<prompt> Which of the following drugs has been found to be useful in acute severe asthma ?Magnesium SulphateAnti-leukotrineCromolyn SodiumCyclosporine  <response>: A high concentration of oxygen should be given by face mask to achieve oxygen saturation of 90.Magnesium sulfate given intravenously or by nebulizer has been found to be effective in acute severe asthma,when added to inhaled beta2 -agonists is well tolerated.It can provide additional bronchodilation in patients whose presenting PEFpeak ejection fractionis below 30 predicted. Reference:Harrisons medicine-18th edition,page no:2113;Davidsons medicine-22nd edition,page no:672. 