Preparation and characterisation of poly(vinyl alcohol)/cyclodextrin microspheres as matrix for inclusion and separation of drugs

Poly(vinyl alcohol) (PVA) microspheres containing cyclodextrin (CD) were obtained by chemical cross-linking with glutaraldehyde of an acidified mixture solution of PVA and alpha-, beta- or gamma-CD. The amount of linked CD in microspheres, estimated by tetrazolium blue method, decreases in the order beta- > gamma- > alpha-CD. The dimensions of PVA/gamma-CD microspheres are much higher than those of PVA/alpha- and beta-CD. The cross-linking density of microspheres was estimated by the amount of iodine retained by the polymer matrix. The pore size as well as the porous volume of PVA/CD microspheres decrease significantly on increasing the amount of glutaraldehyde, but are enough large to permit the access of drugs to the CD cavity. In order to test the PVA/CD microsphere inclusion ability, the microspheres were packed in a glass column and the liquid chromatographic behaviour by isocratic elution of different drugs or typical organic compounds, taken as model drugs, was investigated.     

Changes in the conformational structure, microscopic and macroscopic pK(a)s of meloxicam on complexation with natural and modified cyclodextrins

Spectroscopic and phase solubility techniques have been used to study the complexation of neutral meloxicam (Mel) with alpha-, beta-, gamma- and HP-beta-cyclodextrins (CDs). The results indicate that neutral Mel has two conformational structures, enol and zwitterions, with the latter more dominant in water. The two pK(a)s of Mel were found to change in the presence of beta-CD, where a blue shift in lambdamax was observed but not in the presence of alpha, HP-beta- and gamma-CD. Rigorous analysis of phase solubility diagrams indicate that beta- and HP-beta-CD form 1:2 Mel/beta-CD type complexes with Mel while alpha- and gamma-CD form only 1:1 complexes. The fact that the overall 1:2 Mel/CD complex formation constant (beta12) was found significantly higher for beta-CD than for HP-beta-CD, combined with further spectroscopic studies, indicate that beta-CD favors inclusion of the neutral enol form over the zwitterion. Unlike alpha-, HP-beta- and gamma-CDs, the hydrophobic microenvironment of a tight 1:2 Mel/beta-CD complex was found to mimic those of organic solvents, thus favoring inclusion of the enol rather than the zwitterion, and hence shifting the tautomerization equilibrium towards the enol conformer.     

The influence of alkali fatty acids on the properties and the stability of parenteral O/W emulsions modified with solutol HS 15.

Arachis oil based parenteral O/W emulsions were prepared using soya bean phosphatidylcholine (SPC) and different combinations of co-emulsifiers containing polyethylene glycol fatty acid esters (Solutol HS 15) and alkali fatty acids (sodium laurate, sodium stearate). The parameters measured were droplet size (both by photon correlation spectroscopy and laser diffractometry), pH and zeta potential. All emulsions were subjected to autoclaving. The addition of polyethylene glycol 12-hydroxy stearate (Solutol HS 15) led to a significant decrease of mean oil droplet size. For long-term stability the amount added turned out to be the most important factor. With increased amounts of Solutol HS 15 the packing density of the emulsifier layer and the zeta potential decreased leading to instability. The optimum load of Solutol HS 15 was found to be 15 micromol/ml. Alkali fatty acids markedly improved the physical stability of the emulsions. Improved stability properties conferred to emulsions by alkali fatty acids could be attributed to the zeta potential increase even in the presence of Solutol HS 15. Consequently a mixed emulsifier film was established in which the ionized fatty acids determined the interface charge. In addition to this a strengthening of the molecular interactions occurring between phospholipid and Solutol HS 15 emulsifier in the presence of ionized fatty acids at the O/W interface can be assumed (L. Rydhag, The importance of the phase behaviour of phospholipids for emulsion stability, Fette Seifen Anstrichm. 81 (1979) 168-173). Different co-emulsifier mixtures were shown to have a pronounced impact on the plasma protein adsorption onto emulsion droplets.     

