Stability-Indicating High-Performance Thin-Layer Chromatographic Method for Simultaneous Estimation of the Active Pharmaceutical Ingredients Metolazone and Spironolactone

This work represents the validation of a stability-indicating thin-layer chromatographic technique for the simultaneous estimation of metolazone (METO) and spironolactone (SPIRO) from marketed formulation (tablets). Thin-layer chromatography was performed using precoated silica gel plate 60 F254 using ethyl ac-etate—chloroform—GAA (5:5:0.1 v/v) as the mobile phase for the separation of METO and SPIRO. The stability study forms an integral part of the formulation development process, and its use is also encouraged by various guidelines. Stress study was performed on active pharmaceutical ingredients (APIs) as well as on formulation for establishing a stability-indicating thin-layer chromatographic method for both drugs. The APIs were subjected to change under various environmental conditions such as pH, temperature, oxidation, etc. to determine their effect on the stability of drugs. The developed method was able to resolve drugs and their degradation products formed under the aforementioned conditions. The wavelength selected for quantitation was 238 nm. The method was validated as per the International Conference on Harmonization (ICH) guidelines and found to be linear in the range of 50–300 ng spot−1 for METO and 200–1200 ng spot−1 for SPIRO. The relative standard deviation (% RSD) values of the precision study were <2% which indicated that the developed method was precise; recovery was found to be 99.02–100.58% and 99.26–100.17% for METO and SPIRO, respectively. It could be concluded from the stability study that METO was prone to acidic hydrolysis and photolysis while SPIRO was prone to alkaline degradation.