Ensifentrine (RPL-554) is an inhaled first-in-class dual inhibitor of phosphodiesterase 3 (PDE3) and PDE4 with IC 50 s of 0.4 nM and 1479 nM, respectively. Ensifentrine has bronchoprotective and anti-inflammatory activities. Ensifentrine can be used for chronic obstructive pulmonary disease (COPD) research In Vitro Ensifentrine (RPL-554) inhibits, in a concentration-dependent manner, lipopolysaccharide-induced TNF-α release from human monocytes (IC 50 of 0.52 μM) and proliferation of human mononuclear cells to phytohemagglutinin (IC 50 of 0.46 μM). Electrical field stimulation-induced contraction of guinea pig superfused isolated tracheal preparations is significantly inhibited by Ensifentrine (10 μM). Contractile responses are suppressed for up to 12 h after termination of superfusion with RPL-554 demonstrating a long duration of action. MCE has not independently confirmed the accuracy of these methods. They are for reference only. In Vivo Ensifentrine (RPL-554; 10 mg/kg; Oral administration; once) significantly inhibits eosinophil recruitment following antigen challenge in ovalbumin-sensitized guinea pigs . The inhalation of dry powder containing Ensifentrine by conscious guinea pigs (25% in micronized lactose) 1.5 h before antigen exposure significantly inhibits the recruitment of eosinophils to the airways . Exposure of conscious guinea pigs to inhalation of dry powder containing Ensifentrine (2.5%) in micronized lactose significantly inhibits histamine-induced plasma protein extravasation in the trachea and histamine-induced bronchoconstriction over a 5.5-h period . MCE has not independently confirmed the accuracy of these methods. They are for reference only. Animal Model: Male Dunkin Hartley guinea pigs (200-300 g) injected with ovalbumin . Dosage: 10 mg/kg Administration: Oral administration; once Result: Significantly inhibits eosinophil recruitment following antigen challenge in ovalbumin-sensitized guinea pigs. Form:Solid IC50& Target:PDE3 0.4 nM (IC 50 ) PDE4 1479 nM (IC 50 )