Lay summary
Asthma is the most common chronic disease of childhood. The greatest burden is in children aged <5 years. The evidence base for the treatment of childhood asthma is considerably less than for adult asthma. In adults, treatment with a single inhaler that contains both preventer and reliever medications, used as-needed for asthma symptoms, is markedly better at reducing asthma attacks compared to the common approach of taking a reliever-only inhaler as-needed. This new treatment regimen has not been studied in preschool children. If comparable improved efficacy with as-needed preventer+reliever inhaler treatment is shown in childhood as with adult asthma, then implementation of this approach would markedly reduce the burden of asthma in preschool children internationally. In this randomised controlled trial, undertaken in partnership with community general practitioners, the effect of the combined budesonide+formoterol inhaler taken as-needed will be compared with salbutamol as-needed in children aged 24 to 59 months.