disintegrant

A disintegrant is the ingredient that makes a tablet fall apart again once it is swallowed. A binder holds the tablet together; the disintegrant is its opposite, programmed to break the bond apart in the gut so the drug can be released and dissolved. Without it, a hard tablet could pass through the body almost intact.

Most disintegrants work by soaking up water and swelling, prying the compressed particles apart like a dry sponge expanding. Modern superdisintegrants — croscarmellose sodium, sodium starch glycolate and crospovidone — are so effective that only a few percent is needed, and they can shatter a tablet into fine fragments within seconds. Some are added before granulation, some after, and many formulators split the dose between the two to act both inside and outside the granules.

The catch is that disintegration is not the same as dissolution: breaking the tablet into pieces only exposes more surface so the drug can then dissolve. A tablet can disintegrate fast yet still release a poorly soluble drug slowly, so disintegration alone does not guarantee fast absorption.