PHARMACOKINETICS AND ADVERSE EFFECTS OF DRUGS - MECHANISMS AND RISKS FACTOR

Abstract

Green tea reportedly possesses many health beneficial effects as a beverage. Its usage has even been elevated to therapeutic level for treatment of diseases, including cancer, after increasing the catechin constituents in green tea extract or through purified catechins compounds. However, the therapeutic effectiveness of green tea extract or catechin for mulae on different diseases is still questionable and inconsistent in reported studies. One reason is the low and variable bioavailability of catechins or unknown constituents in green tea extract. The plasma levels of total catechins are usually at submicromolar level which is well below the effective dose in many in vitro studies. Besides their variable chemical structures that cause heterogeneity of absorption, green tea catechins are subject to extensive metabolism by phase II process and catabolism by colonic microbes that result in complicated pharmacokinetics. It is essential to understand the factors affecting the pharmacokinetics and metabolic profiles in plasma and tissues based on animal and human studies before green tea catechins can be applied for therapeutic use. Keywords: green tea extract, catechins, pharmacokinetics, bioavailability, absorption, metabolism