Protonation equilibrium and lipophilicity of moxifloxacin

This study was performed to characterise the protonation equilibrium at the molecular level and pH-dependent lipophilicity of moxifloxacin. After determining macro- and micro-constants, distribution features of four microspecies in aqueous phase were assessed. The apparent partition coefficient versus pH profile of moxifloxacin showed a parabolic curve in n-octanol/buffer system which reached near pI. The true partition coefficient was calculated from the log P(app) and microconstants values.     

磺胺二甲嘧啶的溶解度及油水分配系数的研究

目的:研究磺胺二甲嘧啶(SM2)在不同pH值下的平衡溶解度和油水分配系数(Ko/w),为SM2制剂的开发提供基础研究。方法:配制不同pH值的磷酸盐缓冲液,采用饱和法测定其表观溶解度;通过SM2分配平衡后在油相(正辛醇)和水相的浓度比,计算油水分配系数。结果:SM2在pH2·0和pH9·0时平衡溶解度较高,分别为1·916、1·375g·L-1,油水分配系数在pH8·0时最高,为3·9070。结论:SM2在水中的平衡溶解度及油水分配系数与介质的pH值有关,pH<3·0或pH>6·8时溶解度较好。pH3～8时SM2在油相中分配较多,较易被机体吸收。     

川芎嗪平衡溶解度及油/水分配系数的研究

目的测定川芎嗪在不同pH值下的平衡溶解度和油水分配系数(P)。方法采用摇瓶法测定表观溶解度,通过药物分配平衡后在油相和水相中的浓度比,计算油水分配系数。结果川芎嗪在二氯甲烷、乙腈、乙酸乙酯等有机溶剂中溶解度较大,在聚乙二醇400中不溶。在蒸馏水中几乎不溶,随着pH值增大,川芎嗪的溶解度变小;川芎嗪正辛醇溶液质量浓度对川芎嗪油水分配系数无明显影响,pH值对川芎嗪油水分配系数有影响,随pH值增大川芎嗪油水分配系数增大。结论药物在水中的平衡溶解度及油水分配系数与介质的pH值有关,当pH>7.24时,川芎嗪的溶解度陡然下降;当pH>6.8时,药物在油相中分配较多,川芎嗪在正辛醇-水体系中的油水分配系数P=12.33。     

Assessment of rate of drug release from oil vehicle using a rotating dialysis cell.

The rate constants for transfer of model compounds (naproxen and lidocaine) from oily vehicle (Viscoleo) to aqueous buffer phases were determined by use of the rotating dialysis cell. Release studies were done for the partly ionized compounds at several pH values. A correlation between the overall first-order rate constant related to attainment of equilibrium, k(obs), and the pH-dependent distribution coefficient, D, determined between oil vehicle and aqueous buffer was established according to the equation: logk(obs)=-0.71 logD-0.22 (k(obs) in h(-1)). Based on this correlation it was suggested that the rate constant of a weak electrolyte at a specified D value could be considered equal to the k(obs) value for a non-electrolyte possessing a partition coefficient, P(app), the magnitude of which was equal to D. Specific rate constants k(ow) and k(wo) were calculated from the overall rate constant and the pH-dependent distribution coefficient. The rate constant representing the transport from oily vehicle to aqueous phase, k(ow), was found to be significantly influenced by the magnitude of the partition coefficient P(app) according to: logk(ow)=-0.71 logP(app)-log(P(app)+1)-0.22 (k(ow) in h(-1)).     

布洛芬平衡溶解度及表观油水分配系数的测定

目的：测定布洛芬在不同pH磷酸盐缓冲溶液中的平衡溶解度与表观油水分配系数。方法采用紫外－可见分光光度法测定布洛芬的质量浓度,气浴恒温振荡－摇瓶法测定布洛芬的平衡溶解度及表观油水分配系数。结果37℃时布洛芬在pH2．0、3．0、4．0、5．0、6．0、6．8、7．4、8．0、9．0缓冲溶液中的平衡溶解度分别为0．05874、0．04078、0．06404、0．1930、1．027、2．551、4．613、3．866、4．409mg? mL －1;表观油水分配系数分别为10．19、17．11、12．55、6．390、4．911、5．976、4．925、2．599、1．716。结论布洛芬在磷酸盐缓冲溶液中的平衡溶解度及表观油水分配系数与介质的pH值相关,介质的pH值的增大,布洛芬的平衡溶解度增大;表观油水分配系数减小。     

