Context: Relinqing granules (RLQ) are being used alone or in combination with antibacterial drugs to treat urological disorders.
Objective: This study investigates the pharmacokinetics of RLQ in humans and the potential for RLQ-perpetrated interactions on transporters.
Materials and methods: Twelve healthy subjects (six women and six men) participated to compare single- and multiple-dose pharmacokinetics of RLQ. In the single-dose study, all 12 subjects received 8 g of RLQ orally. After a 7-d washout period, the subjects received 8 g of RLQ for seven consecutive days (t.i.d.) and then a single dose. Gallic acid (GA) and protocatechuic acid (PCA) in plasma and urine samples were analysed using LC-MS/MS. The transfected cells were used to study the inhibitory effect of GA (50-5000 μg/L) and PCA (10-1000 μg/L) on transporters OAT1, OAT3, OCT2, OATP1B1, P-gp and BCRP.
Results: GA and PCA were absorbed into the blood within 1 h after administration and rapidly eliminated with a half-life of less than 2 h. The mean peak concentrations of GA (102 and 176 μg/L) and PCA (4.54 and 7.58 μg/L) were lower in males than females, respectively. The 24 h urine recovery rates of GA and PCA were about 10% and 5%, respectively. The steady-state was reached in 7 d without accumulation. GA was a potent inhibitor of OAT1 (IC50 = 3.73 μM) and OAT3 (IC50 = 29.41 μM), but not OCT2, OATP1B1, P-gp or BCRP.
Discussion and conclusions: GA and PCA are recommended as PK-markers in RLQ-related pharmacokinetic and drug interaction studies. We should pay more attention to the potential for RLQ-perpetrated interactions on transporters.
Keywords: Chinese patent medicine; Herb-drug interactions (HDI); organic anion transporter; pharmacokinetic markers (PK-markers).