Kenjiro Koga

Application of pressure-controlled colon delivery capsule to oral administration of glycyrrhizin in dogs.

A colon delivery system has been used to improve the bioavailability of glycyrrhizin, a glycoside of glycyrrhetic acid. The bioavailability of glycyrrhizin is low when administered in conventional oral galenic dosage forms because glycyrrhizin is enzymatically hydrolysed both in the stomach and in the intestine. It was reasoned that if large amounts of glycyrrhizin were directly delivered to the colon, enzymatic activity should be reduced due to saturation so that intact glycyrrhizin could be absorbed into the systemic circulation. Based on this assumption, pressure‐controlled colon delivery capsules (PCDCs) were used as a colon delivery system. Eight types of glycyrrhizin solution were prepared and were introduced into PCDCs. After oral administration of the test PCDCs to beagle dogs, blood samples were obtained over 24 h and plasma glycyrrhizin concentrations were measured by an HPLC method. With PCDCs containing aqueous glycyrrhizin and propylene glycol solutions, plasma glycyrrhizin levels were extremely low and the bioavailabilities of glycyrrhizin were 0.6% and 0.4%, respectively. When Labrasol was added to both types of glycyrrhizin solution, the bioavailability was improved to 4.6 % for aqueous solution and 3.8% for propylene glycol solution. When a surfactant, Polysorbate 80, was added in combination with Labrasol, synergistic effects were not obtained. Furthermore, dose‐dependent effects of Polysorbate 80 were not obtained. Labrasol, which is a component of self‐emulsifying drug delivery systems (SEDDS), has been shown to strongly improve the bioavailability of glycyrrhizin from the colon.

Nano-sized water-in-oil-in-water emulsion enhances intestinal absorption of calcein, a high solubility and low permeability compound.

Our goal was to develop safe and stable multilayer emulsions capable of enhancing intestinal absorption of biopharmaceutics classification system (BCS) class III drugs. First, w/o emulsions were prepared using calcein as a model BCS class III compound and condensed ricinoleic acid tetraglycerin ester as a hydrophobic emulsifier. Then water-in-oil-in-water (w/o/w) emulsions were prepared with shirasu porous glass (SPG) membranes. Particle size analyses and calcein leakage from oil droplets in w/o/w emulsions led us to select stearic acid hexaglycerin esters (HS-11) and Gelucire 44/14 as hydrophilic emulsifiers. Analyses of the absorption-enhancing effects of w/o/w emulsions on intestinal calcein absorption in rats showed that calcein bioavailability after intraduodenal (i.d.) administration of HS-11 or Gelucire 44/14+polyvinyl alcohol (PVA) w/o/w emulsions prepared with 0.1-microm pore-sized SPGs was significantly higher than that of the calcein control. However, serum calcein concentration vs. time profiles after i.d. administration of w/o/w emulsions prepared with 1.1-microm and 30-microm pore-sized SPGs and an emulsion prepared with a calcein-containing outer water phase were comparable to control profiles. These results suggested that HS-11 or Gelucire 44/14+PVA are safe outer water phase additives and that 0.1-microm pore-sized SPGs are important for preparing w/o/w emulsions that enhanced intestinal calcein absorption.

In vitro and in situ evidence for the contribution of Labrasol® and Gelucire 44/14 on transport of cephalexin and cefoperazone by rat intestine

