CFTR and chronic bronchitis: In further support of the significance of CFTR activation as a treatment modality for COPD, we have previously reported the CFTR-activating properties of roflumilast [20], a currently approved type 4 cyclic nucleotide phosphodiesterase (PDE4) inhibitor that reduces exacerbations in patients with chronic bronchitis and a history of frequent exacerbations [21].