Powders PDF

Powders In Pharmaceutics, (medicated) Powders are pharmaceutical preparations composed of dry, finely divided drugs and/or chemicals intended for external or internal use. Examples include: BNT powder (Zinc bacitracin, Neomycin sulphate & Tryothricin) - topical; Baneocin (Zinc Bacitracin) - topical...

Powders In Pharmaceutics, (medicated) Powders are pharmaceutical preparations composed of dry, finely divided drugs and/or chemicals intended for external or internal use. Examples include: BNT powder (Zinc bacitracin, Neomycin sulphate & Tryothricin) - topical; Baneocin (Zinc Bacitracin) - topical; Nystop (Nystatin) - topical; Nurofen (Ibuprofen) - oral. Although the use of medicated powders is limited, their use in the preparation of other dosage forms is extensive: 1. Powdered substances may be blended with powdered fillers and other pharmaceutical ingredients to form tablets and capsules; 2. They may be dissolved or suspended in solvents or liquid vehicles to make various liquid dosage forms; 3. They may be incorporated into semisolid bases to form ointments and creams. Advantages: 1. Flexibility to compound as they are easy to prepare; 2. Good chemical stability; 3. Fast dissolution due to small particle size; 4. Fast action and better bioavailability. Disadvantages: 1. Time-consuming preparation; 2. Inaccuracy of dosage (size of measuring spoon); 3. Not suitable for many unpleasant tasting, hygroscopic (take water from surroundings) and deliquescent (turns into liquid) drugs. Before their use in pharmaceutical preparation, the solid material must first be characterised by their chemical and physical properties: 1. Solubility 2. Flowability 3. Particle size 4. Morphology 5. Compatibility 6. Uniformity 7. Stability 8. Purity Particle Size & Analysis The particle size of powders and granules can range from extremely coarse 10 mm (1 cm) in diameter to very fine ranging from 1 um or less. According to the USP, they are characterised as 1. Very coarse 2. Coarse 3. Moderately coarse 4. Fine 5. Very fine This is determined by its ability to pass through the opening of standard sieves during a specific period while shaken by a mechanical sieve shaker. Classification of Powders 1. Based on use a. Internal b. External 2. Based on quantity a. Bulk b. Divided Bulk Density Defined as the mass of the powder divided by its bulk volume. Based on bulk volume powders are classed as “light” and “heavy”; 1. Light powders having a high bulk volume 2. Heavy powders have low bulk volume. The bulk density relies on the powders: Particle size distribution Particle shape Its ability to adhere to one another Light vs Heavy Powders Light powders have a low bulk density and a high bulk volume, while heavy powders have a high bulk density and a small bulk volume. There are two categories of pharmaceutical Technology involved in Powder Manufacturing: 1. Comminution of drugs (Particle size reduction) a. Trituration b. Pulverisation by intervention c. Levigation 2. Blending of powders a. Spatulation  b. Geometric dilution c. Shifting d. Tumbling Comminution of drugs Aims to reduce the particle size of a solid substance, to facilitate: Crude drug extraction Increase dissolution of the drug Aids in the formulation process Greater drug absorption On a small scale, pharmacists use a mortar and pestle to reduce the particle size of a drug, with finer grinding using a rough surface such as a porcelain mortar opposes a smooth surface like a glass mortar, and this grinding process is known as trituration or comminution. 1. Trituration a. Used to comminute and mix powders with a porcelain mortar preferred over a glass. A glass mortar is only preferred if the chemical can stain, and granular or crystalline substances must be individually triturated before they are mixed in one mortar. b. On a large scale, mills and pulverisers are used for comminuting powders, such as the Fitzmill comminuting machine which has a collection system to: i. Prevent product loss ii. Protect the environment from chemical dust iii. Prevent product contamination 2. Levigation a. Used in small-scale ointment and suspension preparation to reduce the particle size of the added powder by the following method: i. A mortar and pestle or an ointment tile is used; ii. A paste is formed by combining the powder and a small amount of liquid (the levigating agent) in which the powder is insoluble; iii. The paste is triturated to reduce the particle size, then incorporated into an ointment base and made smooth by rubbing them with a spatula on the ointment tile. iv. Mineral oil and glycerin are commonly used as levigating agents. 3. Pulverisation by Intervention a. Substances are reduced and subdivided with an additional material i.e. a solvent that can be easily removed after pulverisation is completed. b. This process is used for gummy compounds that tend to re-agglomerate or resist grinding such as camphor, so alcohol or a volatile solvent is used to reduce it to a fine powder. Blending Powders When two or more powdered substances are to be uniformly blended, their particle size must be individually reduced before weighing and blending. Depending on the ingredients' nature and the equipment, powders are blended via spatulation, geometric dilution, tumbling, and shifting. 1. Spatulation a. Uses a spatula and tile or sheet for mixtures that liquify or form eutectic mixtures. This method is not suitable for potent drugs due to the lack of homogenous mixing. 