Potential association of VAMP5 polymorphisms with total colonic aganglionosis in Hirschsprung disease.

BACKGROUND: Hirschsprung disease (HSCR) is a congenital bowel disease caused by the absence of nerve cells in portions of the intestine. Our recent genome-wide association study has identified a variant (rs1254900) of vesicle-associated membrane protein 5 (VAMP5) as a potential risk locus for total colonic aganglionosis (TCA) in HSCR. In addition, VAMP5 is a member of the VAMP/synaptobrevin protein complex, which participates in nerve signal transduction by regulating the vesicular fusion of the neurotransmitter in synaptic transmission. METHODS: A total of 11 single nucleotide polymorphisms (SNPs), including those in the functionally important coding region, were selected on the basis of linkage disequilibrium and genotyped in 187 HSCR patients and 283 unaffected controls by using a TaqMan assay. Logistic analysis was conducted to investigate the possible association between VAMP5 SNPs and the risk of HSCR. KEY RESULTS: Genetic variants of VAMP5 showed increased association signals in the TCA subgroup of HSCR patients (minimum p = 9.69 × 10(-5) , OR = 3.93 at rs10206961) compared to other subgroups, even after Bonferroni correction (pcorr = 0.002). In haplotype analysis, three haplotypes (BL1_ht1, BL2_ht1, and BL2_ht2) were associated with the risk of TCA (minimum pcorr = 0.005). In additional combined analysis after imputation based on our previous GWAS, five SNPs still retained significant associations with the TCA subtype (minimum pcorr = 0.006 at rs10206961). CONCLUSIONS & INFERENCES: Considering that differential genetic effects on the development of the enteric nervous system, our results suggest that VAMP5 may be associated with the TCA of HSCR. However, further replications and functional evaluations are required.

Genetic variants of IL-11 associated with risk of Hirschsprung disease.

BACKGROUND: Hirschsprung disease (HSCR) is a congenital and heterogeneous disorder characterized by the absence of enteric ganglia during enteric nervous system (ENS) development. Our recent genome-wide association study has identified a variant (rs6509940) of interleukin-11 (IL-11) as a potential susceptible locus for HSCR. As interleukins play important roles in the ENS, we further studied associations with HSCR of nine common single nucleotide polymorphisms (SNPs) on IL-11. METHODS: Biopsy specimens or surgical materials from all patients that were tested for histological examination based on the absence of the enteric ganglia were collected. A total of nine SNPs on IL-11 were genotyped in 187 HSCR patients and 283 unaffected controls using TaqMan genotyping assay. KEY RESULTS: Combined analysis revealed that several SNPs (minimum p = 1.57 × 10(-7) ) showed statistically significant associations with HSCR, even after Bonferroni correction (pcorr  = 1.73 × 10(-6) for the SNP). Moreover, the most common haplotype was strongly associated with HSCR (pcorr  = 2.20 × 10(-6) ). In further analysis among three HSCR subtypes (short segment, S-HSCR; long segment, L-HSCR; total colonic aganglionosis, TCA) based on the extent of aganglionic segment, the result showed a different association pattern depending on the subtypes (minimum pcorr  = 6.12 × 10(-5) for rs6509940 in S-HSCR; but no significant SNP in L-HSCR and TCA). CONCLUSIONS & INFERENCES: Although further replication in a larger cohort and functional evaluations are needed, our findings suggest that genetic variations of IL-11 may be associated with the risk of HSCR and/or the mechanisms related to ENS development.

Effect of renal impairment and haemodialysis on the pharmacokinetics of gemigliptin (LC15-0444).

This study evaluated the effects of renal impairment (RI) and haemodialysis (HD) on the pharmacokinetics of gemigliptin, a novel dipeptidyl peptidase-4 (DPP-4) inhibitor. After a 100 mg administration to subjects with normal renal function (n = 23) or RI (n = 24), plasma, urine or dialysate samples were analysed. Control subjects were matched to patients based on age, gender and body mass index. Patients with mild, moderate, severe RI and end-stage renal disease (ESRD) showed 1.20, 2.04, 1.50 and 1.66-fold (1.10, 1.49, 1.22 and 1.21-fold) increase of mean area under the time-plasma concentration curve from 0 to infinity (AUCinf) [maximum plasma concentration (Cmax)] of gemigliptin, respectively. Pharmacokinetics of gemigliptin was comparable between HD and non-HD periods in ESRD patients. Less than 4% of the dose was removed by 4 h HD. RI appeared to have modest effect on the gemigliptin disposition. No dose adjustment in patients with RI is proposed on the basis of exposure-response relationship. Impact of HD on the removal of gemigliptin was negligible.

