Circadian rhythmicity and the pharmacologic management of insomnia.

The circadian clock modulates timing of sleep and wakefulness. In certain situations, the circadian potentiation of wakefulness may interfere with desired sleep-scheduling, particularly in the elderly and shift workers. Known abnormalities of circadian regulation are defined by their impact on sleep-wake state expression. In delayed sleep phase syndrome, patients have trouble going to sleep and arising at reasonable hours and are alert in the evening and sleepy in the morning. Patients with advanced sleep phase syndrome are sleepy in the evening and awaken very early and alert in the morning. In shift-work sleep disorder, individuals attempt to wake and sleep out of phase with the circadian clock. As with jet lag, the clock is functioning normally, but the requirements on the clock are abnormal. Typical insomnia can also be associated with circadian rhythm alterations. Practice guidelines and clinical studies data are needed to lead appropriate therapy selection and effective management.