Muzna Hameed Dar, S. M. . Alam, Q. ul A. . Bukhari, K. . Ismail, and S. A. H. . Zaidi, “Low Dose Theophylline and Tiotropium Rotacap as Add on Therapy in COPD Patients-Clinical Trial”, J. Bahria Univ. Med. Dent. Coll., vol. 10, no. 2, pp. 137–141, Mar. 2021.