Archive for category Quercetin'

Quercetin: Practice Points – Patient Counselling. FAQ

Quercetin is a flavonol belonging to a group of polyphenolic substances known as flavonoids or bioflavonoids and is found in many fruits, vegetables and some herbal medicines. • According to experimental studies, it has antioxidant, anti-inflammatory, antiviral, mast cell stabilisation, neuroprotective, gastroprotective, hepatoprotectiveand possibly cardioprotective actions. • In practice, it is used for respiratory allergies such as hayfever, as an adjunct in asthma management, preventing diabetic complications such as cataracts and symptom relief in prostatitis; however, large controlled studies are not available to determine its effectiveness. • Numerous drug interactions are theoretically possible, mainly due to P-glycoprotein and CYP inhibition. • Quercetin is generally well tolerated. Adverse effects may include nausea, dyspnoea, headache and mild tingling of the extremities Answers to Patients’ Frequently Asked Questions What will this supplement do for me? Quercetin has several pharmacological effects and may provide some symptom relief in allergic conditions and prostatitis, and be beneficial in diabetes and cardiovascular disease; however, further research is required to clarify Read more […]

Quercetin: Significant Interactions. Pregnancy Use.

Adverse Reactions Quercetin is generally well tolerated and appears to be associated with little toxicity when administered orally or intravenously. Adverse effects may include nausea, dyspnoea, headache and mild tingling of the extremities. Significant Interactions Possible modulation of P-glycoprotein and inhibition of CYP1A1, CYP1A2 and CYP 3A4 activity should be considered when prescribing. CISPLATIN Quercetin pretreatment may sensitise human cervix carcinoma cells to cisplatin-induced apoptosis — beneficial interaction theoretically possible under professional supervision. CYCLOSPORIN Animal studies demonstrate that coadministration of quercetin significantly decreases the oral bioavailability of cyclosporin — avoid concurrent use. DIGOXIN An increase in drug bioavailability is theoretically possible and has been observed in an in vivo study. Although human studies at lower doses are not available, the narrow therapeutic range of digoxin and the serious nature of the interaction should not be underestimated. Avoid concurrent use. DILTIAZEM Pretreatment of rabbits with quercetin resulted in an increased bioavailability of the calcium channel blocker, diltiazem, which may be the result of inhibition Read more […]

Quercetin: Clinical Use. Dosage

ALLERGIES Quercetin is used in the treatment of acute and chronic allergic symptoms, such as hayfever and chronic rhinitis. The anti-inflammatory activity of quercetin and its ability to stabilise mast cells, neutrophils and basophils and inhibit histamine release provides a rationale for its use in these indications. In a study of 123 patients sensitised to house dust mite and displaying nasal symptoms of mild to severe perennial allergic rhinitis, nasal scrapings were taken and histamine release measured as a percentage of the total content in the specimen. Antigen exposure resulted in an increase in mast cells of the epithelial layer of the nasal mucosa resulting in nasal hypersensitivity. Quercetin inhibited histamine release by 46-96% in a dose-dependent manner. Large-scale human trials are required to fully elucidate the potential for quercetin to inhibit allergic symptoms caused by the release of histamine. ASTHMA Quercetin has also been used as an adjunct in the management of asthma, often in combination with vitamin C because of its anti-allergic activity and ability to inhibit leukotriene synthesis. Controlled studies are still required to determine its effectiveness. PREVENTING DIABETIC COMPLICATIONS As Read more […]

Quercetin: Background. Actions

Background and Relevant Pharmacokinetics Quercetin is a flavonol belonging to a group of polyphenolic substances known as flavonoids or bioflavonoids. The first flavonoids were identified in 1936 by Albert Szent-Györgyi, who was awarded the Nobel Prize for his discovery of vitamin C. Studies on the absorption, bioavailability, and metabolism of quercetin after oral intake in humans have produced contradictory results. The nature of quercetin metabolites in plasma is currently unclear and requires further elucidation, which may in part explain these inconsistencies. There appears to be marked individual variation in absorption rates ranging from 0% to over 50%. Factors that may improve bioavailability include: gender (especially females taking oral contraceptives), gastrointestinal flora, and concurrent intake of bromelain and papain. Absorption from onions is three times that of apples and twice that of black tea. The main determinant for the absorption of quercetin conjugates is the nature of the sugar moiety. Glucose-bound glycosides (quercertin glucosides) are effectively absorbed from the small intestine because the cells possess glucoside-hydrolysing activity and their glucose transport system is capable Read more […]