Simultaneous effect of cyclodextrin complexation, pH, and hydrophilic polymers on naproxen solubilization

The effect of pH variation on complexation and solubilization of naproxen (pK(a) 4.2) with natural betaCyclodextrin (betaCyD) and various neutral, cationic and anionic betaCyD-derivatives has been investigated. The combined effect of pH variation and hydrophilic polymer addition on CyD solubilizing and complexing efficiency has also been determined. Phase-solubility analysis in buffered aqueous solutions (pH from 1.1 to 6.5) was used to study the interaction of the drug with each CyD, in the presence or not of the water-soluble polymer. A clear influence of the substituent type was observed, the methylderivative being the most efficient agent; on the contrary, unexpectedly, no influence of the CyD charge in the interaction with the ionizable drug was detected. As expected, total drug solubility increased with increasing pH; however, the solubility increment with respect to drug alone obtained by CyD complexation progressively decreased, with a parallel reduction of the complex stability, attributed to the reduced affinity of charged drug for the hydrophobic CyD cavity. The addition of the polymer in part counterbalanced the destabilizing effect obtained with increasing pH, by improving the CyD complexation power towards naproxen. In particular, the presence of PVP allowed an increase of the complex stability constant with hydroxypropyl betaCyD up to 60% with respect to the corresponding drug-CyD binary system. Therefore, the combined strategy of pH control and polymer addition to the CyD complexing medium can be successfully exploited to improve naproxen solubilization and reduce the amount of CyD needed. The construction of theoretical drug solubility curves as a function of pH for any given CyD and polymer concentration enables selection of the best experimental conditions for obtaining the desired drug solubility value.     

Combined effect of pH and polysorbates with cyclodextrins on solubilization of naringenin

pH control and inclusion complex formation are commonly used as solubilization techniques in formulating ionizable drugs. Naringenin is a weakly acid compound with a low water solubility. The role of both ionized and unionized species of naringenin in solution by complexation with beta-cyclodextrin, 2-hydroxypropyl-beta-cyclodextrin and methyl-beta-cyclodextrin was investigated. This combined use of ionization and complexation increases not only the solubility of the unionized naringenin, but also that of the ionized one. This study puts on evidence the role of pH, pKa and complexation constants in increasing drug total aqueous solubility, determined by the single components in solution, as ionized and unionized naringenin both in free and complexed forms. Moreover, the presence of non-ionic surfactants in the media of complexation gives a positive contribution to the improvement of the solubility of naringenin, alone or in combination with beta-cyclodextrin.     

The effect of pH on cyclodextrin complexation of trifluoperazine

The characteristics of host-guest complexation between cyclodextrins (beta-CD, DM-beta-CD, HP-beta-CD) and protonated (pH 1.9, 6.2) or basic (pH 10.2) forms of trifluoperazine (TF) were investigated by spectrometric method. The association constants of complexes obtained at different temperatures and pH were calculated using Scott's equation and the thermodynamic parameters (deltaH, deltaS and deltaG) associated with the inclusion process were determined from Van't Hoff plot. The influence of pH and CD complexation on photostability of TF in solutions of different pH was followed. It was found that the photochemical decomposition of TF alone and in the presence of CD proceeds according to the first order reaction. It was also established that the increase in the TF photostability was dependent on the stability of TF-CD association. Spatial configuration of obtained complexes has been proposed on the basis of 2D NMR technique.     

Combined effect of cosolvent and cyclodextrin on solubilization of nonpolar drugs

Solubility enhancement has broad implications in parenteral formulation design. A simple mathematical model has been developed to describe the combined effect of cosolvency and complexation on nonpolar drug solubilization. The total drug solubility is determined by the summation of three drug species present in the solution: free drug [D], drug-ligand binary complex [DL], and drug-ligand-cosolvent ternary complex [DLC]. The proposed model established the dependencies of these three species upon the intrinsic drug solubility, [D(u)], the cosolvent solubilizing power, sigma, the binary and ternary intrinsic complexation constants, K(b)(int) and K(t)(int), and the cosolvent destabilizing powers for the binary and the ternary complexes, rho(b) and rho(t). A nonpolar solute, Fluasterone, is used to evaluate the newly generated equation. The model explains the decline in drug solubility produced by low cosolvent concentrations as well as the increase in the solubility produced by high cosolvent concentrations that are observed at all cyclodextrin concentrations.     

