Pharmaceutical Dosage Forms-powders 271g1r

Pharmaceutical Dosage Forms Powder

Powders as Dosage Forms Definition Powders are intimate mixtures of dry, finely divided drugs and/or chemicals that may be intended for internal or external use.

Advantages of Powders as Dosage Form 1.

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Flexibility of compounding-easy to prepare Good chemical stability Rapid dissolution due to small particle size Fast action and better bioavailability

Disadvantages of Powders as Dosage Form 1. 2. 3.

Time consuming Inaccuracy in dose Unsuitable for many unpleasant tasting, volatile, oxidizing, hygroscopic and deliquescent drugs.

Classification 

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Based on Usage -powders for external use. -powders for internal use. Based on quantity -bulk powders -divided powders

Granules Agglomerates of powders  Used as such as dosage form or used to prepare tablets e.g. effervescent granules- to mask unpleasant taste of drugs. 

Pharmaceutical Technology involved in the Manufacturing of Powders 

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Comminution of Drugs (Particle Size reduction of drugs) Blending of Powders

Comminution of Drugs 

Trituration -Grinding with mortar and pestle.

Mills and pulverizers e.g. FitzMill  Levigation- a paste is formed by combining the powder and a small amount of liquid (levigating agent) in which the powder is insoluble. The paste is then triturated to reduce particle size. The levigated paste may be mixed with base well with help of a spatula and tile. Mineral oil and glycerin are generally used levigating agent.  Pulverization by intervention- size reduction using a solvent and which is removed after size reduction. Suitable for resins and gummy substance. E.g. camphor. 

Blending or Mixing Powders a. Spatulation -Mixing is done using spatula and tile or sheet -useful for solid substances that liquefy or form eutectic mixtures (i.e., mixtures that melt at a lower temperature than any of their ingredients; when in close, prolonged with one another) -not suitable for potent drug -lack of homogenous mixing

Blending or Mixing Powders b. Trituration It is used both to comminute and to mix powders.  If comminution is desired, a porcelain or ceramic mortar with a rough inner surface is preferred to a glass mortar with a smooth working surface.  A glass mortar is preferable for chemicals that stain a porcelain or ceramic surface as well as for simple ixture of substances without special need for comminution. A glass mortar cleans more readily after use.

Blending or Mixing Powders c. Geometric dilution It is used when potent substances must be mixed with a large amount of diluent.  The potent drug and an approximately equal volume of diluent are placed in a mortar and thoroughly mixed by trituration.  A second portion of diluent, equal in volume to the powder mixture in the mortar, is added, and trituration is repeated. The process is continued; equal volumes of diluent are added to the powder mixture in the mortar until all of the diluent is incorporated.

Blending or Mixing Powders d. Sifting. Powders are mixed by ing them through sifters similar to those used to sift flour. This process results in a light, fluffy product. Usually, it is not acceptable for incorporating potent drugs into a diluents base. e. Tumbling is the process of mixing powders in a large container rotated by a motorized process. These blenders are widely used in industry, as are large-volume powder mixers that use motorized blades to blend the powder in a large mixing vessel.

Use and Packaging of Powders Depending on their intended use, powders are packaged and dispensed as 1. bulk powders or 2. divided powders.

a. Bulk Powders They are dispensed in bulk containers. A perforated, or sifter, can is used for external dusting, and an aerosol container is used for spraying onto skin. A wide-mouthed glass jar permits easy removal of a spoonful of powder. E.g. of bulk powders are as follows (a) Antacid and laxative powders (b) Douche powders (c) Medicated and non medicated powders for external use (d) Dentifrices or dental cleansing powders are used for oral hygiene. (e) Powders for the ear, nose, throat, tooth sockets, or vagina are istered with an insufflator, or powder blower. 

b. Divided Powders  

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These are dispensed in individual doses, usually in folded papers. They may also be dispensed in metal foil, small heat-sealed or resealable plastic bags, or other containers. After the ingredients are weighed, comminuted, and mixed, the powders must be accurately divided into the prescribed number of doses. 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.

