Determination of Fulvestrant in Rat Plasma by LC–MS–MS: Application to a Pharmacokinetic Study

Development of an LC-MS/MS method for determining the pharmacokinetics of clonidine following oral administration of Zhenju antihypertensive compound

Zhenju antihypertensive compound (ZJAHC) is a combined Chinese-Western medicine formula including clonidine (CLO), hydrochlorothiazide (HCT), rutin, Chrysanthemum indicum extract and pearl powder. Compared with CLO preparations, ZJAHC shows improved activities and decreased adverse effects. It is believed that the side effects of CLO are caused by its high peak plasma concentration. Hence, study of the influence of ZJAHC on the pharmacokinetic behaviors of clonidine seems essential. In present study, the plasma concentrations of CLO were determined with a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. The MS/MS transitions monitored for clonidine and internal standard were 230.2 → 213.1 and 152.2 → 110.2, respectively. The analyte was quantified in a single run within 3 min. The pharmacokinetic study showed that the area under the plasma concentration-time curve of CLO in ZJAHC (60 µg/kg CLO) was similar to that of CLO-HCT-high (120 µg/kg CLO) but the peak concentration was much lower than that in CLO-HCT-high. ZJAHC could enhance the bioavailability without greatly increasing peak concentration of clonidine. This comprehensive effect of enhancing the bioavailability and avoiding the high peak plasma concentration for CLO might mainly result from the co-contribution of Western medicine and traditional Chinese medicine (TCM), while the effect of TCM was stronger than that of Western medicine.

Determination of lomerizine in human plasma by liquid chromatography/tandem mass spectrometry and its application to a pharmacokinetic study

A rapid, sensitive and selective high performance liquid chromatography-electrospray ionization-tandem mass spectrometry method (HPLC-ESI-MS/MS) was developed and validated for the determination and pharmacokinetic investigation of lomerizine in human plasma. Protein precipitation process was used to extract lomerizine from human plasma. Plasma samples were separated by HPLC on an Agela Venusil XBP Phenyl column (100 mm × 2.1 mm, 5 μm) using a mobile phase consisting of methanol-2mM ammonium acetate-formic acid (70:30:0.1, v/v/v) and the flow rate was set at 0.35 mL/min. The total run time was 4.0 min and the elution of lomerizine was at 1.9 min. The detection was performed on a triple quadrupole tandem mass spectrometer in the multiple reaction-monitoring (MRM) mode using the respective [M+H](+) ions m/z 469.2→181.0 for lomerizine and m/z 405.2→202.9 for the I.S. The calibration curve was linear over the range of 0.1-25 ng/mL (r(2)>0.99) with a limit of quantitation (LOQ) of 0.1 ng/mL. The intra- and inter-day precision (relative standard deviation, RSD) values were below 9.65% and the mean accuracy was from 99.00 to 103.00% at four quality control levels. Lomerizine was stable during stability studies, i.e., long term, auto-sampler and freeze/thaw cycles. The method was successfully applied for the evaluation of pharmacokinetics of lomerizine after single oral doses of 10 mg lomerizine to 18 healthy volunteers.