潜溶剂和环糊精对难溶性药物的联合增溶作用

目的研究潜溶剂和环糊精对难溶性药物的联合增溶作用。方法采用相溶解度法研究药物在不同混合溶剂中的相溶解度，利用已建立的数学模型对这种联合增溶作用作出评价和解释，非线性回归分析估计模型参数。结果两个难溶性药物的增溶模型判定系数R^{2分别为0.993和0.992，拟合效果很好，溶解度的实测值和模型预测值一致。结论该数学模型可以用于解释和预测潜溶剂和环糊精对难溶性药物的联合增溶作用。}     

The effect of pH and triethanolamine on sulfisoxazole complexation with hydroxypropyl-beta-cyclodextrin.

A novel complexation of sulfisoxazole with hydroxypropyl-beta-cyclodextrin (HP-beta-CD) was studied. Two systems were used: binary complexes prepared with HP-beta-CD and multicomponent system (HP-beta-CD and the basic compound triethanolamine (TEA)). Inclusion complex formation in aqueous solutions and in solid state were investigated by the solubility method, thermal analysis (differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)), Fourier-transform infrared spectroscopy (FT-IR) and dissolution studies. The solid complexes of sulfisoxazole were prepared by freeze-drying the homogeneous concentrated aqueous solutions in molar ratios of sulfisoxazole:HP-beta-CD 1:1 and 1:2, and sulfisoxazole:TEA:HP-beta-CD 1:1:2. FT-IR and thermal analysis showed differences among sulfisoxazole:HP-beta-CD and sulfisoxazole:TEA:HP-beta-CD and their corresponding physical mixtures and individual components. The HP-beta-CD solubilization of sulfisoxazole could be improved by ionization of the drug molecule through pH adjustments. However, larger improvements of the HP-beta-CD solubilization are obtained when multicomponent systems are used, allowing to reduce the amount of CD necessary to prepare the target formulation.     

Effect of pH and complexation on transdermal permeation of gliquidone

Gliquidone, a second generation sulfonylurea has been investigated for transdermal delivery. The poor aqueous solubility of the drug prompted the use of hydroxypropyl-beta-cyclodextrin (HP-beta-CD), a cyclic oligosaccharide, which is known to facilitate transdermal permeation of many drugs by enhancing the solubility and thus improving the diffusible species of the drug molecules at the skin-vehicle interface. In order to optimize the transdermal delivery of gliquidone, the effect of pH along with complexation on the solubility and permeation has been investigated. The solubility profiles of the drug, on increasing the concentration of HP-beta-CD were of Higuchi's AL type at the three pH values evaluated. However, the solubilization slope of the drug at pH 7.0 was 22 times that at pH 3.0 as a result of greater intrinsic solubility of the ionized form of the drug at pH 7.0. Transdermal flux of gliquidone at pH 7.0 was significantly greater than the flux at pH 3.0 in the presence of 15% w/v HP-beta-CD, attributable to the better solubility of the drug at pH 7.0 in the presence of HP-beta-CD. The effect of increasing concentrations of HP-beta-CD investigated at variable drug loading in the donor phase at pH 7.4 endorsed the earlier observations from studies on other drugs, that the drug has to be present at saturation in HP-beta-CD aqueous vehicle to achieve an optimized flux. While at saturation, the steady state flux of gliquidone from the aqueous HP-beta-CD (25% w/v) vehicle was enhanced 31 times compared to pure drug suspension at pH 7.4, unsaturation in the donor phase resulted in the decreased flux of gliquidone. It was concluded from the present study that enhanced transdermal flux of gliquidone can be achieved by adjusting the pH and the concentration of HP-beta-CD to achieve a better solubility of the drug.     