CYP2D6 genotype and adjuvant tamoxifen: meta-analysis of heterogeneous study populations.

The International Tamoxifen Pharmacogenomics Consortium was established to address the controversy regarding cytochrome P450 2D6 (CYP2D6) status and clinical outcomes in tamoxifen therapy. We performed a meta-analysis on data from 4,973 tamoxifen-treated patients (12 globally distributed sites). Using strict eligibility requirements (postmenopausal women with estrogen receptor-positive breast cancer, receiving 20 mg/day tamoxifen for 5 years, criterion 1); CYP2D6 poor metabolizer status was associated with poorer invasive disease-free survival (IDFS: hazard ratio = 1.25; 95% confidence interval = 1.06, 1.47; P = 0.009). However, CYP2D6 status was not statistically significant when tamoxifen duration, menopausal status, and annual follow-up were not specified (criterion 2, n = 2,443; P = 0.25) or when no exclusions were applied (criterion 3, n = 4,935; P = 0.38). Although CYP2D6 is a strong predictor of IDFS using strict inclusion criteria, because the results are not robust to inclusion criteria (these were not defined a priori), prospective studies are necessary to fully establish the value of CYP2D6 genotyping in tamoxifen therapy.

Population pharmacogenetic-based pharmacokinetic modeling of efavirenz, 7-hydroxy- and 8-hydroxyefavirenz.

The purpose of this study was to determine the demographic and pharmacogenetic covariates that influence the disposition of efavirenz (EFV) and its major metabolites. A population pharmacokinetic (PK) model was developed from a randomized, cross-over, drug-interaction study in healthy male Korean subjects (n = 17). Plasma concentrations of EFV and its hydroxy-metabolites (0-120 hours) were measured by LC/MS/MS. Genomic DNA was genotyped for variants in the cytochrome P450 (CYP) 2A6, 2B6, 3A5, and MDR1 genes. A PK model was built in a stepwise procedure using nonlinear mixed effect modeling in NONMEM 7. The covariate model was built using the generalized additive modeling and forward selection-backward elimination. Model-based simulations were performed to predict EFV steady-state concentrations following 200, 400, and 600 mg daily oral dose among different CYP2B6 genotypes. The final model included only CYP2B6 genotype as a covariate that predicts EFV clearance through the formation of 8-OH EFV that represented 65% to 80% of EFV clearance. The total clearance of EFV in CYP2B6*6/*6 genotype was ∼30% lower than CYP2B6*1/*1 or CYP2B6*1/*6 alleles (P < .001). Clopidogrel reduced both formation and elimination clearances of 8-OH EFV by 22% and 19%, respectively (P = .033 and .041). Other demographics and genotype of accessory CYP pathways did not predict EFV or metabolites PK. CYP2B6 genotype was the only significant predictor of EFV disposition. The developed model may serve as the foundation for further exploration of pharmacogenetic-based dosing of EFV.

Pharmacokinetics and bioequivalence evaluation of leflunomide tablets in Korean healthy volunteers.

Leflunomide is a disease-modifying antirheumatic drug. The purpose of this study was to evaluate the bioequivalence of a test drug (CJ leflunomide) and a commercially available reference drug (Arava®) at 2 doses (10 and 20 mg) in healthy Korean volunteers. This was a single-dose (28 individuals enrolled at each dose group), randomized, open-label, 2-way crossover study. The 2 treatment periods were separated by a 56-day wash-out interval. Blood sampling was conducted until 672 h after drug administration. Plasma teriflunomide (active metabolite of leflunomide) concentrations were determined, and pharmacokinetic parameters were calculated. Bioequivalence was evaluated using an ANOVA model, based on the AUCt and the Cmax after administration of leflunomide tablets. Bioequivalence was defined as the 90% confidence intervals (CIs) of the geometric mean ratios (GMRs) of AUCt and Cmax for the test and reference drugs being within the range of 0.80-1.25. The GMRs (90% CI) for AUCt and Cmax were 0.9506 (0.9091-0.9941) and 0.9861 (0.9360-1.0389), respectively, in the 10 mg study, and 0.9524 (0.9101-0.9968) and 0.9740 (0.9314-1.0186), respectively, in the 20 mg study. The 90% CIs of AUCt and Cmax at each dose were within the accepted range for bioequivalence. Based on the results, the test drug (CJ leflunomide) was bioequivalent to the commercially available reference drug (Arava®) at both doses.

