Simultaneous determination of forsythin and its major metabolites in human plasma via liquid chromatography-tandem mass spectrometry.

Forsythiae suspensa is widely used in China as a traditional Chinese medicine. Forsythin is extracted from Forsythiae Fructus and has undergone phase II clinical trials as an antipyretic drug in China. The main metabolites of forsythin in human plasma are aglycone sulfate (KD-2-SOH) and aglycone glucuronide (KD-2-Glc). In the present study, a sensitive and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and fully validated for the simultaneous analysis of forsythin, KD-2-Glc, and KD-2-SOH, in human plasma. After precipitating proteins with methanol, these three analytes were separated on a Gemini-C18 column along with teniposide as an internal standard. Mass spectrometry detection, under multiple reaction monitoring, was then carried out in negative mode using the Triple Quad™ 6500 LC-MS/MS system coupled with an electrospray ionization (ESI) ion source. The transitions of m/z 371.1→356.1 for forsythin, m/z 547.2→356.0 for KD-2-Glc and m/z 451.2→356.2 for KD-2-SOH were chosen to effectively maintain the balance between selectivity and sensitivity. The developed method was linear over the following concentrations in human plasma samples: 1.00-1000 ng/mL for forsythin, 2.50-2500 ng/mL for KD-2-Glc, and 5.00-5000 ng/mL for KD-2-SOH. Assays were validated and satisfied the acceptance criteria recommended by the CFDA guidance. Furthermore, this LC-MS/MS method was successfully implemented in a Phase I, first-in-human, dose-escalation pharmacokinetic study among Chinese healthy participants after single oral administration of forsythin tablets.