Efficacy and safety of RPL554, a dual PDE3 and PDE4 inhibitor, in healthy volunteers and in patients with asthma or chronic obstructive pulmonary disease: findings from four clinical trials - Franciosi, L G; Diamant, Z; Banner, K H; Zuiker, R; Morelli, N; Kamerling, I M; de Kam, M L; Burggraaf, J; Cohen, A F; Cazzola, Mand all (Lancet Respir Med, 2013)