Pharmacokinetics of gallic acid and its relative bioavailability from tea in healthy humans

Gallic acid (GA), a food component that is especially abundant in tea, is an antimutagenic, anticarcinogenic and anti-inflammatory agent. We conducted a study using acidum gallicum tablets that contained 10% GA and 90% glucose and a black tea brew that contained 93% of its GA in free form to determine the pharmacokinetics and relative bioavailability of GA in healthy humans. After the administration of a single oral dose of acidum gallicum tablets or tea (each containing 0.3 mmol GA) to 10 volunteers, plasma and urine samples were collected over various time intervals. Concentrations of GA and its metabolite, 4-O-methylgallic acid (4OMGA), were determined, and the pharmacokinetic parameters were calculated. GA from both the tablets and tea was rapidly absorbed and eliminated with mean half-lives of 1.19 ± 0.07 and 1.06 ± 0.06 h and mean maximum concentrations of 1.83 ± 0.16 and 2.09 ± 0.22 μmol/L (plasma), respectively. After oral administration of the tablets and black tea, 36.4 ± 4.5 and 39.6 ± 5.1% of the GA dose were extracted in urine as GA and 4OMGA, respectively. The relative bioavailability of GA from tea compared with that from the tablets was 1.06 ± 0.26, showing that GA is as available from drinking tea as it is from swallowing tablets of GA.