This study aims to generate additional safety data on the propellant component of the reformulated product by comparing metered dose inhaler (MDIs) containing HFA-152a (test) with HFA-134a (reference).

Inclusion Criteria:

• Participant must be aged greater than equal to (>=)18 years at the time of signing the informed consent.

• Participants with asthma for >= 6 months, defined as:

  • Documented history of asthma, as defined by Global Initiative for Asthma (GINA)

• Receiving one of following asthma treatments for at least 12 weeks prior to the screening visit and which is anticipated to remain stable for the duration of the study:

• Short-Acting beta2-Adrenoreceptor Agonists (SABA) as needed (prn) only

• Inhaled corticosteroid (ICS)/SABA prn only

• SABA prn plus ICS prn

• SABA prn plus ICS maintenance

• ICS/SABA prn plus ICS maintenance

• SABA prn plus ICS/ Long-acting beta agonist (LABA) maintenance

• ICS/SABA prn plus ICS/LABA maintenance

• SABA prn plus ICS/ Long-acting muscarinic antagonist (LAMA)/LABA maintenance (open or closed triple therapy)

• ICS/Formoterol combination therapy as reliever therapy

• ICS/Formoterol combination therapy as maintenance therapy plus ICS/Formoterol combination as reliever therapy.

• Leukotriene receptor antagonist (LTRA) as add-on any of the above is permitted

• Xanthines as add-on to any of the above permitted

• Biological therapies indicated for the treatment of asthma as add-on to any of the above are permitted (for example, but not limited to, mepolizumab, dupilumab, tezepelumab).

• Participants with severity of disease:

• Baseline pre-bronchodilator Forced expiratory volume in 1 second (FEV1) >=50 percent (%) of predicted at screening.

• Asthma Control Status

• Asthma Control Questionnaire (ACQ)-6 score less than (<) 1.5 at screening (and randomization).

• Asthma that has remained stable with no severe exacerbations within the last 3 months.

• Participants who are current non-smokers, who have not used any inhaled tobacco or vaping products within 12 months of the start of the study, and with a total pack year history of less than equal to (<=)10 pack. The use of inhaled marijuana, even with a valid prescription, is prohibited within 12 months prior to study start.

• Participants who demonstrate ability to use pressurized MDI device in a satisfactory and repeatable manner, as judged visually by the investigator or designee.

• Male and female participants are eligible.

A female participant is eligible to participate if they are not pregnant or breastfeeding, and one of the following conditions applies:

• Is a Participant of nonchildbearing potential (PONCBP) or

• Is a Participant of childbearing potential (POCBP) and using a contraceptive method that is highly effective, with a failure rate of <1%, 30 days prior to and during the study intervention period and for at least 24 hours after the last dose of study intervention. - A POCBP must have a negative highly sensitive pregnancy test (urine or serum as required by local regulations) within 24 hours before the first dose of study intervention in each Treatment Period.

  • Adults capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the Informed consent form (ICF).

Exclusion Criteria:

• Participants with a history of life-threatening asthma.
• Participants with other significant pulmonary diseases, including (but not limited to): pneumothorax, pulmonary fibrotic disease, bronchopulmonary dysplasia, chronic bronchitis, emphysema, chronic obstructive pulmonary disease, tuberculosis, or other significant respiratory abnormalities other than asthma.
• Respiratory Infection: Culture-documented or suspected bacterial or viral infection of the upper or lower respiratory tract, sinus or middle ear that is not resolved within 4 weeks of screening.
• Participants with severe asthma exacerbation: Defined as any asthma exacerbation requiring >=3 days systemic corticosteroids or that resulted in overnight hospitalization or Emergency Department visit requiring additional treatment for asthma within the 3 months prior to screening.
• Participants with Other concurrent Diseases/Abnormalities: A participant has any clinically significant, uncontrolled condition or disease state that, in the opinion of the investigator, would put the safety of the participant at risk through study participation or would confound the interpretation of the study results.
• Participants with current use of cholinesterase inhibitor medication (e.g. for myasthenia gravis).
• Participants with any other prescription or over the counter medication which would significantly affect the course of asthma, or that could interact with sympathomimetic amines.
• Participants with Drug or Excipient Allergy: Known or suspected sensitivity to the constituents of salbutamol MDI (e.g. HFA-134a, Oleic acid etc.).
• Participants with exposure to more than four new chemical entities within 12 months prior to the first dosing day or participation in a clinical study within 30 days of study start, or 5 half-lives of study drug if that is longer.
• Participants with a known or suspected history of alcohol or drug abuse.
• Any planned or anticipated changes in asthma medications during the study period.
• Any planned environmental changes (e.g. employment changes, travel) which, in the Investigator's opinion, could lead to e.g. increased allergen exposure.
• 12-Lead ECG abnormality: Significant abnormality in the 12-lead ECG performed at screening.
• Alanine transaminase (ALT) >2 times Upper limit of normal (ULN).
• Total bilirubin >1.5 times ULN; For participants with Gilbert's syndrome can be included with total bilirubin >1.5 times ULN if direct bilirubin is <=1.5 times ULN.
• Participants with Cirrhosis or current unstable liver or biliary disease.
• Participants with QTc >480 milliseconds (msec).

Study Sponsor will assess requests from qualified researchers for anonymized individual patient-level data and related study documents. Data sharing is subject to certain criteria, conditions, and exceptions. For further information, refer to https://www.gsk-studyregister.com/gsk-patient-level-data-sharing-july2025.pdf

Anonymized IPD will be made available within 6 months of publication of primary, key secondary and safety results for studies in product with approved indication(s) or terminated asset(s) across all indications.

Anonymized IPD is shared with researchers whose proposals are approved by an Independent Review Panel and after a Data Sharing Agreement is in place. Access is provided for an initial period of 12 months but an extension may be granted, when justified, for up to 6 months.

This will be a double blind study.