Preparation and characterization of emulsifiable glasses: Oil-in-water and water-in-oil-in-water emulsions

Formulation strategies to improve the bioavailability of poorly absorbed drugs with special emphasis on self-emulsifying systems

Poorly water-soluble drug candidates are becoming more prevalent. It has been estimated that approximately 60–70% of the drug molecules are insufficiently soluble in aqueous media and/or have very low permeability to allow for their adequate and reproducible absorption from the gastrointestinal tract (GIT) following oral administration. Formulation scientists have to adopt various strategies to enhance their absorption. Lipidic formulations are found to be a promising approach to combat the challenges. In this review article, potential advantages and drawbacks of various conventional techniques and the newer approaches specifically the self-emulsifying systems are discussed. Various components of the self-emulsifying systems and their selection criteria are critically reviewed. The attempts of various scientists to transform the liquid self-emulsifying drug delivery systems (SEDDS) to solid-SEDDS by adsorption, spray drying, lyophilization, melt granulation, extrusion, and so forth to formulate various dosage forms like self emulsifying capsules, tablets, controlled release pellets, beads, microspheres, nanoparticles, suppositories, implants, and so forth have also been included. Formulation of SEDDS is a potential strategy to deliver new drug molecules with enhanced bioavailability mostly exhibiting poor aqueous solubility. The self-emulsifying system offers various advantages over other drug delivery systems having potential to solve various problems associated with drugs of all the classes of biopharmaceutical classification system (BCS).

Development of cyclosporine A-loaded dry-emulsion formulation using highly purified glycerol monooleate for safe inhalation therapy

The main objective of this study was to improve the safety and oxidative stability of glycerol monooleate (GMO)-based dry-emulsion (DE) formulation containing cyclosporine A (CsA) for inhalation therapy. GMO or highly purified GMO (hpGMO) was used as surfactant for the DE formulations (GMO/DE or hpGMO/DE), the toxicological and physicochemical properties of which were characterized with a focus on oxidative stability, in vitro/in vivo toxicity, and dissolution property. Incubation of GMO at oxidation accelerating conditions for 10 days at 60°C resulted in the formation of lipid peroxides as evidenced by increased malondialdehyde (111 μmol/mg); however, hpGMO samples exhibited increase of only 20.7 μmol/mg in malondialdehyde level. No significant acute cytotoxicity was observed in rat alveolar L2 cells exposed to hpGMO (0.28mM), and intratracheal administration of hpGMO powder in rats did not cause an increase of the plasma LDH level. The hpGMO/DE exhibited marked improvement in dissolution behavior of CsA, and stable fine micelles with a mean diameter of 320 nm were formed when suspended in water. A respirable powder formulation of hpGMO/DE (hpGMO/DE-RP) was newly prepared, and its in vitro inhalation property and in vivo efficacy were also evaluated. The hpGMO/DE-RP exhibited high dispersibility in laser diffraction analysis and significantly improved potency to attenuate recruitment of inflammatory cells into airway and thickening of airway wall in an animal model. Thus, the strategic use of hpGMO would improve oxidative stability and local toxicity compared with a GMO-based DE formulation, and its application to RP formulation could be a promising approach for effective inhalation therapy.

Cellulose as a novel amphiphilic coating for oil-in-water and water-in-oil dispersions

The amphiphilic character of cellulose molecules provides the opportunity to use it as a novel eco-friendly emulsifying agent for formation of stable oil-in-water or water-in-oil dispersions. This may be done by mixing water, oil and cellulose solution in an ionic liquid. A more practical alternative is to form first a hydrogel from the cellulose/ionic liquid solution by coagulation with water and applying it into the sonicated water/oil or oil/water mixtures. The dissolution/regeneration process affords higher mobility to the cellulose molecules so an encapsulating coating can be formed at the water-oil interface. A solid-state dispersion was obtained by drying liquid dispersions, which can be repeatedly dissolved in excess water reforming a sustainable dispersion. The damp dispersion can be blown under reduced pressure, yielding a nanoporous foam ("aerocellulose"). The n-eicosane based solid dispersion as well as the aqueous dispersion possess a very high effective heat-absorption capacity. X-ray diffraction patterns indicate that the encapsulating cellulose shell is indeed in the amorphous state. Small-angle diffraction patterns of n-eicosane dispersions exhibit two sharp reflections. One is due to the n-eicosane triclinic crystal bulk phase and the other at somewhat smaller angles is interpreted as due to less ordered phase, possibly due to interactions with the encapsulating cellulose.

Preparation of an enteric-soluble solid-state emulsion using oily drugs

To improve the patient's compliance and enhance the stability of oily drugs in the gastric fluid, an enteric-soluble solid-state emulsion (ESE), was developed. The ESE was prepared by spreading liquid o/w-emulsions on a flat glass and drying at the oven maintained at 40 degrees C. Aerosil 200 was applied as solid carrier and emulsifier. And Eudragit L30D-55 was used as enteric coating material. The influence of various preparation parameters on the residual volatile oil and the release behavior was investigated. Droplet size distribution of the primary emulsions and the emulsion after reconstitution of zedoary turmeric oil (ZTO) ESE in the phosphate buffer were also measured. When ZTO ESE was immersed into phosphate buffer (pH 6.8), the stable emulsion was formed in 20min, but the release was obviously suppressed when it was exposed to the gastric fluid. It was concluded that preparation of enteric-soluble solid-state emulsion by the present method for oral oily drug was feasible.

