Effects of subacutely administered saiboku-to, an oriental herbal medicine, on pharmacodynamics and pharmacokinetics of diazepam in rodents

Restorative Effect of Repetitive Administration of Shaoyao-Gancao-tang on Bioavailability of Paeoniflorin Reduced by Antibacterial Synthetic Drugs Treatment in Rats

Paeoniflorin (PF) is an active glucoside in Shaoyao (peony root), and is transformed into an antispasmodic metabolite, paeonimetabolin-I (PM-I), by intestinal bacteria in the gut after oral administration of Shaoyao or Shaoyao-Gancao-tang (SGT, Shakuyaku-Kanzo-To in Japanese). SGT is a pain-relieving traditional Chinese formulation (Kampo-medicine in Japanese) and is often used together with antibacterial synthetic drugs, such as amoxicillin and metronidazole (AMPC-MET), in peptic ulcer therapy. Since the bioavailability of PF in SGT has been reported to be significantly reduced by co-administered antibacterial drugs, we investigated how to minimize this reducing effect of antibacterial treatment in the present study. We found that repetitive administration of SGT starting 24 h after AMPC-MET treatment rapidly restored the plasma PM-I concentration from SGT reduced by AMPC-MET, due to its restorative effect on the decreased PF-metabolizing activity of intestinal bacteria in rat feces. The present findings suggest that it may be clinically useful to administer SGT repetitively, starting 1 or 2 d after treatment with a mixture of AMPC-MET during their combination therapy, to accelerate the recovery of the reduced bioavailability of PF in SGT. Similar administration regimens may also be useful in other combination therapies involving traditional Chinese formulations and antibacterial synthetic drugs to ensure the efficacy of the bioactive glycosides in the formulations.

Potentiation by saiboku-to of diazepam-induced decreases in hippocampal and striatal acetylcholine release in rats

Effects of saiboku-to, a traditional oriental herbal medicine, on diazepam-induced changes in cerebral acetylcholine (ACh) were investigated in rat striatum and hippocampus. Diazepam (10 mg/kg, i.p.) increased tissue concentrations of the ACh in both regions. The increase was enhanced in rats subacutely treated with saiboku-to (2.0 g/kg, p.o., once a day) for 7 days. Diazepam also decreased release levels of ACh in both regions. The release levels were further decreased in saiboku-to-treated rats. On the other hand, no significant changes in ACh synthesizing and the hydrolyzing enzyme activities in either brain region were observed in saiboku-to-, diazepam- and combination-treated rats. These results suggest that not only is the diazepam-induced increase in tissue ACh due to the inhibition of ACh release but also that saiboku-to potentiates diazepam-induced inhibition of ACh release.