Phase II and UGT1A1 genotype study of irinotecan dose escalation as salvage therapy for advanced gastric cancer.

BACKGROUND: To assess the efficacy and safety of individualised dose optimisation of irinotecan monotherapy as salvage treatment for advanced gastric cancer (AGC). METHODS: A total of 43 patients were enrolled. Intravenous irinotecan (350 mg m(-2)) was administered every 3 weeks. The dose was increased (425 mg m(-2) and 500 mg m(-2)) or decreased (250 mg m(-2)) depending on patient tolerance. UGT1A1 genotypes were determined by direct sequencing of genomic DNA extracted from peripheral blood. RESULTS: A total of 183 cycles of irinotecan were administered, with a median of four cycles per patient. The overall response rate was 9.3%, and the disease control rate was 62.8%. Median time to disease progression was 2.8 months, and median overall survival was 8.0 months. Grade 3-4 neutropenia was the most common toxicity (53.5%), and febrile neutropenia was the least common toxicity (4.6%). Compared with defective allele groups, UGT1A1 *1/*1 was associated with a lower incidence of grade 3-4 neutropenia during the first cycle (P=0.018). CONCLUSION: Individualised irinotecan dose escalation based on patient tolerance was not associated with increased toxicity and shows modest activity as salvage chemotherapy for AGC. The role of UGT1A1 genotype in clinical toxicity requires further evaluation.

Frequency of CYP2C9 variant alleles, including CYP2C9*13 in a Korean population and effect on glimepiride pharmacokinetics.

WHAT IS KNOWN AND OBJECTIVE: Cytochrome P450 (CYP) 2C9 is a clinically important enzyme involved in the metabolism of many drugs commonly used in humans. Of several allelic variants known to affect the catalytic activity of the CYP2C9 enzyme, the frequencies of the CYP2C9*3 and CYP2C9*13 alleles in the Korean population have been reported as 1·1% and 0·6%, respectively. Our objective was to re-evaluate the frequencies of CYP2C9 allelic variants in the Korean population, including the CYP2C9*13 allele by pyrosequencing, and to investigate the pharmacokinetics of glimepiride in relation to CYP2C9 genotypes, including CYP2C9*3/*3. METHODS: 295 subjects were genotyped for CYP2C9*2 and CYP2C9*3 using the TaqMan procedure, and for CYP2C9*13 using pyrosequencing. These data were combined with our previously reported data to assess the CYP2C9 allele and genotype frequencies in 869 Korean subjects. Data from 24 of the 295 genotyped subjects (22 CYP2C9*1/*1 homozygotes, one CYP2C9*1/*3 heterozygote and one CYP2C9*3/*3 homozygote) who had participated in a bioequivalence study were analysed retrospectively to examine the effects of CYP2C9 genotype on glimepiride pharmacokinetics. RESULTS: The frequencies of the CYP2C9*1/*3, *3/*3, and *1/*13 genotypes in the study population (n = 295) were 0·081 (n = 24), 0·010 (n = 3) and 0·003 (n = 1), respectively. In the 869 subjects from the combined studies, allele frequencies for CYP2C9*3 and CYP2C9*13 were 0·025 (95% CI: 0·018, 0·033) and 0·002 (95% CI: 0·000, 0·010), respectively. Relative to CYP2C9*1 homozygotes, the one CYP2C9*3 homozygous subject was found to have a higher AUC(0-∞) value (490% of the reference value) and a lower oral clearance rate (18% of the reference). WHAT IS NEW AND CONCLUSION: This study is the first examination of CYP2C9*3 homozygotes in the Korean population. Our data on the one subject with this genotype suggest that CYP2C9*3/*3 momozygotes have lower clearance of glimepiride and are exposed to higher levels of the drug than wild-type homozygotes. Although we identified a subject with the CYP2C9*13 allele using a new pyrosequencing assay, we were unfortunately unable to investigate its effects on glimepiride pharmacokinetics.

