Transdermal Delivery of Isoproterenol HC1: An Investigation of Stability,Solubility, Partition Coefficient,and Vehicle Effects

Effects of solubility, partition coefficient, and selected adjuvants (propylene glycol and Azone) on percutaneous penetration of isoproterenol HC1 have been investigated using human cadaver skin. Isoproterenol was found to be stable (<1% decomposition) for 24 hr at 22 ± 0.5°C in the pH range 1 to 7 in the following solvents: water, normal saline, propylene glycol and a series of propylene glycol–water mixtures (10, 20, 40, and 60%; v/v); however, decomposition was significant beyond pH 8. In normal saline, the rate of decomposition increased significantly with an increase in temperature to 37°C. The solubility of isoproterenol HC1 decreased and its skin/vehicle partition coefficient increased with increasing proportions of propylene glycol in the vehicle, while the product of the solubility and partition coefficient appeared to plateau at 20% propylene glycol in water. Optimal penetration enhancing effects of Azone were seen when incorporated at a concentration of 1% (v/v) in the 20% (v/v) propylene glycol–water blend and, more significantly, when skin was pretreated with pure Azone for 60 min prior to application of the drug formulation.     

The effect of glycerol, propylene glycol and polyethylene glycol 400 on the partition coefficient of benzophenone-3 (oxybenzone)

Sunscreen products are widely used to protect the skin from sun-related deleterious effects. The objective of the study was to investigate the potential effect of glycerol, propylene glycol and polyethylene glycol 400 on dermal absorption of oxybenzone by studying their effects on its partition coefficient. The partition coefficient was evaluated in a chloroform-water system at room temperature. It was found that glycerol and propylene glycol decreased the partition coefficient of oxybenzone, while an increase in partition coefficient was observed with polyethylene glycol 400. The findings suggest that polyethylene glycol 400 in contrast to glycerol and propylene glycol has the potential of increasing the vehicle-skin partition coefficient of oxybenzone when cosmetic products containing such an UV absorber are topically applied to the skin.     

氯诺昔康凝胶剂的研制

目的制备氯诺昔康凝胶剂,考察其体外经皮渗透性。方法采用紫外分光光度法测定氯诺昔康的表观溶解度和油水分配系数,采用Franz扩散池考察载药凝胶剂的体外经皮渗透性,以6 h累积渗透量为指标,采用正交试验设计筛选最佳处方,探讨了卡波姆浓度、氮酮及丙二醇用量对氯诺昔康凝胶剂经皮渗透的影响,并考察其局部刺激性。结果氯诺昔康在水、pH 6.8和pH 7.4磷酸盐缓冲液中的表观溶解度分别为8.65,86.0和324.0μg/mL,油水分配系数为1.52;正交试验优化的最佳处方为:含0.75%卡波姆、30%丙二醇、4%月桂氮卓酮。制备的凝胶剂外观细腻,黏度适宜,pH值为6.8~7.0,体外经皮渗透实验结果符合零级动力学方程,家兔各涂药部位无水疱、疹块、红肿等现象。结论氯诺昔康凝胶剂制备工艺简单,质量可控。     

Physicochemical properties of carbovir, a potential anti-HIV agent

(+-)-Carbovir [(+-)-9-[4 alpha-(hydroxymethyl)-cyclopent-2-ene-1 alpha-yl]guanine; NSC 614846] is a novel carbocyclic nucleoside analogue which has been shown to be a potent and selective inhibitor of HIV in vitro. As part of an effort to develop a parenteral formulation for subsequent clinical and toxicological evaluation of this compound, the aqueous solution stability of carbovir as a function of pH and temperature and various physicochemical properties of carbovir including its pKa, solubility versus pH and solvent composition, and octanol-water partition coefficient have been examined. Ultraviolet spectrophotometry indicated that carbovir has pKa values of 3.15 and 9.68, respectively, at 25 degrees C and 0.01 ionic strength. The aqueous solubility of carbovir over the pH range 7-10.5 was consistent with that expected of a weak acid with a pKa of 9.65 and an intrinsic solubility of 1.24 mg/mL. Due to the limited solubility of carbovir at physiological pH, methods for solubilizing carbovir in aqueous solution were explored, including propylene glycol-water cosolvents and complexation with hydroxypropyl-beta-cyclodextrin. As expected for carbovir, a semipolar compound with an octanol-water partition coefficient of 0.29, propylene glycol:water cosolvents were not highly effective in enhancing solubility. Complex formation between carbovir and 2-hydroxypropyl-beta-cyclodextrin was found to be more effective, with a K1:1 of 105 M-1 for the complexation. The pH profiles generated at 50, 70, and 90 degrees C were accounted for by acid-catalyzed degradation at low pH leading to the formation of guanine and a neutral degradation pathway which dominates above pH 4. Prototype lyophilized formulations containing (after reconstitution) 10 mg/mL of carbovir at a pH of 10.6 were developed and evaluated.     

