Emulsions semisolid

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. 

Topical Formulations. Topical formulations by their very nature are usually multicomponent, and it is not surprising that neural networks have been applied to deal with this complexity. The first work was performed on hydrogel formulations containing anti-inflammatory drugs in Japan in 1997 [57], followed up by further studies in 1999 [58] and in 2001 [59]. Lipophilic semisolid emulsion systems have been studied in Slovenia [60, 61] and transdermal delivery formulations of melatonin in Florida [62]. In all cases, the superiority of neural networks over conventional statistics has been reported. 

However, the fundamental theory of simple foams is not as well formulated as the theory for simple emulsions. Because foams consist of gases dispersed in a semisolid film, the properties and behavior immediately become more dramatically subject to external variables, such as temperature and external air pressure. Minute changes in surface tension of the film can make or break the foam. However, a similar approach might be suggested in the foam field. In this case, the variable with which we are most concerned is whether or not a stable foam is produced and the diagrams would be drawn accordingly. 

Of all these formulations, it is the diverse semisolids that stand out as being uniquely topical. Semisolid systems fulfill a special topical need as they cling to the surface of the skin to which they are applied, generally until being washed off or worn off. In contrast, fluid systems have poor substantivity and readily streak and run off the desired area. Similarly, powders have poor staying properties. Importantly, the fundamental physicochemical characteristics of solutions, liquid emulsions and suspensions, and powders are independent of their route of application, and are discussed adequately elsewhere in this text and need not be reconsidered. This is not to say the compositions of such systems cannot be uniquely topical, for there are chemicals that can be safely applied to the... 

To be semisolid, a system must have a three-dimensional structure that is sufficient to impart solidlike character to the undistributed system that is easily broken down and realigned under an applied force. The semisolid systems used pharmaceutically include ointments and solidified w/o emulsion variants thereof, pastes, o/w creams with solidified internal phases, o/w creams with fluid internal phases, gels, and rigid foams. The natures of the underlying structures differ remarkably across all these systems, but all share the property that their structures are easily broken down, rearranged, and reformed. Only to the extent that one understands the structural sources of these systems does one understand them at all. 

Creams are semisolid emulsion systems having a creamy appearance as the result of reflection of light from their emulsified phases. This contrasts them with simple ointments, which are translucent. Little agreement exists among professionals as to what constitutes a cream, and thus the term has been applied both to absorption bases containing emulsified water (w/o emulsions) and to semisolid o/w systems, which are physicochemically totally different, strictly because of their similar creamy appearances. Logically, classification of these systems should be based on their physical natures, in which case absorption bases would be ointments and the term cream could be reserved exclusively for semisolid o/w systems, which in all instances derive their structures from their emulsifiers and internal phases. 

Changes in the natures of individual phases of or phase separation within a formulation are reasons to discontinue use of a product. Phase separation may result from emulsion breakage, clearly an acute instability. More often it appears more subtly as bleeding—the formation of visible droplets of an emulsion s internal phase in the continuum of the semisolid. This problem is the result of slow rearrangement and contraction of internal structure. Eventually, here and there, globules of what is often clear liquid internal phase are squeezed out of the matrix. Warm storage temperatures can induce or accelerate structural crenulation such as this thus,... 

Creams are semisolid preparations meant for external application as emollients or as topical medications. They are semisolid emulsions of either the oil-in-water or the water-in-oil type. 

The properties of asphalt emulsions (ASTM D977, D2397) allow a variety of uses. As with other petroleum products, sampling is an important precursor to asphalt analysis, and a standard method (ASTM D140) is available that provides guidance for the sampling of asphalts, liquid and semisolid, at point of manufactnre, storage, or delivery. 

Creams are semisolid preparation (usually emulsion) for external use. They are oily and non-greasy in nature. 

Liquid medicines generally include oral liquids, suspensions, emulsions, inhalations, nasal solutions and suspensions, topical semisolids and topical liquids, ophthalmics, and parenterals. There are numerous excipients used for liquid... 

Oral liquid and semisolid formulations containing water as part of the vehicle may be prone to microbial spoilage in the absence of a preservative. In the case of pharmaceutical creams, these are usually oil-in-water emulsions stabilized using a surfactant. Phenolic preservatives, e.g., parabens esters, are inactivated in the presence of nonionic surfactants, and this detrimental interaction can have serious consequences for preservation of the product (20). 

Creams/Lotions Semisolid emulsions that contain fully dissolved or suspended drug substances for external application. Lotions are generally of lower viscosity. Diluent A vehicle in a phannaceutical formulation commonly used for making up volume and/or weight (e.g., water, paraffin base). 

Car polishes can be solid, semisolid, or liquid. They can be solvent-based or emulsions. In either case, liquid and solid forms are possible. Compilations of suggested formulas are given in References 3, 12, and 44. A representative liquid emulsion product may contain 10—15 wt % abrasive,... 

Creams are semisolid emulsions either water-in-oil (w/o) or oil-inwater (o/ v). 

In the simplest emulsions just described, the final separation is into two liquid phases upon destabilization. The majority of emulsions are of this kind, but in some cases the emulsion is divided into more than two phases. One obvious reason for such a behavior is the presence of a material that does not dissolve in the oil or the water. One such case is the presence of solid particles, which is common in emulsions for food, pharmaceuticals, and cosmetics. Another less trivial reason is that the surfactant associates with the water and/or the oil to form a colloidal structure that spontaneously separates from the two liquid phases. This colloidal structure may be an isotropic liquid or may be a semisolid phase, a liquid crystal, with long-range order. 

Liquids and semisolids. Include oral liquids, injectable, aqueous, and oil-based liquids, emulsions, suspensions, dispersions, solutions, drops, lotions, creams, ointments, pastes, gels, liniments, aerosols and foams, suppositories, and pessaries. 

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. 

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