M. U. Farooq, I. Saeed, S. Ul Hassan, S. Zaman, M. Shah, and S. Hussain, “Role of Low-Dose Theophylline on Functional Improvement in Patients of Moderately Severe Chronic Obstructive Pulmonary Disease”, Pak Armed Forces Med J, vol. 73, no. 1, pp. 306–09, Mar. 2023, doi: 10.51253/pafmj.v73i1.7254.