Stability-Indicating HPTLC Method for Simultaneous Determination of Lisinopril Anhydrate and S-Amlodipine Besylate in Pharmaceutical Dosage Form

A stability indicating high performance thin layer chromatography (HPTLC) method was developed and validated for determination of Lisinopril Anhydrate (Lisino) and S-Amlodipine Besylate (S-Amlo) in combined dosage form used for treatment hypertension. Pre-coated silica gel HPTLC plates were used as stationary phase and n-butanol: methanol: 25% ammonia solution (4:4:2 v/v/v) as the mobile phase to resolve the two drugs with Rf values 0.28 and 0.80 for Lisino and S-Amlo respectively. A TLC scanner set at 218 nm was used for direct evaluation of the chromatograms in the reflectance/absorbance mode. The correlation coefficients of calibration curves were found to be 0.991 and 0.995 in the concentration range of 2000-12000 ng/band and 1000–6000 ng/band for Lisino and S-Amlo respectively. Method was validated according to ICH guidelines. The method had an accuracy of 99.70–99.91% for Lisino and 99.66–99.92% for S-Amlo. The method determined the two drugs simultaneously from dosage forms without any interference of the tablet excipients. Lisino and S-Amlo were also subjected to acid, base, oxidation, heat and photodegradation studies. The degradation products obtained were well resolved from the pure drugs. As the method could effectively separate the drugs from its degradation products, it can be used as a stability-indicating assay.