盐酸氨溴索平衡溶解度和表观油水分配系数的测定

目的 测定盐酸氨溴索在多个pH值介质中的平衡溶解度及表观油水分配系数,为其制剂研究与处方筛选提供依据。方法 采用紫外分光光度法测定盐酸氨溴索在水及10种有机溶剂中的平衡溶解度,通过盐酸氨溴索分配平衡后在油相和水相中的浓度比,计算其油水分配系数。结果 盐酸氨溴索在各pH值介质中的平衡溶解度均较高,尤其是在蒸馏水以及pH值为2.0、5.8的缓冲液中,平衡溶解度分别为26.04、27.91、28.24 mg/mL;油水分配系数在pH7.4时最高,lgP为1.78。结论 盐酸氨溴索的平衡溶解度及表观油水分配系数与各介质的pH值有关,且可推测其在人体内的胃肠吸收良好,有较好的应用价值。     

秦皮甲素平衡溶解度及表观油/水分配系数的研究

目的:研究秦皮甲素的平衡溶解度及表观油/水分配系数,为其吸收机制研究奠定基础。方法:将秦皮甲素分别溶解于pH 1.2～8.0的不同介质中,以饱和法测定其平衡溶解度,摇瓶法测定其表观油/水分配系数。结果:秦皮甲素的平衡溶解度在pH1.2～6.8之间略有波动,pH 7.4时开始急剧增大,并在pH 8.0达到峰值(10.58 g·L-1);其表观油/水分配系数在pH 1.2～6.0之间变化缓慢,pH 6.0时开始明显下降,并在pH 8.0达到最低值(0.03)。结论:秦皮甲素的平衡溶解度及表观油/水分配系数与介质的pH值有关,其口服后无降低血尿酸作用的原因可能与胃肠道吸收较差有关。     

黄芩苷在不同pH值缓冲液中理化常数的测定

目的考察黄芩苷在不同pH值中的平衡溶解度与表观油水分配系数,为制剂研究奠定基础。方法采用摇瓶-紫外分光光度法测定温度为25和37℃时,黄芩苷在不同pH值磷酸盐缓冲溶液中的平衡溶解度及在正辛醇/缓冲液体系中的表观油水分配系数。结果 25℃时,黄芩苷在pH=2.0,3.0,4.0,5.0,6.0,6.8,7.4,8.0和9.0缓冲液中的平衡溶解度分别为0.032,0.034,0.119,0.873,3.329,12.96,11.49,4.605和11.87mg.mL-1,相应条件下表观油水分配系数(P)值分别为0.363,0.244,0.292,0.137,0.057,0.046,0.036,0.028和0.029。37℃时,黄芩苷在pH=2.0,3.0,4.0,5.0,6.0,6.8,7.4,8.0和9.0缓冲液中的平衡溶解度分别为0.028,0.048,0.095,0.950,4.881,14.15,26.65,14.48和17.89mg.mL-1,相应条件下表观油水分配系数(P)值分别为0.234,0.224,0.365,0.103,0.074,0.049,0.034,0.034和0.035。结论黄芩苷的平衡溶解度在酸性及中性条件下受温度影响很小,在碱性条件下随着温度升高而增加;黄芩苷在酸性条件下的P值比在碱性条件下大,Pmax=0.363(T=25℃,pH=2),Pmax=0.365(T=37℃,pH=4),随着碱性的增加P值变化不明显,且温度对黄芩苷的P值几乎无影响。     

高效液相色谱法测定去氧氟尿苷在不同介质中的平衡溶解度和表观油水分配系数

目的测定去氧氟尿苷在不同介质中的平衡溶解度以及在正辛醇-水和正辛醇-缓冲液体系中的表观油水分配系数。方法采用HPLC法测定去氧氟尿苷的浓度,采用摇瓶法测定去氧氟尿苷的表观油水分配系数。结果37℃,pH=7时去氧氟尿苷在水中的平衡溶解度为2.570 1 g.L-1,在pH〈5磷酸盐缓冲液中的平衡溶解度较低;去氧氟尿苷在正辛醇和水相中表观油水分配系数Papp为0.97;当pH〈7时,受pH影响不显著,表现为亲水性。结论去氧氟尿苷在水中的平衡溶解度及油水分配系数与介质的pH值有关,可以通过改变pH值,增加该药物新剂型的稳定性。     