Solubilization of flavopiridol by pH control combined with cosolvents, surfactants, or complexants.

This study investigates the roles of both ionized and un-ionized species of flavopiridol in solubilization by complexation, micellization, and cosolvency. Control of pH was used in combination with surfactants (polysorbate 20 and polysorbate 80), cosolvents (ethanol and propylene glycol), as well as uncharged and anionic complexing agents [hydroxypropyl beta-cyclodextrin (HPbetaCD) and sulfobutyl ether beta-cyclodextrin (SBEbetaCD)] to solubilize flavopiridol. These combined techniques increase not only the solubility of the un-ionized flavopiridol but also the solubility of the ionized drug. This study confirms that previously developed equations effectively characterize the roles of pH, pK(a), and either complexation constant, micelle partition coefficient, or cosolvent solubilizing power in determining drug total aqueous solubility.     

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。     

Development of parenteral formulations and evaluation of the biological activity of the trypanocide drug benznidazole

Chagas disease, caused by Trypanosoma cruzi, is a major public health problem in Latin America. According to the World Health Organization, around 20 million people are infected and another 40 million are at risk of acquiring the disease. One of the drugs most frequently used for the treatment of Chagas disease is benznidazole (BZL). It is practically insoluble in water (0.4 mg/ml), which precludes the preparation of liquid dosage forms, in particular, parenteral formulations. Thus, the aim of this work was to investigate the solubilization of BZL at two pH values using various cosolvents such as ethyl alcohol, propylene glycol, polyethylene glycol 400, benzyl alcohol, diethylene glycol monoethyl ether (Transcutol) and surfactants such as polysorbates (Tween) 40 and 80, and sodium dioctyl sulfosuccinate (AOT). Solvent systems based on PEG 400, with the addition ethyl alcohol and/or potassium biphthalate buffer solution, increased the BZL solubility up to 10 mg/ml. These alcoholic vehicles showed no toxicity against parasite when assayed at 1%. Physical and chemical stability studies showed that the formulations were stable for at least 1.5 years. In agreement with the biological activity results, the selected formulations are suitable for further clinical studies. Moreover, increasing the aqueous solubility of BZL reduced the problems in vitro testing techniques and bioassays leading to more reliable results and/or reproducibility.     

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。     

Stabilization of solid dispersions of nimodipine and polyethylene glycol 2000.

Previous investigations revealed that solid dispersions consisting of 20% (m/m) nimodipine and 80% (m/m) polyethylene glycol 2000 prepared by the melting method, represent supersaturated solid solutions of nimodipine recrystallizing upon storage at +25 degrees C. The objective of this study was the improvement of the storage stability by preventing recrystallization. The first approach in order to prevent recrystallization was the development of thermodynamically stable solid solutions by using solvents aiming to enhance the solubility of nimodipine in the carrier material. As potential solubility enhancing additives, polyethylene glycol 300, poly(ethylene/propylene glycol) copolymer, polypropylene glycol 1020, propylene glycol, glycerol and ethyl acetate were evaluated. The second approach enhancing storage stability was the addition of recrystallization inhibitors to supersaturated solid solutions, thereby delaying the transformation of the metastable supersaturated system to the thermodynamically stable state. Macrogol cetostearyl ether, macrogol glycerol monostearate, polysorbate 60, cetostearyl alcohol, glycerol monostearate and sodium lauryl sulphate as well as hydroxypropylcellulose, butylmethacrylat-(2-dimethylaminoethyl)methacrylat-methylmethacrylat-copolymer, polyacrylic acid, polyvinyl alcohol and povidone K17 were included in the study. It could be shown that povidone K17 effectively prevents recrystallization in solid solutions containing 20% (m/m) of nimodipine during storage at +25 degrees C over silica gel thereby ensuring a substantial increase in the dissolution rate and degree of supersaturation in water. On the contrary, stabilization by solubility enhancement was only successful at drug loadings not exceeding 1% (m/m) using polyethylene glycol 300 as solubility enhancing additive.     

