Multiple emulsions nonionic surfactants

Polyoxyethylene alkyl ethers are nonionic surfactants widely used in topical pharmaceutical formulations and cosmetics, primarily as emulsifying agents for water-in-oil and oil-in-water emulsions and the stabilization of microemulsions and multiple emulsions. 

All of the above processes are influenced by the nature of the two emulsifiers used to prepare the multiple emulsion. Most reports on multiple emulsions are based on conventional nonionic surfactants, but unfortunately most of these surfactant systems produce multiple emulsions with Hmited shelf-Uves, particularly if the system is subjected to large temperature variations. During the past few years, multiple emulsions have been formulated using polymeric surfactants for both the primary and multiple emulsion preparation. These polymeric surfactants proved to be superior over conventional nonionic surfactants in maintaining the physical stability of the multiple emulsion, such that today they may be applied successfully to the formulation of agrochemical multiple emulsions. The results obtained using these polymeric surfactants offer several potential applications in formulations. The key in the latter cases is to use polymeric surfactants that are approved by the FDA for pharmacy and food, by the CTA for cosmetics, and by the EPA for agrochemicals. 

Choice of surfactant(s) for the preparation of multiple emulsions can, in principle, be made from any of the four classes of surfactants discussed in Chapter 3, although nonionics tend to be materials of choice because they are more easily tailored to meet the needs of the system. The choice will be determined by the characteristics of the final emulsion type desired, such as the natures of the various phases, additives, and solubilities. In many applications (e.g., foods, drugs, cosmetics), the choice may be further influenced by such questions as toxicity, interaction with other addenda, and biological degradation. In a given system, several different surfactants may perform adequately in terms of stability, but produce different types of multiple emulsions (A, B, or C in Figure 11.15), so that the choice will depend on application as well as function. 

Formulation Surfactants are used for the formulation of many pharmaceutical formulations such as suspensions, emulsions, multiple emulsions, semisolid and gels for topical application. In all cases the surfactants must be approved by the Food and Drug Admins-tration (FDA) and this limits the choice in pharmaceutical applications. Several surfactant molecules have been approved by the FDA, both of the ionic and nonionic type. The latter are perhaps the most widely used molecules in pharmaceuticals, e.g., sorbitan esters (Spans) and their ethoxylated analogues (Tweens). Polymeric surfactants of the PEO-PPO-PEO block type or Poloxamers (ICl, U.K.) are also used in many formulations. Many pharmaceutical emulsions, e.g., lipid and anesthetic emulsions, are formulated using egg lecithin which has to be pure and free from any toxic impurities. 

Florence AT, Whitehill D. 1985. StabUity and stabilization of water-in-oil-in-water multiple emulsions. ACS Symp Ser 272 (Macro- and Microemulsions). 359-380. Florence AT, Law TK, Whateley TL. 1985. Nonaqueous foam structures form osmoti-cally swollen W/O/W emulsion droplets. J Colloid Interface Sci 107(2) 584-588. Florence AT, Rogers JA. 1971. Emulsion stabilization by nonionic surfactants Experiment and theory. / Pharm Pharmacol 23 153-169. 

Garti N, Aserin A, Cohen Y. 1994. Mechanistic considerations on the release of electrolytes form multiple emulsions stabilized by BSA and nonionic surfactants. J Controlled Release 29 41-51. 

Law TK, Whateley TL, Florence AT. 1986. Stabilization of W/O/W multiple emulsion by interfacial complexation of macromolecules and nonionic surfactants. J Controlled Release 3 279-290. 

Matsumoto S. 1987. W/O/W type multiple emulsions. In Nonionic surfactant physical chemistry, Schick MJ, eds. New York Marcel Dekker, pp 549-600. 

Ng SM, Frank SG. 1982. Formation of multiple emulsions in a four-component system containing nonionic surfactants. / Disper Sci Tech 3 217. 

Omotosho et al. (1986) were the first to study the influence of BSA with a nonionic surfactant in the inner aqueous phase to stabilize W/O/W emulsions. They concluded that interfacial complexation between BSA and the non-ionic surfactant occurs at the inner W/O interface. This complex membrane has been found to enhance the stability of multiple emulsions and to slow down release of solute entrapped within the emulsion droplets. BSA has been investigated as a replacement for some of the monomeric surfactants in the inner phase and found to provide good stabilization for W/O/W multiple emulsions (Fredrokumbaradzi and Simov, 1992 Evison et al., 1995). 

Cytarabine loaded W/OAV multiple emulsions were prepared using nonionic surfactants (Tween and Span ) by the emulsification-sonication technique and characterized by studying the osmotic behavior. The system exhibited prolonged release pattern (Kim et al., 1995). 

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