Inhibition of human drug-metabolising cytochrome P450 and UDP-glucuronosyltransferase enzyme activities in vitro by uremic toxins

Objective

To investigate the potential inhibitory effects of uremic toxins on the major human hepatic drug-metabolising cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes in vitro.

Methods

Benzyl alcohol, p-cresol, indoxyl sulfate, hippuric acid and a combination of the four uremic toxins were co-incubated with human liver microsomes and selective probe substrates for the major human drug-metabolising CYP and UGT enzymes. The percentage of enzyme inhibition was calculated by measuring the rates of probe metabolite formation in the absence and presence of the uremic toxins. Kinetics studies were conducted to evaluate the K _i values and mechanism(s) of the inhibition of CYP2E1, CYP3A4, UGT1A1 and UGT1A9 by p-cresol.

Results

The individual uremic toxins inhibited CYP and UGT enzymes to a variable extent. p-Cresol was the most potent individual inhibitor, producing >50 % inhibition of CYP2E1, CYP3A4, UGT1A1, UGT1A9 and UGT2B7 at a concentration of 100 μM. The greatest inhibition was observed with UGT1A9. p-Cresol was shown to be an uncompetitive inhibitor of UGT1A9, with unbound K _i values of 9.1 and 2.5 μM in the absence and presence of bovine serum albumin (BSA), respectively. K _i values for p-cresol inhibition of human liver microsomal CYP2E1, CYP3A4 and UGT1A1 ranged from 43 to 89 μM. A combination of the four uremic toxins produced >50 % decreases in the activities of CYP1A2, CYP2C9, CYP2E1, CYP3A4, UGT1A1, UGT1A9 and UGT2B7.

Conclusions

Uremic toxins may contribute to decreases in drug hepatic clearance in individuals with kidney disease by inhibition of hepatic drug-metabolising enzymes.     

Breast Cancer Resistance Protein-Mediated Efflux of Luteolin Glucuronides in HeLa Cells Overexpressing UDP-Glucuronosyltransferase 1A9

Purpose

UDP-glucuronosyltransferases (UGTs) are responsible for the formation of glucuronides of polyphenolic flavonoids. This study investigated the UGT1A9-mediated glucuronidation of luteolin and the kinetics of luteolin glucuronide efflux.

Method

HeLa cells overexpressing UGT1A9 (HeLa-UGT1A9) were used to determine the kinetics of breast cancer resistance protein (BCRP)-mediated transport of luteolin glucuronides. Human UGT isoforms were used to determine glucuronidation rates.

Results

UGT1A9 was found to catalyze the production of four luteolin glucuronides, including three known monoglucuronides and a novel 3′, 4′-diglucuronide. Ko143, a potent specific inhibitor of BCRP, significantly inhibited efflux of luteolin monoglucuronides from HeLa1A9 cells and increased their intracellular levels in a dose-dependent manner. The formation of luteolin diglucuronide was observed when intracellular concentration of total monoglucuronides went above 0.07 nM.

Conclusions

Intracellular accumulation of diglucuronide was detected at high monoglucuronide concentrations (>0.07 nM). Diglucuronide production is speculated to be a compensatory pathway for luteolin disposition.     

Accurate Prediction of Glucuronidation of Structurally Diverse Phenolics by Human UGT1A9 Using Combined Experimental and In Silico Approaches

Purpose

Catalytic selectivity of human UGT1A9, an important membrane-bound enzyme catalyzing glucuronidation of xenobiotics, was determined experimentally using 145 phenolics and analyzed by 3D-QSAR methods.

Methods

Catalytic efficiency of UGT1A9 was determined by kinetic profiling. Quantitative structure activity relationships were analyzed using CoMFA and CoMSIA techniques. Molecular alignment of substrate structures was made by superimposing the glucuronidation site and its adjacent aromatic ring to achieve maximal steric overlap. For a substrate with multiple active glucuronidation sites, each site was considered a separate substrate.