Buccal permeation of buspirone: mechanistic studies on transport pathways

The transport of buspirone across porcine buccal mucosa in vitro was investigated to elucidate the mechanisms of transport and permeation enhancement. The apparent permeability increased with an increase in pH to a lesser degree than the dependence of the partition coefficient. Whereas the lipophilic or apparent transcellular pathway was found to be the dominant buccal transport route for buspirone, ionized species contributed significantly to transport at acidic pH. At neutral pH, bile salts did not increase the flux of the lipophilic species of buspirone, and in contrast to its effect on stratum corneum, aqueous propylene glycol alone did enhance the flux of buspirone across buccal mucosa in vitro. The use of an enhancer combination containing 5% oleic acid, 40% propylene glycol in buffer resulted in the greatest flux, and this was consistent with the effect of this combined enhancer on the flux of lipophilic drugs across stratum corneum and the dominance of the transcellular pathway for buspirone at neutral pH.     

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。     

Micellar Solubilization of Timobesone Acetate in Aqueous and Aqueous Propylene Glycol Solutions of Nonionic Surfactants

The micellar solubilization of timobesone acetate, a novel topical corticosteroid, was studied in aqueous and aqueous propylene glycol solutions of 1 to 5% nonionic surfactants at 25°C. The surfactants used were polyoxyethylene (POE) sorbitan monofatty acid esters (polysorbates), fatty acid esters (Myrj), and fatty alcohol ethers (Brij), as well as sucrose monolaurate (Crodesta SL40). The increase in the solubility of timobesone acetate in the micellar solutions was dependent on the type and concentration of surfactant. The solubilizing capacity of the surfactant micelles and the distribution coefficient of timobesone acetate in aqueous micellar solutions were found (1) to increase with increasing length of the hydrophobic fatty acid group; (2) to increase according to the structure of the hydrophilic group in the order of POE sorbitan ester, sucrose ester, POE ester, and POE ether; (3) to be unaffected by the increase in POE chain length; and (4) to tend to decrease in surfactant containing unsaturated fatty acid groups. In aqueous propylene glycol solution, the solubilizing capacity increased slightly, i.e., up to 1.5-fold in 50% propylene glycol solution, for the ester-type surfactants (polysorbates and Myrj). But this increase was not observed in the ether-type surfactant (Brij) solution. The distribution coefficient decreased logarithmically with increasing concentrations of propylene glycol in the solution. This was caused by the logarithmic increase in the timobesone acetate solubility in the bulk phase, while the solubility in the micellar phase was practically unchanged. The results support the equilibrium distribution model of micellar solubilization.     

Effect of propylene glycol,Azone and n-decylmethyl sulphoxide on skin permeation kinetics of 5-fluorouracil

The effect of propylene glycol (PG), azone (LDA) and n-decylmethyl sulfoxide (LDB) on the permeation course of fluorouracil through the hairless mouse skin was studied. Steady-state fluxes and permeability coefficients were measured in buffer solutions and in systems containing the enhancing agents. The permeation rates of fluorouracil have been shown to be highly pH dependent in the pH range of 5–9, the rate decreases with an increase in pH. The solubility of fluorouracil in pure propylene glycol at equilibrium measured by the solubility method was found to be 2.2 mg · ml^?1 at 25°C which is a relatively low value as compared to the solubility in water. The effect of various concentrations of propylene glycol in aqueous donor solutions on the drug permeation rate was examined at pH's 5.7 and 9.0. It was found that propylene glycol decreases the permeation flux when increasing concentrations are added to the aqueous pH 5.7 system; however, at pH 9, a strong enhancement effect was shown. PG was also found to decrease the drug reservoir in the hairless mouse skin e.g. 8.4 and 2.8 mg · (mg skin)^?1 for buffer pH 9 and PG/aqueous solution pH 9 systems, respectively. The concentration dependent enhancement effects of azone and n-decylmethyl sulfoxide have been measured. Both have been found to be potent enhancing agents. However, at relatively low concentrations such as 5%, Azone induced a 50-fold and n-decylmethyl sulfoxide only a two-fold enhancement of the drug steady-state flux. At high concentrations as much as 40%, n-decylmethyl sulfoxide appears to be more effective than Azone. The fluxes measured with these systems were 0.21, 0.17 and 0.003 mg · cm^?2 · h^?1 for the n-decylmethyl sulphoxide, Azone and PG/H₂O systems, respectively.     

Evaluation of transcutol as a clonazepam transdermal permeation enhancer from hydrophilic gel formulations

The influence of diethyleneglycol monoethyl ether (transcutol), alone or in combination with propylene glycol, on clonazepam permeation through an artificial membrane and excised rabbit ear skin from Carbopol hydrogels was investigated. Drug kinetic permeation parameters were determined for both series of experiments and compared. Rheological characteristics, drug solubility and membrane/vehicle partition coefficient for each gel formulation were also determined, and their role in the formulation performance was investigated. Both series of experiments showed an increase of drug permeation as a function of transcutol content in the formulation. The combination of transcutol and propylene glycol resulted in a synergistic enhancement of clonazepam flux. A different trend was found in experiments with gels containing mixtures of the two enhancers, where an increase (in the case of artificial membrane) or a decrease (in the case of rabbit ear skin) of drug permeation was found by increasing the transcutol/propylene glycol ratio in the mixture. Such a result is explained on the basis of the particular mechanism of action demonstrated for transcutol which associates the increase of drug solubility to the potent effect of a depot in the skin.     

