Background and ObjectiveTaohong Siwu Decoction (TSD) is a classic traditional Chinese medicine (TCM) compound with pharmacological effects such as vasodilation and hypolipidemia. Paeoniflorin (PF) is one of the active ingredients of TSD. The aim of this study was to evaluate the pharmacokinetics of PF in herbal extracts and their purified forms in rats.MethodA sensitive and rapid high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) method for the determination of PF in rat plasma was developed. Rats were divided into three groups, and given PF solution, water extract of white peony root (WPR), or TSD by gavage. At different predetermined timepoints after gavage, blood was collected from the orbital vein. The pharmacokinetic parameters of PF in the plasma of rats in the three groups was determined.ResultsThe pharmacokinetic studies showed that the time to reach maximum concentration (T-max) of PF in the purified forms group was relatively high, while the half-lives (T-1/2) of PF in the TSD and WPR groups were longer. Among the three groups, PF in the purified forms group had the maximum area under the concentration-time curve (AUC(0-t) = 732.997 mu g/L center dot h) and the largest maximum concentration (C-max = 313.460 mu g/L), which showed a significant difference compared with the TSD group (P < 0.05). Compared with the purified group, the clearance (CLz/F = 86.004 L/h/kg) and the apparent volume of distribution (V-z/F = 254.787 L/kg) of PF in the TSD group increased significantly (P < 0.05).ConclusionsA highly specific, sensitive, and rapid HPLC-MS-MS method was developed and applied for the determination of PF in rat plasma. It was found that TSD and WPR can prolong the action time of paeoniflorin in the body.