Medications for Obstructive Sleep Apnea In Children With Down Syndrome

This is a randomized, double blind, cross-over study of the combination of atomoxetine and oxybutynin (ato-oxy) in children with DS and OSA documented by polysomnography (PSG). Participants will receive high dose ato-oxy for four weeks as well as low dose ato-oxy for four weeks in random order. During the high dose ato-oxy period, participants will take 5 mg oxybutynin and 0.5mg/kg/day (max 40 mg) atomoxetine nightly for one week. Atomoxetine dose will then be increased to 1.2 mg/kg/day (max 80 mg). During the low dose ato-oxy period, participants will take 5 mg oxybutynin and 0.5mg/kg/day (max 40 mg) atomoxetine. Dosing of the study treatment will occur approximately 30 minutes prior to bedtime. Participants who withdraw from the study will not be replaced. Study participants will undergo eligibility screening that will include an initial screening to determine whether non- PSG enrollment criteria are met, followed by a 1 night in-lab PSG and health-related quality of life assessment for participants who qualify based on non-PSG criteria. For participants who are eligible and enroll in the study, the screening PSG night will serve as the baseline measure for apnea hypopnea index (AHI) and other PSG endpoints. On the final night of dosing for both high dose ato-oxy and low-dose ato-oxy, participants will return for inpatient PSG and health-related quality of life assessment. The primary efficacy endpoint is the change in obstructive AHI from baseline (high dose ato-oxy vs. low dose ato-oxy).