YM-264 is a selective and orally active antagonist of platelet-activating factor (PAF) (pKi value of 8.85 for rabbit platelet membranes).

PAF (rabbit platelet membranes):pki： 8.85

YM-264 inhibits [3H] platelet-activating factor binding to rabbit platelet membranes with a pKivalue of 8.85. YM-264 inhibits the platelet-activating factor-induced human, rabbit and guinea-pig platelet aggregation with pA2 values of 8.68, 8.33 and 8.14, respectively[1].

Antigen exposure-induced airway hyperresponsiveness is significantly reduced with YM-264 administration. The control group shows a baseline airway resistance (Rrs) value of 0.40 (0.02) cm H2O/mL/s (n=6), compared to YM-264 treated groups which exhibit baseline Rrs values of 0.39 (0.01) cm H2O/mL/s for 1 mg/kg (n=5) and 0.36 (0.01) cm H2O/mL/s for 3 mg/kg (n=6). During immediate allergic reactions, Rrs notably increases to 0.92 (0.10) cm H2O/mL/s in the control (p=0.0002), contrasted with lesser increases of 0.81 (0.12) cm H2O/mL/s at 1 mg/kg (p=0.01) and 1.06 (0.29) cm H2O/mL/s at 3 mg/kg (p=0.048) in the YM-264 treated groups. Furthermore, a significant re-elevation of Rrs to 0.72 (0.10) cm H2O/mL/s (p=0.0101) from baseline is observed in the control group 6 hours post-antigen challenge, whereas YM-264 at doses of 1 and 3 mg/kg markedly inhibits this rise in comparison. Additionally, YM-264 demonstrates a dose-dependent inhibition of eosinophil infiltration.