RP-HPLC assay method development for Paracetamol and Lornoxicam in combination and characterization of oxidative degradation products of Lornoxicam

A simple, specific, accurate and precise reverse phase high pressure liquid chromatographic method has been developed for the simultaneous determination of Paracetamol and Lornoxicam from tablets and to characterize degradation products of Lornoxicam by reverse phase C18 column (Inertsil ODS 3V C-18, 250 x 4.6 mm, 5 ?). The sample was analyzed using Buffer (0.02504 Molar): Methanol in the ratio of 45:55, as a mobile phase at a flow rate of 1.5 mL/min and detection at 290 nm. The retention time for Paracetamol and Lornoxicam was found to be 2.45 and 9.40 min respectively. The method can be used for estimation of combination of these drugs in tablets. The method was validated as per ICH guidelines. The linearity of developed method was achieved in the range of 249.09 - 747.29 ?g/mL (r2=0.9999) for Paracetamol and 4.0125 - 12.0375 ?g/mL (r2=0.9999) for Lornoxicam. Recoveries from tablets were between 98 and 102%. The method was validated with respect to linearity, accuracy, precision, robustness and forced degradation studies which further proved the stability-indicating power. During the forced degradation studies lornoxicam was observed to be labile to alkaline hydrolytic stress and oxidative stress (in the solution form). However, it was stable to the acid hydrolytic, photolytic and thermal stress (in both solid and solution form). The degraded products formed were investigated by electrospray ionization (ESI) time-of-flight mass spectrometry, NMR and IR spectroscopy. A possible degradation pathway was outlined based on the results. The method was found to be sensitive with a detection limit of 0.193 ?g/ml, 2.768 ?g/ml and a quantitation limit of 0.638 ?g/ml, 9.137 ?g/ml for lornoxicam and paracetamol, respectively. Due to these attributes, the proposed method could be used for routine quality control analysis of these drugs in combined dosage forms.