Results

3D-QSAR analyses produced statistically reliable models with good predictive power (CoMFA: q²?=?0.548, r²?=?0.949, r _pred ² ?=?0.775; CoMSIA: q²?=?0.579, r²?=?0.876, r _pred ² ?=?0.700). Contour coefficient maps were applied to elucidate structural features among substrates that are responsible for selectivity differences. Contour coefficient maps were overlaid in the catalytic pocket of a homology model of UGT1A9, enabling identification of the UGT1A9 catalytic pocket with a high degree of confidence.

Conclusion

CoMFA/CoMSIA models can predict substrate selectivity and in vitro clearance of UGT1A9. Our findings also provide a possible molecular basis for understanding UGT1A9 functions and substrate selectivity.     

Effect of a herbal extract containing curcumin and piperine on midazolam,flurbiprofen and paracetamol (acetaminophen) pharmacokinetics in healthy volunteers

Aims

Turmeric extract derived curcuminoids (curcumin, demethoxycurcumin and bisdemethoxycurcumin) are currently being evaluated for the treatment of cancer and Alzheimer''s dementia. Previous in vitro studies indicate that curcuminoids and piperine (a black pepper derivative that enhances curcuminoid bioavailability) could inhibit human CYP3A, CYP2C9, UGT and SULT dependent drug metabolism. The aim of this study was to determine whether a commercially available curcuminoid/piperine extract alters the pharmacokinetic disposition of probe drugs for these enzymes in human volunteers.

Methods

A randomized placebo-controlled six way crossover study was conducted in eight healthy volunteers. A standardized curcuminoid/piperine preparation (4 g curcuminoids plus 24 mg piperine) or matched placebo was given orally four times over 2 days before oral administration of midazolam (CYP3A probe), flurbiprofen (CYP2C9 probe) or paracetamol (acetaminophen) (dual UGT and SULT probe). Plasma and urine concentrations of drugs, metabolites and herbals were measured by HPLC. Subject sedation and electroencephalograph effects were also measured following midazolam dosing.

Results

Compared with placebo, the curcuminoid/piperine treatment produced no meaningful changes in plasma C_max, AUC, clearance, elimination half-life or metabolite levels of midazolam, flurbiprofen or paracetamol (α = 0.05, paired t-tests). There was also no effect of curcuminoid/piperine treatment on the pharmacodynamics of midazolam. Although curcuminoid and piperine concentrations were readily measured in plasma following glucuronidase/sulfatase treatment, unconjugated concentrations were consistently below the assay thresholds (0.05–0.08 μm and 0.6 μm, respectively).

Conclusion

The results indicate that short term use of this piperine-enhanced curcuminoid preparation is unlikely to result in a clinically significant interaction involving CYP3A, CYP2C9 or the paracetamol conjugation enzymes.     

Concentration effect relationship of CYP3A inhibition by ritonavir in humans

Purpose

To investigate the dose and concentration dependency of CYP3A inhibition by ritonavir using the established limited sampling strategy with midazolam for CYP3A activity.

Methods

An open, fixed-sequence study was carried out in 12 healthy subjects. Single ascending doses of ritonavir (0.1–300 mg) were evaluated for CYP3A inhibition in two cohorts using midazolam as a marker substance.

Results

Ritonavir administered as a single oral dose produced a dose-dependent CYP3A inhibition with an ID₅₀ of 3.4 mg. Using the measured ritonavir concentrations an exposure–inhibition effect curve was established with an IC₅₀ of 600 h pmol/L (AUC_2–4). Over the ritonavir dose range studied non-linear exposure of ritonavir was observed.

Conclusions

Ritonavir shows a dose and concentration effect relationship of CYP3A inhibition. In addition, a proposed auto-inhibition of ritonavir metabolism resulted in a non-linear exposure of ritonavir with sub-proportional concentrations at low doses. A time-dependent CYP3A activity may result when inhibitors of CYP3A with short elimination half-lives are used.     

