Introduction: This study was an extension into an operational setting of previous laboratory work investigating the use of zopiclone and melatonin to facilitate early circadian sleep in transport aircrew. The previous laboratory-based study demonstrated that both melatonin and zopiclone were effective in inducing early circadian sleep without impacting on psychomotor performance after a 7-h sleep period.
Methods: In a repeated measures, placebo-controlled protocol, 30 aircrew flew 3 transatlantic missions over which they took each of the 3 medications (placebo, sustained-release melatonin 2 mg, or zopiclone 5 mg) at an early body clock time (17:00) during their first stopover. They wore wrist actigraphs prior to and throughout the missions, took a single dose of their scheduled medication immediately prior to their early circadian bedtime, and completed a sleep questionnaire on arising from their medicated sleep.
Results: The results of the actigraphic data show that relative to placebo, aircrew on melatonin and zopiclone fell asleep more quickly (melatonin: p < 0.01, zopiclone: p < 0.003), slept more (melatonin: p < 0.02, zopiclone: p < 0.005), had fewer awakenings after sleep onset (melatonin: p < 0.004, zopiclone: p < 0.01), and spent less time awake after sleep onset (melatonin: p < 0.01, zopiclone: p < 0.05). The results of the questionnaire data show that relative to placebo, aircrew on melatonin and zopiclone experienced less difficulty getting to sleep (melatonin: p < 0.0001, zopiclone: p < 0.001), had fewer awakenings (melatonin: p < 0.005, zopiclone: p < 0.001), less difficulty returning to sleep after awakening (melatonin: p < 0.0001, zopiclone: p < 0.0001), and reported a better sleep quality (melatonin: p < 0.0003, zopiclone: p < 0.0004). There were no statistically significant differences between melatonin and zopiclone in any of the actigraphic or questionnaire sleep parameters.
Conclusions: Melatonin and zopiclone, in the dosages we used, are equipotent facilitators of early circadian sleep during transmeridian air transport operations.