All powder particles pass through a No. 8 sieve and not more than 20% pass through No. 60 sieve. Coarse Powder (No. 20 powder) All powder particles pass through No. 20 sieve and not more than 40% through a No. 60 sieve. Moderately Coarse Powder (No. 40 powder) All particles pass through a No. 40 sieve and not more than 40% through a No. 80 sieve. Fine Powder (No. 60 powder) All particles pass through a No. 60 sieve and not more than 40% through a No. 100 sieve. Very Fine Powder (No. 80 powder) All particles pass through a No. 80 sieve. There is no limit for greater fineness.
INFLUENCES OF PARTICLE SIZE: Dissolution rate Micronization can increase the rate of drug dissolution and its bioavailability. Suspendability or rate of settling Helps suspend drug particles and disperse uniformly in liquid preparation (0.5 to 10 microns). Uniform distribution in a powder mixture Ensure dose to dose uniformity. Penetrability of powders in inhalation solutions Reduced particle size facilitate delivery of therapeutically important drug to the respiratory tract (1-5 micron). Topical preparations Grittiness in ointments, creams, ophthalmic and aerosol preparations (50-100 microns). COMMINUTION : It is the process of reducing the particle size of a solid substance to a finer state of subdivision. - Used to increase dissolution rate and absorption. - Comminution increases the surface area of particles tremendously. - When a cube with 1 mm edge is broken down to cubes with a 10 microns edge, the number of particles can be calculated as follows: - 1 mm = 1000 microns; 1000 microns/10 microns = 100 particles are produced when only one axis is considered. - However, the cube has three axes. Therefore the number of particles produced are 100 x 100 x 100 = 1,000,000 particles Particle Size Reduction – Increases SA Each cube of 1 mm side has a surface area of 1 mm 2 . Since it has 6 sides, its surface area is 6 mm 2 . Each 10 micron cube has 6 surfaces, and therefore, 6 x 100 micron 2 . This equals 600 micron 2 for one 10 micron particle.
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- Summer '14
- Pharmacology, Pharmaceutical formulation, Acacia, Drug Delivery Systems, active ingredient, Pharmaceutics