Aerosol OT microemulsions as carriers for transdermal delivery of hydrophobic and hydrophilic local anesthetics

The skin permeation enhancement of many kinds of drugs and cosmetic substances by microemulsions has been widely known; however, the correlations between microemulsion microstructures and the efficiency of skin permeation are not fully elucidated. Therefore, the aim of our study was to investigate the influence of microemulsion types on in vitro skin permeation of model hydrophobic drugs and their hydrophilic salts. The microemulsion systems were composed of isopropyl palmitate (IPP), water, a 2:1 w/w mixture of Aerosol OT (AOT) and 1-butanol, and a model drug. The concentrations of surfactant mixture and model drug were maintained at 45% and 1% w/w, respectively. The concentrations of IPP and water were 15% and 39% w/w, respectively, for oil-in-water (o/w) type and vice versa for water-in-oil (w/o) type. The samples were prepared by simple mixing and characterized by visual appearance, pH, refractive index, electrical conductivity, viscosity, and determination of the state of water and IPP in the formulations using differential scanning calorimetry. Transdermal flux of lidocaine, tetracaine, dibucaine, and their respective hydrochloride salts from the drug-loaded AOT-based microemulsions through heat-separated human epidermis was investigated in vitro using modified Franz diffusion cells. The o/w microemulsions resulted in the highest fluxes of the model drugs in base form as compared with the other formulations within the same group of drugs. Moreover, the skin permeation of drug from microemulsions depended on drug molecular structure and interaction between drug and surfactant.     

Transdermal delivery of methotrexate: iontophoretic delivery from hydrogels and passive delivery from microemulsions

In vitro assays were performed to investigate the effectiveness of transdermal administration of methotrexate (MTX) by iontophoretic delivery from two types of hydrogel and passive delivery from two types of microemulsion. Both iontophoretic delivery of MTX from hydrogels and passive delivery from microemulsions were more effective than passive delivery from aqueous solutions of the drug. In the iontophoretic delivery assays, the type of hydrogel used and the concentration of the drug in the loading solution had little influence on effectiveness of delivery. In the passive delivery assays, we used both water/oil (w/o) and oil/water (o/w) microemulsions: effectiveness of delivery was higher from o/w systems. At the end of all assays, significant amounts of MTX were detected in the skin. These results suggest that both hydrogels and microemulsions may be of value for the topical administration of MTX in the treatment of psoriasis.     

In vitro percutaneous absorption of metronidazole and glucose: Comparison of o/w,w/o/w and w/o systems

The percutaneous absorption of model hydrophilic drugs with intermediate and high polarity, metronidazole and glucose, respectively, from three emulsion types (o/w, w/o/w and w/o) has been studied. All the emulsions were prepared with exactly the same composition in order to avoid the influence of the formulation and to study the role of the emulsion type alone. The yield of the w/o/w emulsion containing glucose was high (95.8%), while that of the w/o/w emulsion containing metronidazole was lower (77.6%), although the multiple character of the emulsion was not in question. Absorption of metronidazole across hairless rat skin over 24 h ranged from 55 to 69% of the applied dose and was similar for the three emulsions studied. Absorption of glucose ranged from 1 to 4% and was found to be greater from the o/w emulsion than that observed from the w/o/w or w/o emulsions. The amount of glucose found in the dermis seems to be dependent on the emulsion type: o/w > w/o/w ≅ w/o. The differences between the emulsions cannot be attributed only to the evaporation rate of water alone. X-ray diffraction patterns obtained after treatment of the stratum corneum with the three emulsions did not display any difference, but were somewhat different from that observed with untreated stratum corneum.     

Pickering w/o emulsions: drug release and topical delivery

The skin absorption from Pickering emulsions as a new dosage form was investigated for the first time. Pickering emulsions are stabilized by adsorbed solid particles instead of emulsifier molecules. They are promising dosage forms that significantly differ from classical emulsions within several features. The skin permeation of a hydrophilic model penetrant (caffeine) was investigated from a w/o Pickering emulsion and compared to a w/o classical emulsion stabilized with an emulsifier. Both emulsions had the same composition and physicochemical properties in order to focus on the effect of the interfacial layer on the drug release and skin absorption processes. The highest permeation rates were obtained from the Pickering emulsion with a pseudo-steady state flux of 25 microg cm(-2)h(-1), threefold higher than from a classical emulsion (9.7 microg cm(-2)h(-1)). After 24h exposure, caffeine was mostly in the receptor fluid and in the dermis; cumulated amounts of caffeine were higher for the Pickering emulsion. Several physicochemical phenomena were investigated for clearing up the mechanisms of enhanced permeation from the Pickering emulsion. Among them, higher adhesion of Pickering emulsion droplets to skin surface was disclosed. The transport of caffeine adsorbed on silica particles was also considered relevant since skin stripping showed that aggregates of silica particles entered deeply the stratum corneum.     

