Pharmacokinetics and modeling of quercetin and metabolites

Purpose. To determine the pharmacokinetics of quercetin and its glucuronide/sulfate conjugates and to develop a pharmacokinetic model to simultaneously describe their disposition after intravenous and oral administration in rats. Methods. After oral, intraportal, and intravenous administration of quercetin, serial plasma, urine, and fecal concentrations of quercetin and its conjugates were determined by an HPLC method. Enterohepatic recirculation was evaluated in a linked-rat model as well as after oral administration of bile containing quercetin and its metabolites. Based on the experimental data, a specific compartmental model was developed and validated to describe and predict the plasma concentration-time profiles of quercetin and its conjugates after oral and intravenous administration. Results. Only 5.3% of unchanged quercetin was bioavailable, although the total quercetin absorbed was as high as 59.1%. After oral administration, about 93.3% of quercetin was metabolized in the gut, with only 3.1% metabolized in the liver. No significant enterohepatic recirculation was observed for both quercetin and its conjugated metabolites. The pharmacokinetic model fitted well the observed data of quercetin and its conjugates. Conclusions. Our study clarifies the relative importance of the gut, liver, and bile in the metabolism and excretion of quercetin and its conjugates. The pharmacokinetic model appears to be suitable for describing the absorption and disposition of the quercetin and its conjugates and may be applicable to other flavonoids that undergo similar pharmacokinetic pathways.