Da-Chaihu-Tang alters the pharmacokinetics of nifedipine in rats and a treatment regimen to avoid this.

OBJECTIVES: To investigate the influence of co-administrated Da-Chaihu-Tang (DCT; a traditional Chinese formulation) on the pharmacokinetics of nifedipine, as well as the safe optimal dosing interval to avoid the adverse interactions. METHODS: A single dose of DCT was administered with nifedipine simultaneously, 2 h before, 30 min before or 30 min after nifedipine administration. Pharmacokinetics of nifedipine with or without DCT were compared. The influences of DCT on nifedipine intestinal mucosal and hepatic metabolism were studied by using rat in-vitro everted jejunal sac model and hepatic microsomes. KEY FINDINGS: A simultaneous co-administration of DCT significantly increased the area under concentration-time curve from time zero to infinity (AUC0-inf ) of nifedipine. In-vitro mechanism investigations revealed that DCT inhibited both the intestinal and the hepatic metabolism of nifedipine. Further study on the optimal dosing interval for nifedipine and DCT revealed that administration of DCT 30 min before or after nifedipine did not significantly change the AUC of nifedipine. CONCLUSIONS: The bioavailability of nifedipine is significantly increased by a simultaneous oral co-administration of DCT. This increase is caused by the inhibitory effect of DCT on both the intestinal mucosal and the hepatic metabolism of nifedipine. The dose interval between DCT and nifedipine needs to be set for over 30 min to avoid such drug-drug interactions.

Baicalein 6-O-ß-D-glucopyranuronoside is a main metabolite in the plasma after oral administration of baicalin, a flavone glucuronide of scutellariae radix, to rats.

Baicalin (BG) and its aglycone, baicalein (B) are strong antioxidants that exert various pharmacological actions and show unique metabolic fates in the rat. The aim of the present study was to identify major metabolite(s) besides BG in rat plasma after oral administration of BG or B. The main metabolite was detected by HPLC equipped with an electrochemical detector at a potential of +500 mV and identified as baicalein 6-O-ß-D-glucopyranuronoside (B6G) by HPLC/MS/MS. When BG at a dose of 20 mg/kg was administered orally to Wistar rats, the level of B6G in plasma was higher than that of BG. Cmax and the area under the concentration-curve from 0 to 24 h (AUC0-24 h) values of the plasma B6G were 1.66 ± 0.34 µM and 19.8 3.9 ± µM · h, respectively, whereas those of BG were 0.853 ± 0.065 µM and 10.0 ± 3.1 µM · h, respectively. When B was administered, similar results were also obtained. B6G-producing activities from B were found in microsomes of both rat jejunum and liver, in spite of the low activity. Rat everted jejunal sacs formed B6G after application of B, but only in a small amount that was excreted into the mucosal side, and not the serosal side, indicating little contribution to the appearance of B6G in plasma. On the other hand, when B was injected into the rat portal vein, B6G was detected at a higher level than BG in the systemic circulation, demonstrating the hepatic contribution to the appearance of plasma B6G.

Antispasmodic activity of licochalcone A, a species-specific ingredient of Glycyrrhiza inflata roots.

Licochalcone A, a species-specific and characteristic retrochalcone ingredient of Glycyrrhiza inflata root, has been shown to possess multiple bioactive properties. However, its muscle relaxant activity has not been reported previously. Licochalcone A showed a concentration-dependent relaxant effect on the contraction induced by carbachol (50% effective concentration (EC50) = 5.64 +/- 1.61 microM), KCl (EC50 5.12 +/- 1.68 microM), BaCl2 (EC50 1.97 +/- 0.48 microM) and A23187 (EC50 2.63 +/- 2.05 microM). Pretreatment with licochalcone A enhanced the relaxant effect of forskolin, an adenylyl cyclase activator, on the contraction in a similar manner to 3-isobutyl-1-methylxanthine (IBMX), a phosphodiesterase (PDE) inhibitor. Furthermore, the IC50 (22.1 +/- 10.9 microM) of licochalcone A against cAMP PDE was similar to that of IBMX (26.2 +/- 7.4 microM). These results indicated that licochalcone A may have been responsible for the relaxant activity of G. inflata root and acted through the inhibition of cAMP PDE.

Isoliquiritigenin, one of the antispasmodic principles of Glycyrrhiza ularensis roots, acts in the lower part of intestine.

