Studies on the pH-Dependent Solubility of Various Grades of Calcium Phosphate-based Pharmaceutical Excipients

Calcium phosphate-based pharmaceutical excipients, including calcium hydrogen phosphate anhydrous and dihydrate, calcium hydroxide phosphate have been well established in pharmaceutical technology for a very long time. Nowadays, they are of increasing interest to the pharmaceutical industry because, in addition to their advanced functional properties, they offer beneficial biocompatible and biodegradable properties. Yet, there is limited availability of embracing information regarding the solubility of these popular excipients, especially in variable pH conditions, reflecting those of the gastrointestinal tract (GIT). The study has shown that the solubility of calcium phosphates as well as their dissolution rate decreases significantly with increasing pH of dissolution fluids. The highest solubility was observed for dibasic calcium phosphate dihydrate, the lowest for tribasic calcium phosphate. This article provides also a comparison of various calcium phosphate types originating from different manufacturers, which may prove to be useful and help formulation scientists to design new medicinal products.