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)