Study of Sleep-maintenance Activity of 3 Doses of SKP-1041

• subjective (patient's) assessment of wake time after sleep [ Time Frame: 9 hours after tablet ingestion ] [ Designated as safety issue: No ]
• Visual Analog Scale [ Time Frame: 9 hours after tablet ingestion ] [ Designated as safety issue: Yes ]
  To evaluate the potential for next-day residual effects
• Digit Symbol Substitution Test [ Time Frame: 9 hours after tablet ingestion ] [ Designated as safety issue: Yes ]
  To evaluate the potential for next-day residual effects.

SKP-1041 is a new formulation of a marketed sleeping agent called zaleplon. Zaleplon is currently available as Sonata as well as several generic formulations. Sonata and its generics induce sleep soon after ingestion. SKP-1041, however, is a formulation that is designed to become active 2-3 hours after ingestion. It is intended for use in people who have no trouble falling to sleep but who often awaken in the middle of the night. This trial will determine the best dose to prevent those awakenings.

Patients will participate in the study for approximately 44 to 56 days, including a 14- to 21-day Screening Period, 4 Treatment Periods each followed by washout periods, and a final Follow-up Visit. Patients will receive their randomly assigned study medication and spend 2 nights in a sleep laboratory, subsequently returning home for a 4- to 7-day washout period between each treatment period. The fourth and final treatment period will include a third night at the site during which all patients will continue to receive the same study medication as on the first 2 nights of this treatment period. Blood will be drawn from all patients for pharmacokinetic analyses at specific time intervals. Patients will undergo final safety assessments 2 to 5 days after the last dose of study medication.

• Sleep Disorder
• Primary Insomnia

• Drug: placebo
  tablet at bedtime
  Other Name: sugar pill
• Drug: SKP-1041 (experimental formulation of zaleplon)
  tablet at bedtime
  Other Name: zaleplon

• Placebo Comparator: placebo (sugar pill)
  Intervention: Drug: placebo
• Experimental: 10 mg SKP-1041
  Intervention: Drug: SKP-1041 (experimental formulation of zaleplon)
• Experimental: 15mg SKP-1041
  Intervention: Drug: SKP-1041 (experimental formulation of zaleplon)
• Experimental: 20mg SKP-1041
  Intervention: Drug: SKP-1041 (experimental formulation of zaleplon)

Inclusion Criteria:

• Primary insomnia characterized by chronic difficulty maintaining sleep

Exclusion Criteria:

• History of restless legs syndrome, sleep apnea, narcolepsy, or parasomnias;
• Any clinically relevant acute or chronic diseases which could interfere with the patient's safety during this trial or with this tablet's absorption;
• Pregnancy;
• History of medication allergies;
• Use of medication that might interfere with this study;
• Recent travel across more than 3 time zones.