Prediction of clinical bacteriological efficacy of oral antibiotics using a mechanism-based pharmacokinetic-pharmacodynamics modeling.

The objective of this study was to predict the clinical bacteriological efficacy of antibiotics and to examine the pharmacodynamics (PD) characteristics of antibiotics against bacterial strains using a mechanism-based pharmacokinetic-pharmacodynamics (PK-PD) modeling developed on the basis of interaction between drug concentrations and antibacterial activities. Dynamic PD parameters (epsilon, gamma, EC50) and growth rate of organisms (lambda) were obtained from in vitro time-kill profile data of oral antibiotics, tebipenem pivoxil (TBPM-PI) and cefditoren pivoxil (CDTR-PI) against Streptococcus pneumoniae or Haemophilus influenzae. PD characteristics of both drugs against S. pneumoniae or H. influenzae were examined, which indicated TBPM was concentration-dependent as well as time-dependent, and CDTR was mainly time-dependent to exhibit their bactericidal activities. Next, we simulated TBPM and CDTR concentrations in plasma after oral administration according to the dosage regimen of each drug specified in package insert, using population pharmacokinetic parameters of both drugs in pediatric patients with infections. In addition, changes in viable in vivo bacterial counts in humans were simulated using dynamic PD parameters and mean plasma concentrations of each drug. As a result, simulated profile of viable counts of S. pneumoniae and H. influenzae were well corresponding to the bacteriological efficacy results in clinical double-blinded comparative study of TBPM-PI and CDTR-PI in oral administration to pediatric patients with acute otitis media. As mentioned in the above, it was considered to be possible to clarify the PD characteristics of TBPM and CDTR against each bacterial strain using the mechanism-based PK-PD model developed on the basis of interaction between drug concentrations and antibacterial activities, and to estimate the clinical bacteriological efficacy of those drugs.

Population pharmacokinetics of cefditoren pivoxil in non-infected adults.

Population pharmacokinetic analysis was conducted on cefditoren pivoxil (CDTR-PI), a third generation oral antibiotic to evaluate the effect of covariates on pharmacokinetic parameters. Plasma concentrations of cefditoren (CDTR, total number of sampling points: 2864) obtained from healthy adult subjects, elderlies, and subjects with renal dysfunction (287 subjects) after CDTR-PI administration as well as demographic data of those subjects were used for analysis. We conducted the population pharmacokinetic analysis of CDTR-PI using a nonlinear mixed effects modeling (NONMEM) method. A one-compartment model with a first-order absorption and lag time fitted well to plasma concentration-time curve for CDTR. The subject covariate significantly affecting pharmacokinetic parameters of CDTR-PI was demonstrated by population pharmacokinetic analysis. The absorption rate constant (ka: hr(-1)) of CDTR-PI decreased with age, total clearance adjusted by bioavailability (CL/F: L/hr/kg) increased with increasing creatinine clearance adjusted by body weight (Ccr: mL/min/kg) and volume of distribution adjusted by bioavailability (Vd/F: L/kg) decreased with increasing body weight (WT: kg). In addition, the lag time (Tlag: hr) depends on formulation (tablet or granule) of CDTR-PI and the absorption lag time of the tablet was longer than that of the granule. We could obtain the population mean parameters of CDTR-PI together with interindividual variability and intraindividual residual variability after oral administration of CDTR-PI to adult subjects. In the future, this information will enable us to simulate the plasma concentrations of CDTR in subjects with various demographic backgrounds, which contributes to future examination of the efficacy and safety of CDTR-PI.

Population pharmacokinetic analysis of cefditoren pivoxil in pediatric patients with infection.

