Distribution of Prostaglandin E_1 in Lipid Emulsion in Relation to Release Rate from Lipid Particles

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The distribution style of prostaglandin E_1 (PGE_1) in injectable lipid emulsion (Lipo-PGE_1) was analyzed using a three-phase model : an aqueous phase, an oil phase and an oil/water interface. A combination of the oil phase and the oil/water interface was obtained as the particle phase. Initial diffusion rates of PGE_1 from lipid particls to the aqueous phase were determined by the dialysis method, and equilibrium concentrations were calculated by the diffusion rates using an equation derived from Fick's theory. Lipo-PGE_1 enclosed in cellulose tubing was immersed in buffer solutions (pH 5.5,7.4), then incubated at various constant temperatures. Each concentration of PGE_1 in the aqueous phase was measured at appropriate intervals. By using these values, partition coefficients between the particle phase and the aqueous phase were calculated. It was found that a larger portion of PGE_1 was distributed in the particle phase compared with the aqueous phase in Lipo-PGE_1 at each temperature. Furthermore, actural partition coefficients between oil and aqueous phases were measured. From the results of two partition coefficients, the distribution ratio of PGE_1 in Lipo-PGE_1 was determined as : oil : oil/water interface : water=0.2 : 93.1 : 6.7,that is, 93% PGE_1 was found to be distributed in lipid particles. On the other hand, by diluting PGE_1 one hundred times with transfusion, the distribution ratio of PGE_1 in lipid particles decreased as the pH of the transfusion increased. The ratios after 2 h were 74% and 47% for pH 5.5 and 7.4,respectively.In conclusion, a large portion of PGE_1 was found to be distributed in the particle phase when Lipo-PGE_1 was diluted with transfusion. Since most PGE_1 exists in an oil/water interface, it is considered that it has a strong affinity for phospholipids. Thus, this affinity may contribute to the remarkable increase in activity in clinical treatment.
公益社団法人日本薬学会の論文
1994-03-15

Distribution of Prostaglandin E_1 in Lipid Emulsion in Relation to Release Rate from Lipid Particles

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