Microemulsion-based media as novel drug delivery systems

The oral delivery of hydrophobic drug presents a major challenge because of the low aqueous solubility of such compounds. Self-emulsifying/microemulsifying drug delivery system (SEDDS/SMEDDS), which are isotropic mixtures of oils, surfactants, solvents and co-solvents/surfactants, can be used for the design of formulations in order to improve the oral absorption of highly lipophilic drug compounds. The efficiency of oral absorption of said drug from such type of formulation depends on many formulation-related parameters, such as surfactant concentration, oil/surfactant ratio, polarity of the emulsion, droplet size and charge, all of which in essence determine the self-emulsification ability. Thus, only very specific pharmaceutical excipient combinations will lead to efficient self-emulsifying systems. With the growing interest in this field, there is an increasing need for guidelines in excipient selection to obtain effective delivery system with improved bioavailability.The aim of this review is to prese...

Role of excipients in successful development of self-emulsifying/microemulsifying drug delivery system (SEDDS/SMEDDS)

Applications of X-ray scattering in pharmaceutical science.

We review and summarize the three-phase behavior and solubilization of microemulsions with catanionic surfactants. Particular emphasis is placed to the three-phase behavior of mixtures of oil, water and alcohol with mixed surfactants containing one anionic and one cationic surfactant. The effect of salt and catanionic surfactant on the HLB composition and solubilizing capacity of surfactants to form microemulsions is discussed.

Catanionic surfactants: microemulsion formation and solubilization

In a hydrophilic octaethylene glycol dodecyl ether (C12EO8)-water system, a micellar cubic phase is formed below 20°C. Upon addition of decane, the maximum temperature of micellar cubic phase (I1) is increased, and, moreover, the hexagonal liquid crystal region changes to the I1 phase. Beyond the solubilization limit of decane in the I1 phase, highly viscous and gel-like O/I1-emulsions are formed in the two-phase region of I1+O. In the case of a surfactant mixture (C12EO4.8) containing C12EO8+C12EO3, a single I1 phase region is not present in a pseudo ternary phase diagram of water/C12EO4.8/decane system, but an I1+O region appears in the oil-rich region. C12EO4.8 forms lamellar liquid crystal in the aqueous system but C12EO3 in the mixture is dissolved in oil and the mixing fraction of C12EO8 in the surfactant aggregate increases as oil is added. Finally, a two-phase region of I1+O appears. It is considered that the O/I1-emulsion or gel based on the cubic phase corresponds to the gel appeared in the so-called D-phase emulsification process. Upon addition of alkyl polyol such as glycerol or 1,3-butanediol, the transparency of the emulsion in the I1+O region increases because the difference in refractive index between the cubic phase and excess oil is decreased. The maximum temperature of the I1 phase decreases with increasing polyol content. Consequently, the addition of alky polyols is not crucial to form O/I1 gels in an oil-rich region.

Highly Concentrated Cubic-Phase Emulsions: Basic Study on D-Phase Emulsification using Isotropic Gels

Sucrose monoalkanoates (SE) form microemulsions by mixing with lipophilic cosurfactants such as the middle-chain alcohols, or sucrose polyalkanoates. In the case that sucrose monododecanoate is combined with hexanol, a middle-phase microemulsion is produced and coexists with excess water and oil phases at optimum mixing fraction of SE and hexanol. The bicontinuous structure of the microemulsion was confirmed by means of self-diffusion coefficient on NMR measurement. A larger solubilization capability of oil is attained to a mixed mono- and poly-dodecanoate system than that of the middle-chain alcohol. It is probably due to the location of most of surfactant molecules at the micro-interface inside the microemulsion. In this system, instead of forming a three-phase region, a lamellar liquid crystal intrudes into multi-phase region since the surfactant layer is rather rigid as which was supported by the results of SAXS and ESR measurements. Further addition of a short-chain alcohol such as propanol ...

N. Nakamura

Papers

Formation of microemulsion and liquid crystal in biocompatible sucrose alkanoate systems