Effect of pH on Pharmaceutical Ingredients / Drugs / Chemicals

Abstract

The word excipient is derived from the Latin excipere meaning to except, which is simply explained as other than. Pharmaceutical excipients are basically everything other than the active pharmaceutical ingredient. Ideally, excipients should be inert, however, recent reports of adverse reactions have suggested otherwise. Pharmaceutical excipients are substances other than the active pharmaceutical ingredient (API) that have been appropriately evaluated for safety and are intentionally included in a drug delivery system. Solubility, which defines the liquid /solid equilibrium, is a key parameter to control a crystallization process. As the API is a weak acid (pKa = 3.7), its solubility increases with the pH. On the basis of the experimental curve of solubility, a model was defined to fit the evolution of the solubility as a function of pH. In the case of this compound, studies revealed a weak influence of the temperature in comparison with the pH. So, the solubility of the compound is slightly impacted by the temperature. Some experiments were carried out in order to compare the solubility of the API, at the same pH and temperature, for different concentrations of impurities found in the process. The results revealed a solubility increase in presence of acetic acid and a high solubility decrease in presence of sodium chloride. By carrying out experiments on common ions salts, the anion chloride Cl− has been identified as the cause of the solubility decrease.

Keywords: Solubility, API, Impurity, Ph