RP-HPLC测定左炔诺孕酮与孕二烯酮表观油水分配系数及平衡溶解度

Determination of apparent oil-water partition coefficient and equilibrium solubility of levonorgestrel and gestodene by RP-HPLC

目的：分别测定第2代和第3代避孕药代表性药物左炔诺孕酮（levonorgestrel,LNG）与孕二烯酮（gestodene,GES）的表观油水分配系数及平衡溶解度,为长效避孕微球注射剂制备工艺及体外释放介质的选择提供坚实的处方前研究基础。方法：采用RP-HPLC测定LNG与GES在正辛醇-水、正辛醇-pH 1.2~8.0磷酸盐缓冲液等9种体系中的表观油水分配系数及在水、缓冲液、常用有机溶剂等19种介质中的平衡溶解度。结果：LNG与GES在水中的lgPapp值分别为3.62和3.43;在不同pH值PBS中该值相近,但在pH3.0时例外,LNG与GES的该值均增大。此外,两药均难溶于水,易溶于二氯甲烷、三氯甲烷等有机溶剂;GES的水溶性是LNG的8~10倍,且GES比LNG更易溶于有机试剂;两者在pH 3.0时溶解度均有下降趋势,而在其他pH值条件下无明显差别,该情况与两者表观油水分配系数的变化规律相一致。结论：表观油水分配系数结果提示：LNG与GES在微球制备过程中可获得较好的包封率,同时将延长微球在体内的释药周期。平衡溶解度结果提示：在微球体外释放评价时应添加合适的增溶剂以增加药物溶解度来满足漏槽条件;制备微球采用常规工艺的水包油（O/W）型乳剂-液中干燥法微囊化具有可行性。

Objective：Levonorgestrel（LNG） or gestodene（GES） are the second and the third generation contraceptive representative drugs,respectively,which have promising applications.The studies on their apparent oil-water partition coefficient and equilibrium solubility can provide valuable data and further strategies for the formulation,process and the screening of dissolution mediums.Here we conducted the key preformulation studies for the development of a long-acting LNG-or GES-loaded injection for contraception using PLA /PLGA microspheres as carrier.Methods：Oil-water partition coefficients in nine systems（n-octanol-water and phosphate buffer solutions with different pH from 1.2 to 8.0） were determined by shaking flask method,and the concentrations of LNG and GES were analyzed by RP-HPLC method.Their equilibrium solubility in nineteen types of media（water,buffer solutions and organic solvents） were also determined by RP-HPLC.Results：The values of lgPapp in water of LNG and GES were 3.62 and 3.43,respectively;and the similar values in different PBS,expect for pH 3.0.While at pH 3.0,both of them increased.In addition,the two APIs were insoluble in water and soluble in CH2Cl2,CHCl3 and other organic solvents.The water solubility of GES was 8 ~ 10 times of LNG,and also with more solubility in organic solvents than LNG.Interestingly,there was a same trend in the data of oil-water partition coefficient,i.e.the solubility of them both decreased at PBS with pH 3.0,but there was no significant difference at other pH values.Conclusions：Data of oil-water partition coefficient suggest that choice of LNG and GES as the API for the development of microspheres could achieve desired encapsulation efficiency during the preparation,and promising long-acting contraceptive effect in vivo.Their equilibrium solubilities suggest that during in vitro dissolution test of the microspheres,some appropriate solubilizers should be added to increase the solubility of the APIs to meet sink conditions.Furthermore,it is feasible to prepare the microspheres by oil in water（O /W） emulsion-in liquid evaporation process which is one of the most-often processes.