Drug absorption process

It is well established today that drug absorption through the alimentary canal walls is a complex event, which involves, in many cases, parallel or sequent microprocesses at the apical membrane of the absorptive cell (enterocyte) or between them (paracellular absorption). In addition to the various types of diffusion processes across the enterocyte membrane, numerous specific proteins—transporters and efflux pumps—are involved in the intricate drug absorption process. In the following sections the various epithelial tissues of the different organs of the GI tract will be looked at briefly. A review of major drug absorption mechanisms across epithelial cells, as they are customary today will follow. 

We have selected a simple example to illustrate the use of Laplace transform methods. A more advanced application is given in the next chapter, in which equations are derived for a two-compartment model. It will be shown subsequently that Laplace transform methods also are helpful in pharmacokinetics when convolution/deconvolution methods are used to characterize drug absorption processes. 

Provided that metabolism and active transport systems are not the dominating factors for the drug absorption process, there are - in general terms - two factors that fairly well characterize the oral absorption the solubility in combination with the permeability throngh membranes. Consequently, four classes of substances have been defined by Amidon G. et al. ... 

Solubility is of great importance in pharmaceutical systems since a drug must be dissolved before it is absorbed. When the drug absorption process is limited by dissolution, enhancing solubility can increase dissolution rate and in this way improve bioavailability.In addition to the dissolution rate, the ability to dissolve the therapeutic dose of the drug and the selection of solubilization techniques are critical for product development. 

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