Stability-indicating LC method for the simultaneous determination of lisinopril and hydrochlorothiazide.

A simple and rapid stability-indicating liquid chromatographic method was developed and validated for the simultaneous determination of lisinopril and hydrochlorotiazide (HCTZ) in drug substances and dosage forms in the presence of degradation products. Forced degradation studies were conducted on the pure drugs under hydrolytic, oxidative, thermal and photolytic conditions. A chromatographic separation of the two drugs and its degradation products was achieved with an RP-18 column, using methanol, acetonitrile and phosphate buffer (pH 7.1; 0.05 M) (15:15:70, v/v/v) as mobile phase at a flow rate of 0.8 mL min(-1) and UV detection at 210 nm. Lisinopril and HCTZ were well resolved from its degradation products showing the stability-indicating capability of the method. The described method was linear over a range of 40-200 µg mL(-1) for lisinopril and 25-175 µg mL(-1) for HCTZ. The assay was also selective, accurate and precise for lisinopril and HCTZ determination. This method represents an alternative to the United States Pharmacopeia (USP) method showing shorter retention time. The method was successfully applied for determination of lisinopril and HCTZ in combined commercial tablets. The results showed that the proposed method was found to be suitable for quantitative determination and the stability study of lisinopril and HCTZ in pharmaceutical samples.