Clinical drug-drug interactions（DDIs） induced by CYP3A may reduce the exposure and pharmacological activity of CYP3A substrate.Up-regulation of CYP3A mRNA is often used to evaluate inductive effect of test compounds on CYP3A. A quantitative real time PCR assay was developed and validated for the absolute quantification of CYP3A1 and CYP3A2 mRNA.Specific primers of CYP3A1,CYP3A2 and GAPDH（glyceraldehyde-3-phosphate dehydrogenase,as a house-keeping gene） were well designed.The relationship between threshold cycle（Ct） and logarithm of the concentrations of CYP3A1, CYP3A2 and GAPDH was linear ranged from 1 attomol/μL to 1×10~6 attomol/uL with great inter- and intra-assay reproducibility. This method was successfully applied to investigate the time courses of CYP3A1 and CYP3A2 mRNA induction in rat liver after 100 mg/kg dexamethasone（DEX） administration by intraperitoneal（i.p.） injection.The baseline levels of CYP3A1 and CYP3A2 mRNAs were 37.78 attomol/ug（total RNA） and 252.31 attomol/ug（total RNA）,respectively.CYP3A1 and CYP3A2 mRNA values increased gradually to their peak levels（19- and 8- fold vs.baseline） within 24 h and 42 h,respectively,and then returned to their baseline 60 h after DEX administration.
Population pharmacokinetic meta-analysis method was used in order to obtain the pharmacokinetic characteristics of risperidone and its active metabolite. Eighteen studies were selected from published papers from 1995 to 2011. A model consisted of two compartments for parent drug and one compartment for its active metabolite combined with a flexible absorption process was developed based on the meta-dataset. The population-predicted apparent clearance for risperidone and 9-hydroxyrisperidone, the active metabolite was 7.66 L/h and 7.38 L/h, and the apparent volume of distribution in the central compartment was 70.6 L and 117 L, respectively. The final model was evaluated by visual predictive check（VPC） based on 1000 times model simulation. This model was adequately used to predict clinical therapeutic drug monitoring（TDM） data from 42 Chinese inpatients. Bias（mean prediction errors, MPE） and precision（root mean squared prediction errors, RMSE） were calculated to statistically analysis the population prediction error. It was demonstrated that the model developed from the meta-dataset was reliable and can be used to facilitate the individualized treatment for a target population.
An efficient and sensitive ion-pair HPLC-UV method using atenolol as internal standard （IS） was developed and validated for the determination of metformin in the plasma of diabetic rats. Plasma samples were deproteinated with 10% （v/v） perchloric acid. Separation was achieved on a UltimateTM AQ-C18 column （250 mm×4.6 mm, 5 μm） with a mobile phase （pH 5.05） composed of acetonitrile-water （31：69, v/v, containing 0.002 M sodium dodecyl sulfate, 0.0125 M potassium dihydrogen phosphate, 0.015 M triethylamine） at a flow rate of 1.0 mL/min. The calibration curve was linear （r〉0.994） between 7.5 and 4000 ng/mL. The lower limit of quantification （LLOQ） was 7.5 ng/mL. The precision was validated and the relative standard deviation was in the range of 1.87% to 15.70%; the accuracy was between 93.98%-106.89%. The mean recoveries were 95.40% and 95.31% for metformin and IS, respectively. The relative error （RE） of stability at different storage conditions was within ±9.00%. This method was used to determine the concentration-time profile of metformin in diabetic rat plasma following an oral administration of metformin at the dose of 10 mg/kg. Our results indicated that ion-pair HPLC-UV method using UltimateTM AQ-C18 column was effective for the pharmacokinetic studies of high polarity compounds like metformin.