青蒿素在不同溶剂中平衡溶解度和表观油水分配系数的测定

目的测定青蒿素在不同pH缓冲液和7种非极性溶剂中的平衡溶解度以及在正辛醇-水中的表观油水分配系数,为青蒿素新剂型的研究与开发提供实验基础。方法采用高效液相-柱后衍生化-紫外检测法测定青蒿素在不同pH缓冲溶液及7种非极性溶剂中的平衡溶解度;采用摇瓶法测定青蒿素的表观油水分配系数。结果 37℃时青蒿素在纯水中的平衡溶解度为82.4μg/mL,随着pH的增大平衡溶解度呈先增大（pH5.0～6.8）后减小（pH6.8～8.0）的趋势;37℃时青蒿素在肉豆蔻酸异丙酯（IPM）、油酸乙酯（EO）和中链甘油酸三酯（MCT）中平衡溶解度较大,分别为10.34、9.28、8.46mg/mL,青蒿素的正辛醇-水表观油水分配系数P为12.2（lgP=1.09）。结论青蒿素水溶性差,在非极性溶剂IPM、EO、MCT中平衡溶解度较大。     

基于HPLC法测定醋酸甲羟孕酮的平衡溶解度与油水分配系数

目的对醋酸甲羟孕酮(MPA)在不同溶剂中的平衡溶解度及其在正辛醇-缓冲液体系中的油水分配系数进行测定。方法采用HPLC法测定MPA的质量浓度,测定MPA在水、有机溶剂、缓冲溶液和加十二烷基硫酸钠的缓冲溶液中的平衡溶解度,采用摇瓶法结合HPLC法测定MPA在正辛醇-缓冲液体系中的质量浓度,从而计算油水分配系数。结果 37℃时,MPA在蒸馏水和丙酮中的平衡溶解度分别为0.52±0.04和238.70±0.47μg·mL~(-1);在体积分数为90%的乙醇溶液中的平衡溶解度最大;在加十二烷基硫酸钠的缓冲溶液中的平衡溶解度增大;在水中的表观油水分配系数为1.99(lgP=0.30),脂溶性较强;在pH值为1.2~6.8的缓冲溶液中,平衡溶解度随pH值的升高而减小,油水分配系数随pH值的升高而增大。结论该实验建立的测定方法可准确测定MPA的平衡溶解度和油水分配系数。     

VBE-1平衡溶解度和表观油水分配系数的测定及其酸碱稳定性的考察

目的：测定VBE-1的平衡溶解度和表观油水分配系数,并考察其酸碱稳定性,为药物的制剂设计提供实验依据。方法：采用平衡法和摇瓶法测定VBE-1在不同溶剂中的平衡溶解度以及在正辛醇-水/缓冲溶液中的表观油水分配系数,采用高效液相色谱法测定两者的浓度,并用紫外分光光度法考察VBE-1的酸碱稳定性。结果：VBE-1在PEG-400中的溶解度较大,为（677.47±48.09）g·L^-1。在pH4.0~8.0范围内,pH对VBE-1的表观油水分配系数有影响,表现出表观油水分配系数随着pH升高而降低的趋势。pH的升高会引起VBE-1颜色的改变,但此变化为可逆反应。结论：VBE-1具有一定的透过能力,可满足经皮给药的一般要求,其对pH较敏感,实验过程中应避免在强碱条件下操作。     

高效液相色谱法测定蝙蝠葛碱的平衡溶解度和油水分配系数

目的:测定蝙蝠葛碱在不同pH条件下的平衡溶解度以及在正辛醇-缓冲液体系中的油水分配系数。方法:采用HPLC法测定蝙蝠葛碱的浓度,以饱和法测定平衡溶解度,采用摇瓶法-HPLC法测定蝙蝠葛碱在正辛醇和水相中浓度,从而计算油水分配系数。结果:37℃下蝙蝠葛碱的平衡溶解度随pH的升高而增大;油水分配系数随pH的升高而增大,在pH 6.8～8.0范围内(小肠的pH环境),蝙蝠葛碱的lgP约为0.5,说明其脂溶性较强。结论:蝙蝠葛碱平衡溶解度和油水分配系数都受pH的影响;本试验所建立的方法可准确测定蝙蝠葛碱的平衡溶解度和油水分配系数,并预测其体内过程。     