Preparation and evaluation in vitro of solutions and o/w microemulsions containing levobunolol as ion-pair

Aqueous and aqueous-PEG 200 solutions, and o/w microemulsions containing levobunolol (LB) coupled to octanoic acid (OA) as lipophilic ion-pair were submitted to a preliminary investigation in vitro, in view of possible ophthalmic applications. Evaluation of the following was carried out: n-octanol/water partition coefficient, permeation through an artificial lipophilic membrane and through hairless mouse skin, isotonicity and eye irritation in albino rabbits. Permeation studies in aqueous and in aqueous-PEG 200 solutions through the artificial membrane indicated a higher apparent lipophilicity of LB-OA with respect to the drug alone. The transport rate of LB-OA through hairless mouse skin was lower from a microemulsion containing 0.5% w/w drug than from a water-PEG 200 solution simulating the continuous phase, thus suggesting a possible reservoir effect of the dispersed phase of the microemulsion. The microemulsion, which was isotonic and non-irritating on rabbit eyes, appears as a potentially interesting ophthalmic vehicle for LB.     

Effects of formulation variables on characteristics of poly (ethylcyanoacrylate) nanocapsules prepared from w/o microemulsions

The effect of several formulation variables on some of the physico-chemical characteristics of poly (ethyl cyanoacrylate) (PECA) nanocapsules prepared by the interfacial polymerisation of biocompatible water-in-oil microemulsions was investigated. In all cases, yields were high (>90%) and the polydispersity in size of nanocapsules was narrow. The molecular weight of the nanocapsules formed was influenced by the pH of the aqueous component of the microemulsion, increasing with increasing pH. The size of the nanocapsules formed (ranging from around 130 to 180 nm) was a function of the ratio of the mass of monomer used to the water weight fraction of the microemulsion, increasing as this ratio was increased. This is due to the formation of a thicker polymer wall resulting from the increased mass of monomer available per unit interfacial area as this ratio is increased. The rate of release of insulin from nanocapsules was also influenced by this ratio, in agreement with its effect on wall thickness. This study demonstrates that many pharmaceutically relevant physico-chemical properties of poly (alkyl cyanoacrylate) (PACA) nanocapsules prepared by interfacial polymerisation of microemulsions can readily be manipulated by changing either the pH of the aqueous component, the water weight fraction of the microemulsion or the mass of monomer used for polymerisation.     

Release of 5-fluorouracil from intramuscular w/o/w multiple emulsions

Comparative in vivo studies of aqueous solution, multiple w/o/w, and w/o emulsions showed that formulating 5-fluorouracil in emulsion systems significantly sustained the release of the drug from intramuscular injection sites in the rat. Intramuscular injection of the drug in both w/o and w/o/w emulsion systems produced sustained blood concentrations with a later blood level peak than observed following intramuscular injection of aqueous solutions of the drug. The multiple w/o/w emulsion exhibited a more rapid release of drug from the injection site than the w/o emulsion because of partitioning of the drug to the external aqueous phase during secondary emulsification. The fate of the oil phase following intramuscular injection of a water/hexadecane/water multiple emulsion spiked with 1-14C-hexadecane has been studied in rats as a function of stabilizer concentrations. Increasing the lipophilic surfactant (Span 80) concentration facilitated the clearance of the oily vehicle from the injection site, by mechanisms which remain to be elucidated.     