Combined effect of SLS and (SBE)(7M)-beta-CD on the solubilization of NSC-639829

Complexation and micellization are two effective ways of solubilizing drugs. In this study, the combined effect of surfactant and complexant on the solubilization of a poorly water soluble compound (NSC-639829) is investigated. With increasing concentration of sodium lauryl sulphate (SLS) in solutions of fixed concentration of (SBE)(7M)-beta-CD, the total solubility of the drug decreases linearly, reaches a minimum and then increases linearly. At each minimum, the molar ratio of SLS to (SBE)(7M)-beta-CD is close to unity. The above observation is attributed to the fact that the surfactant molecule competes with the drug to "fit" in the non-polar cyclodextrin cavity. The surfactant depletes cyclodextrin to form a 1:1 complex. Once the concentration of free SLS reaches the CMC, it starts forming micelles and hence, solubilizes the drug. A slight decrease of the solubilizing power is noticed in the presence of SLS/(SBE)(7M)-beta-CD complex. The combined use of two solubilizing agents, a surfactant and a complexant, results in a much lower solubility than when either one is used alone at the same concentration. The surfactant molecule acts as a competitive inhibitor in the solubilization of the drug by the complexant. Similarly the complexant "pulls" the surfactant out of solution, making it unavailable for solubilizing the drug.     

羟丙基-β-环糊精与介质pH值对前列腺素E_1溶解度的综合影响（英文）

目的研究羟丙基-β-环糊精（HP-β-CD）与介质pH值对前列腺素E1（PGE1）溶解度的综合影响并进一步推导出该药物溶解度的理论方程。方法首先测定药物在不同pH值水中的溶解度;然后分别测定在酸性及中性系列浓度的HP-β-CD溶液中,药物的溶解度;最后推导出以HP-β-CD与介质pH值为变量的药物溶解度方程并对其合理性进行验证。结果溶解度测定结果表明,提高介质的pH值或以HP-β-CD为增溶剂,均可增加PGE1的溶解度。分子型药物或离子型药物与HP-β-CD测得的相溶解度图均为典型的AL型,提示药物结构上的五元碳环部分已嵌入HP-β-CD的疏水性孔穴中,从而形成1：1摩尔比包合物。结论以HP-β-CD作为增溶剂,同时提高介质的pH值,可对PGE1的溶解度产生协同增加效应。本研究中导出的PGE1溶解度方程,可有效表征HP-β-CD与介质pH值二者对该药物溶解度的综合影响。     

Aqueous solubilization of furosemide by supramolecular complexation with 4-sulphonic calix[n]arenes

The solubilization of the practically water insoluble drug furosemide by guest:host inclusion complexation with 4-sulphonic calix[n]arenes has been reported. The 4-sulphonic calix[n]arenes are water-soluble phenolic cyclooligomers that form inclusion complexes with neutral molecules. The solubility of furosemide in acidic (pH < 4) aqueous solutions containing increasing concentrations of the calixarenes was determined at 30 degrees C and the concentration of furosemide in solution was determined by HPLC. Results showed that the molecular size of the 4-sulphonic calix[n]arenes and the concentration of the calix[n]arenes significantly influenced the increase in the solubility of furosemide. 4-Sulphonic calix[6]arene improved the solubility of furosemide the most (+/-104%) followed by 4-sulphonic calix[8]arene (+/-84-102%), while 4-sulphonic calix[4]arene increased the solubility of furosemide the least (+/-73-81%). The increase in furosemide solubility afforded by the calixarenes was most probably the result of the incorporation of the non-polar portions of the furosemide molecule into the non-polar cavities of the calixarenes similar to furosemide:cyclodextrin complexes. The driving force for this interaction was the reduction in the non-polar-water interfacial surface area when the furosemide (guest) molecules were inserted into the 4-sulphonic calix[n]arenes (host).     

Inclusion complexation and solubilization of paclitaxel by bridged bis(beta-cyclodextrin)s containing a tetraethylenepentaamino spacer

A novel water-soluble paclitaxel complex has been prepared by inclusion complexation with bridged bis(beta-cyclodextrin)s and characterized by means of (1)H NMR, SEM, powder X-ray diffraction patterns, TG-DTA, DSC, FT-IR, and 2D NOESY. The cyclodextrins were able to solubilize paclitaxel to levels as high as 2 mg/mL. Furthermore, the cytotoxicity of the novel complexes was assessed using a K562 leukemia cell line which indicated that drug concentrations of 10 pg/mL elicited an inhibitory effect.     

Tetronic micellization, gelation and drug solubilization: Influence of pH and ionic strength.

