Validated stability indicating RP-HPLC method for simultaneous determination and in vitro dissolution studies of thiocolchicoside and diclofenac potassium from tablet dosage form

A simple, rapid, and robust stability indicating RP-HPLC method has been developed and validated to measure thiocolchicoside (TH) and diclofenac potassium (DP) at single wavelength (258 nm) in order to assess assay and in vitro drug release profile of drug from tablet formulation. A gradient elution of samples performed on Zorbax SB CN 250 mm × 4.6 mm, 5 μm column with buffered mobile phase consisting solvent A (5 mM sodium dihydrogen phosphate, pH 2.5) and solvent B (methanol) delivered at flow rate 1.0 mL/min. For dissolution study, the sink condition has been established from quantitative solubility of TH and DP API in different dissolution medium recommended by USP for immediate release formulation and the optimized dissolution condition was: pH 6.8 deaerated potassium dihydrogen phosphate buffers, paddle rotation speed 50 rpm and vessel volume 900 mL. Discriminating release of TH and DP achieved more than 96% of labeled amount over 45 min and drug dissolution was concluded after 60 min. The HPLC method and dissolution test condition were validated to meet requirement for regulatory filling and this validation inferred from specificity, precision, accuracy, linearity and robustness. In addition filter suitability, standard and sample solution stability was demonstrated.All results were acceptable and this confirmed that the method is suitable for its intended use in routine quality control and assay of drugs.