Development and validation of stability indicating reversed-phase liquid chromatographic method for simultaneous...

Methotrexate (MTX) and teriflunomide (TEF) are the two most effective disease-modifying antirheumatic drugs used as combination therapy for rheumatoid arthritis and no robust high-performance liquid chromatography (HPLC) method is available for their simultaneous estimation to date. Therefore, we have developed and validated an isocratic reversed-phase HPLC method for simultaneous analysis of MTX and TEF spiked in the form of active pharmaceutical ingredients, tablets and nanoformulations. The best separation was achieved on a BDS, C₁₈ , 4.6 × 250 mm, 5 μm analytical column (Thermo Hypersil) with methanol-ethylammonium formate-potassium dihydrogen phosphate buffer (55 mm, pH 3.5; 65:5:30, v/v) as mobile phase at a flow rate of 0.8 mL/min. All the samples were subjected to force degradation studies. Responses of MTX and TEF were found to be a linear function of concentration over the range 1-50 μg/mL (r²  = 0.9976 and 0.9982). The limits of detection and limit of quantification were 7.74 and 25.82 ng/mL and 10.74 and 35.80 ng/mL, respectively. Degradation products produced under the stress studies did not interfere with the detection of MTX and TEF and therefore the developed method can be regarded as stability indicating.