Population pharmacokinetic analysis was conducted on cefditoren pivoxil (CDTR-PI, Brand name: MEIACT, Meiji Seika Pharma Co., Ltd.), a third generation oral antibiotic, using plasma concentrations of cefditoren (CDTR, total number of sampling points: 578) obtained from pediatric patients (153 subjects, dose: 5.62 +/- 1.62 mg/kg) after CDTR-PI administration as well as demographic data of those subjects. NONMEM (Ver. VI LEVEL 2.0) was used as software. The first-order conditional estimation (FOCE) method without interaction was employed as algorithm. A one-compartment model with first-order absorption was used as a pharmacokinetic model. As the result of analysis, the following population pharmacokinetic parameters were obtained for CDTR. Population mean parameters: ka (hr(-1)) = 0.527, CL/F (L/hr/kg) = -0.474 x Scr + 0.82, Vd/F (L/kg) = 0.77, Tlag (hr) = 0.282 x (1+0.435 x NAT) (NAT: 0 = Japan, 1 = USA, interindividual variability: omega (ka) = 17.23%, omega (CL/F) = 33.02%, omega (Vd/F) = 86.66%, intraindividual residual variability: sigma = 0.428 microg/mL. Bayes estimation was carried out for each subject using the final model to calculate secondary parameters such as C(max), T(max), AUC, and t1/2. C(max) and AUC increased significantly with dose. However, T(max) was approximately 2hours and t1/2 was approximately 1 hour at any dose level, showing no significant dose-dependent changes. When CDTR-PI was administered orally to a child, a significant increase was noted in plasma CDTR concentrations, suggesting high efficacy. In addition, pharmacokinetics of CDTR were simulated in patients with renal impairment using the final model. As a result, a delay in T(max) and increases in AUC, C(max), and t1/2 were presumed with increased Scr, and the degrees of such increases were also quantitatively estimated. As mentioned above, the population pharmacokinetic parameters of CDTR were obtained, which is sure contribute to simulation of its plasma concentrations in patients with various backgrounds and to speculation of its efficacy and safety.

Intestinal absorption mechanism of tebipenem pivoxil, a novel oral carbapenem: involvement of human OATP family in apical membrane transport.

Tebipenem pivoxil (TBPM-PI) is an oral carbapenem antibiotic for treating otolaryngologic and respiratory infections in pediatric patients. This agent is a prodrug to improve intestinal absorption of TBPM, an active form, and an absorption rate of TBPM-PI is higher than those of other prodrug-type ß-lactam antibiotics. In the present study, we hypothesized that a certain mechanism other than simple diffusion is involved in the process of improved intestinal absorption of TBPM-PI and examined the mechanism. TBPM-PI uptake by Caco-2 cells was decreased by ATP-depletion and lowering the temperature to 4 °C, suggesting the contribution of carrier-mediated transport mechanisms. This uptake was partially decreased by ACE inhibitors, and the reduction of the absorption by captopril was observed by in vivo study and in situ single-pass intestinal perfusion study in rat, supporting the contribution of influx transporters. Since some ACE inhibitors and ß-lactam antibiotics are reported to be substrates of PEPT and OATP families, we measured transporting activity of TBPM-PI by intestinally expressed transporters, PEPT1, OATP1A2, and OATP2B1. As a result, significant transport activities were observed by both OATP1A2 and OATP2B1 but not by PEPT1. Interestingly, pH dependence of TBPM-PI transports was different between OATP1A2 and OATP2B1, showing highest activity by OATP1A2 at pH 6.5, while OATP2B1-mediated uptake was higher at neutral and weak alkaline pH. OATP1A2 exhibited higher affinity for TBPM-PI (K(m) = 41.1 µM) than OATP2B1 (K(m) > 1 mM) for this agent. These results suggested that TBPM-PI has high intestinal apical membrane permeability due to plural intestinal transport routes, including the uptake transporters such as OATP1A2 and OATP2B1 as well as simple diffusion.

[Pharmacokinetics of tebipenem pivoxil, a novel oral carbapenem antibiotic, in experimental animals].