Do amphiphile aggregate morphologies and interfacial compositions depend primarily on interfacial hydration and ion-specific interactions? The evidence from chemical trapping

Surface-active amphiphiles aggregate spontaneously in water to form association colloids such as micelles, microemulsions, and vesicles. The hydrophobic effect drives aggregation, but the opposing forces that provide balance and determine equilibrium morphologies are not understood, in particular, how specific ion effects, which often follow a Hofmeister series, affect the properties of association colloids. We have harnessed the competitive trapping of arenediazonium ions by weakly basic nucleophiles such as halide counterions, anionic headgroups, alcohols, urea, and water, to estimate their concentrations in the interfacial regions of association colloids from reaction product yields. In the chemical trapping method, product yields are proportional to the concentrations of water and other nucleophiles within the interfacial region, not their stoichiometric concentrations in solution. Changes in the balance of forces controlling aggregate structure are reflected in changes in interfacial concentrations of water and other components in association colloids as reported by the chemical trapping method. Significant changes in interfacial water and counterion concentrations are observed during structural transitions. Specific ion effects on sphere-to-rod transitions of cationic amphiphiles are interpreted in terms of the strengths of headgroup and counterion pairing and ion hydration interactions. Trapping results also provide important information on interfacial compositions of microemulsions, vesicles, nonionic micelles and macroemulsions, reverse micelles, micelles in aqueous urea, and anionic polyelectrolytes. Identifying relationships between aggregate morphology and interfacial composition by chemical trapping has just begun.

An enteric-coated dry emulsion formulation for oral insulin delivery

A novel oral dosage formulation of insulin consisting of a surfactant, a vegetable oil, and a pH-responsive polymer has been developed. First, a solid-in-oil (S/O) suspension containing a surfactant-insulin complex was prepared. Solid-in-oil-in-water (S/O/W) emulsions were obtained by homogenizing the S/O suspension and the aqueous solution of hydroxypropylmethylcellulose phthalate (HPMCP). A microparticulate solid emulsion formulation was successfully prepared from the S/O/W emulsions by extruding them to an acidic aqueous solution, followed by lyophilization. The insulin release from the resultant dry emulsion responded to the change in external environment simulated by gastrointestinal conditions, suggesting that the new enteric-coated dry emulsion formulation is potentially applicable for the oral delivery of peptide and protein drugs.

Physical stability of redispersible dry emulsions containing amorphous sucrose

The objective of the present study was to estimate the stability of redispersible dry emulsions containing amorphous sucrose. Dry emulsions were prepared by spray drying liquid o/w-emulsions in a laboratory spray dryer. The effect of hydroxypropyl methylcellulose (HPMC) on the glass transition temperature T(g) of spray dried sucrose-HPMC mixtures, relative to the T(g) of amorphous sucrose, was investigated. For the sucrose-HPMC mixtures the values of T(g) followed the ideal Gordon-Taylor equation up to 30% HPMC. For dry emulsions containing 40% HPMC, 30% lipid and 30% sucrose, the T(g) was increased by 12 degrees C relative to the T(g) of amorphous sucrose. The stability of the dry emulsions was investigated by a conventional stability study and by an enthalpy relaxation study. The measured enthalpy recovery of amorphous sucrose below T(g) was used to calculate molecular relaxation time parameters based on the Williams-Watts equation. The molecular mobility of amorphous sucrose at temperatures 50 degrees C below T(g) was low and negligible with respect to the shelf life stability. It was concluded that the dry emulsions are physically stable with respect to the lifetime of a pharmaceutical product when stored in dry condition and at temperatures up to 28 degrees C.

Preparation of redispersible dry emulsions by spray drying

Development of stable dry emulsions being able to reform the original o/w-emulsion by reconstitution in water is presented. Dry emulsions were prepared by spray drying liquid o/w-emulsions in a laboratory spray dryer. Three hydroxypropylmethylcellulose (HPMC) types were applied as solid carrier and emulsifier. The lipid phase was fractionated coconut oil. The ratio of solid carrier to lipid phase influenced the reconstitution properties. It was possible to prepare redispersible dry emulsions of a lipid content up to 40% dry powder mass. The different HPMC types had no noticeable effect on the reconstitution properties, but too viscous liquid o/w-emulsions were difficult to atomise. The type of rotary atomizer, or the rate of rotation did not affect the technical properties of the dry emulsions containing 40% lipid. It was concluded that low viscosity HPMC was a useful solid carrier. The dry emulsions remained physically stable for at least 6 months.

Multiple emulsions for the delivery of proteins

Multiple emulsions are unique in that a true liquid phase is maintained separate from an external aqueous phase. This may be especially important for bioactive molecules that cannot be appropriately stabilized in the solid state. In addition, the separation of aqueous phases enables highly specialized environments, conducive to protein activity, to be prepared. The physical instability of conventional systems remains a major factor limiting their wider application. Attempts to improve the physical stability of the aqueous dispersions through interfacial complexation and the use of micro-emulsions are improving the short-term stability. As an alternative approach, solid-state emulsions attempt to store the multiple emulsion as a solid. Although solid-state emulsions appear to have the potential to be useful protein delivery systems, a substantial experimental data base has yet to be generated.