No serious adverse events were observed. Conclusions In older adults, evening PR-M intake did not impair postural stability during the night. The postural instability with zolpidem demonstrated assay sensitivity and validated the outcome.