Pharmacokinetics of tebipenem pivoxil (TBPM-PI), a novel oral carbapenem antibiotic, were known in various laboratory animal. (1) In mouse, rat, dog and monkey, TBPM-PI were absorbed quickly, and the bioavailability was (71.4, 59.1, 34.8 and 44.9%, respectively. (2) TBPM-PI was quickly converted to tebipenem (TBPM), an active form of TBPM-PI. Through blood circulation, TBPM was distributed into the kidney at a high concentration and eliminated quickly. There was no other tissue than the kidney, in which TBPM was highly distributed and remained for a long time. In addition, low penetration to the central nervous system was confirmed. The penetration ratio of TBPM to ELF, that is the ratio of ELF concentration to plasma concentration of TBPM, was 21.8 +/- 14.7%. (3) Serum protein bindings of TBPM in the range of 0.1-100 microg/ml were 90.4-98.3% for mouse, 78.5-90.0% for rat, 15.7-18.7% for dog, 35.3-39.3% for monkey and 59.7-73.9% for human. (4) In vitro metabolism was investigated in plasma, liver S9 fractions and small intestinal S9 fractions derived from infant and adult animals. TBPM-PI was transformed into TBPM quickly in any matrices. It was confirmed that absorbed TBPM-PI was quickly transformed into TBPM or LJC 11,562 (opened ring TBPM) in the plasma after oral administration of 14C-TBPM-PI to infant or adult rat and monkey. TBPM-PI and opened ring TBPM-PI was not detected in plasma and urine samples. In rat and monkey, the oral absorption, distribution, metabolite and excretion of TBPM-PI were not so much different between infant and adult animals. (5) Liver metabolic enzyme system was little affected by 7-days repeated administration of 1-100 mg/kg TBPM-PI. IC50 values of TBPM-PI and TBPM for human CYP isoforms were estimated to be 100 microg/ml or higher. (6) After single oral administration of 10 mg/kg 14C-TBPM-PI to rat, 36.9-42.7% and 58.3-62.2% of radioactivity was excreted to urine and feces, respectively, by 120 hours after administration. The majority of dosage was excreted out of body by 48 hours after administration. After single intravenous administration of 10 mg/kg 14C-TBPM, 87.4% and 11.4% of radioactivity was excreted in urine and bile, respectively, by 24 hours after administration. The majority of dosage was excreted out of body by 4 hours after administration.

[Convulsive liability of an oral carbapenem antibiotic, tebipenem pivoxil].

Tebipenem pivoxil (TBPM-PI), the first oral carbapenem antibiotic both in Japan and abroad, was examined on its convulsive liability. We used ICR male mice and Sprague-Dawley male rats to examine the pro-convulsive effect and anticonvulsive effect of TBPM-PI and its active metabolite, TBPM. (1) When mice were treated with TBPM-PI (30-1000 mg/kg, p.o.) or TBPM (10-300 mg/kg, i.v.), no convulsion was noted at any dose level. When rats were treated with TBPM (300 mg/kg, i.v.), no convulsant effects were noted in electroencephalography or behavioral observation. In intraventricular injection of TBPM in mice, clonic convulsion was observed in 7/10 animals at 100 microg but no effect at 30 microg. On the other hand, the administration of 10/10 microg imipenem/cilastatin (IPM/CS) resulted in clonic convulsion in all animals and tonic convulsion in 3/10 animals, and 4/10 animals died. The administration of 100 microg meropenem did not cause any effects. (2) When mice were co-administered with pentylenetetrazole (45 mg/kg: maximum dose level at which no convulsion is induced) and TBPM-PI (30-300 mg/kg, p.o.) or TBPM (300 mg/kg, i.v.), convulsion enhancing effect was not noted. On the other hand, the co-administration of pentylenetetrazole with IPM/CS (300/300 mg/kg, i.v.) enhanced a convulsive effect of pentylenetetrazole. (3) When mice were treated with TBPM-PI (30-300 mg/kg, p.o.) or TBPM (100 mg/kg, i.v.), inhibitory effect was not noted on convulsions induced by electrostimulation, pentylenetetrazole or strychinine. In conclusion, there were no pro-convulsive effects or anticonvulsive effect in the oral administration of TBPM-PI or intravenous administration of TBPM. Pro-convulsive effect was observed in the intraventricular injection of TBPM as in the case of other carbapenem antibiotics, but such action was weaker than that in IPM/CS administration. Accordingly, the risk of occurrence of convulsion related to TBPM-PI administration was low compared to IPM/CS administration, and TBPM-PI was considered to be less potential to induce convulsions in clinical use.

