Pharmaceutics 1 Lecture 10 Emulsions PDF

Pharmaceutics 1 Lecture 10 Emulsions  Introduction to Emulsions Definition: Emulsions are dispersed systems where one liquid phase is dispersed as droplets in another immiscible liquid. Types of Emulsions: Oil in Water (o/w) Water in Oil (w/o)...

Pharmaceutics 1 Lecture 10 Emulsions  Introduction to Emulsions Definition: Emulsions are dispersed systems where one liquid phase is dispersed as droplets in another immiscible liquid. Types of Emulsions: Oil in Water (o/w) Water in Oil (w/o) Multiple Emulsions: Water in Oil in Water (w/o/w), Oil in Water in Oil (o/w/o) Key Points: Stabilized by emulsifying agents (e.g., surfactants). Without emulsifiers, emulsions separate into two phases.  Characteristics and Uses of Emulsions Characteristics of an Acceptable Emulsion: Physical stability (no separation). Ease of application (spreadability for skin or suitable flavor for oral use). Aesthetic and textural appeal. Uses in Pharmacy: Improve solubility of hydrophobic drugs. Mask unpleasant tastes. Enhance therapeutic effects of oils (e.g., liquid paraffin). Reduce irritancy of topical drugs. Formulation and Control of Emulsions Key Formulation Factors: Type of emulsion (o/w or w/o). Route of administration (oral, topical, or parenteral). Droplet size and internal phase volume. Control of Rheological Properties: Volume concentration: Impacts viscosity and phase inversion. Particle size: Smaller droplets increase viscosity. Continuous phase viscosity: Thickening agents enhance stability but may accelerate creaming. Emulsifier system: Hydrophilic colloids improve viscosity and stability.  Advantages and Disadvantages Advantages: Enhanced drug absorption for lipophilic drugs. Suitable for patients with swallowing difficulties. Versatility in topical and oral applications. Disadvantages: Thermodynamically unstable—requires stabilization. Challenging to manufacture consistently.  Emulsions Introduction & Definitions The term emulsions refer to disperse systems in which one immiscible phase is dispersed as droplets within a second liquid phase. There are two principal types of emulsion termed oil in water (o/w) and water in oil (w/o). In the former system the oil (or internal) phase is dispersed as droplets through the external aqueous phase. Conversely, in w/o emulsions, the internal phase is composed of water droplets and the external phase is non-aqueous. 7 8  These are also multiple emulsions termed water in oil in water (w/o/w) and oil in water in oil (o/w/o) emulsions. However, uses of these are limited due to their possible reversion to the parent primary emulsion. For example, an o/w/o emulsion may revert to a w/o emulsion. in the absence of emulsifying agents, emulsions will separate into the two separate phases. The emulsifying agents used are principally 9 surface-active agents. Emulsion  Characteristics of an Acceptable Emulsion 1. Physical Stability: No phase separation. 2.Flow Properties: The formulation should be easily removable from the container. 3.Ease of Application: For topical use, it should spread easily on the skin; for oral use, it should have a suitable flavor. The formulation must be easily spread over the affected area. 4.Aesthetic Appeal: The formulation must be texturally and visually pleasing.  Advantages of Pharmaceutical Emulsions Improved Drug Delivery: Useful for drugs with low aqueous solubility. The drug dissolves in the internal phase, enhancing absorption. Taste Masking: The internal phase can mask unpleasant tastes, while the external phase is flavored appropriately. Therapeutic Oil Administration: For example, the cathartic effect of liquid paraffin is enhanced in o/w emulsions. Reduced Irritancy: For topical irritant drugs, encapsulating them in the internal phase can reduce irritation. Ease of Administration: Suitable for patients with difficulty swallowing solid dosage forms. 13 Disadvantages Pharmaceutical emulsions are thermodynamically unstable and therefore must be formulated to stabilize the emulsion from separation of the two phases. Pharmaceutical emulsions may be difficult to manufacture. 14  Formulation of pharmaceutical Emulsions In the formulation of pharmaceutical emulsions there are a number of questions that require to be initially addressed including: the type of emulsion required (o/w or w/o), the route of administration of the emulsion (e.g. oral or topical, the latter as a cream) the volume of the internal phase the droplet size and the consistency required. Now we will discuss each of these aspects individually. 15  Both o/w and w/o types are most widely used for external application. Semisolid emulsions are termed creams and more fluid preparations are called lotions, and that intended for massage into the skin, liniments. The o/w emulsion is used for the topical application of water- in soluble drugs, mainly for local effect. They do not have the greasy texture associated with oily bases and are therefore pleasant to use and easily washed from skin surfaces. Moisturizing creams, designed to prevent moisture loss from the skin and thus inhibit drying of the stratum corneum, are more efficient if formulated as w/o emulsions, which produce a coherent, water- repellent 12 film.  Choice of oil phase fixed oils of vegetable origin like sesame, cottonseed and maize are widely used as emulsion for oral use because of their lack of toxicity. Cottonseed oil, Soya bean oil and safflower oil are used for emulsions for intravenous feeding for their high calorific value Turpentine oil, benzyl benzoate and liquid paraffin are used for externally applied emulsions. 13  Choice of emulsifying agent Non-ionic surfactants, e.g. polysorbates, are less irritant and less toxic emulsifying agents Cationic surfactants in general are toxic even at lower concentrations Some emulsifiers, such as the anionic alkali soaps, often have a high pH and are thus unsuitable for application to broken skin. When choosing an emulsifying agent for parenteral use, only certain types of non-ionic materials are suitable. These include lecithin, polysorbate 80, methylcellulose, gelatin and serum albumin.  Emulsion consistency A w/o preparation will have a greasy texture and often exhibits a higher apparent viscosity than o/w emulsions. This conveys a feeling of richness to many cosmetic formulations. Oil-in-water emulsions will, however, are more easily washed from the skin surface. Also it is important for emulsion to flow freely when shaken, poured from the container or injected through a hypodermic needle. 20  Methods to control the rheological properties of an emulsion 1. Concentration of the dispersed phase As the concentration of dispersed phase increases, so does the apparent viscosity of the product. Care must be taken to ensure that the dispersed phase concentration does not increase above about 60% of the total, as phase inversion may occur. 21 2- Particle size of the dispersed phase The apparent viscosity of an emulsion can be increased by reduction in mean globule diameter and this can be achieved by homogenization. 3. Viscosity of the continuous phase Sweetening agents like Syrup and glycerol, which are used in oral emulsions will increase the viscosity of the continuous phase. Their main disadvantage is in increasing the density difference between the two phases, and thus possibly accelerating creaming. 22 4. Nature and concentration of the emulsifying system Hydrophilic colloids form multi-molecular films at the oil/water interface, and increase the viscosity of the continuous phase of an o/w emulsion. So increasing concentration of this type of emulgent will increase the viscosity of the product. 23