glidant

A glidant is a tiny additive that helps powder flow freely, like a sprinkle that keeps sugar from clumping in a shaker. On a tablet press the powder must pour evenly and quickly into each die so every tablet gets the same fill; a sticky, cohesive powder flows unevenly and produces tablets of varying weight. The glidant fixes that.

Glidants are very fine powders, most often colloidal silicon dioxide (fumed silica), sometimes talc. Their tiny particles coat the surface of the larger drug and excipient particles, acting like miniature ball bearings that reduce friction and break up the static and surface forces that make fine powders stick together. Only a fraction of a percent is usually needed.

Because they work by surface coating, there is an optimum amount: a little improves flow markedly, but too much can actually hinder it. Glidants are easy to confuse with lubricants — both are slippery and used in small amounts — but a glidant improves powder flow into the die, whereas a lubricant reduces sticking between the formed tablet and the metal.