[Pharmacokinetics analysis of tebipenem pivoxil in a phase II clinical trial in otolaryngological infections].

In a phase IIb clinical study (dose-finding test, 450 mg dosing group: 150 mg t.i.d., 500 mg dosing group: 250 mg b.i.d., 900 mg dosing group: 300 mg t.i.d.) of tebipenem pivoxil (TBPM-PI) for treatment of otolaryngological infections in adults, TBPM concentrations in the patient plasma were quantified. The primary pharmacokinetic parameters such as ka, kel, Vd/F and Tlag were estimated by the Bayesian method and then the secondary pharmacokinetic parameters such as tmax, Cmax, t1/2 and AUC were calculated. As for the patients whose primary parameters were not properly estimated by the Bayesian method, the secondary parameters were calculated by the trapezoidal method. The primary pharmacokinetic parameters obtained by the Bayesian method in 450 mg dosing group (150 mg t.i.d.), 500 mg dosing group (250 mg b.i.d.), and 900 mg dosing group (300 mg t.i.d.) were 5.64 +/- 2.76, 5.11 +/- 3.06 and 2.51 +/- 1.13 hr(-1) for ka, 1.75 +/- 0.25, 2.03 +/- 0.10 and 1.34 +/- 0.27 hr(-1) for kel, 17.62 +/- 5.09, 15.83 +/- 6.14 and 19.34 +/- 8.80 L for Vd/F, and 0.48 +/- 0.11, 0.38 +/- 0.03 and 0.39 +/- 0.26 hr for Tlag, respectively. The secondary parameters obtained by the Bayesian method and the trapezoidal method were 0.85 +/- 0.29, 0.81 +/- 0.33 and 1.18 +/- 1.53 hr for tmax, 5.08 +/- 2.05, 7.92 +/- 4.02 and 8.69 +/- 4.01 microg/ml for Cmax, 0.40 +/- 0.06, 0.34 +/- 0.01 and 0.54 +/- 0.10 hr for t1/2, 5.22 +/- 1.90, 7.93 +/- 4.04 and 13.62 +/- 6.29 microg x hr/ml for AUC after each dosing (AUC(0-8h) or AUC(0-12h)) and 15.65 +/- 5.70, 15.85 +/- 8.08 and 40.87+/- 18.87 microg x hr/ml for AUC(0-24h), respectively. As shown in the above, Cmax and AUC after each dosing were increased with a rise in the dose level, and AUC(0-24h) was increased with a rise in the total dose level per day. Regardless of the dosage, tmax was about 0.8-1.2 hr and t1/2 was about 0.3-0.5 hr, showing almost constant values. Changes in the regimen and dosage did not influence the pharmacokinetic properties of TBPM-PI. Pharmacokinetics of TBPM-PI in adult patients with otolaryngological infection were similar to those in healthy subjects.

Active uptake of ulifloxacin from plasma to lung that controls its concentration in epithelial lining fluid.

Ulifloxacin is a new quinolone antibiotic and it is effective against pneumonia. We previously showed that it is highly distributed into the epithelial lining fluid (ELF) in rats, which might be resulting from certain active transport. The transport system has not been, however, clarified yet. In this study, we attempted to characterize the distribution mechanism of ulifloxacin into the rat ELF. We also aimed to elucidate the feature of ulifloxacin uptake in rat lung and human lung adenocarcinoma cells (Calu-3). In infusion studies, ulifloxacin concentrations in the ELF and lung were higher than that in the plasma, and decreased by co-administration of sparfloxacin or azithromycin to the level of plasma concentration. Integration plot analysis showed that active uptake of ulifloxacin from the plasma to lung was also inhibited by sparfloxacin and azithromycin. In in vitro studies, time and temperature-dependent uptake into Calu-3 was observed, and this uptake was inhibited by sparfloxacin and azithromycin as observed in the rat lung. Additionally sparfloxacin inhibited the active uptake of ulifloxacin into Calu-3 more strongly than levofloxacin as observed in the rat lung. These results suggest that active uptake of ulifloxacin from the plasma to lung controls the distribution of ulifloxacin from the plasma to ELF, and that the uptake of ulifloxacin into Calu-3 has partly similar characteristics to its uptake into the rat lung. We believe our study will contribute to much better understanding of antibiotic efficacy against pathogens which cause pneumonia.