Isotropic systems of medium-chain mono- and diglycerides for solubilization of lipophilic and hydrophilic drugs

The aim of this study was to investigate isotropic mono- and diglyceride-based (MCMDG) systems, which are potential vehicles for injectable products containing both hydrophilic and lipophilic drugs. For two-component systems, MCMDG was mixed with various masses of water. For three-component systems, the samples were prepared by mixing propylene glycol or glycerol formal or short-chain alcohols with MCMDG prior to the addition of water. The isotropic region was examined by visual inspection and confirmed using polarized light microscopy. Viscosities of formulations were measured. Solubilities of levamisole phosphate (hydrophilic) and abamectin (lipophilic) were determined in the isotropic formulations using high-performance liquid chromatography assay. The isotropic region in the two-component systems had a water content of up to 18% at 25 degrees C. Solvents such as propylene glycol (PG), glycerol formal (FG), and ethyl alcohol increased the isotropic region. The area of isotropic region in these three-component systems increased with increasing temperature. The area of the isotropic region became larger with decreasing dielectric constant and solubility parameter of the series of short-chain alcohols, except n-butyl alcohol, at 25 degrees C. The systems exhibited Newtonian behavior. The solubility of both hydrophilic and lipophilic drugs was high in formulations at 25 degrees C. It was concluded that more water was solubilized in MCMDG/short-chain alcohols/water systems, and the isotropic region in the short-chain alcohol systems enlarged compared with MCMDG/PG/water or MCMDG/GF/water systems, except the n-butyl alcohol system. Hydrophilic and lipophilic drugs solubilize in the systems. The isotropic formulations containing MCMDG may represent an alternative to more traditional formulations for injectable formulations containing both lipophilic and hydrophilic drugs.     

Feasibility of transdermal delivery of prazosin hydrochloride

Preformulation studies were conducted to determine the feasibility of a transdermal dosage form of prazosin hydrochloride (PZHC1). A target PZHC1 skin flux of 6.3 μg/cm²/h was set to attain a steady-state plasma concentration of 10 ng/ml (from a 20-cm² skin area). The octanol/water partition coefficient of the drug and its solubility in water, phosphate-buffered saline (pH 7.4), and propylene glycol were measured. PZHC1 flux through human cadaver skin was determined with and without 3% (w/v) azone as a penetration enhancer. The epidermis was found to be the rate-limiting barrier for the permeation of PZHC1 through the human cadaver skin. Transdermal delivery of prazosin may be feasible with a suitable penetration enhancer.     

Improvement of clonazepam release from a Carbopol hydrogel.

The performance of Tween 80, Tween 60, oleic acid, oleyl alcohol and Azone as enhancers of clonazepam permeation from a Carbopol hydrogel through a cellulose nitrate membrane was investigated. The effect of incorporating methyl beta-cyclodextrin (DS 1.8) in combination with clonazepam as a solid phase into some vehicles was also tested. In vitro release studies were carried out with a Sartorius apparatus and the following parameters were evaluated: drug solubility in the vehicle; partition coefficient of the drug between lauryl alcohol (the solvent which impregnates the membrane) and the vehicle; steady state flux; permeability constant; diffusion coefficient; lag time. The release kinetics followed a nearly zero-order pattern, although the diffusion-controlled mechanism might also have been operative. Maximum drug release (2.5 times that of the gel base) was achieved for the formulation containing clonazepam and methyl beta-cyclodextrin in a 1:1 (mol/mol) ratio as a solid phase, in a vehicle composed of water, propylene glycol, Tween 80 and Azone at a mass fraction of 43%, 50%, 2% and 5%, respectively.     

Solubilization of valsartan by aqueous glycerol, polyethylene glycol and micellar solutions

To increase the solubility of valsartan in aqueous solutions was considered of interest. This study therefore investigated the solubilization of valsartan by cosolvency and micellization. Of the solubilization agents used, sodium lauryl sulfate was found to be the most effective. The increase in solubility at the maximum concentration studied was in the following order: sodium lauryl sulfate > polysorbate-80 > polyethylene glycol 400 > glycerol. The effect of propylene glycol on the solubility of valsartan in a 2% w/v polysorbate-80 solution was also investigated and was found that propylene glycol decreased the solubilizing power of polysorbate-80 at the concentrations studied.     

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。     

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。