Which one of the following is not recommended for the immediate treatment of acute severe asthma?

Due to slow onset of action , Salmeterol would not be useful .Ipratropium is an anti-cholinergic drug and is useful nebulization. Magnesium sulphate has been used in nebulization form ( surprisingly) or intravenous and antagonizes the effect of intra-cellular calcium. Hence it can reduce the bronchospasm Its used has been mentioned in current edition of Harrison. Hydrocoisone accentuates the effect of broncho-dilators and also inhibit production of leukotrienes.