Liquid dosage forms emulsions

Liquid dosage forms which are disperse systems (colloidal, i.e., microspheres, nanoparticles, and micelles suspensions and emulsions) often contain preservatives which are methyl, ethyl, propyl, and butyl esters of para-hydroxybenzoic acid in various combinations. A typical example is the antacid suspensions which have high pH values which make the esters of the preservatives susceptible to hydrolysis. One way to circumvent this problem is to use several preservatives in combination with the hope that some quantities of the preservatives will remain to prevent the suspension from microbial attack. A report showing the assay of the four esters and the parent acid (one of the decomposition products) in drug products in which all the preservatives were used has been given [13]. 

Dispersed systems are dosage forms composed of two or more phases, where one phase is distributed in another [2], If a dispersed system is formed by liquid phases, then it is known as an emulsion. In contrast, the dispersed system is named a suspension when the liquid dosage form is accomplished by the distribution of a solid phase suspended in a liquid matrix. The solid phase of a suspension is usually the drug substance, which is insoluble or very poorly soluble in the matrix [12],... 

Particle Size in Emulsions When a solid drug is suspended in an emulsion, the liquid dosage form is known as a coarse dispersion. In addition, a colloidal dispersion has solid particles as small as 10nm-5pm and is considered a liquid between a true solution and a coarse dispersion [44],... 

Lotion An emulsion, liquid dosage form. This dosage form is generally for external application to the skin. 

Pharmaceutical liquids require very minimal sample preparation they can be injected directly, diluted in mobile phase or other suitable diluent, or extracted into an organic solvent. A diluent is chosen to maintain solubility of the analyte as well as compatibility with the chromatographic system. Pharmaceutical suspensions must be pretreated to dissolve the drug prior to analysis. Another liquid dosage form is an emulsion, in which the liquid is suspended in a second immiscible liquid such as polydimethylsilicone. The sample preparation must break the emulsion. In the analysis of a polydimethylsilicone suspension, a liquid-liquid extraction is generally used to break the emulsion and prepare the sample for simethicone measurement. 

The patient s age has a profound influence on the types of dosage forms in which a drug may be given. Pharmaceutical liquids rather than solid dosage forms should be considered for infants and children who are under the age of five years. The liquid dosage forms are generally flavored aqueous solutions, syrups, hydroalcoholic solutions, suspensions, or emulsions, which are administered directly into the oral cavity or administered with food to aid consumption. 

Different oral liquid dosage forms offer the possibility to adjust the dosage form optimally to the requirements. The options are solutions, suspensions, emulsions or solubilisates. The flow scheme in Fig. 5.1 shows a route to the oral liquid form that is to be preferred due to the qualities of the active substance, particularly solubility, stability and taste. The required concentration influences the choice as well. 

This chapter describes the basic principles involved in the development of disperse systems. Emphasis is laid on systems that are of particular pharmaceutical interest, namely, suspensions, emulsions, and colloids. Theoretical concepts, preparation techniques, and methods used to characterize and stabilize disperse systems are presented. The term particle is used in its broadest sense, including gases, liquids, solids, molecules, and aggregates. The reader may find it useful to read this chapter in conjuction with Chapters 8, 12, and 14, since they include some of the most important applications of disperse systems as pharmaceutical dosage forms [1]. 

An interface is defined as a boundary between two phases. The solid/liquid and the liquid/liquid interfaces are of primary interest in suspensions and emulsion, respectively. Other types of interfaces such as liquid/gas (foams) or solid/gas interfaces also play a major role in certain pharmaceutical dosage forms, e.g., aerosols. 

L. C. Bailey, K. T. Tand, and B. A. Rogozinki, The determination of 2,6-diisopropylphenol in an oil in water emulsion dosage form by high-performance liquid chromatography and by second derivative UV spectroscopy, J. Pharm. Biomed. Anal., 9 501 (1991). 

Pharmaceutical products can be classified as liquid solutions, disperse systems (e.g., emulsions, suspensions), semisolids (e.g., ointments), and solid dosage forms. Liquid solutions are homogeneous mixtures of one or more substances in pharmaceutical liquids. The understanding of the physicochemical properties of liquid solutions and processes to prepare the liquid solutions is an important step in preparing final liquid solution dosage forms. In this chapter, the solutions of gases in liquids, liquids in liquids, and solids in liquids, as well as colligative properties of solutions and their application to pharmacy, are discussed. Disperse systems will be discussed in Chapter 4. 

Nonsolids Typical liquid-based oral dosage forms are elixirs, emulsions, extracts, fluid extracts, solutions, gels, syrups, spirits, tinctures, aromatic waters, and suspen-... 

Injectable dosage forms are sterile and represent one of the highest risk drug products. Injectable drug products may be liquids in the form of solutions, emulsions, and suspensions or dry solids that are to be combined with an appropriate vehicle to yield a solution or suspension. 

Emulsion A dosage form consisting of a two-phase system comprised of at least two immiscible liquids, one of which is dispersed as droplets (internal or dispersed phase) within the other liquid (external or continuous phase), generally stabilized with one or more emulsifying agents. (Note Emulsion is used as a dosage form term unless a more specific term is applicable, e.g. cream, lotion, ointment.). 

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