Bile acid-induced elevated oxidative stress in the absence of farnesoid X receptor.

The major function of farnesoid X receptor (FXR) is to maintain bile acid and lipid homeostasis. Fxr-null mice, in which the levels of hepatic bile acid and lipid have been elevated, develop spontaneous liver tumors. We evaluated differences in hepatic bile acid and triglyceride concentrations, and in generation of oxidative stress between wild-type mice and Fxr-null mice. The hepatic levels of 8-hydroxy-2'-deoxyguanosine (8OHdG), thiobarbituric acid-reactive substance (TBARS) and hydroperoxides, oxidative stress-related genes, and nuclear factor (erythroid-2 like) factor 2 (Nrf2) protein in Fxr-null mice were significantly higher than those in wild-type mice. An increase in the hepatic bile acid concentration in Fxr-null mice fed a cholic acid (CA) diet resulted in an increase in the hepatic levels of hydroperoxides, TBARS and 8OHdG, whereas a decrease in the hepatic concentration in mice fed a diet containing ME3738 (22beta-methoxyolean-12-ene-3beta,24(4beta)-diol) resulted in a decrease in these oxidative stress marker levels. A good correlation was observed between the hepatic bile acid concentrations and the hepatic oxidative stress marker levels, although there was no significant correlation between the hepatic triglyceride concentrations and oxidative stress. The results show that oxidative stress is spontaneously enhanced in Fxr-null mice, which may be attributable to a continuously high level of hepatic bile acids.

Proposal of membrane transport mechanism of protein-unbound ulifloxacin into epithelial lining fluid determined by improved microdialysis.

Microdialysis method (MD) is useful for sampling protein-unbound substances in vivo. Generally in the MD, a reference compound is used to correct differences in drug permeation clearance through a dialysis membrane in vivo and in vitro. No reference compound was, however, used for determination of a protein-unbound drug concentration in the epithelial lining fluid (ELF). In this study, we firstly examined the propriety of endogenous urea as a reference compound to determine the protein-unbound ulifloxacin concentrations in rat ELF by MD. Endogenous urea was used to correct differences in the permeation clearance in vivo and in vitro which reflect the differences in the extent of contact between a tip probe and ELF in vivo and in vitro. The results showed that our MD is applicable to determine the various concentrations of ulifloxacin and urea, and that we can use endogenous urea as a reference compound even if the extent of the contact between a tip of the probe and the ELF is small. In addition, use of urea concentrations does not affect drug distribution from plasma to ELF because we used endogenous urea. These results support usefulness of endogenous urea as a reference compound to determine protein-unbound drug concentration in ELF by MD. In addition, our results also suggest the existence of certain distribution mechanisms which cause the high penetration ulifloxacin into ELF. Our MD can help progress in pharmacokinetic-pharmacodynamic analysis of various antibiotics in the case where the concentrations in ELF are not equal to that in plasma.

Population pharmacokinetics of tebipenem pivoxil (ME1211), a novel oral carbapenem antibiotic, in pediatric patients with otolaryngological infection or pneumonia.