Phase II study of S-1 combined with oxaliplatin as therapy for patients with metastatic biliary tract cancer: influence of the CYP2A6 polymorphism on pharmacokinetics and clinical activity.

BACKGROUND: Advanced biliary cancer is often treated with fluoropyrimidine-based chemotherapy. In this study, we evaluated the efficacy and tolerability of a combination of S-1, an oral fluoropyrimidine prodrug, and oxaliplatin in patients with metastatic biliary cancer. METHODS: Patients with histologically confirmed metastatic biliary cancer and no history of radiotherapy or chemotherapy were enrolled. Oxaliplatin was administered intravenously (130 mg m(-2)), followed by 14-day administration of oral S-1 (40 mg m(-2) twice daily) with a subsequent 7-day rest period every 21 days. Pharmacokinetic analysis of S-1 was performed at cycle 1. Patients were genotyped for CYP2A6 polymorphisms ((*)1, (*)4, (*)7, (*)9 or (*)10), and pharmacokinetic and clinical parameters compared according to the CYP2A6 genotype. RESULTS: In total, 49 patients were evaluated, who received a median of four cycles. The overall response rate was 24.5%. Median progression-free and overall survival was 3.7 and 8.7 months, respectively. The most common haematological grade 3 out of 4 toxicity was neutropenia (14%), while non-hematological grade 3 out of 4 toxicities included anorexia (14%), nausea (12%), asthenia (10%), vomiting (10%), and diarrhoea (4%). Biotransformation of S-1 (AUC(0-24 h) of 5-fluorouracil/AUC(0-24 h) of tegafur) was 1.85-fold higher for the *1/*1 group than for the other groups (90% confidence interval 1.37-2.49). Diarrhoea (P=0.0740), neutropenia (P=0.396), and clinical efficacy (response rate, P=0.583; PFS, P=0.916) were not significantly associated with CYP2A6 genotype, despite differences in 5-FU exposure. CONCLUSION: The combination of S-1 and oxaliplatin appears to be active and well tolerated in patients with metastatic biliary cancer, and thus is feasible as a therapeutic modality. CYP2A6 genotypes are associated with differences in the biotransformation of S-1. However, the impact of the CYP2A6 polymorphism on variations in clinical efficacy or toxicity requires further evaluation.

Genetic variants of organic cation transporter 2 (OCT2) significantly reduce metformin uptake in oocytes.

1. The authors sought to evaluate the contribution of organic cation transporters (OCTs) to the renal tubular transport of metformin using LLC-PK1 cells as an in vitro model for the renal proximal tubule, and to investigate the effects of three non-synonymous genetic variants of OCT2 on the transport activity of metformin in vitro using an oocyte over-expression system. 2. The basolateral-to-apical transport of metformin was significantly greater than the apical-to-basolateral transport and showed concentration dependency with the kinetic parameters: maximum transport rate (V(max)), 922 pmol min(-1) per 5 x 10(5) cells; Michaelis-Menten constant (K(m)), 393 microM; intrinsic clearance (CL(int)), 2.35 microl min(-1) per 5 x 10(5) cells; and diffusion constant (K(d)), 0.33 microl min(-1) per 5 x 10(5) cells. The basolateral-to-apical transport of metformin was inhibited by phenoxybenzamine, an inhibitor of OCTs, but not by cyclosporine A, MK571, or fumitremorgin C, which are inhibitors of P-glycoprotein, multidrug resistance proteins (MRPs), and breast cancer resistance protein (BCRP), respectively, suggesting that OCTs play a role in renal tubular secretion of metformin. 3. Metformin uptake was much greater in oocytes expressing OCT2-wild type (OCT2-WT) than OCT1-WT compared with uptake in water-injected oocytes. Uptake was significantly decreased in oocytes expressing OCT2-T199I, -T201M, and -A270S compared with that in OCT2-WT, suggesting that metformin is a better substrate for OCT2 than for OCT1 and that the amino acid-substituted variants of OCT2 cause a functional decrease in metformin uptake. 4. In conclusion, the genetic variants of OCT2 (OCT2-T199I, -T201M, and -A270S) decreased the transport activity of metformin and thus may contribute to the inter-individual variation in metformin disposition as OCT2 plays a pivotal role in renal excretion, the major disposition route of metformin.

