Micromeritics is the science and technology of small particles. The knowledge and control of the size of particles is of importance in pharmacy and materials science. The size, and hence the surface area of a particle, can be related to the physical, chemical and pharmacologic properties of drugs. Clinically, the particle size of a drug can affect its release from dosage forms that are administered orally, parenterally, rectally and topically. The successful formulation of suspensions, emulsions and tablets; both physical stability and pharmacologic response also depends on the particle size achieved in the product.
The term was created by J. M. DallaValle in his book Micromeritics: the technology of fine particles. It was derived from the Greek words for small and part. The size range which he covered in the book was from 10−1 to 105 micrometers. Anything smaller than this but bigger than a molecule was referred to at the time as a colloid but is now often referred to as a nanoparticle. Applications included soil physics, mineral physics, chemical engineering, geology, and hydrology. Characteristics discussed included particle size and shape, packing, electrical, optical, chemical and surface science.
Release and dissolution
Particle size and surface area influence the release of a drug from a dosage form that is administered orally, rectally parenterally and topically. Higher surface area brings about intimate contact of the drug with the dissolution fluids in vivo and increases the drug solubility and dissolution.
Absorption and drug action
Particle size and surface area influence the drug absorption and subsequently the therapeutic action. The higher the dissolution, the faster the absorption and hence the quicker and greater the drug action.
Micromeritic properties of a particle, i.e. the particle size in a formulation, influence the physical stability of the suspensions and emulsions. The smaller the size of the particle, the better the physical stability of the dosage form owing to the Brownian motion of the particles in the dispersion.
Good flow properties of granules and powders are important in the manufacturing of tablets and capsules. The distribution of particles should be uniform in terms of number and weight. Very small particle size causes attraction, which in turn destabilises the suspension by coagulating.
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