A Study to Investigate How Budesonide and Formoterol Move Through the Body (Pharmacokinetics) When Delivered With Different Devices in Participants Aged 4 to Less Than 12 Years Old With Asthma

The purpose of this study is to assess the pharmacokinetics (PK) and safety of symbicort aerosphere and symbicort pressurized metered dose inhaler (pMDI) in participants with asthma aged 4 to less than 12 years.

This is a phase I single-dose, 2-period cross-over, multicenter study in which the participants will be randomized 1:1 to one of two treatment sequences - AB or BA. In the first study period, participants will receive a single dose of either - 1. Treatment A: Symbicort Aerosphere budesonide/formoterol fumarate × 2 puffs (test formulation) 2. Treatment B: Symbicort pMDI budesonide/formoterol fumarate × 2 puffs (reference formulation) After a washout period of at least 28 days and no longer than 42 days, participants who first received Treatment A will receive a single dose of Treatment B, and participants who first received Treatment B will receive a single dose of Treatment A in the study period 2.

Key Inclusion Criteria: * Participants who have clinician-diagnosed asthma for at least 3 months. * Body mass index ≤ 95 percentile for age and body weight of at least 15 kg or higher. * Be on a stable dose of one of the following asthma treatments for at least 4 weeks prior to screening (Visit 1): 1. Short-acting β2 agonist (SABA) used as rescue/reliever medication (as needed) only. 2. Low- or medium-dose inhaled corticosteroids (ICS). 3. Leukotriene receptor antagonist (LTRA). 4. Low-dose ICS/long-acting β2-agonist (LABA). 5. Medium-dose ICS/LABA. * Female participants who experience menarche must have a negative urine pregnancy test at screening. Key Exclusion Criteria: * Current evidence of pneumonia, pneumothorax, atelectasis, pulmonary fibrotic disease, allergic bronchopulmonary aspergillosis, cystic fibrosis, bronchopulmonary dysplasia, or other severe respiratory abnormalities other than asthma. * History of life-threatening asthma defined as any asthma episode associated with loss of consciousness, intubation or admission to an intensive care unit. * History of severe asthma exacerbation within 8 weeks of Visit 1. * Inability to change from any budesonide therapy to another suitable corticosteroid. * Participants with a known hypersensitivity to budesonide and/or formoterol fumarate or any of the excipients of the product. * Not be able to refrain from consuming alcohol and smoking (including electronic cigarettes, vaping, and marijuana) from the time of screening until after the safety follow-up visit. * Unstable asthma. * Received regular maintenance treatment with prohibited anti-inflammatory or long-acting bronchodilator asthma medication. * Evidence of active liver disease. * Prolonged QT interval corrected for heart rate using Fridericia's correction (QTcF).