Influence of co-administered antibiotics on the pharmacokinetic fate in rats of paeoniflorin and its active metabolite paeonimetabolin-I from Shaoyao-Gancao-tang.

The effects of orally co-administered antibiotics on the pharmacokinetics of paeoniflorin (PF) and paeonimetabolin-I (PM-I), a bioactive metabolite derived from PF by intestinal bacteria, from the traditional Chinese formulation, Shaoyao-Gancao-tang (SGT), were investigated in rats to clarify the effect of administering SGT together with some synthetic drugs. Co-administration of the antibiotics amoxicillin and metronidazole (AMPC-MET) significantly increased the area under the plasma concentration versus time curve (AUC) of PF, whereas it markedly decreased that of PM-I, to 2.6% of the normal AUC by administration of a single dose, and less than 1% by a 3-day pretreatment. Similar effects were observed using the combination of ofloxacin with SGT. The PF-metabolizing activity of intestinal bacteria was reduced to 16% and 33% of normal levels by treatment with AMPC-MET and ofloxacin, respectively, which caused alterations of that degree in the extent of absorption of PF and PM-I, but did not affect their rate of absorption or elimination. The present study suggests that it may not be appropriate to use SGT simultaneously with antibiotics such as AMPC-MET or ofloxacin, and also reveals the important role of intestinal bacteria in the pharmacokinetics of the active components of this traditional Chinese formulation.