pH值对马来酸噻吗洛尔角膜透过性的影响

目的　研究pH值对马来酸噻吗洛尔(TM)角膜透过性的影响,为其处方设计提供理论依据。方法　测定TM的表观油水分配系数(DC_app)。用体外扩散实验考察各种pH值条件下离体兔眼角膜对TM的透过性。结果　由DC_app求得TM的分配系数和pKa分别为63.63和9.17。在生理介质中,TM的表观透过系数为1.43×10^-5cm·s^-1。随着pH值由6.65升高至9.20 ,TM透过角膜的滞后时间缩短到1/20 ,累积透过量增加1.3倍。计算得到游离型噻吗洛尔的角膜透过系数为解离型的3.3倍。结论　噻吗洛尔主要以分子状态经细胞内途径透过角膜,且角膜上皮是其扩散的主要屏障。     

延胡索乙素在不同溶剂中平衡溶解度及其油水分配系数的测定

目的测定延胡索乙素在各种溶剂中的平衡溶解度以及在正辛醇-水中的表观油水分配系数,为延胡索乙素经皮给药制剂的制备提供实验基础。方法采用紫外分光光度法测定延胡索乙素在不同pH缓冲液中的平衡溶解度;采用高效液相色谱(HPLC)方法,测定不同介质中延胡索乙素的平衡溶解度;采用摇瓶法测定延胡索乙素的表观油水分配系数。结果 32℃延胡索乙素在pH7.4缓冲液中的平衡溶解度为32.47mg/L,在酸性缓冲液中溶解度增大;32℃延胡索乙素在油酸、吐温80中有较好的增溶能力,其溶解度分别为22165.21mg/L、69653.86mg/L;延胡索乙素的表观油水分配系数为3.12。结论延胡索乙素水溶性差,在油酸和吐温80中有较好的增溶能力。     

pH-dependent functional activity of P-glycoprotein in limiting intestinal absorption of protic drugs: kinetic analysis of quinidine efflux in situ

The purpose of this investigation is to evaluate the quantitative contribution of pH-dependent passive permeability on the functional activity of P-glycoprotein (P-gp) in limiting intestinal absorption of weakly basic drugs, in order to include this effect in prediction models. pH-dependent octanol/buffer partition coefficient, artificial membrane permeability and in situ rat intestinal permeability of quinidine were determined in the physiological pH range of gastrointestinal tract. In situ permeability, as a function of luminal pH, was also determined in the presence of P-gp inhibitor, verapamil (500 microM). Octanol/buffer partition coefficient, transport across artificial membrane, and rat in situ permeability showed high pH-dependency. Absorption quotient (AQ), calculated from in situ permeability to express the functional activity of P-gp, declined with increase in luminal pH or increase in luminal quinidine concentration because of the increased passive permeability or saturation of P-gp. AQ was 0.57 +/- 0.02 and 0.41 +/- 0.05, while passive permeability was 0.32 +/- 0.01 x 10(-4) cm/sec and 0.43 +/- 0.02 x 10(-4) cm/sec, in jejunum and ileum, respectively, at pH 7.4. Further, apparent Michaelis-Menten constants (K(M), J(P-gp,max)) for the quinidine efflux in jejunum indicated that efflux activity was more at luminal pH 4.5 over pH 7.4. K(M) values for jejunum quinidine efflux at pH 4.5 and pH 7.4 were determined to be 77.63 +/- 10.90 and 22.86 +/- 5.22 microM, with J(P-gp,max) values of 1.47 +/- 0.08 and 0.62 +/- 0.04 nM/cm2/sec, respectively. AQ vs passive permeability showed significant relationship indicating dependency of P-gp-mediated efflux on pH-dependent passive permeability, which is dictated by ionization status for a protic or ampholytic drug. In conclusion, an orally administered drug is absorbed from various segments of intestine, which inherit difference in luminal pH, transcellular permeability and P-gp expression. In situ data suggests that pH-dependency and regional variability in passive permeability of protic substrates significantly influence their P-gp-mediated efflux and may have implications on predictions of the in vivo drug absorption.     

