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Summary of Powder And Granules:-

Definition - Powder
A Pharmaceutical powder is a mixture of finely divided drugs or chemicals in a dry form meant for internal or external use. 

Definition - Granules
They are prepared agglomerates of smaller particles of powders, They are irregular shaped but may be prepared to be spherical. They vary between 0.2 to 4 mm depending upon use of granules. 

  1. Internal &external use.
  2. More stable than liquid.
  3. Convenient for the physician.
  4. Chances of less incompatibility.
  5. Onset of action is rapid.
  6. Easy to carry.
  7. Large quantity can be administered.
  8. Convenient for small child & elderly patient.
  9. More economical

Disadvantages :-
  1. Can’t dispense bitter, nauseous & unpleasant taste drug.
  2. Can’t dispense hygroscopic & deliquescent drugs.
  3. Dispensing is time consuming process.
  4. Quantity less than 100mg can’t weigh on dispensing balance.
  5. Can’t dispense volatile drugs. 

Classification of Powders :-
  1. Bulk powders for internal use.
  2. Bulk powders for external use.
  3. Simple & compound powder for internal use.
  4. Powder enclosed in cachets & capsule.
  5. Compressed powders(tablets)

Preparation of powders :- 
Step 1 Particle size reduction :- 
For the preparation of powder, each ingredient should be needed in finely ground form; hence manufacture must use a number of procedures and equipment to reduce the particle size of powder ingredients, this process is called as comminution. The most common method used for particle size reduction is powder formulation is trituration, which involves placing the solid in a mortar and continually grinding the chemical between the mortar and the pestle using a firm, downward pressure. The powder must be frequently scraped from the sides of the mortar to ensure that all particles are evenly reduced and mixed. A levigating agent, such as glycerin, may be added to the solid and processed by either continued trituration or by placing the mixture on an ointment slab and using spatulation to wet the solid and further reduce the particle size of a powder after it has been triturated. 

Step (2) Preparing a homogenous mixture 
The powders may be mixed by any one of the following methods :-
  1. Spatulation
  2. Trituration
  3. Geometric dilution
  4. Sifting and
  5. Tumbling 

1. Spatulation : In this method, mixing of powders is done by the movement of a spatula throughout the powders on a sheet of a paper or on a porcelain tile. The method is very useful in mixing a small amount of powder or solid substances that liquiefy (eutectic mixtures) 

2. Trituration : It is used for both reduce particle size and mix powders. If the particle size reduction is desired along with mixing of powders, a porcelain mortar with a rough inner surface is preferred to glass mortar with a smooth working surface. 

3. Geometric dilution : The method is used when potent substances are too mixed with a large amount of diluent. The potent drug is placed upon an approximately equal volume of the dilute in a mortar and the substances are slightly 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 adding diluent equal in volume to the mixture in the mortar at each step until all the diluent is incorporated. For example, if 100mg of potent drug is required to be mixed with 900mg of lactose then according to geometric dilution, the following procedure should be followed:- 100mg of potent drug + 100mg of lactose = 200mg of mixture, 200mg of the mixture + 200 mg of lactose= 400 mg of mixture 400mg of the mixture + 400mg of lactose =800mg of mixture 800mg of the mixture + remaining portion = 1000mg of mixture of lactose 

4. Sifting : the powders are mixed by passing through sifters. This process results in alight fluffy product and is generally not acceptable for incorporation of potent drugs into a diluent base 

5. Tumbling : Is the process of mixing powders in a large container rotated by an electric motor. These blenders are widely employed in industry as large volume powder mixers Equipment’s used in powder mixing are Tumbler mixing, Ribbon mixer, Screw mixer etc Factors that influence mixing quality such as mixing time, speed of mixing rotation, the type of the mixer, dry or wet mixing process and so on 

Step - 3 Packaging of powders Bulk powders for external use are often dispensed in a shaker top container to facilitate topical application. They may also be dispensed in a wide mouth jar or a plastic container with flip-top lid. The jar or plastic container can be closed tightly to provide increased stability and protection from light and moisture, especially for compounds that contain volatile ingredients. Package should contain label as “For external use only”.