Zinc oxide paste, preparation

Heat the oil phase and water phase to about 65° C. Add the oil phase slowly to the aqueous phase with stirring to form a crude emulsion. Cool to about 50°C and homogenize. Cool with agitation until congealed. Note In this classic preparation, the stearic acid reacts with the alkaline borate to form the emulsifying stearate soap. VIII. Paste (zinc oxide paste, USP) Zinc oxide 25%... 

How many grams of coal tar should be added to 925 g of zinc oxide paste to prepare an ointment containing 6% of coal tar ... 

What is the percentage of zinc oxide in an ointment prepared by mixing 140 g of a 8% zinc oxide ointment, 200 g of a 12% zinc oxide paste, and 160 g of white petrolatum (diluent) ... 

Among the few pastes in use today is zinc oxide paste (Lassar s Plain Zinc Paste) (Example 12), which is prepared by levigating and then mixing 25% each of zinc oxide and starch with white petrolatum. The product is very firm and is better able to protect the skin and absorb secretions than is zinc oxide ointment. 

Creams tend to be invisible on the skin. The same is true for ointments, although the oiliness of ointments causes them to glisten to an extent. Whatever opacity creams and ointments have is due primarily to the presence of insoluble soHds. These often imbue applications with a powdery or even crusty appearance. Dispersed soHds are usually functional, as in calamine lotion, zinc sulfide lotion, zinc oxide paste, and so on, and are an implacable feature of these preparations. However, at times insoluble soHds are added as tints to match the color of the skin and to impart opacity. Since individual skins vary widely in hue (pigmentation) and texture, tinting to a single color and texture is generally unsuccessful. 

Weak pastes may have a liquid or a weak semisolid base. They are used for wetting skin disorders. FormulatirMis differ in their potential to adhere to a very wet skin. The weak zinc oxide paste containing a calcium hydroxide solution (Table 12.39) for example adheres much more on wet skin than a paste based only on an oil (Table 12.40). The phases of the former, water containing, preparation separate after application and as a result the cooling effect is intensified. 

Pastes are also semisolid preparations intended for external application to the skin, and differ from ointments and creams in that they contain a high solid content. Pastes are made stiff by the addition of powders such as starch, zinc oxide, calcium carbonate or their mixtures. 

Pastes Ointment-like mixtures of starch, dextrin, zinc oxide, sulfur, calcium carbonate, or other medicinal substances made into a smooth paste with glycerin, soft soap, petrolatum, lard, or other fats, and medicated with antiseptic or astringent agents, designed for external use. Early pastes, such as Pasta Glycyrrhizae and Pasta Althaeae, were internal preparations, most of which were of gum-like consistency. The modern pastes were introduced by the noted... 

The formulations for resorcinol paste most often used in the past are shovm in Table 24.1. The preparation of this paste involves a lot of work for the pharmacist, who has to use centrifugation and/or ultrasound. The resorcinol crystals have to be thoroughly ground in a mortar before making up the paste to make sure no big crystals remain in it. The resulting mixture will be more homogenous and easier to spread. Unna s paste does not remain active very long, as it oxidizes rapidly. The doctor should therefore always use a freshly made paste. Another formulation contains resorcinol, olive oil, kaolin, zinc oxide, petrolatum and wool fat. 

The zinc phosphate cement dates back to at least 1879, when Rollins reported a formulation based on syrupy orthophosphoric acid [13]. The first really satisfactory cement of this type was reported by Fleck in 1902 [14], His report described a paper based on zinc oxide that had been deactivated by heating, together with a solution of phosphoric acid modified by the inclusion of aluminium and zinc. These two approaches to moderating the reaction led to a setting process that took place at a sufficiently slow speed that a smooth paste could be prepared from the components, and there was time to apply it before hardening took place. 

Pastes are semisolid preparations that consist of a lipophilic phase in which a high percentage of solid substance is dispersed. The range of solid substances is typically 30-50 % or more. The consistency varies dependent on the formulation of the base. In coimection with the amount of solids this classifies the preparations into stiff and weak pastes. Another kind of paste is an aqueous paste containing the solid in a hydrophilic base. Zinc oxide is the most frequently processed solid in pastes. Zinc oxide containing formulations are used as examples of these different kinds of paste. 

The viscosity of the zinc oxide cutaneous paste depicted in Table 12.40 is increased by zinc oleate that is formed from zinc ions with free fatty acids from the fatty oil. The preparation may be considered as a cutaneous oleogel of zinc oleate in arachis oil in which the excess zinc oxide is suspended. During preparation the product is stUl fluid. During storage more zinc oleate is created and the product thickens into a semisolid preparation that may be called a weak paste. This paste is used in subacute and chronic eczemas and in intertrigines. 

Weak pastes are prepared by dispersing the insoluble components (e.g. zinc oxide) (after grinding and sieving if necessary) in the base. Stable weak pastes such as Zinc oxide cutaneous paste (Table 12.40) may be passed through an ointment mill. Sieving of the zinc oxide is not necessary in that case. Active substances, for example corticosteroids, lidocaine, miconazole nitrate and sulfur, can be added to... 

The acid value is a measure of the amount of free fatty acids in the fat. An appropriate acid number, so a correct amoimt of free fatty acids, of groundnut oil is important in the preparation of Zinc oxide calcium hydroxide weak paste FNA (see Table 12.39). The... 

Negative Plates. The negative plates may be prepared by pasting or pressing zinc powder or zinc oxide onto a grid or by electroplating zinc from an alkaline bath to form a very active spongy zinc deposit. 

Zinc oxide occurs in nature as the mineral zincite, and can be prepared from zinc metal by vaporization and oxidation. It can also be prepared from franklinite or zinc sulfide. It is a very fine, odorless, amorphous, white or yellowish white powder. Zinc oxide has a mild astringent, protective and antiseptic action, and is usually formulated into ointment, paste or lotion vehicles. It is used widely in the treatment of dry skin and disorders such as acne vulgaris, prickly heat, insect bites, ivy poisioning, diaper rash, seborreha, impetigo, and psoriasis. It is also contained in some simscreens. 

In the ketone method, the central carbon atom is derived from phosgene (qv). A diarylketone is prepared from phosgene and a tertiary arylamine and then condenses with another mole of a tertiary arylamine (same or different) in the presence of phosphoms oxychloride or zinc chloride. The dye is produced directly without an oxidation step. Thus, ethyl violet [2390-59-2] Cl Basic Violet 4 (15), is prepared from 4,4 -bis(diethylamino)benzophenone with diethylaruline in the presence of phosphoms oxychloride. This reaction is very useful for the preparation of unsymmetrical dyes. Condensation of 4,4 -bis(dimethylamino)benzophenone [90-94-8] (Michler s ketone) with AJ-phenjl-l-naphthylamine gives the Victoria Blue B [2580-56-5] Cl Basic Blue 26, which is used for coloring paper and producing ballpoint pen pastes and inks. 

---