Characterization of Pharmacokinetics and Oral Bioavailability of Saikosaponin A in Rats Using a Validated UFLC–MS/MS Method

ABSTRACT Saikosaponin A (SSa) is an oleanane type triterpenoid saponin isolated from Radix Bupleuri ( Bupleurum chinense DC). While SSa has demonstrated significant pharmacological activities including anti‐inflammatory, antioxidant, and antidepressant effects, its pharmacokinetic profile remains poorly characterized. This study developed and validated a sensitive LC–MS/MS method for quantifying SSa in rat plasma. After acetonitrile‐mediated protein precipitation, SSa and the internal standard (IS) were separated on a Waters Acquity BEH C18 column using MS detection operated in negative multiple reaction monitoring (MRM) mode. The assay was linear over the concentration range of 2–1000 ng/mL with satisfactory validation parameters of intra‐and inter‐day precision (3.50%–10.01%) and accuracy (−5.93% to −2.68%), extraction recovery (73.75%–82.50%), stability, and matrix effect (88.49%–103.64%). Application in pharmacokinetic studies revealed distinct administration‐related characteristics. Intravenous administration (5 mg/kg) resulted in high clearance with an elimination half‐life ( t 1/2 ) of 2.29 h and was accompanied by hemolysis. Oral administration at doses of 50, 100, and 200 mg/kg showed dose‐dependent systemic exposure with consistently low bioavailability (0.04%). The limited absorption is likely attributable to poor gastrointestinal permeability and extensive metabolism mediated by intestinal microbiota and hepatic first‐pass effects, as indicated by the extremely low system exposure. These findings provide useful information for optimizing SSa therapeutic applications.