Methotrexate transport from the internal phase of multiple w/o/w emulsions

Release rates of Methotrexate (MTX) encapsulated in the internal phase of w/o/w emulsions stabilized by the interfacial interaction between albumin and sorbitan mono-oleate(Tween 80) were measured as functions of two formulation variables--the oil phase and the secondary emulsifier composition. The release rate was significantly affected by the nature of the oil phase and decreased in the order isopropyl myristate greater than octadecane greater than hexadecane greater than dodecane greater than octane, which was a reflection of the increasing internal droplet size of the emulsions. The release rate data conform with first order kinetics. Comparison of the effective permeability coefficients calculated from the experimental apparent first-order rate constants, with the effective permeability coefficient of water in planar oil layers, containing non-ionic surfactants, determined by a microgravimetric method supported the hypothesis of diffusion of MTX in water loaded inverse micelles. Surfactants with high HLB values, used as the secondary hydrophilic emulsifier increased the release rates, primarily by increasing the rate of diffusion of MTX through the non-aqueous liquid membrane.     

Preparation and evaluation of multiple emulsions water-in-oil-in-water (w/o/w) as delivery system for influenza virus antigens

In this study, investigations have been carried out to prepare adjuvant active delivery systems; multiple water-in-oil-in-water (w/o/w) emulsion formulations, containing influenza virus surface antigen Hemagglutinin (HA). A modified two-stage emulsification method has been used to prepare multiple emulsions. After improving multiple (w/o/w) emulsion formulations; F1: purified antigen solution (PAS)/soybean oil, HCO-40 and span 80/pluronic F-68, F2: PAS and HPbetaCD/soybean oil, HCO-40 and span 80/pluronic F-68, F3: PAS/squalane, HCO-40 and span 80/pluronic F-68, formulations were selected for the stability study that continued for a 3 month duration. To evaluate the stability of these formulations, microscopic observation, osmolarities of the internal and external aqueous phases, pH, globule size and viscosity were determined. SDS-PAGE (silver staining) was used to evaluate HA and the micro-bicinchoninic acid (mBCA) assay was used to determine the in vitro release of antigen from formulations. Immune responses of formulations were investigated in Wistar Albino rats and compared with the immune response raised against the conventional vaccine. These responses were detected with Hemagglutination Inhibition (HAI) assay. The results of this study demonstrated that HA was well entrapped in the multiple (w/o/w) emulsion formulations. Molecular weight and antigenicity of the entrapped HA were not affected by the emulsification procedure. These results suggest that multiple emulsion formulations entrapping influenza antigen may have potential for immunization studies as one of the vaccine delivery system with adjuvant properties.     

Release of antiseptics from the aqueous compartments of a w/o/w multiple emulsion

A w/o/w multiple emulsion drug carrier system has been developed for local vaginal therapy. To improve its efficacy and to extend the antimicrobial spectrum activity of benzalkonium chloride (CBZ), which is introduced in the external aqueous phase, chlorhexidine digluconate (CHD) was added to the internal aqueous phase of the multiple emulsions. The minimal bactericidal concentrations (MBC) for the association of CHD and CBZ in emulsion were determined towards Escherichia coli and Staphylococcus aureus. The main release mechanism considered for the CHD encapsulated in the inner phase was a swelling-breakdown phenomenon which followed dilution of the emulsion under hypo-osmotic conditions. In order to demonstrate this release, the bactericidal effect of multiple emulsions undiluted and diluted 1-5 and 1-10 in hypo-osmotic conditions at two CHD concentrations was evaluated. To validate and quantify this release, rheological and release kinetics studies were used. The bactericidal activity of combination CBZ-CHD in the emulsion was synergistic on the two bacterial strains and the release of encapsulated CHD in the internal phase was obtained following its dilution in hypo-osmotic conditions. Vaginal administration could be carried out following dilution at 1-5 in sterile water for multiple emulsions containing the lower concentration of CHD.     

Preparation and evaluation of w/o/w type emulsions containing vancomycin

The objective of this contribution is to summarize the preparation and application of water-in-oil-in-water type multiple emulsions (w/o/w emulsions) entrapping vancomycin (VCM). Formulations of the emulsions (the composition of an oily phase or the type and concentrations of surfactants) and emulsification methods (a stirring method and a membrane method) or conditions (rotation rates, pore sizes of membrane or operation pressures) were evaluated in order to prepare stable w/o/w emulsions. The pharmaceutical properties of the w/o/w emulsions - particle sizes, viscosity, phase separation and drug entrapment efficiency were measured and evaluated. We prepared stable w/o/w emulsions with a particle size of about 3 micrometer and an entrapment efficiency of VCM of about 70%. When this emulsion was administered intravenously to rats, plasma concentrations of VCM were prolonged compared to the VCM solution alone. The results of this study show the potential of the w/o/w emulsions for several clinical applications as one of the drug delivery systems.     

