Lay summary
Severe asthma is the most common childhood medical emergency. Up to 8% of children coming to emergency departments with severe asthma need intravenous medication when inhaled treatments are not effective enough to open airways. Despite this, the evidence base for intravenous asthma medications remains poor. In this randomised controlled trial, undertaken in partnership with Australian hospitals, the effect of the two most frequently used intravenous medications, magnesium sulphate and aminophylline, will be compared in children aged 2-15 years presenting to emergency departments with severe asthma. If intravenous magnesium sulphate is superior to intravenous aminophylline for the management of severe asthma paediatric doctors around the world will for the first time have clear evidence to inform practice. Severe childhood asthma is a distressing and dangerous condition. Knowing which treatments are most effective will reduce the burden of severe asthma which disproportionally affects Māori and Pacific children in New Zealand.