Tebipenem pivoxil (TBPM-PI, ME1211) has been under development as the world's first oral carbapenem for treatment of otolaryngological/respiratory infections caused by drug-resistant S. pneumoniae in pediatric patients. In order to treat these infections effectively, it is important to design optimal dosing regimens based on the pharmacokinetics/pharmacodynamics (PK/PD) relationships, which can be characterized by clarifying the pharmacokinetics of tebipenem (TBPM) in the pediatric population. We therefore performed an population pharmacokinetic analysis using plasma TBPM concentrations obtained from pediatric patients with otolaryngological infection or bacterial pneumonia (0.5-16 years old; n=217, 395 points), after repeated oral administration of TBPM-PI at a dose of 4 or 6 mg/kg b.i.d. A one-compartment model with first-order absorption was adopted. In analysis, weight-normalized creatinine clearance (Ccr) and age were the most significant covariates that respectively explained inter-subject variability in weight-normalized apparent clearance (CL/F) and volume of distribution (Vd/F) of TBPM. The CL/F of TBPM increased with Ccr, and the Vd/F decreased with age. Based on the results of the present analysis, validity of the presently recommended dosage regimen of TBPM-PI in pediatric patients is discussed.

New concept and a theoretical consideration of the mechanism-based pharmacokinetics/ pharmacodynamics (PK/PD) modeling for antimicrobial agents.

Pharmacodynamic (PD) characterization (concentration-dependent, time-dependent, etc.) of antibiotics is determined by aspects of the pharmacodynamic interaction between antibiotics and microorganisms. There are three major aspects of the pharmacodynamic interaction between antibiotics and microorganisms; 1) the minimum drug concentration required for the exhibition of antibacterial activity (MIC: minimum inhibitory concentration, MBC: minimum bactericidal concentration, etc.), 2) the relationship between drug concentration and bactericidal activity and 3) the magnitude of any persistent antibiotic activity (sub-MIC effect, post antibiotic effect, etc.). In the PK/PD approach based on the MIC (static MIC approach), information concerning aspect 1) alone is treated as the quantitative PD parameter (MIC), while information concerning aspects 2) and 3) are not represented as quantified PD parameters in spite of their importance in in vivo pharmacodynamic situation. On the other hand, in the PK/PD approach based on the time-kill profile (dynamic PK/PD approach), information concerning aspects 1) - 3) can all be represented as quantitative dynamic PD parameters (epsilon; the maximum kill rate constant, gamma; the Hill coefficient and EC50; the antibiotic concentration at which 50% of the maximum effect is obtained) together with the growth rates of the organisms (lambda). We thought that the PD characterization of antibiotics should be determined by integrating the dynamic PD parameters and the growth rates, so we developed a new concept integrating these parameters so that a good approximation of the time course of in vivo antibacterial activity exhibited by a antibiotic might be predicted from these parameters and the pharmacokinetics of the drug. To achieve this, we analyzed the time-kill profiles of a wide range of antibiotics against various microorganisms and obtained the dynamic PD parameters and the growth rates for the various combinations of antibiotics and microorganisms. Then we analyzed the causal relationship between the PD characteristics of the antibiotics and the dynamic PD parameters and the growth rates. As a result, we derived the following criteria for predicting the PD characteristics of antibiotics. (i) if the epsilon/lambda is greater than about 10 and gamma is less than one, the pharmacodynamics should be concentration-dependent (ii) if the epsilon/lambda is within the range 1-2 and gamma is about 5 or more, the pharmacodynamics should be time-dependent (iii) if the epsilon/lambda is within the range 1-4 and gamma is in the range 1-12, the pharmacodynamics should be time-dependent or both time- and concentration-dependent. The PD characterization of antibiotics against various strains of different microorganisms can be predicted relatively easily and quickly by utilizing these criteria. These findings make it possible to determine the kinds of causative pathogens to which the antibiotics should be applicable in the clinical sites. Furthermore, it is expected that effective strategies for development and establishing the optimum dosage regimen of novel antibiotics could be worked out more scientifically and efficiently than ever on the basis of the PK/PD parameters corresponding to the predicted PD characters.

Transporter-mediated hepatic uptake of ulifloxacin, an active metabolite of a prodrug-type new quinolone antibiotic prulifloxacin, in rats.

