Particle Size Reduction

Comminution of Drugs

Comminution/Grinding

• Defined as the process of particle size reduction

METHODS OF COMMUNITION IN SMALL SCALE

Trituration

• Process of grinding a powder in a mortar and pestle to reduce its particle size

Levigation

• the process of reducing particle size by first forming paste of the solid with a minimum amount of a levigating agent

• Triturating the paste in a mortar or on slab with a spatula

Basis of choice of Levigating agent

• ability to form a smooth paste with the substance

• compatibility in the product so water cannot be used for levigating a substance for oleaginous ointment base

Blending Powders

TUMBLING BY MECHANICAL MIXING

• process of mixing powders by placing in large containers or power blenders that rotates by tumbling motion

• thorough but time consuming

V-Blender

• an efficient and versatile blending machine for mixing and lubrication process of powders homogenously

Ribbon Blender

• an efficient and versatile blending machine for mixing of dry granules and powders homogenously

SPATULATION

• a method by which small amount of powders may be blended by a spatula on a sheet of paper or pill till

• applied to solid substances which liquefy or form eutectic mixtures

Examples

• phenol• camphor• menthol• thymol• ASA• phenylsalicylate• phenacetin

TRITURATION

• may be employed both to comminute and to mix powder using mortar preferably with a rough inner surface

Geometric Dilution

• in case a small amount of potent substance is to be mixed with a large amount of diluent

• employed to obtain uniform mix

SIFTING

• process of mixing by passing the powder through sifters

• not generally acceptable for potent drugs

• results in a light puffy product

DRY GRANULATION

• slugging or roller compaction• involves the pressing of mixed powders into

an object to be reground into a precise powder

• increases particle density• improves powder flow

MILLING

• improve flow• reduce segregation• enhance drying• limit wide particle size distribution

Segregation

• undesirable separation of the different components of the blend

• sifting or percolation• air entrapment (fluidization)• particle entrapment (dusting)

Guidelines to minimize or prevent segregation

• minimum no. of transfer steps and drop heights

• control of dust generation• control of fluidization• slow fill/transfer rate• appropriate venting• use of a deflector, vane or distributor• proper hopper design and operating valves

Hygroscopic Powders

• absorb moisture from the air

Deliquescent Powders

• absorb moisture from the air to the extent that they will partially or wholly liquefy

Efflorescent Powder

• crystalline powder that contains water of hydration or crystallization