intrinsic dissolution rate

The intrinsic dissolution rate strips away the confusing variables of particle size and shape to ask a purer question: how fast does this material itself dissolve, per unit of exposed surface? It is the dissolution behaviour of the substance, not of a particular tablet or powder.

It is measured by compacting pure drug into a disc of known, fixed area, mounting it so that only that one flat face is exposed, and rotating it in a fixed volume of medium under sink conditions. The amount dissolving per unit time is divided by the disc area, giving a rate normalised to surface area — typically reported as milligrams per minute per square centimetre. Because area, stirring and medium are all controlled, the result depends only on the solid's intrinsic properties.

This makes intrinsic dissolution rate a powerful preformulation tool. It reflects how crystal form, salt, polymorph and solid-state nature affect dissolving, independent of how finely the batch happens to be milled. As a guide, an intrinsic dissolution rate below roughly 0.1 mg/min/cm² often warns of dissolution-limited absorption, prompting solubility-enhancing strategies.