A competitive antagonist of C5aR (IC50 = 11.6 nM for the human recombinant receptor); has inverse agonist activity; selective for human recombinant over rat and mouse recombinant C5aRs (IC50 = >10 μM for both) but does have activity at macaque and gerbil receptors (IC50s = 7.3 and 6.4 nM, respectively); inhibits degranulation in C5a-stimulated U937 cells (IC50 = 7.1 nM); prevents C5a-induced neutropenia in gerbils (ED50 = 2.2 mg/kg) and in cynomolgus macaques at 5 and 25 mg/kg