Pharmaceutical Applications of Size Reduction

Size reduction

Size reduction is the process of reducing the particle size of a substance to a finer state of subdivision to smaller pieces, to coarse particles or to powder.

Pharmaceutical Applications of Size Reduction

1.      Size reduction increases the surface area of drugs which helps in rapid solution formation in the case of chemical substances.

2.      With increase in surface area the extraction from animal glands such as liver and pancreas and from crude vegetable drugs is facilitated because solvent can easily penetrate into the tissues resulting in quick extraction of their active constituents.

3.      The therapeutic effectiveness of certain drugs is increased by reducing the particle size e.g. the dose of griseofulvin is reduced to half than that of originally required.

4.      The mixing of several solid ingredients is easier and more uniform if the ingredients are reduced to same particle size.

5.      In the case of powdered pharmaceutical dosage forms it is important to powder the crystalline drugs before mixing them with other drugs in order to mix all the drugs uniformly and to avoid recognition of crystalline drugs by the patients.

6.      Few drugs can be compressed directly; generally they are mixed with excipients and made in the form of suitable size granules which are then compressed.

7.      The stability of emulsions is increased by decreasing the size of the oil globules.

8.      In the case of suspensions the size of the particles plays a great role. If the size of the particles is too small, they may form a cake which may not re-disperse easily but on the other hand large size particles settle quickly but form a loose cake which may re-disperse easily on shaking.

9.      Appropriate particle size is used in the inhalations. Very small particles may be exhaled out of the bronchioles along with air without producing its effect.

10.  The physical appearance of ointments, pastes and creams can be improved by reducing its particle size.

11.  All the ophthalmic preparations and preparations meant for external application to the skin must be free from gritty particles to avoid irritation of the area to which they are applied.

12.  The rate of absorption of a drug depends on the dosage form, route of administration and particle size. The smaller the particle size, quicker and greater will be rate of absorption.

13.  Depending on the particle size, the sustained action of a preparation can be produced.

Disadvantages

•                On grinding, the aromatic and volatile constituents of crude drugs may be lost due to increase in temperature during grinding. Therefore drugs such as cinnamon, clove, cardamom, caraway and other drugs containing volatile oils must not be subjected to heavy grinding to prevent the loss of volatile oils.
•          Since on size reduction the surface area is increased which when exposed to atmospheric conditions may result in oxidation and hydrolysis. Therefore such drugs must be stored in a well closed container and at a cool place.

Factors Affecting Size Reduction

The following factors should be taken into consideration while reducing the particle size of a drug:

1.          Physical properties of drugs such as hardness, toughness, moisture content etc.
2.          Melting or softening point of the material: The heat generated during mechanical grinding present many problems with materials which tend to liquefy, stick with each other and with thermo labile substances.
3.          The size of the starting material: If the size of the original drugs is too large it may be reduced to small particles in stages.
4.          The quantity of the material to be reduced.
5.          Size, shape, flow properties and bulk density of the reduced particles.
6.         The solubility of the drug.
7.          If the material is to be kept free from bacterial contamination, then the reduction will have to be carried out under aseptic conditions.
8.          Overall costs of process involved including power, consumption, space occupied, labour expenditure and time involved.