Luminal degradation and binding

The degradation and formation of nonabsorbable drug complexes in the intestinal lumen is the third factor, in addition to dissolution and permeability, which could affect fraction absorption. Limitations of bioavailability due to these factors seem to be less frequent compared with the two other main factors. Regulatory guidelines for BCS-based biowaivers still ask for in vitro studies of luminal degradation in relevant test media, whereas specific binding studies are not required [17]. 

The light is generated within a few seconds after the formation of NADH and disappears shortly afterwards. However, various problems may arise in this assay (non-specific binding, degradation of NAD+) and sensitive equipment for the measurement of bio-lumines-cence is needed. 

The rate and extent of drug absorption can be affected by degradation, metabolism and complex binding in the GI lumen.There is a general change in the composition of the luminal fluid along the GI tract (Horter and Dressman 1997 Dressman and Yamada 1991). The differences... 

There are several other effects that could contribute to the observations. For exan le, impurities might diffuse to the surface. However, if they are neutral, then the rate of accumulation should depend only on time (and not on current passed or even on whether the device is operated or not). Our data show clearly that degradation is a function of electrical stress, since the luminance does not decay when the device is off. If the impurities are charged, then they must be positive to be attracted to the cathode, and then they would not bind Ca. On the other hand, the inq)urities might be there from the beginning, and could account for reactions whose plausibility is not obvious when examining the structure of the idealized polymer. These "impurities" could also be a part of the polymer chain. 

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