This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Asthma, Subject name: Pharmacology
Which of the following drugs has been found to be useful in acute severe asthma? 
Select and explain. 
A. Magnesium Sulphate, B. Anti-leukotrine, C. Cromolyn Sodium, D. Cyclosporine
A: Magnesium Sulphate
Answer: A: Magnesium Sulphate 
Explanation: Ans. (A) Magnesium sulphate(Ref: Harrison 17th/e p1605)Magnesium sulphate by i.v. or inhalational route has been used for the treatment of acute severe asthma. All other drugs mentioned in the options are used for prophylaxis of asthma.