A study of the stability of W/O/W multiple emulsions.

The stability of W/O/W emulsions has been studied in batch agitators. The surfactants suitable for W/O/W emulsions were screened and the factors affecting the emulsion stability were also studied. Results showed that polyamine E644 was an excellent emulsifier for W/O emulsions since the emulsion stabilized by it has not only good stability but also shows smaller swelling. The stability of the emulsion increases with increase in membrane viscosity and concentration of surfactant, but decreases with increase in concentration of the internal reagent in the internal phase and the carriers in the membrane. Raising the agitation speed and the time for preparing the W/O emulsion is beneficial to membrane stability due to formation of smaller internal droplets, but raising the speed for dispersing the W/O emulsion in the external phase results in an increase in membrane breakage.     

Effect of methylcellulose on the stability of oil-in-water emulsions: influence of the disperse phase

The influence of nature of the disperse phase on the stability of oil-in-water emulsions containing nonionic emulsifiers and methylcellulose 4000 as an auxiliary emulsifier was investigated. One stable and three unstable base emulsions each of olive oil and of mineral oil were formulated with an emulsifier blend of Tween® and Span®. The stable emulsion (SE) contained 2% emulsifier blend optimized for maximum stability. Three unstable emulsions were formulated from the SE formulation: one with 0.5% emulsifier blend as of the SE formulation (UE1), one with excessive hydrophilic emulsifier (UE2) and one with excessive lipophilic emulsifier (UE3). A series of emulsions was prepared containing increasing amounts of methylcellulose 4000 for each base emulsion. The particle size of all olive oil emulsions was reduced (UE2>SE>UE3) and the viscosity was increased (UE2>SE>UE3) on addition of methylcellulose. The stability of these emulsions improved in the presence of methylcellulose. However, the addition of the polymer caused instability in mineral oil emulsions containing lower concentrations of the hydrophilic emulsifier (Tween®). These results suggest that: (i) methylcellulose and the hydrophilic emulsifier associate to form a complex; (ii) this complex when present at the mineral oil-water interface would be dislodged from the interface due to less interaction between the non-polar oil and the polyoxyethylene (POE) chain of the hydrophilic emulsifier; and (iii) this complex when present at the olive oil-water interface would stabilize emulsions due to higher interaction between the polar oil and the POE chain of the hydrophilic emulsifier.     

Solubilization and stabilization of sodium dicloxacillin by cyclodextrin inclusion

The aim of this work is to analyze the effect of cyclodextrin (CD) complexation on the solubilization and stabilization of sodium dicloxacillin in acid aqueous solutions. The effect of four cyclodextrins alpha-, beta-, gamma- and hydroxypropyl-beta-CD was studied. Phase solubility diagrams obtained are AL or BS type, depending on the cyclodextrin used and on the pH of the solution. The highest stability constants of the inclusion complexes are obtained with gamma-CD at pH 1 and 2 and HPbeta-CD at pH 3. The structure of the inclusion complex in solution is characterized by nuclear magnetic resonance (1H-NMR). This study suggests that the 7-oxo-4-thia-1-azabicyclo group is located in the CD cavity. Nevertheless, molecular modelling calculations predict two different orientations of dicloxacillin in the gamma-CD cavity in vacuum and in aqueous solution. In vacuum, the results predict the inclusion of the dichlorophenyl ring of dicloxacillin instead of 7-oxo-4-thia-1-azabicyclo group into the gamma-CD cavity. However, the results are different in aqueous solution and this conformation is confirmed by the NMR study. The effect of gamma-CD and HPbeta-CD in the stability of the drug in solution was studied. The degradation of sodium dicloxacillin in solution follows a pseudo-first-order kinetics and the cyclodextrin do not change this fact. Both cyclodextrins increase the stability of the drug but the efficacy is higher with gamma-CD.     

