The pharmacological mechanism of quercetin as adjuvant therapy of COVID-19

oral supplements such as zinc, vitamin C, vitamin D, folic acid [5] , and flavonoids such as quercetin, as adjuvant pharmacotherapy in the management of . Quercetin (3, 3', 4', 5, 7-pentahydroxyfl avone) (C15H10O7) is a major polyphenol that belongs to the fl avonoid family. It is categorized as fl avonol, one of the six subclasses of fl avonoid compounds. Being the most abundant form of flavonoid molecules, quercetins are ubiquitously distributed in a variety of dietary plants, including apple, berries, onion, kale, tea, tomato, grape, as well as nuts. Furthermore, it is also aff ordably marketed in the form of tablet dietary supplements. Various in vitro and animal model studies have shown that quercetin has numerous physiological eff ects, including antioxidant, anti-infl ammatory, immunomodulatory, and antiviral properties. There is well-documented evidence pointing toward its eff ects in attenuating lipid peroxidation, platelet aggregation, and capillary permeability, which cumulatively result in cardioprotective eff ects, as well as anti-carcinogenic properties [7] . Too few human studies address the effectiveness of quercetin, specifically in the management of viral respiratory infection. Notwithstanding, some human studies have provided signifi cant results in specifi c populations with non-infectious causes of respiratory disease [8] [9] [10] [11] . Current evidence shows the specific pathomechanics of COVID-19-associated acute respiratory distress syndrome (CARDS), which include severe inflammation and pulmonary edema leading to impaired alveolar homeostasis, and alteration of lung physiology, and resulting in lung fi brosis, infl ammation of endothelium, vascular thrombosis, as well as an exaggerated immune response [12] . during the writing of this review [2] . Ergo, scientists and researchers are racing the clock and breaking records to develop COVID-19 vaccines and repurpose several therapeutic options to treat mild to severe COVID-19. Recently, albeit several trials that are underway to produce safe and effective vaccines, in conjunction with its distribution, over 4.9 million vaccine doses have been administered worldwide and obtained emergency use authorization by The United States food and drug administration (FDA) [2] . However, an approach called drug repurposed under ACTIV-6 protocol has been created by the national institute of health (NIH) to explore a pool of up to seven drugs approved by the FDA for other diseases, particularly antiviral drug remdesivir, the anti-infl ammatory baricitinib, and corticosteroid (e.g. dexamethasone) for treating mild to moderate 4] . Furthermore, there have been numerous ongoing trials evaluating