To clarify whether the therapeutic efficacy of lipid microspheres incorporating prostaglandin E-1 (lipo-PGE(1)) is altered when mixed and coinfused with clinical solutions, the original lipo-PGE(1) solution (20 mu g/mL) was mixed with three clinical infusion solutions: 0.9% sodium chloride solution, Hartmann's solution, and fat emulsion for parenteral nutrition. These diluted lipo-PGE(1) (2 mu g/mL) solutions were administered to rats, and their hemodynamic and antiplatelet effects were examined. Peripheral blood flow was increased by 76 +/- 4% from the control level when the lipo-PGE(1) solution diluted with the fat emulsion was administered, while it was increased by 43 +/- 6% and 36 +/- 17%, respectively, when the lipo-PGE(1) solutions diluted with 0.9% sodium chloride and Hartmann's solution were administered. As for the antiplatelet effects of the lipo-PGE(1) solutions, the progression of digit gangrene in thromboangiitis obliterans (TAO) rats was significantly suppressed by the administration of lipo-PGE(1) solution diluted with the fat emulsion, but it was not suppressed by lipo-PGE(1) solution diluted with 0.9% sodium chloride. These findings indicate that the therapeutic efficacy of lipo-PGE(1) is decreased when it is mixed with an aqueous solution such as 0.9% sodium chloride.