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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:
following factors should be taken into consideration while reducing the
particle size of a drug:
- Physical properties of drugs such as hardness, toughness,
moisture content etc. - 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. - 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. - The quantity of the material to be reduced.
- Size, shape, flow properties and bulk density of the
reduced particles. - The solubility of the drug.
- If the material is to be kept free from bacterial contamination,
then the reduction will have to be carried out under aseptic conditions. - Overall costs of process involved including power,
consumption, space occupied, labour expenditure and time involved.