Glycyrrhizae radix is used to treat abdominal pain as a component of shakuyakukanzoto (shaoyao-gancao-tang), a traditional Chinese medicine formulation. Previously, we have reported the isolation of glycycoumarin as a potent antispasmodic with an IC50 value of 2.93+/-0.94 microM for carbamylcholine (CCh)-induced contraction of mouse jejunum from an aqueous extract of Glycyrrhizae radix (licorice), and clarified that its mechanism of action involves inhibition of phosphodiesterase 3. The purpose of the present study was to examine an antispasmodic principle of licorice other than glycycoumarin. Isoliquiritigenin was isolated from an aqueous extract of licorice as a potent relaxant, which inhibited the contraction induced by various types of stimulants, such as CCh, KCl, and BaCl2 with IC50 values of 4.96+/-1.97 microM, 4.03+/-1.34 microM and 3.70+/-0.58 microM, respectively, which are close to those of papaverine. However, the amount of isoliquiritigenin in the aqueous extract of licorice was very small. When the aqueous licorice extract was treated with naringinase, the amounts of glycosides such as isoliquiritin, which were abundant but had much less potent relaxant activity, were decreased while isoliquiritigenin was increased. At the time, the relaxant activity of the treated sample was increased significantly, shifting the IC50 from 358+/-104 to 150+/-38 microg/ml for CCh-induced contraction. Isoliquiritigenin also showed the most potent inhibition of mouse rectal contraction induced by CCh with an IC50 value of 1.70+/-0.07 microM. These results suggest that isoliquiritigenin acts as a potent relaxant in the lower part of the intestine by transformation from its glycosides.

Interaction between Shaoyao-Gancao-Tang and a laxative with respect to alteration of paeoniflorin metabolism by intestinal bacteria in rats.

Shaoyao-Gancao-Tang (SGT), a traditional Chinese herbal medicine (Kampo formulation) containing Shaoyao (Paeoniae Radix) and Gancao (Glycyrrhizae Radix), is co-administered with laxative sodium picosulfate as a premedication for relieving the pain accompanying colonoscopy. Paeoniflorin (PF), an active glycoside of SGT, is metabolized into the antispasmodic agent paeonimetabolin-I (PM-I) by intestinal bacteria after oral administration. The objective of the present study was to investigate whether the co-administered laxative (sodium picosulfate) influences the metabolism of PF to PM-I by intestinal bacteria. We found that the PF-metabolizing activity of intestinal bacteria in rat feces was significantly reduced to approximately 34% of initial levels by a single sodium picosulfate pretreatment and took approximately 6 days to recover. Repeated administration of SGT after the sodium picosulfate pretreatment significantly shortened the recovery period to around 2 days. Similar results were also observed for plasma PM-I concentration. Since PM-I has muscle relaxant activity, the present results suggest that repetitive administration of SGT after sodium picosulfate pretreatment might be useful to relieve the pain associated with colonoscopy.

Glycycoumarin from Glycyrrhizae Radix acts as a potent antispasmodic through inhibition of phosphodiesterase 3.

Glycyrrhizae Radix is used to treat abdominal pain as a component of Shakuyaku-kanzo-to, a traditional Chinese medicine formulation. We aim at clarifying the antispasmodic principles of Glycyrrhizae Radix, and consequently isolated glycycoumarin as a potent relaxant on the carbamylcholine (CCh)-induced contraction of mouse jejunum. In this paper we investigated the effects and the action mechanism of glycycoumarin on the contraction of mouse jejunum. Glycycoumarin inhibited the contraction induced by various types of stimulants, such as CCh, KCl, BaCl(2), and A23187 (calcium ionophore III) with IC(50) values of 2.93+/-0.94 micromol/l (1.08+/-0.35 microg/ml), 2.59+/-0.58 micromol/l (0.95+/-0.29 microg/ml), 4.09+/-1.82 micromol/l (1.51+/-0.67 microg/ml) and 7.39+/-5.19 micromol/l (2.72+/-1.91 microg/ml), respectively, with a potency similar to that of papaverine (a representative antispasmodic for smooth muscle). Furthermore, pretreatment with glycycoumarin enhanced the relaxation induced by forskolin on CCh-evoked contraction, similar to that by pretreatment with IBMX, a non-specific inhibitor of phosphodiesterases (PDEs). Pretreatment with glycycoumarin also enhanced the relaxation effect of rolipram, a specific inhibitor of PDE isozyme 4, as pretreatment with milrinone, a specific inhibitor of isozyme 3, did. Moreover, the effect of glycycoumarin was associated with dose-dependent accumulation of cAMP, but not cGMP, in mouse jejunum. These results indicate that glycycoumarin has an inhibitory effect on smooth muscle contraction induced by various types of stimulants through the inhibition of PDEs, especially isozyme 3, followed by the accumulation of intracellular cAMP.

