Liquid chromatography-tandem mass spectrometry method for determination of total and free teriflunomide concentration in serum of patients with multiple sclerosis.

Teriflunomide belongs to disease-modifying drugs and is used in treatment of multiple sclerosis. According to in vitro studies more than 99.4 % of drug is binding to plasma proteins and only less than 1 % is free for clinical activity. The rapid and simple ultra-performance liquid chromatography-tandem mass spectrometry method (UPLC-MS/MS) was developed and validated for determination of total and free teriflunomide (TFM) in serum of patients with multiple sclerosis. To determine the total teriflunomide samples were precipitated with a precipitation reagent consisting of 11 % solution of ZnSO in acetonitrile/methanol (40:60, v/v). To determine the free fraction of teriflunomide, an ultracentrifugation method was used. The analysis was performed on a UPLC system connected to a XEVO TQ-XS mass spectrometer. Chromatographic separation was carried out on an Acquity UPLC BEH C18 1.7 µm (100 × 2.1 mm) column heated to 30 °C and teriflunomide-D4 was used as an internal standard. Ionization was performed by electrospray in negative ion mode. The developed methods were validated according to the rules of the European Medicines Agency (EMA) for the analytical method validation of bioanalytical methods. The coefficients of variation were in the range of 0.53-14.84 % and the recovery 97.92-108.33 %, respectively. Share of free teriflunomide was 0.15-0.40 % (mean 0.25 ± 0.05 %) of total teriflunomide and there was a significant correlation between free and total teriflunomide r = 0.9083 (p < 0.0001). This newly developed method allows the rapid and easy determination of the teriflunomide concentration with high sensitivity and can be applied to clinical samples of patients with multiple sclerosis.