处方因素对亚微乳物理稳定性的影响

目的 初步探讨亚微乳处方中乳化剂及油相因素对其物理稳定性的影响.方法 采用高速剪切分散和高压均质乳化工艺制备亚微乳,单因素试验法考察处方中乳化剂与油相对亚微乳物理稳定性的影响;以平均粒径、D50值、D99值及ζ电位为指标,考察不同处方中亚微乳灭菌前后的物理稳定性,并留样观察其长期稳定性.结果 泊洛沙姆188与中链油相互配伍不能得到性质稳定的亚微乳,且单独以泊洛沙姆188为乳化剂的各处方制剂长期放置后平均粒径明显增大;聚乙二醇硬脂酸酯( HS15)与各油相结合制得的亚微乳均较稳定,长期放置后各项指标基本不变;聚山梨酯80与大豆油-中链油(1∶1)混合油或大豆油配伍制成的亚微乳在灭菌后产生较大粒径的乳滴,而与中链油相配伍可制得粒径较小且均匀分散的体系;蛋磷脂E80单独作为亚微乳乳化剂,乳化效果欠佳.结论 大豆油、中链油及混合油与不同性质的乳化剂相互作用可共同影响亚微乳的粒径,但不同制剂的处方对亚微乳ζ电位无显著影响.     

Effect of methylcellulose on the stability of oil-in-water emulsions

The objective of this study was to investigate how polymers used as auxiliary emulsifiers improve the stability of oil-in-water emulsions. One stable emulsion and three unstable emulsions were formulated with 30% mineral oil and an emulsifier blend of Tween® 40 and Span® 20. The stable emulsion (SE) contained 2% emulsifier blend optimized for maximum stability. One unstable emulsion, UEI, was formulated to contain 0.5% of the same emulsifier blend as the SE formulation. Two unstable emulsions were formulated to contain an unbalanced emulsifier blend, one with excessive hydrophilic emulsifier (UE2) and one with excessive lipophilic emulsifier (UE3). A series of emulsions was prepared containing increasing amounts of methylcellulose for each base emulsion. Creaming and change in particle size were measured to evaluate stability. The addition of the polymer to the stable emulsion caused instability leading to creaming and eventual oil separation. This effect of the polymer was more pronounced in UEI emulsions. However, the addition of the polymer improved the stability of the UE2 and UE3 series of emulsions. The polymer also caused a reduction in the particle size of UE3 emulsions and a proportionally larger increase in the viscosity of UE2 emulsions. These results suggest that (i) methylcellulose could act as a hydrophilic emulsifier only in the absence of Tween^® 40, (ii) methylcellulose and Tween^® 40 associate to form a complex and (iii) the concentration of Tween^® 40 is the determining factor for the stability of emulsions. A model of the methylcellulose-Tween^® 40 association and its effect at the mineral oil-water interface is proposed.     

Investigation of drug-containing multiple phase emulsions

We studied the efficiency of the formation of w/o/w emulsions as a function of composition and mixing time. We found that the concentration of emulsifier 1, the concentration and HLB of emulsifier 2, the viscosity of the oil phase and the external water phase as well as the mixing time in second step of preparing the emulsion characteristically influence the "efficiency" of emulsification and the stability of the emulsions.     

Improved antiviral activity in vitro of ribavirin against measles virus after complexation with cyclodextrins

Despite vaccination, measles remains a burden in both developed and developing countries and complications may necessitate an efficient therapy. Measles virus (MEV) is susceptible to ribavirin (RBV), but the use of this drug is limited by its toxicity. Cyclodextrins (CDs) can form complexes with numerous molecules, improving their bioavailability and their biological properties. We have evaluated in vitro the antiviral effects of complexes of RBV with alpha-, beta- or gamma-CD against two clade A laboratory strains of MEV (Edmonston and CAM/RB) grown on Vero cells. Complexation of RBV with alpha-CD or beta-CD lead to a five-fold or a two-fold decrease in the 50% inhibitory concentration, respectively, against both MEV strains. In contrast, gamma-CD complexation showed no modification.     

