In the first edition of this encyclopedia the section on absorption covered a range of topics that included discussion of the cell membrane, parenteral and enteral absorption, clinical factors, and pharmacokinetic characterization of absorption.

During the intervening time many of these areas have changed, some more than others. There also have been changes in emphasis, reflected particularly in the rapidly expanding interest and discoveries in membrane penetration, exploitation of various dosage routes, formulation factors, and absorption enhancers.

Emphasis in this section will reflect these activities. In order to conserve space, the pharmacokinetic treatment of drug absorption has been omitted.