Looking over-the-counter Continued from p. 14 contain decamethylcyclopentasiloxane (Cyclomethicone D5, B.P. = 210 C.), which is used to carry the Aluminum Chlorohydrate to the targeted skin areas. It then conveniently evaporates. It replaces most or all of the previous isopropyl myristate, which did not appreciably evaporate and often created unsightly “oil” stains on shirts and blouses. Trofodermin topical spray from Italy treats a variety of skin ailments, including atopic eczema, allergic contact dermatitis, seborrheic dermatitis, facial psoriasis and cystic acne. Packaging is from Coster. 16 Spray August 2015 Vitamins are frequently utilized in pharmaceutical products. Vitamin A has been called the anti-aging vitamin; it combats free radicals formed on the skin by sunlight and ozone. It mitigates scars, stretch marks and dry skin surfaces and reduces irregularities, “sandpaper skin” and discoloration. By minimizing pore sizes, lines and wrinkles, it helps to create a smooth, firm dermal texture. Vitamin B3 (nicatinamide) is claimed to reduce redness and “raw skin” while brightening the skin by hydrating it. It minimizes dark spots and improves the skin’s protective barrier by increasing dermalceramide production. Vitamin C increases collagen production and thus provides an anti-aging effect. Vitamin D is well recognized for its ability to allow calcium-rich foods to build strong bones. Lastly, Vitamin E rehydrates dry skin and appears to enhance the skin’s resistance to the sun’s UV rays by deactivating the free radicals that are produced. Shea Butter is a favorite additive with many formulators. It smoothes and softens dry skin and improves both skin and hair vitality. The emollient is now available in various refined forms, such as clear, transparent oils, which are preferred for some products. The inclusion of several of these specialty ingredients can lead to more impressive label listings and to statements such as “contains six moisturizers,” although any extra benefits may be hard to validate. In some cases, the beneficial skin conditioning of an excipient may be overshadowed by other issues, e.g. the State of California has now determined popular aloe vera leaf extracts to be carcinogens. Products containing these and some other plant extracts are now subject to restrictions under Proposition 65. Loading skin and hair care products with exotic botanical extracts and other naturals is more commonly seen in the domain of cosmeceuticals than in pharmaceuticals. This may change as marketers continuously try to differentiate their products from others in the same category. The choice of the solvent (or dispersion) system has a huge effect on product identity. At present, there is a rather strong interest in emulsions—both wash-off and leave-on types. Foam products deliver nearly all of the drug substance to the skin or hair; a significant amount is lost to the atmosphere with sprays and the possible effects of inhalation must be carefully assessed. Purified water is also less costly than ethanol or other organic solvents. However, when water is used there will always be concerns about the inclusion of emulsifiers, corrosion inhibitors and preservatives. They lead to higher product development costs. Such longterm aspects as hydrolysis and double decomposition are possible. Some drug substances such as benzoyl peroxide (for acne problems) break down in aqueous solutions. The pH of healthy skin is about 5.1 to 5.5 (25°C) so there has been a tendency to adjust the pH of some pharmaceuticals into this range or close to it. This can sometimes cause problems. For instance, a sodium laurate anionic emulsifier will often deposit insoluble lauric acid. Also, sodium benzoate, arguably the most widely used corrosion inhibitor, typically loses its benzoate anion protective activity at pH values below 6.3 to 6.6 (25°C) and may deposit insoluble benzoic acid. Despite these limitations, purified water is often the solvent-diluent of choice. It has the ability to dissolve ionic substances, is non-flammable, fairly volatile, odorless and compatible with the skin and hair. Almost all emulsion (foam) aerosols are based on the use of water. Other types do exist. Quick-breaking foams use water/ ethanol solutions. In a few instances non-aqueous solvents, such as propylene glycol, polyethylene glycol 400 and 1,3-butylene glycol, can form the basis of extremely stable foams. Typical surfactants are Polawax (Croda), polyethylene glycol monostearate (self-emulsifying) and sorbitan monostearate. Because of the very low solvent vapor pressure, some of these foam puffs may last for weeks. When pharmaceutical concentrates are produced with purified (U.S. Pharmacopeia USP Grade) water compounding, they often requires heating to about 70–85°C in order to disperse certain ingredients. Cooling is then required before any heat-sensitive items are added, i.e. certain drug substances, a possible fragrance and so forth. Even if heating is not needed, it is a good practice to pasteurize the purified water at about 70°C, which also significantly diminishes the dissolved air (oxygen) content. Oxygen can attack easily oxidizable vitamins and other sensitive ingredients, so it should be minimized. Batch agitation should be done with a minimum of surface agitation and vortexing. This is especially important for those that contain thickening agents. Filling aerosol cans to a final liquid volume of about 85 to 90% is useful in minimizing oxygen from tramp air in the head space. Finally, vacuum crimping at as high a vacuum as practical is almost always recommended—usually at least 20" Hg. (506mm Hg.). This also reduces the pressure of the aerosol slightly.
Spray August 2015
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