Emulsion Lec 1 (2nd Course) PDF

Middle Technical University Institute of Medical Technology Al-Mansour Department of pharmacy Emulsion Lec 1 First stage/2nd course/  Emulsions: are biphasic heterogeneous systems consisting of two immiscible phases, one of which (the dispersed phase) is fin...

Middle Technical University Institute of Medical Technology Al-Mansour Department of pharmacy Emulsion Lec 1 First stage/2nd course/  Emulsions: are biphasic heterogeneous systems consisting of two immiscible phases, one of which (the dispersed phase) is finely subdivided and uniformly distributed as droplets throughout the other (the dispersion medium). The emulsion consist of: The dispersed phase is the internal phase or discontinuous phase and The dispersion medium is the external or continuous phase. The formation and stabilization (homogeneous) of an emulsion is made possible by the incorporation of a third substance ‘the emulsifying agent. Emulsifying agents have the ability to stabilize the emulsion by one or more mechanism: 1. prevent coalescence of particles. 2. maintain the integrity of individual droplets of dispersed phase. 3. decrease interfacial tension between two liquids.  Types of Emulsion Two types of emulsions may exist: 1.A product in which oil is dispersed as globules in water (o/w):  Oil in water (O/W) emulsions: The oil (internal or dispersed) phase is dispersed as droplets throughout the aqueous phase (external or continuous phase or dispersion medium). (Oil is the dispersed phase and water is the dispersion medium). 2. Water is dispersed as globules in the oil phase(w/o):  Water in oil (W/O) emulsions: The internal phase is composed of water droplets and the external phase is nonaqueous. (Water is the dispersed phase and oil is the Purposes (Advantages) of Emulsions and of Emulsification 1. The process of emulsification enables the pharmacist to prepare relatively stable and homogeneous mixtures of two immiscible liquids, one in each phase of the emulsion. 2. The aqueous phase is easily flavored. 3. The taste of oils can be masked. 4. Absorption is faster when compared to solid dosage forms. 5. Emulsions of the O/W type are administered orally for the following purposes: a) Cover the taste or oiliness of medicinal oils such as liquid paraffin. -The aqueous continuous phase, which will be pleasantly flavored, isolates the unpleasant disperse phase from the tongue. b) To improve the absorption of oils. 6. Semisolid emulsions are O/W (vanishing creams) or W/O (cold creams).  O/W emulsions are preferred over W/O emulsions. They can be easily rubbed into the skin and can be easily removed by washing. 7. It permits the administration of a liquid drug in the form of minute globules rather in bulk. -The reduced particle size of the oil globules may render the oil more digestible and more readily absorbed (more effective) for example, the increased efficacy of mineral oil as a cathartic when in the emulsified form. Based on the use to which they may be put, emulsions are divided into two groups: 1.Emulsions for internal use (orally or by I.V. injection) 2.Emulsions for external use (skin or mucous membrane)  Ideal characteristics of Emulsifying agents 1. It must be compatible with the other formulative ingredients and must not interfere with the stability or efficacy of the therapeutic agent. 2. It should be stable and not deteriorate in the preparation. 3. It should be nontoxic with respect to its intended use and the amount to be consumed by the patient. 4. It should possess little odor, taste, or color. 5. It should be capable to promote emulsification and maintain the stability of the emulsion for the intended shelf life of the product.  Types of Emulsifying Agents 1.Carbohydrate materials such as acacia, tragacanth, agar and pectin These materials form hydrophilic colloids when added to water and generally produce o/w emulsions 2.Protein substances such as gelatin, egg yolk These substances produce o/w emulsion The disadvantage of gelatin as an emulsifier is that the emulsion frequently is too fluid and becomes more fluid upon standing 3.High molecular weight alcohols such as stearyl alcohol, cetyl alcohol and glyceryl monostearate These substances are employed primarily as thickening agents and stabilizers for o/w emulsions used externally Cholesterol and cholesterol derivatives may also be employed in externally used emulsions to promote w/o emulsions 4-Wetting agents ,which may be anionic,cationic or non- ionic. The non-ionic surfactants are effective over pH range (3- 10), cationic surfactants are effective over pH range (3-7) and an ionic surfactants require a pH greater than 8. 5.Finely divided solids, such as colloidal clays including bentonite, magnesium hydroxide and aluminum hydroxide. These substances can form either o/w or w/o emulsions depending on the order of mixing. 21 Mixed EAs or a blend of emulsifiers is more efficient to give a stable emulsion than either each agent alone. -The mixture contributes one or several actions 1.It provides the proper hydrophilic-lipophilic nature. 2.It establishes a stable film at the interface. 3.It supplies the desired consistency to the product. -Tragacanth or agar are frequently combined with acacia to thicken the external phase of an o/w emulsion and reduce the rate of creaming.Pectin, alginates and cellulose esters are used as well for this purpose. Methods of preparation of Emulsion: a) Dry gum method b) Wet gum method c) Bottle method d) In Situ (Nascent) soap method There are two main steps in the preparation of emulsion (dry and wet) 1)Preparation of primary emulsion which is thick, creamy and stable emulsion. Its consist of ( oil, acacia, and water for primary emulsion). 2)Addition of other substances (Dilution). Methods of Emulsification -Emulsions can be prepared by several methods depending on the nature of the emulsion components and the equipment available for use. 1. Continental or Dry Gum Method -The emulsifying agent (usually acacia) is mixed with the oil before the addition of water, that is, dry gum. -(Addition of the external phase to the internal phase containing the EA). The continental method is also referred to as the 4:2:1method (oil: water: emulsifiers) because for every four parts by volume of oil,two parts of water and one part of gum a re-added in preparing the initial or primary emulsion.