Rate of onset of inhibition of gut-wall and hepatic CYP3A by clarithromycin

Aims

To determine the extent and time-course of hepatic and intestinal cytochrome P450 3A (CYP3A) inactivation due to the mechanism-based inhibitor clarithromycin.

Methods

Intestinal and hepatic CYP3A inhibition was examined in 12 healthy volunteers following the administration of single and multiple doses of oral clarithromycin (500 mg). Intestinal biopsies were obtained under intravenous midazolam sedation at baseline and after the first dose, on days 2–4, and on days 6–8 of the clarithromycin treatment. The formation of 1′-hydroxymidazolam in biopsy tissue and the serum 1′-hydroxymidazolam:midazolam ratio were indicators of intestinal and hepatic CYP3A activity, respectively.

Results

Intestinal CYP3A activity decreased by 64 % (p?=?0.0029) following the first dose of clarithromycin, but hepatic CYP3A activity did not significantly decrease. Repeated dosing of clarithromycin caused a significant decrease in hepatic CYP3A activity (p?=?0.005), while intestinal activity showed little further decline. The CYP3A5 or CYP3A4*1B genotype were unable to account for inter-individual variability in CYP3A activity.

Conclusions

Following the administration of clarithromycin, the onset of hepatic CYP3A inactivation is delayed compared to that of intestinal CYP3A. The time-course of drug–drug interactions due to clarithromycin will vary with the relative contribution of intestinal and hepatic CYP3A to the clearance and bioavailability of a victim substrate.     

Correlation of the UGT1A4 gene polymorphism with serum concentration and therapeutic efficacy of lamotrigine in Han Chinese of Northern China

Objective

The pharmacokinetics of lamotrigine (LTG) varies significantly among individuals and particularly among different ethnic groups. This is in part due to the presence of genetic polymorphisms affecting genes that metabolize LTG. UGT1A4 is a major metabolizing enzyme of LTG. The aim of this study was to investigate the effect of two UGT1A4 gene polymorphisms, UGT1A4 (70C?>?A) and UGT1A4 (142 T?>?G), on the levels and efficacy of LTG in Han Chinese patients with epilepsy.

Methods

The study cohort comprised 106 Han Chinese patients patients with epilepsy who were receiving LTG monotherapy. Blood samples were taken and LTG levels measured. The presence of UGT1A4 (70C?>?A) and UGT1A4 (142 T?>?G) was determined. The therapeutic efficacy of LTG at the 1-year time-point was assessed.

Results

All patients were homozygous for the CC genotype of UGT1A4 (70C?>?A), while the distribution of UGT1A4 (142 T?>?G) varied among patients. Two patients had a single nucleotide deletion at position 127 (UGT1A4 127delA). To evaluate the effect of the UGT1A4 (142 T?>?G) polymorphism on LTG pharmacokinetics, patients were divided into two groups. Group A included patients with the 142TG or 142GG polymorphism and Group B patients had the 142TT polymorphism. The normalized blood concentration and the efficacy of LTG were higher in Group B patients than in Group A patients (P?<?0.05). The two patients with UGT1A4 127delA genotype had extremely high blood levels of LTG, and treatment was discontinued in one of these patients due to a severe LTG-associated rash.

Conclusion

Patients with the UGT1A4 142TT polymorphism had a higher blood LTG concentration and better therapeutic efficacy, suggesting that this polymorphism influences LTG activity. The UGT1A4 127delA polymorphism significantly affected LTG levels and increased one of our patient's susceptibility to LTG-related adverse events.     

<Emphasis Type="Italic">In vitro</Emphasis> Phase I- and Phase II-Drug Metabolism in The Liver of Juvenile and Adult Göttingen Minipigs

Purpose

In view of pediatric drug development, juvenile animal studies are gaining importance. However, data on drug metabolizing capacities of juvenile animals are scarce, especially in non-rodent species. Therefore, we aimed to characterize the in vitro biotransformation of four human CYP450 substrates and one UGT substrate in the livers of developing Göttingen minipigs.