The aim of this work was to gain an insight into the self-associative processes and drug solubilization ability of a Tetronic variety, T904 (4 x 15 EO units; 4 x 17 PO units; HLB 15), in aqueous media covering the physiological range of pH and ionic strength, applying isoperibol microcalorimetry, transmission electronic microscopy (TEM), dynamic light scattering (DLS), oscillatory rheometry, and drug diffusion experiments. T904 shows two pK(a) (pK(a1)=4.0 and pK(a2)=7.9) and, at pH<5.8, the diprotonated form predominates over the non-protonated one. Deprotonization of the central diamine group is a required condition for micellization, which is an endothermic entropy-driven process owing to hydrophobic interactions between the PPO chains. As the pH of the solutions decreases, the coulombic repulsions among the positively charged amine groups make the aggregation more difficult, raising the critical micellar concentration (CMC) and decreasing the size of the micelles. The changes in the conformation and hydrophilicity of the Tetronic were reflected in its gelation temperature (around 30 degrees C at neutral-alkaline pH; no gelation at pH<2) and solubilization capacity for griseofulvin (2-fold greater at neutral-alkaline pH than at pH<2) and rate of diffusion (slower at pH 7.4). Such alterations in self-assembly are relevant when using Tetronic in the design of drug delivery systems.     

Prototropic and metal complexation equilibria of nalidixic acid in the physiological pH region

The dissociation of nalidixic acid in the near neutral pH region is shown to be due to a single prototropic equilibrium involving the carboxyl group exclusively. Precise dissociation constants as well as stability constants for the binding of the nalidixate anion by several divalent metal ions were determined. The magnitudes of the formation constants of the metal nalidixate complexes support physiological significance of the 1:1 complexes and the lack of importance of the 2:1 complexes.     

The effect of beta-cyclodextrin complexation on the bioavailability and hepatotoxicity of clotrimazole

Clotrimazole, a poorly water-soluble antimycotic agent, is a promising therapeutic agent for various diseases including cancer and sickle cell anemia. The oral bioavailability and hepatic toxicity of clotrimazole were compared with its beta-cyclodextrin inclusion form which was prepared by the spray-drying method. The inclusion complex gave significantly higher initial plasma concentrations, Cmax and AUC than did clotrimazole alone, indicating that the drug from the inclusion compound could be more easily absorbed in rats. Furthermore, mice treated with the inclusion compound showed significantly higher GOT/GPT values compared to clotrimazole alone. The inclusion compound also induced hypertrophy of hepatic cells by fat accumulation and disappearance of hepatic sinusoids, indications of pathological changes of liver, suggesting that the inclusion compound could induce more severe tissue damage in the liver than clotrimazole alone. Thus, hepatotoxicity of clotrimazole seems to be correlated with the enhanced oral bioavailability by inclusion complexation. Our results suggest that, in the development of a novel oral product, appearance or enhancement of hepatic toxicity must be considered along with oral bioavailability.     

The effect of solubilization on the oral bioavailability of three benzimidazole carbamate drugs

The effect of solubilization by complexation with povidone on the oral bioavailability of three anthelmintic benzimidazole carbamate drugs: mebendazole (MBZ), albendazole (ABZ) and ricobendazole (RBZ), was studied in mice. The following in vitro characteristics of the initial raw materials and the drug-povidone complexes were evaluated: melting point (MP); mean dissolution time (MDT); solubility constants (Cs) in n-octanol, acid (pH 1.2) and neutral (pH 7.4) aqueous media; apparent partition coefficients (P) and capacity factors (k'W) determined by HPLC. The following in vivo parameters were also evaluated: AUC(0-infinity), C(max), T(max) and MRT. The possible relationship between in vitro characteristics and in vivo parameters was explored and it was found that an increase in solubility, especially in acidic medium, leads to an increase in AUC and C(max) and a decrease in T(max). Therefore, dissolution seems to be the absorption limiting step for these drugs. For the in vivo parameters related to the amount of absorbed drug (AUC and C(max)), the best correlation was obtained with the in vitro characteristics related to solubility which are Cs, MP and MDT. On the other hand, there were good linear correlations between T(max) which is an in vivo parameter related to the rate of drug absorption, and the lipophilia/hydrophilia (logP and log k'W) relation-parameters.