This study seeks to determine whether a simple, single intervention of Cetirizine / Zyrtec® use can improve exercise performance of active individuals when acutely exposed to altitude. For this project, healthy subjects will perform steady state and progressive work rate exercise, endurance performance time trials, and repeated sprint performance time trials in the laboratory at a simulated altitude of 3000m (9900ft) after dosing with 10 mg of Cetirizine or a placebo in a repeated measures design.

This study seeks to determine whether a simple, single intervention of Cetirizine / Zyrtec® use can improve exercise performance of active individuals when acutely exposed to altitude. For this project, healthy subjects will perform steady state and progressive work rate exercise, endurance performance time trials, and repeated sprint performance time trials in the laboratory at a simulated altitude of 3000m (9900ft) after dosing with 10 mg of Cetirizine or a placebo in a repeated measures design. Non-invasive techniques (pulse oximetry, near-infrared spectroscopy [NIRS]) will be utilized to measure changes in arterial oxyhemoglobin saturation and skeletal muscle oxygenation at the level of the microvasculature during exercise. It is expected that after Cetirizine, blood and muscle microvascular oxygenation during heavy exercise will improve compared to placebo, ultimately improving exercise performance at altitude. Subjects will be asked to report to the laboratory on a three occasions, separated by a minimum of 48 hours and a maximum of 14 days. For each subject, all testing sessions will be performed at the same time of day. Prior to each testing session, subjects will be asked to abstain from caffeine consumption for 12 hours. Subjects will also be asked to avoid alcohol consumption for 24 hours before testing, be at least 3-hour post prandial and avoid high-intensity exercise during the 24 hours leading to the exercise testing. Finally, subjects will be asked to consume a similar diet the night before, and the morning of, Sessions 2 and 3.

Inclusion Criteria:

• Physically active a minimum of 120 minutes a week, as determined by questionnaire
• 18-35 years of age
• Classified as low risk, based on the modified PAR-Q questionnaire, BMI, and non-smoking status
• No history of pulmonary disease and pulmonary function classified as normal, as defined by the following measurements being 80% of predicted values: forced vital capacity (FVC), forced expired volume in one second (FEV1) and FEV1/FVC, according to the American Thoracic Society standards.

Exclusion Criteria:

• Current smoker
• Women who are pregnant or could possibly be pregnant
• BMI > 25 kg/m2
• A 'yes' answer to any of the 14 questions on the PAR-Q pre-participation questionnaire
• History of pulmonary disease or <80% of predicted FCV, FEV1 and/or FEV1/FVC.
• A history of renal or liver disease, due to possible interaction effect with Cetirizine
• Currently taking any prescription or over the counter medications for the treatment of allergies, or taking any of the below listed drugs known to have a moderate or higher interaction effect with Cetirizine:

isocarboxazid tranylcypromine bosutinib clobazam crizotinib daclatasvir eliglustat hyaluronidase lomitapide lurasidone ombitasvir/paritaprevir/ritonavir phenelzine ponatinib ritonavir vemurafenib

No IPD plan

The baseline characteristics for subjects completing all three study arms (Hypoxia/Cetirizine, Hypoxia/Placebo, Normoxia/Placebo) are included.

Adverse event data was collected at the time of each intervention visit and for a period of up to one month following each intervention visit date.

The definition of adverse event and/or serious adverse event does not differ from clinicaltrials.gov definitions. All-cause mortality was monitored/assessed.