Powders

Pharmaceutical powders are complete mixtures of dry, finely divided drugs and/or chemicals that may be used internally or externally. The most common types are powder papers, bulk powders, and insufflations. Powdered dosage forms are used when drug stability or solubility is a concern. These dosage forms may also be used when the powders are too bulky to make into capsules and when the patient has difficulties in swallowing a capsule. Such disadvantages as the rapid deterioration and the inability to mask an unpleasant taste of some medications restrict the use of the powders.

Blending of powders may be accomplished by trituration in a mortar, stirring with a spatula or sifting. If two ingredients are present in unequal quantities, the technique of geometric dilution is used. When heavy powders are mixed with lighter ones, the heavier powder should be placed on top of the lighter one, and then blended. When mixing two or more powders, each powder should be pulverized separately to about the same particle size before blending together. Light powders are mixed best by using the sifting method. The sifting is repeated three to four times to ensure thorough mixing of the powders. In industry, a tumbling method is more commonly used. Tumbling is the process of mixing powders in a large container rotated by motorized process.

Depending on their intended use, powders are packaged and dispensed by pharmacists as bulk powders or divided powders. Bulk powders are dispensed in bulk containers. A perforated can, or sifter can, is used for external dusting, and an aerosol container is used for spraying onto the skin. A wide-mouthed glass jar permits easy removal of a spoonful of powder.

Powders dispensed in bulk form include antacids and laxative powders, douche powders for vaginal use, dental cleansing powders, and insufflation powders. After a bulk powder has been pulverized and blended, it should be dispensed in an appropriate container. Hygroscopic or effervescent powders (salts) should always be placed in tight wide-mouthed jars. Dusting powders should be placed in a container with a sifter top. Eutechtic mixtures of powders, can cause problems because they may liquefy. Therefore, some inert powder is commonly added, such as magnesium oxide, to separate the eutectic material.

Divided powders are dispensed in individual doses, usually in folded paper (chartulae) or sachets. They may also be dispensed in metal foil, small thermally sealed or resealable plastic bags, or other containers. Depending on the potency of the drug substance, the pharmacist decides whether to weigh each portion separately before packaging, or to approximate portions by the block-and-divide method. The basic types of powder paper include vegetable parchment (thin, semiopaque, moisture-resistant paper), white bond (opaque paper that has no moisture-resistant properties), glassine (a glazed, transparent, moisture-resistant paper), and waxed paper (transparent waterproof paper). Hygroscopic, deliquescent, and effervescent powders require the use of glassine paper as an inside lining. Plastic bags or envelopes with snap-and-seal closures are a convenient alternative to powder papers. The folded papers are dispensed in a powder box or other suitable container; however, these containers are not child-resistant.

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