Two views of the future

A drug is not effective unless it is present at its site of action for an adequate period of time. In the past, most drug doses were determined empirically. 

Adapted from a table that appeared in Nature Biotechnology (Drews, J. and Ryser, S.), which was based on information in [9], 

This text provides a foundation for the rational design of drug delivery systems. The factors that influence rates and patterns of drug movement throughout tissues will be considered drug modifications and delivery systems will be presented in the context of normal patterns of drug movement and clearance. 

Since diffusion is an important mechanism of drug transport in tissues, Chapter 3 presents an analysis of rates and patterns of diffusive transport. 

In Chapter 4, diffusion models are used as the basis for relating local rates of drug movement with local tissue architecture. 

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