It is generally accepted that the pH of the aqueous phase within GI tract ranges from pH 1 to 7 (or 8). This range may further be divided into two sub-groups; one is of pH 1 (perhaps to 3) and a second of pH 5-7. The segment having pH 1 represents the stomach and the other, in the range of 5-7, is the (small) intestinal part.
It is commonly accepted that most of the drug (or food) ingested, gets absorbed from the intestinal part. As absorption depends on dissolution, the majority of the drug should be available in the solution form in this segment of the GI tract. Obviously, for dissolution purposes, it is this environment of pH which appears to be relevant and critical. Therefore, dissolution tests are to be conducted in media having pH in the range of 5-7.
Conducting dissolution tests, thus, in acidic (HCl) media (pH ~1), does not appear to be an appropriate choice.
