In vitro adsorption of various pharmaceutical to montmorillonite.

Dissolution and dialysis studies showed that cationic drugs and certain nonionic drugs bind strongly to montmorillonite clay. The quantity of drug bound by one unit of clay varied considerably. Anionic drugs were weakly bound, and less bioavailabilty problems would be anticipated with these medicinals. The mechanism of binding of cationic drugs to montmorillonite was proposed as a two-step process: a cation-exchange reaction followed by strong surface chemisorption.