Asthma is a common chronic respiratory illness which results in frequent wheezing, cough,reduced quality of life. Standard treatment for asthma attack includes oxygen therapy, β2-agonists (e.g. albuterol) and inhaled anticholinergics and corticosteroids. Although inhaled short-acting β2-agonists (SAB) is the initial choice to control acute asthma exacerbation, there are still some asthmatic children unresponsive to this management. The Global Initiative in National Asthma (GINA) does not recommend intravenous magnesium sulfate (MgSO4) for routine use in asthma exacerbation especially in young children. But intravenous MgSO4 can reduce hospital admission rates in certain patients due to several effects e.g relaxation of smooth muscle,blocking acetylcholine. In addition,adding MgSO4 to nebulized SAB provides greater benefit in severe asthma exacerbation.

Inclusion Criteria:

• asthmatic children with controlled clinical manifestation

Exclusion Criteria:

• fever
• history of chronic disease like bronchopulmonary dysplasia or cystic fibrosis
• allergic to acetylcholine, albuterol or magnesium
• use any bronchodilator agents before the Clinic day