Randomized Double-Blind Controlled Trial of Roflumilast at Acute Exacerbations of Chronic Obstructive Pulmonary Disease - Mackay, AJ; Patel, ARC; Singh, R; Sapsford, RJ; Donaldson, GC; Prasad, N; Goehring, U-M; Nip, TK; Wedzicha, JA (American Journal of Respiratory and Critical Care Medicine, 2017)