ABT-491 is highly potent, selective and orally active platelet-activating factor (PAF) receptor antagonist, developed by Abbott Laboratories for allergic rhinitis treatment. ABT-491 is a potent antagonist of responses linked to the PAF receptor at the cellular level, especially platelets and neutrophils. ABT-491 was also effective in blocking platelet activation in blood, indicating that the presence of high concentrations of protein and other serum factors slightly alters the ability of ABT-491 to interact with PAF receptor. ABT-491 effectively antagonizes PAF-induced platelet and neutrophil responses at submicromolar concentrations in vitro and exhibits in vivo efficacy in alleviating PAF-mediated inflammatory and pathological processes in various animals, including guinea pigs, mice, and rats, via either i.v., i.p. or p.o. routes.