[The stability of hydrochlorothiazide and cyclopenthiazide in various dosage forms. 4. Stability of...

The hydrolytic decomposition of hydrochlorothiazide (1) in an optimized dispensing with polyethyleneglycol 400/ethanol as solvent led to an equilibrium in the isothermic short-term test as well as in the long-term stability test. Corresponding equilibrium concentrations were obtained for forward and back reaction. When comparing the precalculated equilibrium values with the long-term results the evaluation after Van't Hoff proved superior compared with an evaluation after the Arrhenius plot which is only applicable when the equilibrium concentrations are taken into consideration. By adding the decomposition product aminodisulfamide (2) the hydrolysis of 1 can be inhibited completely.