Answer to Question #71556 in General Chemistry for Ahmad Jasem

Question

How can I avoid decreasing solubility while increasing ph?

I have a drug that is soluble in water, when increasing the pH, it breaks down and becomes insoluble (formulates a cloudy white solution), the pH was 3-4 and I need it at pH 7, the drug is ciprofloxacin hydrochloride, can i avoid decreasing solubility while increasing ph?

Answer 1

Мolecules of fluoroquinolines are bipolar ions.
from the literature data it is known that the isoelectric point for ciprofloxacin is 7.4
(W.O. Foye, T.L. Lemke, D.A. Williams. Principles of Medicinal Chemistry. 4th ed, Williams & Wilkins(1995)). At this acidity, a small number of particles are in the ionized state,thus, its solubility in water decreases. On this basis it is necessary to use a phosphate buffer.
In this case the substance is released by 11-13% after 5 minutes and does not change during the entire dissolution. This is obviously connected with the formation of a saturated solution.