Determination of the partition coefficients, acid dissociation constants, and intrinsic solubility of carbenoxolone

The dissociation constants, partition coefficients, and solubility of carbenoxolone (1) were determined using tritium-labeled drug. The partition and solubility methods were used to assess the dissociation constants of carbenoxolone, while the pKa of the structurally related triterpenoid, enoxolone (2) was determined using a spectrophotometric method. The true partition coefficient (TPC) of carbenoxolone was found to be 643.8 in an n-octanol:aqueous buffer system, while its intrinsic solubility (So) was 1.63 x 10(-5) M. The apparent partition coefficient (APC) was independent of the concentration of carbenoxolone over the pH range of 3 to 7. The values of pk1 and pk2 for carbenoxolone, obtained by the partition and solubility methods, were in reasonably good agreement. The observed pKa value of enoxolone enabled the assignment of pk2 (the weaker acid grouping) to the carboxyl group at C-30.     

田蓟苷在不同介质中的平衡溶解度及油水分配系数

目的：测定田蓟苷在不同缓冲溶液和表面活性剂溶液中的平衡溶解度及在正辛醇-水/磷酸缓冲盐中表观油水分配系数（P_app）,为今后新剂型的选择和制备提供参考。方法：通过高效液相色谱法测定田蓟苷在不同溶剂和表面活性剂溶液中的浓度,采用摇瓶法测定田蓟苷在正辛醇-水/磷酸缓冲盐中油水分配系数。结果：田蓟苷在37℃纯水中的平衡溶解度为1.57 mg·L^-1,在甲醇、乙酸乙酯及三氯甲烷有机溶液中溶解性较好;在酸性缓冲溶液中的平衡溶解度较水中有明显增加,在碱性缓冲液中随pH的增高平衡溶解度逐渐减小。在32 g·L^-1的十二烷基硫酸钠溶液中平衡溶解度提高到188.65 mg·L^-1。田蓟苷的油水分配系数为14.63（lg P=1.17）,且随溶液pH的增高逐渐增加。结论：田蓟苷为疏水性药物,脂溶性较强。制剂时,可加入适当浓度的十二烷基硫酸钠助溶。同时,提高其制剂的溶出度可能会提高其生物利用度。     

川芎嗪的猪口腔粘膜透过特性

目的:确定川芎嗪(TMP)在猪口腔粘膜的主要渗透途径并用体外方法研究药物浓度、供给池pH和TMP油水分配系数对药物透过性的影响.方法:采用在线流通扩散池法进行透过实验,并用Scientist~((R))软件对数据进行处理.结果:稳态流量随药物浓度呈线性增大;透过系数和油水分配系数均随pH的增大而增大,且经细胞内的透过系数 9.05 ×10~(-6)cm·s~(-1)远远大于经细胞间的透过系数 2.99 ×10~(-7)cm·s~(-1).结论:药物经猪口腔粘膜吸收是一个被动扩散过程;药物转运的主要通道为细胞内途径.     

The pH-Dependence in the Partitioning Behaviour of (RS)-[3H]Propranolol Between MDCK Cell Lipid Vesicles and Buffer

Purpose. The pH-dependent partitioning of (RS)-[³H]propranolol between unilamellar vesicles of MDCK cell lipids and buffer was determined. Methods. Partitioning studies were performed by means of equilibrium dialysis at 37°C between pH 7 and 11 at a molar propranolol/lipid ratio in the membrane of 10^–6. Results. The partition-pH diagram was bell-shaped. The highest apparent partition coefficient was 1797 at pH 9.7, the lowest was 805 at pH 6.9. Curve fitting with a combination of Henderson-Hasselbalch equations revealed an inflection point at the apparent pK_a of proprano-lol, i.e. 9.7, and two additional pK_a values at pH 7.7 and 10.0. The first one corresponds to the pK_a of free fatty acids (FFA) within lipid bilayers and the other one to the pK_a of phosphatidylethanolamine (PhE). The true partition coefficients (P) of the neutral as well as the ionised solute were fitted for each ionisation status of the membrane. The highest P, i.e. 2123, was calculated for neutral propranolol in the membrane with deprotonated FFA and protonated PhE. Conclusions. The partitioning behaviour of (RS)-[³H]propranolol in a complex membrane/buffer system can be described when considering ionisation changes of drug and lipids.