Muhammad Usman Ullah, M Babar Khan. Jahanzeb Liaqat, Raheel Iftikhar, Sultan Mehmood Kamran, Aamir Khalil. 2013. “Role of Tiotropium As Step Up Therapy for Asthma”. Journal of Rawalpindi Medical College 17 (2). https://journalrmc.com/index.php/JRMC/article/view/441.