Effects of quercetin on the bioavailability of doxorubicin in rats: role of CYP3A4 and P-gp inhibition by quercetin

This rat study tested whether quercetin, a flavonoid closely related to fisetin, changes how much of the chemotherapy drug doxorubicin gets absorbed into the bloodstream. Quercetin inhibited two things doxorubicin depends on for normal clearance — an enzyme called CYP3A4 and a transporter called P-glycoprotein — and this raised oral doxorubicin levels substantially, by roughly 30% to more than double depending on the dose. Doxorubicin given directly into a vein was not affected, showing this is specifically an absorption effect. It is not a fisetin study, but it illustrates that this class of flavonoid can meaningfully change how much of a co-administered drug reaches the bloodstream — relevant context for thinking about fisetin and CYP3A4-metabolised medications, even though fisetin itself has not been tested this way.