Examples of selectivity through distribution

4 Mechanisms that produce loss. Storage and elimination. 84 

6 Metabolic change as an early step in activation. Pro-drugs. 97 

7 Quantitative aspects of distribution. Pharmacokinetics. Sustained release. 109 

Of the various principles that govern selectivity, that concerned with distribution is (even when its contribution is relatively small) never completely absent. At the other extreme, it can be the principal source of the selective gain. In what follows, we shall begin with examples of selectivity achieved by exploiting natural differences in distribution. Next, we examine the various mechanisms by which organisms manage to differentiate in this way. Finally, we shall take a look at the quantitative basis for this selective process. 

The above example clearly demonstrates that even the smallest conceivable agent, namely the hydrogen ion, can exert strong and useful selectivity. 

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