2. Geometric dilution a. Used to incorporate small amounts of potent drugs; b. The potent drug and an approximately equal volume of diluent is added to the mortar and thoroughly mixed. A second portion of diluent equal to the volume of the powder mixture is added and triturated is repeated. The process continues until all the diluent is incorporated. c. Some pharmacist add an inert coloured powder before mixing as a visible sign of the mixing process completion. 3. Sifting a. Powders are mixed by passing them through sifters like those used for flour resulting in a light fluffy product. But it is not feasible for incorporating potent drugs. 4. Tumbling a. Mixing of powders in a rotated container via a motorised process used widely in industry. Factors in Blending Size Shape Density Electrostatic forces Limits of blending Segregation mechanisms ○ This undesirable separation of the blend occurs when forces such as gravity, airflow and vibration cause the smaller particles of the blends to settle at the bottom with the larger ones on top, or when the smaller particles remain suspended in the air, while the larger ones settle. ○ These forces act differently on particles due to their size, shape and density. ○ Segregation may occur vis sifting or percolation, air entrapment(fluidisation) and particle entrapment (dusting). Bulk Powders are classified as Oral powders, Dentrifices, Douche powders, Dusting powders, insufflations and triturations. 1. Oral powders are generally supplied as finely divided powders or effervescent granules intended to be suspended or dissolved with water or mixed in soft foods before administration. Antacids and laxatives are frequently administered in this form.  2. Effervescent granules: a. Contains sodium bicarbonate and either citric acid, tartaric acid or sodium biphosphate mixed with the other ingredients. In solution with water, CO2 is released which helps mask the bitter or unpleasant taste of the medication. The completed product is dispensed in an air-tight glass container to protect from air humidity. b. Preparation: i. Dry or fusion method: 1. A porcelain dish is sufficiently heated before transferring the powder to it. The water needed for the preparation comes from the water liberated during the heating of the citric acid and the water released from the reaction of the citric acid and tartaric acid with sodium bicarbonate. 2. The mixture becomes damp while heating at 40 degrees Celsius and the damp mass is passed through a sieve to produce the granules. ii. Wet method: 1. water/alcohol is used to prepare a wet mass which is passed through a sieve to produce granules. 3. Dentrifices are substances prepared for teeth typically in bulk form containing soap or detergent and a mild abrasive agent. a. The base is calcium carbonate; the detergent is in the form of soap and the abrasive action is finely powdered pumice stone; essential oils are added to provide freshness, flavour and mild antiseptic properties. 4. Douche powders are products completely soluble or intended to be dissolved in water prior to use as cleaning agents in body cavities. Typically for vaginal use, but are also prepared for otic, nasal and ophthalmic use. 5. Dusting powders are locally applied nontoxic applications intended for nonsystemic use. They are to be dispensed in a very fine state to enhance effectiveness and minimise irritation. a. Dusting powders are used as lubricants, absorbents and antiseptics. The main component is starch and talc powder. 6. Insufflations are finely divided powders introduced to body cavities like the ears, nose, throat, tooth suckets and vagina. An insufflator is used to administer these products. Divided powders are dispensed in individual doses, usually in folded paper, metal foil, small heat-sealed or re-sealable plastic bags or related. After the ingredients are weighed, comminuted and mixed they are accurately divided into prescribed portions. However, depending on the potency of the drug substance, the block-and-divide method is used to weigh each portion individually for even dosage. Papers used to pack powders: 1. Vegetable parchment, a thin semi-opaque moisture-resistant paper. 2. White bond, an opaque paper with no moisture-resistant properties.  3. Glassine, a glazed, transparent, moisture-resistant paper. 4. Waxed paper, a transparent waterproof paper used for hygroscopic and volatile drugs. Special problems with powders: Volatile substances may be prevented or retarded by the use of heat-sealed plastic bags or double wrapping in glassine or waxed paper inside bond paper. Hygroscopic and deliquescent drugs are prevented by double wrapping. Eutectic Mixtures Mixtures that melt at temps lower than their ingredients when near one another. E.g. camphor and menthol. Can be minimised by using inert diluents which work by absorbing moisture, reducing interactions or altering melting points. Magnesium carbonate or light magnesium oxide are commonly used and effective. Although kaolin, starch, bentonite and other absorbents are recommended. Packaging and Labeling 1. Hygroscopic, deliquescent or volatile powders are packed in glass jars rather than pasteboard containers. 2. Amber or green glass for light-sensitive components. 3. Should be stored in tightly closed containers. 4. The product must indicate “For External Use Only” on the label.