Stereoselective Metabolism Study Of The Venlafaxine In The Chinese Healthy Volunteers

OBJECTIVESTo estabolish a method for the chiral separation of venlafaxine and O-desmethylvenlafaxine,to study the single dose pharmacokinetics of venlafaxine and its active metabolite O-desmethylvenlafaxine enantiomers and to study the enantiomeric metabolic mechanism of venlafaxine.To study the stereoselective mechanism of venlafaxine in the Chinese CYP2D6^* 10 allele volunteers.METHODSWe recruited 88 Chinese healthyl volunteers.The CYP2D6^*10 genotype of them were determinated by using the RFLP-PCR.Twelve subjects were recruited again to participate into the following pharmacokinetic study of VEN.There were two periods in this research. The subjects were administered 75 mg VEN at the first period and 75 mg venlafaxine and 25 mg benzhydramine at the second period.Blood samples of VEN and ODV were collected before and at 0.5,1.0,1.5,2,3, 4,6,8,10.0,12.0,15.0,24.0 and 36.0 h after the oral administration of VEN at 8:00 AM.Plasma was stored at -80℃to determination.The VEN and ODV enantiomers were determinated by using the method which we have set up in this paper. 1.RFLP-PCR determinate the CYP2D6^* 10 allele genotype in the healthy volunteers1.1 DNA extractThe DNA was taken from the whole blood by using the penol—chloroform method.1.2 RFLP-PCR determinate the CYP2D6^* 10 allele2.Analytic methods in this study2.1 Chiral solid phase method for the chiral separation of VEN and ODV.2.2 HPLC-MS/MS method for the determination of VEN and ODV enantiomers.RESULTS1.Chiral separation of VEN and ODVA method for the enantiomeric determination of VEN and ODV was estabolished.With 92%methol as organic phase and 30 mM ammonium acetate as buffer,VEN and ODV enantiomers were separated well; resolution factor was 1.70,1.60 and separation factor was 1.12,1.18 for VEN and ODV respectively。2.Determination of VEN and ODV enantiomersVEN and ODV enantiomers were determined by chiral method.The calibration curves were linear in the ranges of 0.28～423.00μg·L^-1for S-VEN,0.28～423.00μg·L^-1for R-VEN,0.35～532.80μg·L^-1for S-ODV and 0.35～532.80μg·L^-1for R-ODV.The methodology recoveries were all in the range of 77.70%～110.67%.The intra-day and inter-day RSD were less than 11%.3.The single dose pharmacokinetics of VEN and ODV enantiomersIt's the first time to acquire the pharmacokinetic information of VEN enantiomers in the Chinese healthy volunteers and study the VEN stereoselective metabolism in the Chinese with CYP2D6^* 10 allele.The pharmacokinetic parameters were listed on following:the AUC_(0-∞)of R-VEN and S-VEN were 516.6±273.2 and 769.4±259.0μg·h·L^-1,C_maxwere 33.1±17.7 and 48.1±15.9μg·L^-1,t_1/2were 11.7±4.1 and 8.7±2.0 h,t_maxwere 2.3±0.9,2.5±0.9h,respectively.While the AUC_(0-∞)of R-ODV and S-ODV were 913.3±265.8 and 868.4±336.7μg·h·L^-1,C_maxwere 40.5±18.0 and 50.2±24.9μg·L^-1,t_1/2were 14.4±5.6 and 16.6±8.3 h,t_maxwere 16.6±8.3,14.4±5.6 h,respectively.There were great differences between S-VEN and R-VEN in the AUC_(0-∞)t_1/2,t_max,ka and ke(P＜0.05).While there were only great differences between the R-ODV and S-ODV in the t_1/2,t_max,ka and ke(P＜0.05).The S-VEN was more great than the R-VEN in C_max.and there was great difference between them(P＜0.05).So were the R-ODV and S-ODV.But for the AUC_(0-∞),there were no great difference between R-ODV and S-ODV. 4.The interaction of pharmacokinetics between BEZ and VENAfter the BEZ and VEN were co-administered,the AUC_(0-∞)of the R-VEN,S-VEN,R-ODV and S-ODV increased significantly,the main reason was that BEZ inhibited the CYP2D6,so the metabolism of R-VEN and S-VEN through the CYP2D6 reduced.While the increase of AUC_(0-∞) of the R-ODV and S-ODV was due to the inhibition of CYP2D6,the metabolism of R-ODV and S-ODV to the R-DDV and S-DDV through the CYP2D6 reduced.The ratio of AUC_(0-∞)of the S-ODV to the S-VEN and the ratio of AUC_(0-∞)of the R-ODV to the R-VEN have no difference before the administration of BEZ,which have the great difference after the administration of BEZ(P＜0.05).After the BEZ and VEN were co-administered,the C_maxof R-VEN, S-VEN and R-ODV were increased,especially for the S-VEN and R-ODV(P＜0.05).While for the other two important parameters,the t_max of R-VEN and S-VEN reduced,while the R-ODV and S-ODV have different results,t_maxof R-ODV increased(P＜0.05),S-ODV increased. The t_1/2of R-VEN and S-VEN reduced after co-administration of BEZ, while the t_1/2of R-ODV and S-ODV increased,especially for the S-ODV, there was great differences(P＜0.05).So the CYP2D6 has the stereoselective metabolism for the R-VEN and S-VEN but for the R-ODV and S-ODV. CONCLUSIONS1.The VEN and ODV enantiomers have the great difference in the metabolism in Chinese healthy volunteers.2.BEZ can inhibit the metabolism of VEN specifically to the S-ODV after single administration of BEZ.3.BEZ can inhibt the CYP2D6,so co-administration of BEZ and VEN could have strong influence on the VEN pharmacokinetics.After being inhibited,the VEN enantiomers C_maxand AUC increased.The possible reason is that the metabolism of VEN enantiomers by CYP2D6 deduced for the inhibition of CYP2D6.So the C_maxand AUC of them increased greatly,while the raise of the C_maxand AUC of ODV enantiomers is due to the inhibition of metabolism of ODV to DDV by by BEZ.