A new high-performance liquid chromatography (HPLC) method for the quantitative determination of sitagliptin in rat plasma was developed and validated for pharmacokinetics study. The plasma was spiked with the internal standard (hydrocortisone, IS), treated with sodium hydroxide, and extracted with ethyl acetate. The extracted analyte was injected into an Agilent Zorbax Extend-C18 column (250 mm×4.6 mm, 4 µm) maintained at 30 ºC and monitored at 267 nm. The mobile phase consisting of methanol-water (60:40, v/v, containing 10 mM Tris and 10 mM triethylamine) was titrated to pH 9.0 using 1 mol/L hydrochloric acid. The flow rate was 1.0 mL/min. The method showed high specificity. Calibration curves of the peak area ratio of each analyte/IS versus sitagliptin concentration were linear in the range of 0.75-100.0 µg/mL (r>0.9957). The lower limit of quantification (LLOQ) was 0.75 µg/mL. The intra-day and inter-day coefficient of variation was lower than 10%. The accuracy (relative recovery) at three levels was 105.3% (0.75 µg/mL), 99.8% (10.0 µg/mL) and 99.0% (100.0 µg/mL). The extraction recovery was 81.5%, 82.4% and 84.5% at the concentrations of 0.75, 10.0 and 100.0 µg/mL, respectively. The short-term, long-term, freeze-thaw storage stability of plasma samples and the stability of standard solutions were satisfactory. This HPLC method is suitable for determining the concentration of sitagliptin in rat plasma and it was applied to determine the concentration-time profiles of sitagliptin in rat plasma following oral administration of sitagliptin.
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