Stability-indicating assay for hydrochlorothiazide

A stability-indicating method for determining hydrochlorothiazide in tablet formulations and in the bulk form is described. Hydrochlorothiazide is dissolved or extracted using methanol. An aliquot of the solution, containing sulfadiazine as an internal standard, is chromatographed on a 10 micron C18 column with an aqueous mobile phase containing 5% methanol as the modifier. The pH is adjusted to about 4.5 with acetic acid. The method gave accurate results for nine lots (four different suppliers) of tablets and two bulk drug lots (two different suppliers). The assay has a relative standard deviation of about 1%. The method can also be used as a test for impurities in hydrochlorothiazide. The data in this study indicate that the test should give accurate results for impurities between 0.1 and 5%.