Contribution of cytochrome P450 3A4 and 3A5 to the metabolism of atorvastatin.

Atorvastatin is a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor that is mainly metabolized by cytochrome P450 (CYP) 3A4. A recent study showed that the lipid-lowering effect of statins is affected by the CYP3A5 polymorphism. Therefore, it was investigated whether CYP3A5 contributes to the metabolism of atorvastatin. Two metabolites of atorvastatin, para- and ortho-hydroxyatorvastatin, were produced by human liver microsomes and human recombinant CYP3A enzymes, and the enzyme kinetic pattern exhibited substrate inhibition. The intrinsic clearance (CL(int)) rates of para- and ortho-hydroxyatorvastatin by CYP3A4 were 2.4- and 5.0-fold of the respective CL(int) rates of CYP3A5, indicating that CYP3A4 is the major P450 isoform responsible for atorvastatin metabolism. These results suggest that atorvastatin is preferentially metabolized by CYP3A4 rather than by CYP3A5, and thus the genetic CYP3A5 polymorphism might not be an important factor in the inter-individual variation of atorvastatin disposition and pharmacodynamics in human.

In vitro metabolism of a novel PPAR gamma agonist, KR-62980, and its stereoisomer, KR-63198, in human liver microsomes and by recombinant cytochrome P450s.

1. KR-62980 and its stereoisomer KR-63198 are novel and selective peroxisome proliferator-activated receptor gamma (PPAR gamma) modulators with activity profiles different from that of rosiglitazone. This study was performed to identify the major metabolic pathways for KR-62980 and KR-63198 in human liver microsomes. 2. Human liver microsomal incubation of KR-62980 and KR-63198 in the presence of a beta-nicotinamide adenine dinucleotide phosphate (NADPH)-generating system resulted in hydroxy metabolite formation. In addition, the specific cytochrome P450s (CYPs) responsible for KR-62980 and KR-63198 hydroxylation were identified by using a combination of chemical inhibition in human liver microsomes and metabolism by recombinant P450s. It is shown that CYP1A2, CYP2D6, CYP3A4, and CYP3A5 are the predominant enzymes in the hydroxylation of KR-62980 and KR-63198. 3. The intrinsic clearance through hydroxylation was consistently and significantly higher for KR-62980 than for KR-63198, indicating metabolic stereoselectivity (CL(int) of 0.012 +/- 0.001 versus 0.004 +/- 0.001 microl min(-1) pmol(-1) P450, respectively). 4. In a drug-drug interaction study, KR-62980 and KR-63198 had no effect on the activities of the P450s tested (IC(50) > 50 microM), suggesting that in clinical interactions between KR-62980 and KR-63198 the P450s tested would not be expected.

Genetic variants of the organic cation transporter 2 influence the disposition of metformin.

Genetic variants of the organic cation transporter 2 (protein, OCT2; gene, SLC22A2) were evaluated for their contribution to the variations in the pharmacokinetics of metformin, especially to its renal elimination. Genetic variants of SLC22A2 (c.596C>T, c.602C>T, and c.808G>T) showed significant differences in metformin pharmacokinetics when compared with the reference genotype, with higher peak plasma concentration (C(max)) and area under the curve (AUC) and lower renal clearance (Cl(renal)), thereby suggesting that a decrease in transport function associated with the SLC22A2 variants results in reduced Cl(renal) of metformin and consequently leads to increased plasma concentrations.

Dietary salt does not influence the disposition of verapamil enantiomers in relation to efflux transporter ABCB1 genetic polymorphism in healthy Korean subjects.