Rosmarinus officinalis L. extract and some of its active ingredients as potential emulsion stabilizers: a new approach to the formation of multiple (W/O/W) emulsion

Nowadays, novel topical formulations loaded with natural functional actives are under intense investigations. Therefore, the aim of our study was to evaluate how the rosemary extract and some of its active ingredients [rosmarinic acid (RA), ursolic acid (UA) and oleanolic acid (OA)] affect technological characteristics of multiple emulsion. Formulation has been prepared by adding investigated solutions (10%) in water/oil/water (W/O/W) multiple emulsion consisting of different lipophilic phases: olive oil and liquid paraffin, with 0.5% emulsifying agent (complex of sodium polyacrylate and polysorbate 20) under constant stirring with mechanical stirrer at room temperature. The emulsion parameters were evaluated using centrifugation test, freeze–thaw cycle test, microscopical and texture analyses. Rosemary's triterpenic saponins UA and OA showed the highest emulsion stabilizing properties: they decreased CI from 3.26% to 10.23% (p?<?0.05). According to obtained interfacial tension data, the effect of rosemary active ingredients is not surfactant-like. Even though emulsifier itself at low concentration intends to form directly the multiple emulsion, the obtained results indicate that rosemary extract containing active ingredients does not only serve as functional cosmetic agent due to a number of biological activities, but also offer potential advantages as a stabilizer and an enhancer of W/O/W emulsions formation for dermopharmaceutical and cosmetic preparations.     

The effects of serum on the stability and the transfection activity of the cationic lipid emulsion with various oils

The emulsions with various oils such as linseed oil, soybean oil and squalene were prepared to obtain the relationship between the stability and the transfection activity of the emulsions. 1,2-Dioleoyl-sn-glycero-3-trimethylammonium-propane (DOTAP) was used as a single cationic lipid emulsifier. The droplet sizes and size distributions of DOTAP emulsions were dependent on oils which had different interfacial tensions. The droplet sizes followed the order of squalene emulsionsoybean oil emulsion>linseed oil emulsion>DOTAP liposome. The squalene emulsion showed the least cytotoxicity with or without serum. For in vivo gene transfer, the squalene emulsion also had the most potent transfection activity in the mouse after intravenous administration. Squalene as the oil component can enhance the stability of cationic emulsion more effectively that could be useful for the transfer of genes in vitro and in vivo.     

Water-in-oil-in-water double emulsions loaded with chlorogenic acid: release mechanisms and oxidative stability

Abstract

Chlorogenic acid (CA) is a natural compound used as an antioxidant in the preparation of food, drugs, and cosmetics. Due to their low stability and bioavailability, many researchers have studied the encapsulation of CA in various delivery colloidal systems. The aim of this study was to evaluate the stability of water-in-oil-in-water (W/O/W) double emulsions loaded with CA and its antioxidant capacity. For this purpose, CA-W/O/W double emulsions were prepared using Span 80 and lecithin as lipophilic emulsifiers, and Tween 20 as a hydrophilic emulsifier. The influence of nature of lipophilic emulsifiers, the presence of chitosan (CH) in the internal and external aqueous phases, pH, temperature and the storage time of W/O/W double emulsions were also investigated. Depending on the preparation conditions, the W/O/W double emulsions showed the droplet size in the range 9.13?±?0.55?μm–38.21?±?1.87?μm, the creaming index 34%–78% and the efficiency encapsulation 79.45?±?1.5%–88.13?±?1.9%. Zeta potential values were negative for the W/O/W double emulsion without CH (?36.8?±?2.02mV; ?27.3?±?1.75mV) and positive for the W/O/W double emulsions with CH in the external aqueous phase (+6.5?±?0.42mV; 28.6?±?0.92mV). The study of the release of CA from W/O/W double emulsions has highlighted two mechanisms: one based on the coalescence between the water inner droplets or between the oil globules as well as a diffusion releasing mechanism. The oxidative stability parameters of the W/O/W double emulsions, such as the peroxide value (POV) and the conjugated diene content (CD) were measured.     

