Ontazolast is a small molecule leukotriene B4 receptor (LTB4R) antagonist for the treatment of immune system disorders and respiratory diseases.Ontazolast is a candidate compound for the treatment of asthma.

Ontazolast is a potent inhibitor (IC50 = 1 nM) of calcium ionophore A23187-stimulated leukotriene B4 (LTB4) biosynthesis in human peripheral blood leukocytes. The emulsion formulation and three additional lipid-based formulations were administered by gavage to conscious, minimally restrained rats in a novel, double-cannulated model to determine the effects of formulation on systemic blood absorption and mesenteric lymph transport of ontazolast. The bioavailability of ontazolast was significantly and substantially enhanced by all of the lipid-based formulations. While these formulations also significantly increased the amount of ontazolast transported by the lymph, the total amounts transported were insufficient to account for the improvement in bioavailability, which may be due to the elimination or reduction of the barriers of poor aqueous solubility and slow dissolution to absorption of ontazolast from the gastrointestinal tract, or the effects of lipid on the gastrointestinal membrane permeability, transit time, or metabolism of ontazolast.[1]