Size reduction

Size reduction is a process of reducing large solid particle or masses into small masses/ It is process of reducing large substances into smaller particle.

pharmaceutical powders are the polydisperse, i.e., consisting different size of particle. Polydisperse powder create lots of considerable difficulties in the production of dosage forms(solid liquid and semisolid dosage form).

particle of monosize (same or equal size) may be deal for pharmaceutical purpose.

size reduction can be achieved by two different process namely

  • Precipitation method ; the substance is dissolved in an appropriate solvent. Subsequently, it is finely precipitated by the addition of another of solvent, which is miscible with first, but in later the substance is insoluble. This method is suitable for production of raw material and bulk preparation. Ex; Inorganic chemical like calcium carbonate, magnesium carbonate and mercuric oxide.
  • Mechanical process; in this method mechanical force is require for grinding the material. This method is used for production of tablet capsules. Ex; ball mill, roller mill etc.)

Advantage of size reduction:

  1. Content uniformity: mixing of different types of ingredients can be effective, if the particle size is small and uniform. For potency and low dose drug formulation, constant uniformity is very important.
  2. Uniform flow: smaller particle size and controlled size distribution promote the flow of powder into dies during compression of tablets. Size reduction increases the surface area of material and this further improve rate of dissolution.
  3. Effective extraction of drugs: Smaller particle allow rapid penetration of solvent into the tissue or cell of cells of vegetable and animal origin(liver and pancreas).
  4. Effective drying: Drying will be effective when small sized granules or powders are used.
  5. Improved physical stability: In suspension and emulsion the rate of sedimentation decreases to a large extent if particle size is small.
  6. Improved dissolution rate: Size reduction increases the surface area of material and this further improve rate of dissolution.
  7. Improved rate of absorption: if the particle size is small then greater will the absorption due to dissolution rate.

Disadvantages of size reduction

  1. drug degradation: Thermolabile substances get decomposed during size reduction. This is due to heat produced during milling. cooling system are provided to decreases the heat in milling equipment.
  2. Poor mixing: very small particle posses strong cohesive forces, hence , aggregation of particle is possible. There is chances of contamination during milling and grinding.

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