| The solubility, bioavailability and dissolution rate of drugs are important parameters for achieving in vivo
efficiency. The bioavailability of orally administered drugs depends on their ability to be absorbed via
gastrointestinal tract. For drugs belonging to Class II of pharmaceutical classification, the absorption process
is limited by drug dissolution rate in gastrointestinal media. Therefore, enhancement of the dissolution rate of
these drugs will present improved bioavailability. So far several techniques such as physical and chemical
modifications, changing in crystal habits, solid dispersion, complexation, solubilization and liquisolid
method have been used to enhance the dissolution rate of poorly water soluble drugs. It seems that
improvement of the solubility properties ofpoorly water soluble drugscan translate to an increase in their
bioavailability. Nowadays nanotechnology offers various approaches in the area of dissolution enhancement
of low aqueous soluble drugs. Nanosizing of drugs in the form of nanoparticles, nanocrystals or
nanosuspensions not requiring expensive facilities and equipment or complicated processes may be applied
as simple methods to increase the dissolution rate of poorly water soluble drugs. In this article, we attempted
to review the effects of nanosizing on improving the dissolution rate of poorly aqueous soluble drugs.
According to the reviewed literature, by reduction of drug particle size into nanometer size the total effective
surface area is increased and thereby dissolution rate would be enhanced. Additionally, reduction of particle
size leads to reduction of the diffusion layer thickness surrounding the drug particles resulting in the
increment of the concentration gradient. Each of these process leads to improved bioavailability. |