Assess the Effect of Zolpidem, Silenor & Placebo on Arousability, Ataxia/Balance & Cognition in Healthy Volunteers

Subjects will be screened and asked to complete sleep disorders questionnaires and a sleep
diary to establish normal sleep patterns and to rule out any sleep disorder.

Eligible subjects will be scheduled for a Screening PSG to rule out PLMS, sleep apnea and
other sleep disorders.

Subjects who meet the screening PSG criteria will be randomly assigned to a treatment
sequence order that involves both the study drug and the time subjects are awakened in the
middle-of-the-night using a crossover study design. These four sequences include Silenor 6 mg
with a middle-of-the-night awakening at 4 hours (DXP-4H), zolpidem 10 mg with a
middle-of-the-night awakening at 1.5 hours (ZOL-1.5H), placebo with a middle-of-the-night
awakening at 4 hours (PBO-4H), and placebo with a middle-of-the-night awakening at 1.5 hours
(PBO-1.5H). Study drug will be administered under fasted conditions (at least 4 hours) as a
single dose at bedtime (approximately 2300 hours), and each subject will receive one dose of
each active drug (Silenor 6 mg and zolpidem 10 mg), and two doses of placebo during the
treatment period.

Safety assessments will be performed throughout the study.

During the night of assessment, subjects will be awoken at the estimated T-max of the active
drugs, with a matching placebo group awakened at each of these time points with the same
arousability protocol. Arousability will be assessed using the Auditory Awakening Threshold
test (AAT) .

Once the Auditory Awakening Threshold has been determined, subjects will perform a Tandem
Walk assessment followed by the Berg Balance Scale (BBS) and finally by Free Recall Memory
testing.

Subjects will be discharged from the sleep center once all assessments have been completed. A
final study visit will be performed for subjects either after they have completed all four
Treatment Periods or they have prematurely discontinued the study.

Inclusion Criteria:

- Be in good general health as determined by the investigator;

- Have a 3-month history of a normal nightly sleep pattern based on the subject's self
report ;

- A usual time in bed

- A regular bedtime between 2200 and 2400 hours

- No habitual daytime napping;

- Epworth Sleepiness Scale score ≤ 10;

- Be able to read, understand, and provide written/dated informed consent before
enrolling in the study, and must be willing and able to comply with all study
procedures;

- Be able to follow verbal and written instructions provided in English

Exclusion Criteria:

- Have a body mass index (BMI) >35 kg/m2

- Have symptoms consistent with the diagnosis of any sleep disorder (e.g., insomnia,
sleep apnea, narcolepsy, periodic leg movements, or restless leg syndrome);

- On screening PSG AHI > 10 or PLMAI >10;

- Have a known or suspected diagnosis of Acquired Immune Deficiency Syndrome (AIDS), or
have tested seropositive for human immunodeficiency virus (HIV) antibody or antigen
previously;

- Have any clinically significant abnormal finding in physical examination, neurological
assessment, vital signs, elevated body temperature, or clinical laboratory tests, as
determined by the Investigator;

- Have a known exaggerated pharmacological sensitivity, hypersensitivity, or history of
a clinically significant adverse reaction to zolpidem;

- Have a known or exaggerated pharmacological sensitivity, hypersensitivity, or
intolerance to doxepin HCl, any tricyclic antidepressant, or antihistamine;

- Currently taking cimetidine or a monoamine oxidase inhibitor (MAOI);

- Current diagnosis of severe urinary retention;

- Current diagnosis of untreated glaucoma;

- Intends to use any medication including over-the-counter (OTC) medications that would
interfere with normal sleep architecture (such as systemic steroids, beta-adrenergic
blockers, amphetamines, modafinil, etc.);

- Self-reports use of products containing nicotine of greater than 15 cigarettes daily,
or cannot avoid products containing nicotine during the normal sleep periods;

- Self report consumption of more than five alcoholic beverages on any one day or
greater than 14 alcoholic beverages weekly over the past week;

- Have a history of epilepsy or serious head injury;

- Used CYP450 2D6 inducers or inhibitors within 7 days before screening;

- Have used prescribed or OTC medications within 30 days of screening (Day 0) or intend
to use any prescription or OTC medication during the study that may interfere with the
evaluation of the study drug.

- Have used an investigational drug within 30 days or five half lives (whichever is
longer) before screening, or plans to use an investigational drug during the study or
have used doxepin or zolpidem previously.

- Score of < 40 on the BBS at screening