In vitro release, pharmacokinetic and tissue distribution studies of doxorubicin hydrochloride (Adriamycin HCl) encapsulated in lipiodolized w/o emulsions and w/o/w multiple emulsions.

The lipiodolized w/o emulsion or w/o/w multiple emulsion containing Doxorubicin hydrochloride (1; Adriamycin HCl) with different emulsifiers was prepared to evaluate in vitro sustained-release behavior, pharmacokinetic and tissue distribution function in Sprague Dawley (SD) rats. The results of dissolution indicate that the release of 1 was significantly sustained for both emulsions when HCO-60 (polyoxyethylene (60) hydrogenated castor oil) was used as an emulsifier. The serum concentration of 1 was reduced and prolonged for both emulsions with the increase of HCO-60. The C(max) level was lowered and T(max) value was delayed after administration of w/o emulsions with higher HCO-60 concentration. The apparent terminal half-life for 1 released from some emulsions with higher concentration of HCO-60 was 3-folds higher than that of the 1 solution. The clearance of some w/o or w/o/w ADR emulsions also decreased with the increase of HCO-60. Not only the concentration of 1 in heart and kidney decreased significantly after the administration of w/o emulsions with the higher concentration of HCO-60, but also the hepatic concentration of 1 was higher and increased with HCO-60 concentration. The hepatic 1 level became lower after administration of w/o/w multiple emulsions with the increase of HCO-60; however, the concentration of 1 in heart, lung and spleen increased somewhat. The results indicate that lipiodol and HCO-60 seemed to play an important role in the prolongation and selective retention of w/o emulsion or w/o/w multiple emulsion, in vitro and in vivo.     

Stoichiometric and microenvironmental effects on hydrolysis of propantheline and oxyphenonium bromides in cyclodextrin solutions

The effects of alpha-, beta-, and gamma-cyclodextrins (CDs) on the basic hydrolysis of propantheline bromide (PB) and oxyphenonium bromide (OB) are analyzed in terms of the stoichiometry and microenvironments of their complexes. The rate constant of each species is evaluated with binding constant data for the 1:1, 1:2, and 2:1 complexes. The dielectric constant of the binding site of PB is estimated from the ultraviolet maximum wavelength in reference with the ethanol-water and dioxane-water systems. The energy-optimized structures of some complexes of PB with beta- and gamma-CD are obtained by molecular mechanics. Because the ester linkage of PB in the 1:1 complex with alpha-CD and in the 2:1 complex with gamma-CD is located near hydroxyls of the CD rim, these complexes catalyze the hydrolysis of PB. In contrast, the hydrolysis is inhibited by the formation of the 1:1 and 1:2 complexes of beta-CD and the 1:1 complex of gamma-CD because the ester linkage of PB is rather deeply incorporated into the CD cavities for these complexes. All the CDs inhibit the hydrolysis of OB. The rate constant of the 1:1 complex of OB and CD is in the decreasing order alpha-CD > gamma-CD > beta-CD. This order is consistent with that of the local dielectric constants of the binding sites.     

Some preparative variables influencing the properties of W/O/W multiple emulsions

Abstract

Water-in-oil-in-water multiple emulsions of chloroquine diphosphate were prepared, using olive oil, arachis oil, Span 80, gelatin, acacia and Tween 80. Emulsifiers were employed individually or in combination. An attempt was made to correlate preparative variables with stability and drug release of multiple emulsions of roughly comparative particle size. When the emulsions were satisfactorily stabilized by the optimum blend of surfactants the rate of release varied with the nature and/or combination of emulsifiers employed. The possible effects of phase-inversion temperature, spontaneous emulsification and liquid crystal stabilization on the systems have been discussed. The mechanism probably involved complex interfacial adsorption and hydrodynamic phenomena in the presence of natural oils, co-surfactants and natural stabilizers of individual HLB number, particularly when acacia is present in the system. This could be attributed to the existence of protein in some species of acacia, since there are about 130 species of acacia, the gummy exudations of which are considered official in compendia. The protein content could be a reasonable additional specification for acacia as an emulsifier.     

