Semisolid emulsion systems

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. 

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. 

Gasperlin, M. Tusar, L. Tusar, M. Kristi, J. Smid-Korbar, J. Lipophilic semisolid emulsion systems viscoelastic behaviour and prediction of physical stability by neural 82. network modelling. Int. J. Pharm. 1998,168, 243-254. 

Zupan, J. Kristi, J. Viscosity prediction of lipophilic semisolid emulsion systems by neural network modelling. Int. J. 83. Pharm. 2000, 196, 37-50. 

Ointments are composed mostly of fluid hydrocarbons meshed in a mafrix of higher melting solid hydrocarbons. Common examples of ointment bases include mineral oil, petrolatum, and polyethylene glycol. Creams are semisolid emulsion systems with an opaque... 

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... 

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. 

In sections 7.3.1-7.3.4 we have considered only relatively simple dilute emulsions. Many pharmaceutical preparations, lotions or creams are, in fact, complex semisolid or stmc-tured systems which contain excess emulsifier over that required to form a stabilising mono-layer at the oil/water interface. The excess surfactant can interact with other components either at the droplet interface or in the bulk (continuous) phase to produce complex semisolid multiphase systems. Theories derived to explain the stability of dilute colloidal systems cannot be applied directly. In many cases the formation of stable interfacial films at the oil/water interface cannot be considered to play the dominant role in maintaining... 

Liquid and semisolid disperse systems are distinguished. The act of preparing a dispersion is called to disperse . The term dispersing is used to indicate that a solid or liquid substance is mixed with a liquid or a semisolid substance to obtain a two-phase system, an emulsion or a suspension (see Sect. 18.4). 

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... 

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. 

In addition to traditional dermal and transdermal delivery formulations, such as creams, ointments, gels, and patches, several other systems have been evaluated. In the pharmaceutical semisolid and liquid formulation area,these include sprays, foams, multiple emulsions, microemulsions, liposomal formulations, transfersomes, niosomes, ethosomes, cyclodextrins, glycospheres, dermal membrane structures, and microsponges. Many of these novel systems use vesicles to modulate drug delivery. Novel transdermal... 

These mixed-surfactant systems are used not only for their ability to form complex condensed films at the liquid-liquid interface, enhancing the stability of the emulsion, but also because of their ability to impart body to the product, resulting in a semisolid product rather than a liquid. Mixed emulsifiers control the consistency of a cream by forming a viscoelastic network throughout the continuous phase of the emulsion. The network results from the interaction of the mixed emulsifier with water, forming a liquid crystalline phase. 

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