A Validated LC–MS/MS Method for the Determination of Sulindac and Its Metabolite Su-EP-C in Human Plasma and Their Pharmacokinetic Application in Healthy Volunteers

A rapid, specific, and sensitive LC–MS/MS method for the determination of sulindac and its metabolite Su-EP-C in human EDTA-K2 plasma was developed. The method was fully validated using sulindac-d3 and Su-EP-C-d3 as internal standards. Separation was performed on a Kinetex C18 analytical column (100 Å, 50 × 2.1 mm, 5 μm). MPA consisted of 0.05% formic acid (FA) in water, while MPB comprised 0.05% FA in ACN. The flow rate was maintained at 0.300 mL/min, and the injection volume was 3 μL. Mass spectrometry conditions: ESI, positive mode, MRM. The linear range of detection was from 60.00 to 24,000.00 ng/mL for sulindac and from 30.00 to 12,000.00 ng/mL for Su-EP-C. The intra- and interbatch accuracy deviations of sulindac ranged from −5.1 to 5.0%, and the intra- and interbatch precision ranged from 3.3 to 4.2%. The intra- and interbatch accuracy of Su-EP-C ranged from −3.9 to 6.9%, and the intra- and interbatch precision ranged from 4.8 to 7.2% at all concentration levels. At a dilution of 10, the deviation for sulindac was 3.5% and the precision was 1.5%; the deviation for Su-EP-C was 2.7%, and the precision was 4.4%. The plasma matrix, at both −20 °C and −70 °C, remained stable for 52 days with 5 freeze–thaw cycles. The method was successfully applied to fasting and postprandial pharmacokinetic clinical trials of orally administered sulindac tablets.