Inclusion Criteria:

• Male or female naval flight personnel, ≥18 years of age
• CogScreen-AE Logistic Regression Probability Value < 0.6 at the baseline screening visit
• Normal SaO2 (>95%) as measured by pulse oximetry
• Female subjects must be of nonchildbearing potential (i.e., surgically sterile or at least 1 year postmenopausal); see Section 4.4 for additional information:

Exclusion Criteria:

• Female subjects who are pregnant, lactating, or likely to become pregnant during the study
• Signs or symptoms of currently active allergic disease (seasonal allergic rhinitis, perennial allergic rhinitis, episodic allergic rhinitis) within 2 weeks prior to the screening visit
• Upper respiratory tract infection, sinusitis, asthma exacerbation, or flu-like symptoms within 2 weeks prior to the screening visit
• Medical history or physical examination findings; clinically significant cardiovascular, respiratory, hepatic, neurologic, endocrine, psychiatric, or other major systemic disease; or laboratory or electrocardiograph abnormality making implementation of the protocol or interpretation of the protocol results difficult. Abnormalities which are not clinically significant will not necessarily disqualify subjects provided, in the opinion of the investigator and sponsor, the study validity or the subject's welfare is not compromised.
• Any unusual sleep pattern, including third-shift workers (11:00 PM to 7:00 AM), or sleep < 6 hours the night before each AVT testing at Visits 1-4
• Any excessive amounts of alcohol (no more than two drinks/day on average)
• Any excessive use of caffeine (more than three cups of coffee per day or equivalent)
• Any history of chronic alcohol or mood-altering drug abuse
• Any use of tobacco/nicotine products within 90 days of the screening visit or during the study
• Any disease state or surgery known to affect the gastrointestinal absorption of drugs
• Mental capacity limited to the extent the subject cannot give legal informed consent or accurate information regarding efficacy and side effects/tolerance of drug
• Subjects unable to comply with the protocol requirements (must complete a screening visit and Visits 1-4 within approximately 1-1/2 months)
• Known hypersensitivity to fexofenadine, or the tablet ingredients (croscarmellose sodium, magnesium stearate, microcrystalline cellulose, pregelatinized starch; or the tablet coating made of hydroxypropyl methylcellulose, iron oxide blends, polyethylene glycol, povidone, silicone dioxide, and titanium dioxide)
• Known hypersensitivity to cetirizine or the tablet ingredients (lactose, magnesium stearate, povidone, titanium dioxide, hydroxypropyl methylcellulose, polyethylene glycol, and corn starch)
• Use of an investigational drug within 30 days prior to Visit 1