The Interfacial Barrier Model

In the interfacial barrier model of dissolution it is assumed that the reaction at the solid liquid interface is not rapid due to the high free energy of activation requirement and therefore the reaction becomes the rate-limiting step for the dissolution process (Figure 5.1), thus, drug dissolution is considered as a reaction-limited process for the interfacial barrier model. Although the diffusion layer model enjoys widespread acceptance since it provides a rather simplistic interpretation of...

Time Concentration Profiles

The probabilistic transfer and retention-time models are models evaluating the transition or retention probabilities that are associated with a single particle. This is why these models are called the particle models. In order to account for all the particles in the process and administered amounts, one needs to make further statistical and practical considerations. Let us consider some drug administration practicalities. Up to now, the administered amounts were considered as initial units...

Passive Transport Processes

There appear to be two main ways for solutes to pass through cell membranes, namely, transcellular and paracellular. The most important is the transcellu-lar route, whereby compounds cross the cells by traversing the cell membrane following either passive diffusion or carrier-mediated transport. Undoubtedly, the transcellular passive diffusion is the basic mechanism of solute permeation through cell membranes. According to this mechanism the solute leaves the fluid bathing the membrane,...