Tasimelteon (Hetlioz®), a melatonin receptor agonist, is the first, and, at the time of the publication, the only drug to be approved by the U.S. Food and Drug Administration (FDA) for the treatment of non-24-hour sleep-wake disorder (non-24). This circadian rhythm disorder occurs most commonly in blind individuals without light perception, and it results from their inability to entrain to the 24-hour photoperiod, although the indication does not specify a particular patient population. Non-24 is characterized by a persistent cycle of nighttime insomnia and daytime sleepiness, alternating with asymptomatic periods depending on an individual's degree of circadian rhythm synchronization with the photoperiod at any particular time. Phase II clinical trials in healthy individuals confirmed the circadian phase-shifting potential of tasimelteon. Phase III trials in totally blind subjects diagnosed with non-24 demonstrated the efficacy of tasimelteon in reducing both nighttime wakefulness and daytime napping. Physiologic monitoring revealed that tasimelteon resulted in a higher proportion of individuals becoming entrained to the 24-hour cycle compared with placebo. Safety assessments indicated that tasimelteon is well tolerated, with the most common adverse events being headache, alanine aminotransferase elevation, nightmares or unusual dreams, and upper respiratory or urinary tract infections. Tasimelteon is available as a capsule in a single 20-mg dose and it must be obtained through Vanda Pharmaceutical's HetliozSolutions program with dispensing through a specialty pharmacy. Safety studies in blind individuals diagnosed with non-24 are ongoing and a future clinical trial with Smith-Magenis syndrome patients is planned.
Keywords: Circadian rhythm; Melatonin; Non-24-hour sleep-wake disorder; Tasimelteon.
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