Simple determination and quantification of tofacitinib, a JAK inhibitor, in rat plasma, urine and tissue homogenates by HPLC and its application to a pharmacokinetic study

Purpose Tofacitinib, a janus kinase (JAK) inhibitor, was developed for the treatment of rheumatoid arthritis. To evaluate its pharmacokinetic characteristics, a simple method of quantifying tofacitinib by high-performance liquid chromatography (HPLC) was developed to estimate its concentrations in rat plasma, urine and tissue homogenates. Methods Hydrocortisone was used as an internal standard. The mobile phase was an isocratic system of acetonitrile: 10 mM ammonium acetate, pH 5.0 (30.5:69.5, v/v), and the flow rate was 1.0 mL/min. Chromatograms were monitored by a UV detector at 287 nm. The retention times for tofacitinib and hydrocortisone were 7.21 and 11.3 min, respectively. Results The lower limits of quantification for tofacitinib in rat plasma and urine were 0.01 and 0.1 μg/mL, respectively. The intraday assay precisions (coefficients of variation) were generally low; 3.69–5.88% for rat plasma and 4.21–6.18% for rat urine. The corresponding values of interday assay precisions were 5.06% and 5.46%, respectively. Accuracies ranged from 92.9 to 107%, with no interference by endogenous substances. Tofacitinib has a short half-life (39.0 min) and was widely distributed in rat tissues. Conclusion This HPLC method is very simple and sensitive and can be applied to future preclinical and clinical investigations of tofacitinib.