Papers Used to Pack Individual Powders Four basic types are used:  (a) Vegetable parchment is a thin, semi opaque, moisture-resistant paper.  (b) White bond is an opaque paper that has no moisture-resistant properties.  (c) Glassine is a glazed, transparent, moistureresistant paper.  (d) Waxed paper is a transparent waterproof paper.  Hygroscopic and volatile drugs are best protected with waxed paper that is double wrapped and covered with a bond paper to improve the appearance. Parchment and glassine papers are of limited use for these drugs.

Special Problems Associated with Powders Powders with volatile substances, eutectic mixtures, liquids, and hygroscopic or deliquescent substances present problems 1. Volatile substances  e.g., camphor, menthol, essential oils) can be lost by volatilization after they are incorporated into powders.  It is prevented by using heat-sealed plastic bags or double wrapping with waxed or glassine paper inside white bond paper.

Special Problems Associated with Powders: 2. Incorporation of Liquids Liquids are incorporated into divided powders in small amounts. (1) Magnesium carbonate, starch, or lactose can be added to increase the absorbability of the powders by increasing the surface area. (2) When the liquid is a solvent for a nonvolatile heat-stable compound, it is evaporated gently in a water bath. Some fluid extracts and tinctures are treated in this way.

Special Problems Associated with Powders: 3. Hygroscopic and deliquescent substances       

Hygroscopic and deliquescent substances that become moist because of an affinity for moisture in the air. Substance which absorb moisture are called hygroscopic If high qty of water is absorbed to make the material liquid then it is called as deliquescent. E.g. Potassium citrate, ammonium chloride, citric acid, tartaric acid, sodium iodide. It can be prepared as divided powders by adding inert diluents/ absorbents. Double wrapping is desirable for further protection. Prepared as granules to minimize the exposure to moisture.

Special Problems Associated with Powders: 4. Eutectic Mixtures Some of the drugs when mixed together tend to liquefy due to formation of new compound (due to decrease in melting point). e.g. menthol, thymol, phenol, aspirin, camphor and menthol  One of the ingredient added in a powder may reduce the melting point of other ingredient and forms a liquid. Methods to Overcome: 1. Can be minimized by using inert diluents /absorbent like magnesium carbonate, kaolin, starch, lactose, light magnesium oxide. 2. They can be dispensed in separate sets of powders and labelled with suitable direction 

Special Problems Associated with Powders: 5. Efflorescent powders Crystalline substance liberates water of crystallization due to change in humidity are called efflorescent substances.  e.g. caffeine, cocaine, codeine phosphate, Sodium carbonate, sodium phosphate. Methods to overcome: Use anhydrous salt 

Special Problems Associated with Powders: 6. Explosive substances When some oxidizing and reducing substances are mixed in mortar, there are chances of explosion.  Very rare combinations. e.g. Potassium chlorate and tannic acid.  Method to overcome: separately powder and dispense. 

Packaging and Labeling of Powders 

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Hygroscopic, deliquescent, or volatile powders- packed in glass jars rather than pasteboard containers. Amber or green glass for light-sensitive components. Should be stored in tightly closed containers. Products for external use must indicate “For External Use Only” on the label

Granules Has some advantage over powder  Free flowing  More stable  Better dose measurements  Used in the manufacture of tablets and capsules

Effervescent Granulated Salts  

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Effervescent salts are granules or coarse to very coarse powders containing a medicinal agent. It is a dry mixture composed of sodium bicarbonate, citric acid, and tartaric acid. When added to water, the acids and base react to liberate carbon dioxide, resulting in effervescence. The resulting carbonated solution masks undesirable taste of any medicinal agent. Using granules or coarse particles of the mixed powders rather than small powder particles decreases the rate of solution and prevents violent and uncontrollable effervescence.

Preparation of Effervescent granules Prepared by two general methods: (a) the dry or fusion method : Ingredients are mixed and heated to release water of crystallization from citric acid. Release of water will produce CO2. The mixture will become spongy while heating at 400 C. Then the spongy mass ed through sieve to produce granules. (b) the wet method- water/alcohol used to prepare wet mass which is ed through sieve to produce granules