A review on pharmacological treatment of sleep and circadian rhythm disorders

Approximately one third of our lives are spent in sleeping. Although largely an enigma, sleep is an important component of human behavior and provides an emotional and physical restoration to the body. Abnormalities in the normal physiology of sleep often cause a sleep complaint (e.g., difficulty falling asleep) or result in a sleep disorder (e.g., sleep apnea, narcolepsy). The prevalence of sleep difficulties in the general population is estimated to be 30% to 35%. Sleep is complex psycho-physiologic phenomenon that can be documented in sleep laboratory studies. During sleep the brain is extremely active and produces a characteristic pattern of stages, that cycle during the night. There is a wide inter-individual variability in the amount of sleep required per night (i.e., 3 to 10 hours.) A circadian rhythm of sleep and walking is established shortly after birth and changes over the life cycle. A deceleration of the 24 cycle occurs during adolescence and is typified by difficulty falling asleep. The rhythm returns to 24 hours during adulthood and accelerates with increasing age. Thus elderly individuals commonly complain of falling asleep early in the evening and waking early in the morning. Two oscillators with different period lengths control the suprachiasmic nucleus and the other occurs through neurobiologic mechanism. Two peptides, -sleep inducing peptide and factor S appear to be involved in the biochemical regulation. Synchronization of the oscillators with the 24-hour cycle imposed by the earth's rotation requires a routinely occurring zeitgeber (e.g., clock, light, shower, breakfast) to set the internal clock. Practically, young person should awaken at the same time daily to shorten the oscillators, and elderly persons should delay the onset of sleep until a set time to stretch the oscillators. The neurotransmitter norepinephrine is involved in wakefulness and dreaming, while serotonin is active during non-dreaming sleep. The interaction between the cholinergic system and the noradrenergic system also may play a role in sleep. The pharmacological treatment of sleep and circadian rhythm disorders are updated through this review article.