Oxidation of linoleic acid encapsulated with gum arabic or maltodextrin by spray-drying

Linoleic acid was emulsified with gum arabic or maltodextrin at various weight ratios of the acid to the polysaccharide in the presence or absence of a small-molecule emulsifier. The emulsions were spray-dried to produce microcapsules. Emulsions prepared with gum arabic were smaller in droplet size and more stable than those prepared with maltodextrin, and linoleic acid in a gum arabic-based microcapsule was also most resistant to oxidation than that in a maltodextrin-based microcapsule. Although the oil droplet size in the emulsion with maltodextrin decreased and the emulsion stability was improved by addition of a small-molecule emulsifier to linoleic acid, the oxidative stability of the encapsulated linoleic acid was not significantly improved. Encapsulated linoleic acid of small droplet size oxidized more slowly than that of large droplet size.     

Oxidation of linoleic acid encapsulated with gum arabic or maltodextrin by spray-drying

Linoleic acid was emulsified with gum arabic or maltodextrin at various weight ratios of the acid to the polysaccharide in the presence or absence of a small-molecule emulsifier. The emulsions were spray-dried to produce microcapsules. Emulsions prepared with gum arabic were smaller in droplet size and more stable than those prepared with maltodextrin, and linoleic acid in a gum arabic-based microcapsule was also most resistant to oxidation than that in a maltodextrin-based microcapsule. Although the oil droplet size in the emulsion with maltodextrin decreased and the emulsion stability was improved by addition of a small-molecule emulsifier to linoleic acid, the oxidative stability of the encapsulated linoleic acid was not significantly improved. Encapsulated linoleic acid of small droplet size oxidized more slowly than that of large droplet size.     

Effect of phospholipid emulsifiers on physicochemical properties of intravenous fat emulsions and/or drug carrier emulsions

The physicochemical properties of soy bean oil emulsions stabilized with purified egg lecithins (phosphatides) of various concentrations have been examined. The zeta potential of the emulsion droplets and the mean particle size of oil droplets in 10% (w/w) o/w-type emulsion decreased with increasing emulsifier concentration and then levelled off at more than 1.2% (w/w). In rheological measurements, at the initial stage, the viscosity of 10% (w/w) o/w-type emulsion gradually increased with increasing purified egg lecithin concentration, at the next stage, a plateau was reached at about 1.0-1.4% (w/w), and at the final stage, the viscosity curve showed a dramatic increase. These results indicate that emulsions stabilized by purified egg lecithin at more than 1.2% (w/w) are likely to be sufficiently stable.     

Solution structures of 1:1 complexes of oxyphenonium bromide with beta- and gamma-cyclodextrins

The solution structures of complexes of oxyphenonium bromide (OB) with beta- and gamma-cyclodextrins (beta- and gamma-CDs, respectively) in deuterium oxide have been investigated by 500 MHz proton NMR spectroscopy and molecular mechanics calculations. The chemical shifts induced by complex formation provide the 1:1 binding constants and the chemical shift variations, DeltadeltaOB-CD, with complexation for the protons of OB and the CDs. The observed binding constants are very close to those obtained by other methods and are in the following order: beta-CD > gamma-CD > alpha-CD. Initial structures of the complexes are constructed on the basis of the ROESY spectra and the DeltadeltaOB-CD values and are optimized by molecular mechanics calculations. The intermolecular distances between the protons of OB and CD calculated for these structures are well-correlated with the observed ROESY intensities. The cyclohexyl group of OB penetrates deeply into a beta-CD cavity, and the phenyl group is close to the wide rim of the cavity. The phenyl and cyclohexyl groups of OB are both incorporated into a gamma-CD cavity. Furthermore, these structures of the complexes are consistent with the suppression of bitter taste and basic hydrolysis of OB by CDs and the polarity of binding sites of OB.