Bioavailability of glycyrrhizin from Shaoyao-Gancao-Tang in laxative-treated rats.

Shaoyao-Gancao-Tang (SGT), a traditional Chinese formulation composed of Shaoyao (Paeoniae Radix) and Gancao (Glycyrrhizae Radix), is frequently used in conjunction with laxatives such as sodium picosulfate in colonoscopy to relieve abdominal pains. We have investigated the alterations of the bioavailability of glycyrrhizin when SGT was co-administered with sodium picosulfate and we tried to identify a regimen that might minimize the alterations. Glycyrrhizin is one of the active glycosides in Gancao and SGT and is hydrolysed into the bioactive metabolite, 18 beta-glycyrrhetic acid (GA) by intestinal bacteria following oral administration. We found that the maximum plasma concentration (C(max)) and the area under the mean concentration vs time curve from zero to 24 h (AUC(0-24 h)) of GA from a single dose of SGT administered 5 h after a single pretreatment with sodium picosulfate were significantly reduced to 15% and 20% of the control level in rats, respectively. These reductions were still significant four days after sodium picosulfate pretreatment, but were restored by repetitive administration of SGT following sodium picosulfate pretreatment. Similar reductions and recovery were observed for the glycyrrhizin-metabolizing activity of intestinal bacteria in rat faeces. The results warrant clinical studies for co-administration of laxatives such as sodium picosulfate and SGT.

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.

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.

Repetitive administration of Shaoyao-Gancao-tang to rats restores the bioavailability of glycyrrhizin reduced by antibiotic treatment.

Shaoyao-Gancao-tang (SGT), a traditional Chinese formulation, is often used together with antibiotics such as amoxicillin and metronidazole (AMPC-MET) for the treatment of peptic ulcers in Japan. However, the bioavailability of glycyrrhizin (GL) in SGT is severely reduced by a single administration of AMPC-MET, and the reducing effect continues for 12 days. GL is one of the major pharmacologically important glycosides in SGT and is transformed into the active metabolite 18beta-glycyrrhetic acid (GA) by intestinal bacteria in the gut, followed by absorption of the latter into the blood. In order to reduce the negative effect of AMPC-MET on the bioavailability of GL, the optimum scheduling of the medications was examined. We found that the reduction in the plasma GA concentration and the GL-metabolizing activity in faeces caused by a single dose of AMPC-MET could be sharply attenuated by the repetitive administration of SGT for 4 days. The GA concentration and the GL-metabolizing activity were strongly enhanced by further continuous administration of SGT. These findings suggest that repetitive administration of SGT starting 1 or 2 days after the administration of AMPC-MET speeds the recovery of the bioavailability of GL in SGT. Similar strategies for administering medications may also be useful for combination therapy of antibiotics with other traditional Chinese formulations containing bioactive glycosides.

Development of a simple HPLC method for determination of paeoniflorin-metabolizing activity of intestinal bacteria in rat feces.

A simple and reproducible HPLC method for the determination of paeoniflorin (PF)-metabolizing activity of intestinal bacteria in rat feces was developed and validated. Orally administered PF, a major active constituent of Paeoniae Radix, is metabolized into a bioactive compound, paeonimetabolin I (PM-I) by intestinal bacteria. Direct determination of the PF-metabolizing rate into PM-I is hard to achieve by HPLC due to the lack of intense chromophore in PM-I. However, when PF was incubated with Lactobacillus brevis, an intestinal bacterium, in the presence of phenylmercaptan, the metabolizing rate of PF into 8-phenylthio-paeonimetabolin I (PT-PM-I) was found to be equivalent to that of PF into PM-I. Thus, the PF-metabolizing activity of intestinal bacteria in rat feces was determined by measuring the rate of biotransformation of PF into PT-PM-I, which was detected by HPLC at 255 nm. This method can be utilized in the biopharmaceutical study of traditional Chinese formulations containing Paeoniae Radix.