Gastric emptying process rate

It may take many hours for the contents of the stomach to be processed and moved into the small intestine. Several factors influence gastric motility and therefore the rate of gastric emptying. These include ... 

The absorption of class III drugs is limited by their permeability over the intestinal wall. Thus, as this process is not at all modeled by the classical in vitro dissolution test, no IVIVC should be expected. When drug dissolution becomes slower than gastric emptying, a reduction in the extent of bioavailability will be found in slower dissolution rates as the time when the drug is available for permeation over the gut wall in the small intestine will then be reduced. Thus, the same type of relationship can be expected between bioavailability and in vitro dissolution, as shown in Fig. 21.12 for a class I drug. 

There are several explanations for the double-peak phenomenon after oral administration. There may be two distinct sites of absorption (42), gastric emptying hmited absorption (43), or a variable gastric emptying rate (44-50), or it may be due to formulation characteristics (39). However, the concept of parallel first-order absorption is not limited to two absorption processes (51-55). 

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