Abstract: AIM: To establish an LC-ESI-MS method for determination of ginsenoside 20(R)-Rh₂ and investigate its application to pharmacokinetic and absolute bioavailability study in Beagle dogs.METHODS: According to a randomized two-period crossover design,beagle dogs were given 1 and 0.1mg·kg^-1 20(R)-Rh₂ via po and ivrespectively.Drug plasma concentration was determined by LC-ESI-MS.Pharmacokinetic parameters were evaluated and absolute bioavailability was also calculated.RESULTS: The method was linear over the range of 0.5-200ng·ml^-1 (R₂=0.9998);The recovery of 20(R)-Rh₂ in dog plasma was more than 70%;Intra- and interbatch precision,expressed as the relative standard (RSD) was less than 15%;After iv administration of 20 (R)-Rh₂,the main pharmacokinetic parameters T_1/2,CL,AUC_0-∞ were 8.0±2.8h,0.1±0.03L·kg^-1·h^-1,857.0±209.6ng·h·ml^-1 respectively;after po administration,the major pharmacokinetic parameters T_max,C_max,T_1/2,AUC_0-∞ were 2.6±1.3 h,371.0±199.6ng·ml^-1,5.8±2.6 h,1215.7±598.6ng·h·ml^-1 respectively.The absolute bioavailability was 16.1%±11.3% after the correction of dosage.CONCLUSION: The method described in this report was sensitive and specific,and suitable for pharmacokinetic studies of 20(R)-Rh₂ in dog.The absolute bioavailability of 20(R)-Rh₂ in dog was relative low.

Key words: ginsenoside 20 ( R) -Rh₂, LC-ESI-MS, pharmacokinetics, absolute bioavailability