In vitro and in situ intestinal transport of beta-lactam antibiotics in the presence of two novel pharmaceutical excipients, caprylocaproyl and lauroyl macrogolglycerides (Labrasol and Gelucire 44/14), is described. The objective was to compare the effects of both macrogolglycerides on the intestinal transport of cephalexin, a substrate of oligopeptide transporters, and cefoperazone, a non-substrate of them. The in vitro transport studies were performed using a sheet of rat jejunum mounted in Ussing-type diffusion chambers. The in situ studies used an isolated internal loop model in the rat. Labrasol and Gelucire 44/14 were used as the excipients at low concentrations (0.01-0.5%, w/v). The membrane permeability of both drugs was compared by apparent permeability coefficients (P(app)) determined from changes in the amount of permeation vs. time in in vitro studies and by apparent absorptive clearance (CL(app)) determined from changes in the steady state drug concentration of perfusate in in situ studies. The P(app) value of cephalexin increased with an increase in the concentration of Labrasol (0.05-0.5%) compared to the value without Labrasol. The enhancing effect of Labrasol on cephalexin transport was similarly observed in in situ studies, and when 0.5% Labrasol was used in the presence of glycyl-L-leucine or L-alanyl-L-alanine, 60 or 46% enhancement of the active transport of cephalexin by Labrasol was obtained. On the other hand, Gelucire 44/14 did not affect the P(app) and CL(app) of either drug. The different effects of the excipients on cephalexin transport were thought to be due to the influences of size parameters such as a polydispersity index and particle size, and the change in the short-circuit current of jejunum by the addition of the excipient.

Pharmacokinetics of glycyrrhizin in normal and albumin‐deficient rats

The pharmacokinetics of glycyrrhizin (GZ) was compared in albumin‐deficient rats (NAR) and normal rats (SDR) after intravenous administration. The study sought to clarify the relationship between GZ concentration and its elimination rate in serum, liver and bile when the serum protein binding of GZ decreased. Serum protein binding in SDR and NAR, respectively, was 99.7% and 68.2% for a GZ concentration of 2.5 µg/ml. At steady‐state conditions after i.v. infusion of GZ (0.5–2.0 mg/h), the relationship between the GZ concentration in serum and liver was linear in the SDR but nonlinear in the NAR. For both NAR and SDR, the GZ liver level and the elimination rate was nonlinear, indicating that the elimination of GZ from liver into bile was the rate‐limiting step regardless of serum protein binding, and that the liver GZ level was extremely high when serum protein binding was decreased. It is concluded that a typical dose of GZ in chronic hepatitis patients whose serum albumin level is low will not cause a decrease of therapeutic effect compared with patients with a normal serum albumin level. Copyright

Determination of 18α-glycyrrhizin and 18β-glycyrrhizin in dog plasma by high-performance liquid chromatography

Abstract A high-performance liquid chromatographic method has been developed for the separation and determination of 18α-glycyrrhizin (α-GZ) and 18β-glycyrrhizin (β-GZ) in dog plasma. The two compounds were separated on a reversed-phase column and detected by UV absorption at 254 nm. The mobile phase was a mixture of water–methanol–60% perchloric acid (45:55:0.5, v/v) and was adjusted to pH 8.0 with 25% ammonia solution. Indomethacin was added to the plasma as an internal standard. Methanol was selected for the extraction of both the compounds and internal standard. α-GZ and β-GZ could be precisely determined in concentration of 1 mg/ml in a 0.1 ml sample.

Antitumour effects and pharmacokinetics of combination of vinblastine with a staurosporine derivative, NA-382, in P388/ADR-bearing mice.

The effects of a staurosporine derivative, N‐ethoxycarbonyl‐7‐oxostaurosporine (NA‐382), on the pharmacokinetics of vinblastine were evaluated, compared with those of verapamil, in multidrug‐resistant P388/ADR‐bearing mice.

Saturable function of P-glycoprotein as a drug-efflux pump in multidrug-resistant tumour cells.

P‐glycoprotein acts as an active drug‐efflux pump in multidrug‐resistant tumour cells. We studied the capacity of P‐glycoprotein to extrude drugs from the cells.

Intestinal absorption and biliary elimination of glycyrrhizic acid diethyl ester in rats.

