Lipophilic creams

The second category of semisoUd eye preparations is a lipophilic cream the active substance is dissolved in water or a (preserved) aqueous vehicle and emulsified in the ointment base. An example to mention is a sodium chloride 5 % eye cream (Table 10.14). 

Lipophilic cream Cream W/o cream Cooling ointment ENA (Table 12.31), Hydrophobic cream base DAC (Table 12.32)... 

A slightly dry skin may be treated with an extra fat containing hydrophUic cream. Patients with a very dry skin use cutaneous preparatirms with a high amount of hpophUic components. Lipophilic creams are suitable for the treatment of the chronic state of atopic eczema. Hydrophobic ointments or saturated hydrocarbons are not indicated because they have an occlusive effect, which causes heat accumulation and enhances itching. 

In general hydrophilic creams (o/w-creams) and emulsions are used without a bandage. Whether to cover the application site after application of lipophilic creams (w/o-creams) and ointments depends on the skin conditions. To soften a skin area with a strong keratinisation covering the lipophilic preparation with a bandage is effective. Fatty pastes and pastes with a cooling effect can be put on lint first. Thereafter the application site is dressed with a bandage. 

Another approach is that for hydrophilic creams the amount should be limited to as much as the skin can absorb. Lipophilic creams and hydrophobic ointments should be applied in a thin layer until the skin feels slightly fatty. 

Hydrocarbons such as liquid paraffin and white soft paraffin are also called mineral oils. They hardly penetrate the skin and in cutaneous preparations they are mainly used for protection of the surface of the skin or occlusion. They absorb little or no water. Because they cover the skin they prevent evaporation of water and hydrate the skin. Hydrocarbcais are used in lipophilic creams, hydrophobic ointments and pastes. 

Lipophilic creams or w/o-creams are emulsions with a lipophilic outer phase. Active substances are dissolved in the aqueous or lipophilic phase or are dispersed. 

Lipophilic creams are usually prepared by melting the lipid components and the surfactant (and possibly lipid soluble... 

The weak paste with zinc oxide and calcium hydroxide solution in Table 12.39 is actually a lipophilic cream, but because of the large amount of solid substance it is classified as a paste. The w/o emulsifiers calcium oleate and zinc oleate are created during the preparadmi process in the presence of oleic acid. The amount of oleic acid necessary for emulsifying depends not mily on the acid value of the used arachis oil (corresponding to the amount of fatty acid already present), but also on the method of preparatiOTi. When mixed and dispersed well usually no oleic acid is needed. When too much oleic acid is added, the emulsion will break. 

With sterile lipophilic creams the cooled aqueous phase is added drop wise to the oil phase and mixed in aseptic circumstances. With sterile hydrophilic creams the preparation method should be planned as such that both phases are cooled to around 70 °C at the same time. The aqueous phase is aseptically processed with the oil phase to a hydrophilic... 

Emulsifiers are classified by the hydrophilic—lipophilic balance (HLB) system. This system indicates whether an emulsifier is more soluble in water or oil, and for which type of emulsion (water-in-oil or oil-in-water) it is best suited. Emulsifiers having alow HLB value are more oil soluble, and are better suited for water-in-oil appHcations such as margarine. Conversely, emulsifiers having a high HLB value are more water soluble, and function more effectively in oil-in-water emulsions such as ice cream (34). The use of this system is somewhat limited because the properties of emulsifiers are modified by the presence of other ingredients and different combinations of emulsifiers are needed to achieve a desired effect. The HLB values of some common emulsifiers are given (35). 

Orange shades are realized with lipophilic natural colorants like paprika oleo-resin, P-carotene, and canthaxanthin after previous emulsification to yield water-dispersible forms. Yellow shades can be achieved using turmeric as a water-soluble solution, but the solution is light sensitive. To maintain constant color, 3 to 6 ppm of P-carotene may be added. Stable brown coloration is obtained from caramel a concentrated syrup is easily incorporated, well flavored and stable in creams. ... 

FIG. 13. Transmission electron micrograph of a freeze fractured w/o cream. The aqueous phase is dispersed as droplets within the continuous lipophilic phase the interface consists of multiple bilayers of hydrated surfactant molecules, bar 500 mn. From Miiller-Goymann, C., Halbfeste emulsionsahnliche Zustande, Seifert, Ole, Fette, Wachse, 110 395-400 (1984). 

Lipophilic (oily) cream is an emulsion of water in oil, easier to spread than oil paste or oil ointments. 

Excellent separations of corticosteroids can be achieved on an ODS column with a suitable ratio of methanol/water as an eluent. In this assay hydrocortisone is quantified using betamethasone as an internal standard. The structure of betamethasone is close to that of hydrocortisone but since it is more lipophilic it elutes from the ODS column after hydrocortisone (Fig. 12.12). The assay is a modification of the BP assay for hydrocortisone cream. In the assay described here the internal standard is added at the first extraction step rather than after extraction has been carried out in order to ensure that any losses in the course of sample preparation are fully compensated for. Extraction is necessary in the case of a cream because the large amount of oily excipients in the basis of the cream would soon clog up the column if no attempt was made to remove them. The corticosteroids are sufficiently polar to remain in the methanol/water layer as they have a low solubility in hexane, while the oily excipients are removed by extraction into hexane. The sodium chloride (NaCl) is included in the sample extraction solution to prevent the formation of an emulsion when the extract is shaken with hexane. Solution 2, where the internal standard is omitted, is prepared in order to check that there are no excipients in the sample which would interfere with the peak due to the internal standard. 

Formulation additives used in topical drug or pesticide formulations can alter the stratum comeum barrier. Surfactants are least likely to be absorbed, but they can alter the lipid pathway by fluidization and delipidization of lipids, and proteins within the keratinocytes can become denatured. This is mostly likely associated with formulations containing anionic surfactants than non-ionic surfactants. Similar effects can be observed with solvents. Solvents can partition into the intercellular lipids, thereby changing membrane lipophilicity and barrier properties in the following order ether/acetone > DMSO > ethanol > water. Higher alcohols and oils do not damage the skin, but they can act as a depot for lipophilic drugs on the skin surface. The presence of water in several of these formulations can hydrate the skin. Skin occlusion with fabric or transdermal patches, creams, and ointments can increase epidermal hydration, which can increase permeability. 

In adults, the side effects associated with topical treatment are minimal but the reasons for treatment failures are numerous. Needless-to-say the selection of a cream base (hydrophilic or lipophilic, nonocclusive or semiocclusive) is important not only for the antimicrobial and pharmacologic effects, but also for compliance reasons. 

A beverage emulsion is a concentrate added to sugar and carbonated water to make soda and fruit drinks. The oil-in-water emulsion provides flavor as well as opacity in products such as orange soda. Traditionally, gum arabic has been used to stabilize these emulsions. Interfacial starch derivatives (Section 20.4.2) are used to prevent creaming (phase separation), sedimentation, and loss in flavor and opacity, where desired, both in the concentrate and in the finished beverage. The concentrate is made by homogenizing the oils with an equal amount of the solubilized lipophillic starch, citric acid, sodium benzoate and color. A fine emulsion, typically 1 micrometer or less, is required for stability and for opacity, where desired. 

Ointments are greasy and are thicker than creams. Some are both lipophilic and hydrophilic, i.e. by occlusion they promote dermal hydration, but are also water miscible. Other ointment bases are composed largely of lipid by preventing water loss... 

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