Int he rat, small intestinal absorption of FOY305^[○!R] was improved by the addition of citric acid, probably through the reduction of enzymatic degradation of FOY305 by esterase in the intestinal lumen. A solid formulation prepared with trilaurin also increased the intestinal absorption of FOY305, probably through an effect of laurate, which is produced from triaurin by lipase activity in the small intestinal lumen. The combination of citric acid and trilaurin in the solid formulation resulted in a significant increase of intestinal absorption of FOY305, amounting to 10 times that after administration of a simple FOY305 solution.