BL-5255, a tetrazolylpyrimidinone with potent oral antiallergy activity in animals.

BL-5255, 2-(2-n-propoxyphenyl)-5-(5-1 H-tetrazolyl)pyrimidin-4 (3H)-one, effectively inhibited allergic reactions in sensitized rats or guinea pigs when administered by oral or intravenous routes as the water-soluble sodium or ethanolamine monohydrate salts. In the IgE-mediated rat PCA, BL-5255 was 50 times more potent than disodium cromoglycate by intravenous administration. When administered orally in this model, BL-5255 inhibited the PCA reaction by 50% at 0.1 mg/kg. At less than 0.1 mg/kg p.o., the compound protected conscious actively sensitized guinea pigs from aerosolized antigen-induced collapse. In N. brasiliensis-sensitized rats, BL-5255 administered at 0.1--10 mg/kg p.o. inhibited antigen-induced airway constriction in a dose-related manner. BL-5255 is not a histamine or serotonin antagonist but appears to exert its antiallergic effect by inhibiting the release of mediators.