Which of the following b2 agonists is given by inhalation, and is suitable for both terminating acute asthma attacks as well as for twice daily prophylaxis?

(Ref: KDT 6/e p218) Terbutaline is a fast acting bronchodilator useful for terminating the acute attack of bronchial asthma. Due to sho duration of action, it is not suitable for chronic prophylaxis. Bambuterol, salmeterol and formoterol are long acting b2 agonists useful for chronic prophylaxis. Bambuterol and salmeterol are delayed acting, therefore are not suitable for acute attacks. Formoterol is fast acting also, therefore can be used for the treatment of acute attack of asthma.