Please explain which drug would be used to treat bronchial asthma?

Depends: If attacks are infrequent and , mild, a rescue inhaler and avoidance of triggers would suffice. If they are frequent , and severe, a "controller" inhaler or oral drugs will be needed in addition to the rescue inhaler. Rescue inhalers open your bronchioles and allow you to breathe easier. Controllers reduce inflammation and minimize your attacks. When used together, most asthmatics do pretty well.

CONTROLLER&Reliever: There are Controller MAEDICTIONS which some patients have to take every day to keep Asthma under control These are Long Term beta agonists(Long Term Bronchodilaters) Steroids Inhaled and Leucotrine like Singular Reiever or Resque Meds Quick acting Bronchodilaters like Albuterol,Xopenex Short Course of Steroids Most meds are given via inhaler or Nebuliser Except Singular or Oral Steroids