Mid-gastrointestinal tract

The gastrointestinal tract is conveniently divided into a number of areas, primarily on the basis of morphology and function. For most pharmaceutical purposes, we can group the target tissues into three regions the upper, mid- and lower gastrointestinal tract. 

When an API shows a dose solubility ratio of 250 ml or lower at 37 °C over a pH range of 1.2-6.8, it can be classified as highly soluble . The decrease in pH from 7.5 in the FDA guidances to 6.8 reflects the need to dissolve the drug before it reaches the mid-jejunum to ensure absorption from the gastrointestinal tract. 

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