Lirimilast (BAY 19-8004) is a potent, selective and orally active phosphodiesterase-4 (PDE4) inhibitor with an IC₅₀ value of 49 nM. Lirimilast can be used for the treatment of asthma or chronic obstructive pulmonary disease (COPD). Lirimilast has potently anti-inflammatory properties^[1][2]. In Vitro: In PDE4 assays Lirimilast (BAY 19-8004) is reported to be 5-fold more potent than Cilomilast and equipotent with CDP-840 using freshly prepared PDE4 from human PMNL^[1]. In Vivo: Since Lirimilast (BAY 19-8004) is orally active in the guinea-pig at 3 mg/kg and, more critically, in primates at 0.1 mg/kg/day it appears to have a good therapeutic ratio. In addition Lirimilast is found to be 3-fold more potent than Cilomilast when compared in a rat model of lung neutrophilic inflammation^[2].