I'll have a drug release test, that is the most important part of my research. My mentor choose some pH value for me to having a drug release in vitro, which is 2; 4.5; 7.4 and 10.
In those pH value, I just know the pH 2 is the value of pH in stomach and pH 7.4 is the value of pH in blood. But the pH 4.5 and pH 10 is available in which parts of human body?
Hi.
The answer may be physiological, but may also be chemical.
In the body, the pH of an empty stomach can be well below 2, while the pH of the stomach in the fed state can reach 4 or 5. The pH increases as you look further along the GI tract... it is around 4.5 or so in the upper intestines (close to the stomach), and reaches 5-6 before moving too far along. As you move toward the lower intestines, it is 7 and above. (Just guidelines... the exact locations can be found in the literature.) I know of no region where pH 10 occurs physiologically.
If you have an enteric coating, the pH along the GI tract is an important consideration when doing in vitro dissolution testing. For instance, at a very low pH, there should be no release (or minimal leakage) for an enteric coated tablet... this is a test of coating integrity among other things. Depending on the coating, at pH 7.4 and definitely 10, the coating should dissolve and release the drug.
On the other hand, if the drug is a weak acid or base, the pKa of the drug will affect its solubility. For a weak acid, the solubility in aqueous media goes up as the pH increases, increasing very slowly with increasing pH until you get close to the pKa, Once pH is above pKa, the solubility increase per increase in pH gets larger. For a weak base, the opposite is true... solubility goes down as pH goes up, dropping rapidly until approaching the pKa, then dropping more slowly with increasing pH.
Some weak bases do have pKa's above 9 and 10. (For instance, phenyephrine along with a number of others.)
Bottom line... without knowing your drug, it's hard to say what dictates the choice of pHs. It could be physiological, chemical or both.
Hope this is food for thought!
Robert A Bellantone I'm sorry that I forgot to provide the information about my drug. It's Bovine serum albumin
Hi.
Thanks for the update. For BSA, I'm not sure why pH 10 would be of relevance. (Very well could be that I am missing something here.) The others could be useful because of physiological considerations. Assuming you are using BSA as a carrier, then the pH ranges might be of interest for release.
If you want to consider oral release, for instance, those ranges would be relevant. (I'm not familiar with using BSA oral release, that doesn't mean it can't be done... just that I am not aware of it.) Of course, as you know, for injection the pH of 7.4 is of interest.
On the other hand, the pH range might be important for drug loading and formulation. If BSA is a carrier, the drug loading efficiency (via drug-protein binding) will depend on its solubility as well as the binding capacity. For a weak acid or base, the pH ranges become relevant in terms of dissolved concentration, and possibly differences due to charged vs. neutral drug forms.
Good luck!
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