Factors Affecting Dissolution: Particle Size and Effective Surface Area

Recall the Noyes-Whitney equation, which suggests a direct correlation between dissolution rate and a drug's surface area.

A solid drug's surface area is inversely related to its particle size.

A drug's smaller particle size increases its effective surface area and enhances drug-solvent interaction, leading to rapid drug dissolution.

Certain drugs, such as griseofulvin, nitrofurantoin, and steroids, such as hydrocortisone exhibit poor oral absorption due to low aqueous solubility.

Such drugs are micronized to reduce particle size. This increases the drug's surface area, enhancing the dissolution rate and elevating oral absorption while decreasing dosing frequency in certain drugs.

Hydrophobic drug micronization can benefit from surfactant addition, like polysorbate 80, which promotes wetting and solubility by lowering the surface tension between the ingredients.

At times,  micronization fails to resolve solubility-related bioavailability issues. So, nanosizing an alternate technique, is used to yield drug particles in nanometer size, which can be administered orally or injected intravenously as nanosuspensions.