Development of a microdialysis system to monitor lamivudine in blood and liver for the pharmacokinetic application in herbal drug interaction and the gene expression in rats.

The aim of study is to develop a novel multiple microdialysis technique coupled to a validated chromatographic system for the measurement of protein-unbound form lamivudine and investigation of its herb-drug interaction in rat blood and liver. Furthermore, gene expression changes of drug metabolizing enzymes in rat were evaluated by microarray analysis after being treated with a traditional Chinese herbal formulation, Long-Dan-Xie-Gan-Tang (LDXGT). The analyte was separated by a reverse-phase C18 column using the mobile phase comprising methanol and 10mM KH2PO4 (15:85, v/v, adjusted to pH 6.0 with NaOH) with the flow rate of 0.8mL/min, and the UV wavelength was set at 270nm. The processes of method validation followed Food and Drug Administration (FDA) guidelines. The pharmacokinetic data demonstrated that the area under the concentration-time curve (AUC) of the lamivudine alone and the LDXGT pretreated group were 532±37.6 and 550±44.2minμg/mL in rat blood after lamivudine administration (10mg/kg, i.v.) and 682±196 and 642±153minμg/mL in rat liver, respectively. The herb-drug pharmacokinetic interaction showed that with either lamivudine alone or in combination with pretreated with LDXGT, the pharmacokinetic parameters were not significantly changed except the apparent volume of distribution (Vd) at a high dose of lamivudine (30mg/kg). In addition, microarray analysis showed that among 70 altered genes (selection criteria: |Fold change|≧2 and p<0.05), only 11 genes were involved in drug metabolism and indicated that a relatively small portion of drug metabolizing genes in liver were altered at the genome level after the therapeutic dose of LDXGT treatment. In conclusion, these studies provide constructive information to interpret the herb-drug interactions between lamivudine and a popular Chinese herbal formulation.