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.