Background The purpose of this study was to evaluate absorption and elimination from the gastrointestinal tract of glycyrrhizic acid diethyl ester (GZ-DE) which was prepared as a prodrug of glycyrrhizic acid (a poorly absorbed compound) in rats. Methods After the GZ-DE solution was administered via the intravenous, intraduodenal, intraileal, and stomach routes, GZ-DE and GZ concentrations in bile were determined by high-performance liquid chromatography. The stability of GZ-DE was estimated from residual GZ-DE and GZ produced in GZ-DE solutions prepared with distilled water, a pH 1.2 solution, 0.9% NaCl solution, and phosphate-buffered solution (pH 7.4) at 37°C. Results GZ-DE was eliminated into bile by the pharmacokinetic parameters of apparent distribution rate constant (4.56 ± 0.36 per hour) and apparent elimination rate constant (0.245 ± 0.042 per hour). After intravenous and intraduodenal administration of GZ-DE, the concentration ratio of GZ-DE to GZ in bile was approximately 4:1, and the bioavailability of GZ containing GZ-DE was three-fold higher compared with the bioavailability of GZ after intraduodenal administration. GZ-DE was immediately precipitated in pH 1.2 solution and was converted to GZ by hydrolysis in pH 7.4 solution. Conclusion Improvement of intestinal absorption of GZ was made possible by administration of GZ-DE into the intestine where absorption of GZ is lower than in the strong acidic environment of the stomach. However, because the elimination rate in bile simulated from kinetic parameters of GZ-DE was higher than the conversion rate from GZ-DE to GZ by hydrolysis, it is thought that the availability of GZ as a revolutionary prodrug was not high from the viewpoint of bioavailability of GZ in the liver by intestinal administration of GZ-DE.

Comparative study for pharmaceutical quality among bland-name drug and generic drugs of compound glycyrrhizin injections in China

The physicochemical properties (pH and osmolarity), ingredients, and impurities containing in compound glycyrrhizin injections (eight items) marketed in China were compared with those in bland-name drug (Stronger Neo-Minophagen C injection). Glycyrrhizin (GZ), glycine (Gly), and l-cysteine (CysH) as the ingredients, moreover, glycyrrhetinic acid (GA), 3-monoglucuronyl-glycyrrhetinic acid (MGGA), and l-cystine (CysS) as the impurity were determined by HPLC. The pH and osmolarity were different every each pharmaceutical product, but the variation between batch was very small. On the other hand, although the contents of GZ, Gly, and CysH in bland-name drug were approximately 100% of the label claim, the contents of GZ in generic drugs were the range of 91.8-100.9%, indicating the GZ contents in four products were clearly less than value indicated in label (<97%). The remarkable difference was not accepted by impurities content such as GA and MGGA. The contents of CysH in generic drugs were the range of 79.9-100.4%, and CysS was determined in all generic drugs, suggesting that CysH may decompose to be CysS depending on the pH of injections in generic drug only. Because the variation of the ingredient content was big and products with a little quantity for the ingredients were recognized, establishment of the preparation that can maintain the prescribed ingredient content and the severity of the assay will be required.

Approach to enhancing the distribution of glycyrrhizin in the liver: intravenous infusion studies in a rat model of bile duct ligation

We adopted a pharmaceutical approach to enhancing the distribution of glycyrrhizin (GZ) in the liver based on continuous administration of GZ for chronic hepatitis therapy. The present study characterizes the changes in GZ concentration in serum, bile, and liver under steady-state conditions after drip GZ infusion (0.5-2.0 mg/ml/h) in rats with bile duct fistulas. Eight hours after infusion, approximately 90% of GZ was excreted into bile as an intact compound regardless of the GZ dose tested. We observed a non-linear relationship between steady-state serum GZ concentrations and GZ dose (i.e. serum GZ concentrations abruptly increased with increasing GZ dose). GZ concentrations in the liver 8 h after infusion paralleled those in serum under steady-state conditions, but did not parallel those in bile. These results led us to conclude that under our experimental conditions transport activity responsible for the excretion of GZ to bile was in a rate-limiting step compared to that responsible for the uptake of GZ by hepatocytes. We therefore predicted that GZ concentration in the liver will increase with obstructing an efflux transport system such as canalicular multi-specific organic anion transporters. Probenecid among inhibitors or substrates for efflux transporters significantly enhanced the liver GZ concentration in the infusion studies. In conclusion, the concomitant administration of probenecid would be useful for liver protection therapy under continuous injection of the limited amount of GZ.