Prulifloxacin (PUFX) is a prodrug-type new quinolone antibiotic and immediately converted to an active metabolite, ulifloxacin (UFX). It has been previously reported that UFX is highly excreted into the bile, although the hepatic uptake process of UFX has not been investigated yet. In this study, we attempted to characterize the mechanism of hepatic uptake of UFX in rats. The hepatic uptake in vivo was evaluated by integration plot analysis. Furthermore, the uptake of [(14)C]-UFX by isolated rat hepatocytes was measured, and the effects of several transporter inhibitors and other quinolone antibiotics on the uptake were examined. The hepatic uptake clearance of UFX (1 mg/kg) was calculated to be 37.7 mL/min/kg, which was larger than those at doses of 5 and 25 mg/kg and was decreased by co-administration of cyclosporine A (CysA; 30 mg/kg). The uptake of [(14)C]-UFX by isolated rat hepatocytes linearly increased up to 1 min and also inhibited by CysA. Other quinolone antibiotics inhibited the [(14)C]-UFX uptake in a concentration-dependent manner, whereas taurocholate and estrone-3-sulfate partially inhibited the [(14)C]-UFX uptake. These results demonstrate that a carrier-mediated transport system which is common to the quinolone antibiotics is involved in the uptake of UFX in the rat liver.

ME3738 protects against lithocholic acid-induced hepatotoxicity, which is associated with enhancement of biliary bile acid and cholesterol output.

ME3738 (22beta-methoxyolean-12-ene-3beta, 24(4beta)-diol), a derivative of soyasapogenol, attenuates liver disease in several models of chronic liver inflammation. In the present study, we have investigated a protective effect of ME3738 in a typical bile acid-induced cholestatic liver model, lithocholate (LCA) feeding mouse. Co-administration of ME3738 resulted in decreases in plasma alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities and hepatic bile acid level, and increases in biliary outputs of bile acid and cholesterol, as compared with the results in mice treated with LCA alone. LCA sulfation by hydroxysteroid sulfotransferase 2a and hydroxylation have been reported to be involved in protection against LCA-induced hepatotoxicity. ME3738-treatment, however, had no clear influence on the hydroxysteroid sulfotransferase 2a protein level and LCA 6alpha-, 6beta- and 7alpha-hydroxylase activities, but increased biliary cholesterol output. Cholate (CA)-treatment has been shown to induce hepatotoxicity in farnesoid X receptor-null mice, which is scarcely dependent on bile acid sulfation and hydroxylation but associated with decreased biliary bile acid output. Co-administration of ME3738 decreased the ALT and ALP activities and hepatic bile acid level, and increased biliary outputs of bile acid and cholesterol in farnesoid X receptor-null mice, as compared with the results in the mice treated with CA. Moreover, a clear correlation between biliary outputs of cholesterol and bile acid was observed in these two bile acid-induced hepatotoxicity mouse models. These results suggest that ME3738 protects against bile acid-induced hepatotoxicity through increased biliary bile acid output that is not related to bile acid metabolism but associated with cholesterol output.

Protective effect of inactive ingredients against nephrotoxicity of vancomycin hydrochloride in rats.

A generic form of vancomycin for I.V. infusion (MEEK) is more soluble and stable than the brand-name form of vancomycin hydrochloride (VCM) due to the addition of two inactive ingredients: D-mannitol and Macrogol400 (PEG400). The aim of the present study was to compare the nephrotoxicity of MEEK with that of brand-name VCM (S-VCM) and to analyze the pharmacokinetics of these preparations. Following administration to rats at the clinical dose of 40 mg/kg, there was no difference between MEEK and S-VCM with regard to pharmacokinetics and effects on the kidneys, indicating that MEEK should be as effective as S-VCM. When administered at the nephrotoxic dose of 400 mg/kg, S-VCM caused impairment of renal function and kidney damage, and an increase of the plasma concentration due to decreased renal clearance was observed. In contrast, MEEK had virtually no effect on renal function or the kidneys and did not cause a marked change of renal clearance. These findings suggest that the inactive ingredients in MEEK play a role in reducing the nephrotoxicity of VCM.