[Study on degradation kinetics or potassium dehydroandrographolidi succinas].

Objective: To investigate the hydrolytic degradation of the kinetic characteristics of Potassium Dehydroandrographolidi Succinas (DAS-K) in aqueous solution.

Methods: The HPLC method was used to determine the degradation kinetic parameters of DAS-K aqueous solution at different initial concentration, different pH, different ionic strength. various temperatures and in different buffer solutions.

Results: DAS-K hydrolytic degradation followed first-order kinetics as measured by HPLC. From pH 8, the hydrolytic degradation rate of DAS-K markedly increased with pH. DAS-K was unstable in alkaline pH solution. The species of buffer solutions seem to have different impact on the catalytic process. The ionic strength did not have significant effect on the stability of the drug. According to the Arrhenius plot, the dependence of the decomposition on temperature was a determining factor, the activation energy was estimated to be 95.68 KJ/mol in phosphate buffer solution at pH 8 and temperature from 60 to 90 degrees C.

Conclusion: It was found that the hydrolytic degradation of DAS-K complied with first-order kinetics. The rate of hydrolytic degradation of DAS-K depended on the pH of solution, the buffer concentration, the buffer species and the temperature. Especially, pH value was an important factor in determining the rate of the hydrolytic degradation of the drug.