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.     

Preparation and evaluation of double-walled microparticles prepared with a modified water-in-oil-in-oil-in-water (w1/o/o/w3) method

Abstract

In this study, a modified water-in-oil-in-oil-in-water (w₁/o/o/w₃) method was developed to prepare double-walled microparticles containing ovalbumin (OVA). The microparticles were characterized with respect to their morphology, particle size, encapsulation efficiency, production yield, thermal properties and in vitro drug release. Microscopy observations clearly showed that microparticles have spherical shape and smooth surface. These microparticles were characterized to have double-walled structure, with a cavity in the centre. By using w₁/o/o/w₃ method, a significant decrease in mean particle size and a significant increase in encapsulation efficiency were obtained. The mean particle size and the encapsulation efficiency of double-walled microparticles were also affected by the changing amount of OVA and mass ratio of polymers. Microparticles prepared with two polymers exhibited a significantly lower initial burst release followed by sustained release compared to microparticles made from poly(d,l-lactide-co-glycolide) 50/50 only. It can be concluded that these microparticles can be a potential delivery system for therapeutic proteins.     

The influence of emulsifiers on drug diffusion from o/w creams

Histamine diffusion from various o/w creams containing different emulsifiers was studied. To confirm the diffusion study, possible drug-emulsifier interactions were studied by dialysis of their aqueous solutions. Interaction between histamine and anionic sodium laurylsulphate resulted in the absence of free diffusible histamine. No interaction was observed with the non-ionic cetomacrogol. Repulsion by the cationic cetrimide increased histamine diffusion rate and total diffusing amount because distribution occurred in accordance with the Donnan membrane equilibrium.     

The nature of the oil phase and the release of solutes from multiple (w/o/w) emulsions

The effect of the nature of the oil phase of w/o/w emulsions stabilized by interfacial complexation between span 80 (sorbitan mono-oleate) and albumin has been studied. The long-term stability of the systems has been assessed by photomicrography and by measuring the quantity of an internal marker (NaCl) remaining entrapped with time. The number of multiple oil drops and the diameters of the internal aqueous droplets were determined over 6 weeks, and the amounts of NaCl entrapped over the same period were followed. There were no significant changes in w/o/w emulsions prepared with a range of hydrocarbons (octane, dodecane, hexadecane, toluene and cyclohexane), indicating stable multiple emulsions. The release of NaCl and 5-fluorouracil (5-FU) separately entrapped in the internal aqueous phase of w/o/w emulsions was measured. Diffusion of the un-ionized species of 5-FU across the oil phase or through localized thin oil lamellae is the primary transport mechanism. In the presence of surface active agents, water is solubilized in inverse micelles which would possess the ability to solubilize other water-soluble components, such as NaCl and 5-FU. The mixed inverse micellar units of Span 80 and polysorbate (Tween) 80 therefore act as solute carriers across the liquid hydrocarbon membrane separating the two aqueous phases of the emulsions. The main factor in determining the differences in rates of release from the hydrocarbon emulsions appears to be the droplet size of the internal aqueous phase.     

Synthesis and surface activity properties of hydrophobic/hydrophilic peptides

In order to explore the ability of amphiphilic peptides to behave as surface-active agents with emulsifying properties, several short peptides of leucine and glutamine were synthesized with different periodicity, length and hydrophobic characteristics. The stepwise liquid-phase procedure using the N-hydroxysuccinimide ester was deployed in all chain-lengthening steps, and the same procedure was also used subsequently to modify some of the products by introducing a lipophilic moiety such as a palmitoyl residue. The surface-active properties of these products were evaluated by measuring the variation of surface (y_s) and interfacial (y_i) tensions and the formation of micelles as a function of concentration in aqueous solution. The alternating sequence (Leu-Gln)_n showed good surface activity behaviour, similar to those of recognized surfactants, albeit with no emulsifying function. More hydrophobic compounds, such as lipopeptides, lowered the surface tension of water at concentrations markedly below those usually observed for classical surfactants, and emulsifying properties were observed in all the peptides substituted with lipophilic moieties.