Figure 7.26 Permeabilities with and without sink, 2% DOPC model. DOPC under Sink Conditions

Figure 7.26 shows the effect of the sink condition on the effective permeabilities in the 2% DOPC system (model 1.1). Just about all of the lipophilic bases showed a two- to three-fold increase in Pe. The simplest interpretation of this is that when lipophilic molecules reach the acceptor wells, they are bound to the surfactant, and the concentration of the unbound (membrane-permeating) form of the drug greatly diminishes. Hence, the reverse flux, based on the unbound portion of the concentration CA (t) in Eq. (7.1), is nil. Thus, half of the UWL resistance effectively disappears, leading to a doubling of Pe for the diffusion-limited molecules. The topic of the UWL is discussed in greater detail in Section 7.7.6. The binding of the positively charged lipophilic molecules by the negatively charged micelles is

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