Muhammad Usman Ullah, M Babar Khan. Jahanzeb Liaqat, Raheel Iftikhar, Sultan Mehmood Kamran, Aamir Khalil. “Role of Tiotropium As Step Up Therapy for Asthma”. Journal of Rawalpindi Medical College, vol. 17, no. 2, Dec. 2013, https://journalrmc.com/index.php/JRMC/article/view/441.