To evaluate the effects of dietary salt on the stereoselective disposition of verapamil enantiomers in relation to the transporter ABCB1 2677GG/3435CC and 2677TT/3435TT haplotypes, ten healthy subjects were asked to take diets of three different salt levels for 7 days in a randomized, three-way crossover manner. The plasma concentrations of verapamil and norverapamil enantiomers were determined after a single oral dose of 240 mg verapamil on the last day of each phase. Pharmacokinetic parameters were calculated by non-compartmental analysis techniques and compared among the three different dietary salt phases. Compared with the medium salt diet, the high and low salt diets had no significant effect on the disposition of verapamil enantiomers. Moreover, the ABCB1 haplotypes did not alter the impact of dietary salt, although ABCB1 2677TT/3435TT subjects had slightly, but not significantly, higher C(max) and area under the curve (AUC) and lower T(max) for the verapamil enantiomers than did 2677GG/3435CC subjects in each salt phase.

Effects of dietary salt on the expression of drug transporters, cytochrome P4503a, and nuclear receptors in rats.

Quantitative reverse-transcription polymerase chain reaction (RT-PCR) and Western blot analyses were carried out to investigate the regulation of genes responsible for the transport and metabolism of drugs in response to different levels of salt intake. A high-salt diet compared with medium- and low-salt diets reduced the expression levels of the mdr1a and mdr1b genes in the liver and kidney, but increased their expression levels in the duodenum, jejunum, and ileum. Likewise, the expression levels of other transporters and CYP3a3 genes varied in different tissues. The expression levels of nuclear receptors, such as Pxr, Fxr, and Car, were also modulated differently in the liver, kidney, and intestines. The protein levels of Mdr1, Oct1, CYP3a, Pxr, Fxr, and Car were correlated with the changes in mRNA levels of the respective genes. In conclusion, the changes in the expression of drug transporters, metabolic enzymes, and nuclear receptors were tissue specific.

Development of the "Inje cocktail" for high-throughput evaluation of five human cytochrome P450 isoforms in vivo.

To develop and validate an in vivo cocktail method for high-throughput phenotyping of CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A, 12 healthy subjects received five probe drugs alone or simultaneously. The in vivo phenotyping index of CYP2C9, the ratio of 8 h urine concentration of losartan to its metabolite after a single administration of losartan, was not significantly different from that obtained using the five-drug cocktail. Similarly, the ratios of [omeprazole]/[5-hydroxyomeprazole] (CYP2C19) and [paraxanthine]/[caffeine] (CYP1A2) in 4 h plasma samples and the log ratio of [dextromethorphan]/[dextrorphan] (CYP2D6) in 8 h urine samples and the 4 h plasma concentrations of midazolam (CYP3A) after single administration or well-established three-drug cocktail of caffeine, omeprazole, and dextromethorphan were not significantly different from those after the new five-drug cocktail. In conclusion, the new five-drug cocktail regimen, named the "Inje cocktail," can be used as a tool to phenotype in vivo enzyme activities of CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A with only 4 h blood sampling and 8 h urine collection following simultaneous administration of the five probe drugs.

Acute-phase response alters the disposition kinetics of cefepime following intravenous administration to rabbits.

The effect of experimentally induced fever on the pharmacokinetics of cefepime administered intravenously at a dose of 75 mg/kg bw was studied in six healthy rabbits. The study was conducted in two consecutive phases, separated by a washout period of 2 weeks. Infection was induced by the intravenous inoculation of 5 x 10(8) cfu of Escherichia coli 24 h before the pharmacokinetic investigation was carried out. Serial blood samples for cefepime concentration determination were obtained for 48 h following drug administration. The concentrations of cefepime in the plasma were determined by a quantitative microbiological assay using an agar-gel diffusion method employing Bacillus subtilis ATCC 6633 as the test organism, with a level of detectability of approximately 0.10 microg/ml. Cefepime plasma concentrations versus time were evaluated by non-compartmental methods using WinNonLin. Cefepime was well tolerated and no serious adverse events were observed. Rectal temperature increased 1 degree C 24 h post injection in infected animals. Highly significant differences in the blood plasma concentrations of cefepime were observed between febrile and healthy animals at all the sampling times. This could explain the greater area under the plasma level-time curve of the drug in febrile compared with healthy animals. The results from pharmacokinetic calculations showed that both the distribution volume at steady state (V (dss)) and body clearance (CL(tot)) were affected in febrile as compared to healthy animals. The mean values of V (dss) and CL(tot) of cefepime in healthy rabbits were 1.168 L/kg and 0.303 L/kg/h, respectively. As compared with healthy animals, the mean estimates of V (dss) (0.917 L/kg) and CL(tot) (0.205 L/kg per h) of cefepime were significantly lower, whereas t (1/2lambda), MRT and AUMC were significantly higher in febrile rabbits. It is concluded that, although experimental infection had an effect on the disposition kinetics of cefepime in healthy and febrile rabbits, this was not sufficiently pronounced to require alteration of the dosage during disease.

