Effect of single-dose and short-term administration of quercetin on the pharmacokinetics of talinolol in humans - Implications for the evaluation of transporter-mediated flavonoid-drug interactions.

Quercetin has been shown to inhibit intestinal P-glycoprotein-mediated drug efflux. A crossover clinical study was performed in 10 healthy volunteers to assess the effect of single-dose and repeated quercetin intake on the pharmacokinetics of talinolol, a substrate of intestinal P-glycoprotein. Unexpectedly, mean area under the plasma concentration-time curve (AUC0-48h) and maximal plasma concentration (cmax) were slightly decreased following concomitant and short-term quercetin administration (3186.0 versus 2468.3 and 2527.7 ng h/ml, p>0.05; 309.7 versus 212.0 and 280.6 ng/ml, p>0.05). Individual analysis revealed that talinolol AUC0-48h was lowered by 23.9% up to 60.6% in 5 subjects and cmax was decreased by 29.2% up to 78.7% in 7 subjects after quercetin co-administration. These effects were less pronounced following repeated quercetin intake. Overlapping modification of efflux and uptake transport involving carrier proteins of the OATP superfamily as well as site-dependent interaction are possible explanations for these observations. In conclusion, clinically relevant quercetin-drug interaction cannot be ruled out.