Contra-Indications | Safety in pregnancy and breastfeeding has not been established. Cyclosporin: Quercetin may increase plasma levels and prolong the half-life of cyclosporin. Cytochrome P450 2C8, 2C9, 2D6, 3A4: Preliminary evidence indicates that quercetin may inhibit these enzymes and this may lead to reduced elimination and higher plasma levels of medicines metabolised by these substrates. Some medicines that could be affected include: amiodarone, docetaxel, tretinoins, repaglinide, verapamil, celecoxib, diclofenac, fluvastatin, glipizide, ibuprofen, irbesartan, losartan, phenytoin, piroxicam, tamoxifen, tolbutamide, torsemide, warfarin, amitriptyline, codeine, flecainide, haloperidol, imipramine, metoprolol, ondansetron, paroxetine, risperidone, tramadol, venlafaxine, calcium channel blockers, chemotherapeutic agents antifungals, glucocorticoids, alfentanil, fentanyl, losartan, fluoxetine, midazolam, omeprazole, lansoprazole, propranolol, fexofenadine, amitriptyline, amiodarone, citalopram, sertraline and numerous others. P-glycoprotein substrates: There is preliminary evidence that quercetin inhibits the gastrointestinal P-glycoprotein efflux pump. This may increase the bioavailability and the serum levels of medicines transported by the pump. Medicines transported by the pump include: paclitaxel, diltiazem, cyclosporine, saquinavir, digoxin, chemotherapeutic agents (etoposide, vinblastine, vincristine, vindesine), antifungals (ketoconazole, itraconazole), protease inhibitors (amprenavir, indinavir, nelfinavir), H2 antagonists (cimetidine, ranitidine), verapamil, corticosteroids, erythromycin, fexofenadine, loperamide, quinidine, and others. Quinolone antibiotics: Quercetin might competitively inhibit quinolone antibiotics by binding to the DNA gyrase site on bacteria. Quinolone antibiotics include: ciprofloxacin, levofloxacin, ofloxacin, moxifloxacin, gatifloxacin and others. |