Inhibition of human cytochrome P450 isoforms and NADPH-CYP reductase in vitro by 15 herbal medicines, including Epimedii herba.

OBJECTIVE: We evaluated the potential of 15 herbal medicines (HMs), commonly used in Korea, to inhibit the catalytic activities of several cytochrome P450 (CYP) isoforms and microsomal NADPH-CYP reductase. METHODS: The abilities of 1-1000 microg/mL of freeze-dried aqueous extracts of 15 HMs to inhibit phenacetin O-deethylation (CYP1A2), tolbutamide 4-methylhydroxylation (CYP2C9), S-mephenytoin 4'-hydroxylation (CYP2C19), dextromethorphan O-demethylation (CYP2D6), chlorzoxazone 6-hydroxylation (CYP2E1), midazolam 1-hydroxylation (CYP3A4) and NADPH-CYP reductase were tested using human liver microsomes. RESULTS: The HMs Epimedii herba, Glycyrrhizae radix and Leonuri herba inhibited one or more of the CYP isoforms or NADPH-CYP reductase. Of the three HMs, Epimedii herba extracts were the most potent inhibitors of several CYP isoforms (IC(50) 67.5 microg/mL for CYP2C19, 104.8 microg/mL for CYP2E1, 110.9 microg/mL for CYP2C9, 121.9 microg/mL for CYP3A4, 157.8 microg/mL for CYP2D6 and 168.7 microg/mL for CYP1A2) and NADPH-CYP reductase (IC(50) 185.9 microg/mL ). CONCLUSION: These results suggest that some of the HMs used in Korea have the potential to inhibit CYP isoforms in vitro. Although the plasma concentrations of the active constituents of the HMs were not determined, some herbs could cause clinically significant interactions because the usual doses of those individual herbs are several grams of freeze-dried extracts. Controlled trials to test the significance of these results are necessary.

Stereoselective inhibition of cytochrome P450 forms by lansoprazole and omeprazole in vitro.

The stereoselectivity of the inhibitory interaction potential of lansoprazole and omeprazole isomers on six human cytochrome P450 forms was evaluated using human liver microsomes. Lansoprazole enantiomers showed stereoselective inhibition of CYP2C9-catalysed tolbutamide 4-methylhydroxylation, CYP2C19-catalysed S-mephenytoin 4'-hydroxylation, CYP2D6-catalysed dextromethorphan O-demethylation, CYP2E1-catalysed chlorzoxazone 6-hydroxylation and CYP3A4-catalysed midazolam 1-hydroxylation, whereas omeprazole only inhibited CYP2C19 stereoselectively. Of the P450 forms tested, CYP2C19-catalysed S-mephenytoin 4'-hydroxylation was extensively inhibited by both the lansoprazole and omeprazole enantiomers in a competitive and stereoselective manner; the S-enantiomers of both drugs inhibited the hydroxylation more than the R-enantiomers. The estimated K(i) values determined for CYP2C19-catalysed S-mephenytoin 4'-hydroxylation were 0.6, 6.1, 3.4 and 5.7 microM for S-lansoprazole, R-lansoprazole, S-omeprazole and R-omeprazole, respectively. The results indicate that although both lansoprazole and omeprazole are strong inhibitors of CYP2C19, the inhibition of CYP2C19 by lansoprazole is highly stereoselective, whereas the inhibition by omeprazole is less stereoselective. In addition, S-lansoprazole, the most potent CYP2C19 inhibitor, is not a good CYP2C19-selective inhibitor owing to its inhibition of other P450 forms.