Favourable drug-lead pharmacokinetic features for designing gallic acid-standardized Syzygium polyanthum aqueous extract-based product

In this study, Syzygium polyanthum was standardized against gallic acid (GA), and a complete pharmacokinetic test was conducted using in vitro and in vivo models against this phytochemical. High-performance liquid chromatography showed that GA is a major phytochemical in aqueous extract of S. polyanthum. It exhibited a low equilibrium solubility and physiochemical stability at pH 2.0 and 7.4, but it deteriorated rapidly at pH 9.2. It showed low permeability toward Caco-2 intestinal absorption with eight times slower absorption in oral than intravenous administration. GA was unstable in mouse, rat, and dog plasma sera with in vitro half-lives (t1/2) of 60, 53, and 56 min, respectively, but was relatively stable in human plasma serum (t1/2 = 185 min). Approximately 5.6% of GA (10 µM) bound to the human plasma proteins. GA was stable in mouse, rat, dog, and human microsomal extracts with in vitro microsomal intrinsic clearance values of 72, 68, 6, and 22 µL/min/mg, respectively. GA selectively inhibited or stimulated the activity of the tested CYP450 enzymes. The in vivo oral bioavailability of GA was 54%, with short elimination half-life and a high volume of distribution. Thus, the mention pharmacokinetic features of GA must be considered during the development of GA-based products to yield the optimum dosage and pharmacological effect.