Development of Liquid Chromatography – UV Method for Simultaneous Determination of Leflunomide and NSAIDs in API and Pharmaceutical Formulations : It ’ s Application to In vitro Interaction Studies

An efficient analytical method for the simultaneous determination of leflunomide and non steroidal anti-inflammatory drugs in API and formulations by LC-UV has been developed. The analytes were separated on Purospher Star, C 18 (5 µm, 250×4.6 mm) column at ambient temperature with methanol: water (80:20, v/v, pH at 2.7) at flow rate of 1.5 mL min-1. Experiment was conducted in two phases. Leflunomide was separated with flurbiprofen and ibuprofen (phaseI) and diclofenac sodium and mefenamic acid (phase II). Calibration curves were linear over the range 0.625–5 µg mL-1 in both phases for leflunomide while for flurbiprofen, ibuprofen, diclofenac sodium, mefenamic acid linearity were achieved in the range of 0.625-5, 11.25-90, 1.56-50 and 0.78-25 µg mL -1 , respectively with r 2 >0.9998. Intraday variation was <1.2 and <1.4 %, while in inter-day ranged between 0.042-1.45% and 0.08-1.27% in phase-I and II, respectively. Mean recovery values for intra-day ranged from 99.04-100.4% and 98.48-100.2% and for inter-day were between 98.54-100.29% and 98.85-100.54% in phase-I and II, respectively. The LLOD of leflunomide was 13 ng mL-1, while LLOQ was 39ng mL-1, respectively. LLOD and LLOQ for flurbiprofen, ibuprofen, diclofenac sodium and mefenamic acid were 6.9, 296, 71 and 1.2 ng mL -1 and 21, 897, 214.3 and 3.676 ng mL -1 , respectively. Present study showed that nanogram quantities of all the compounds can be estimated accurately. The newly established method was successfully applied to study in vitro interactions between leflunomide and NSAIDs.