nanosuspension

A nanosuspension is a liquid in which nanosized particles of pure drug float dispersed, held apart by a small amount of stabiliser. It is essentially an ordinary suspension scaled down: instead of micrometre-sized drug particles that settle and feel gritty, the drug is milled or precipitated to nanometre size so it stays evenly spread and dissolves much faster. The dispersed solid is drug nanocrystals; the liquid around them is usually water with surfactant or polymer.

Nanosuspensions exist to rescue poorly water-soluble drugs. By making the particles tiny they expose an enormous surface area to dissolving fluid, which sharply raises dissolution rate and improves oral or injectable absorption, with almost no inert carrier weight added. They are produced mainly by wet bead milling (top-down) or controlled precipitation (bottom-up), then stabilised against regrowth.

The defining challenge is keeping the nanoparticles apart over time. Tiny particles have a strong drive to clump or to dissolve and recrystallise into larger ones — a process called Ostwald ripening — so the right stabiliser at the right concentration is essential, and many nanosuspensions are dried into powders to be redispersed before use to avoid storage instability.