Bioavailability of glycyrrhizin and licorice extract in rat and human plasma as detected by a HPLC method.

The pharmacokinetic behaviour of glycyrrhizin (1) was investigated in order to evaluate the difference in bioavailability after oral administration of licorice extract (LE) or glycyrrhizin (1) to rats and humans. For this study, two reliable HPLC methods were developed for the dosage of the levels of 1 and of its metabolite, the glycyrrhetic acid (2) in plasma samples. The determinations were carried out by HPLC on a reversed phase column with UV detector (251 nm), after a careful extraction step of 1 and 2 from the biological matrix. These methods afford good accuracy and satisfactory precision and they allow the determination of both compounds at levels as low as 200 ng/ml. The analytical results improved the knowledge of 1 pharmacokinetics, showing a significantly reduced bioavailability, when administered as LE compared to 1 when administered as such.