Methods

Liver microsomes from late fetal, Day 1, Day 3, Day 7, Day 28, and adult male and female Göttingen minipigs were incubated with a cocktail of CYP450 substrates, including phenacetin, tolbutamide, dextromethorphan, and midazolam. The latter are probe substrates for human CYP1A2, CYP2C9, CYP2D6, and CYP3A4, respectively. In addition, the UGT multienzyme substrate (from the UGT-Glo^TM assay), which is glucuronidated by several human UGT1A and UGT2B enzymes, was also incubated with the porcine liver microsomes.

Results

For all tested substrates, drug metabolism significantly rose postnatally. At one month of age, 60.5 and 75.4% of adult activities were observed for acetaminophen and dextrorphan formations, respectively, while 35.4 and 43.2% of adult activities were present for 4-OH-tolbutamide and 1’-OH-midazolam formations. Biotransformation of phenacetin was significantly higher in 28-day-old and adult females compared with males.

Conclusions

Maturation of metabolizing capacities occurred postnatally, as described in man.

     

Evaluation of felodipine as a potential perpetrator of pharmacokinetic drug-drug interactions

Objective

To evaluate felodipine as a potential perpetrator of pharmacokinetic drug-drug interactions (PK-DDIs) involving cytochrome P450 (CYP) enzymes and P-glycoprotein (P-gp).

Methods

Felodipine extended-release 10 mg was administered daily to six healthy subjects for 7 days (days 1–7). Subjects were administered a modified Inje cocktail comprising the selective probe substrates caffeine 100 mg (CYP1A2), losartan 25 mg (CYP2C9), omeprazole 20 mg (CYP2C19), dextromethorphan 30 mg (CYP2D6), midazolam 2 mg (CYP3A) and digoxin 250 μg (P-gp) on day 0 (prior to felodipine exposure) and day 7 (after felodipine exposure). Plasma samples were collected over 24 h and drug concentrations measured by UPLC-MS/MS.

Results

The geometric means of the area under the plasma concentration–time curve ratios (probe AUC after felodipine exposure/probe AUC prior to felodipine exposure) and 95 % confidence intervals for each probe were: caffeine 0.91 (0.64–1.30), losartan 1.05 (0.95–1.15), omeprazole 1.17 (0.78–1.76), dextromethorphan 1.46 (1.00–2.12), midazolam 1.23 (0.99–1.52) and digoxin 1.01 (0.89–1.15).

Conclusion

Felodipine may be a weak in vivo inhibitor of CYP3A and CYP2D6 but is unlikely to act as a significant perpetrator of PK-DDIs.     

Factors influencing the pharmacokinetics of prophylactic posaconazole oral suspension in patients with acute myeloid leukemia or myelodysplastic syndrome

Objectives

To estimate the pharmacokinetic (PK) properties of posaconazole in patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) undergoing chemotherapy in a clinical setting.

Methods

Posaconazole concentrations in patients with AML/MDS receiving prophylactic posaconazole were determined by high-performance liquid chromatography. A population PK model with nonlinear mixed effect modeling was developed. The list of tested covariates included age, weight, height, gender, posaconazole dose, ethnicity, co-administration of antineoplastic chemotherapy, ranitidine or pantoprazole, coincident fever, diarrhea, leukocyte counts, and γ-glutamyltransterase plasma activity.

Results

A total of 643 serum concentrations of posaconazole from 84 patients were obtained. A one-compartment model with first order absorption and elimination as the basic structural model appropriately described the data, with an apparent clearance of 56.8?L/h [95% confidence interval (CI) 52.8–60.8?L/h] and an apparent volume of distribution of 2,130 L (95% CI 1,646–2,614?L). Significant effects on apparent clearance (CL/F) were found for presence of diarrhea and for co-medication with proton-pump inhibitors (1.5- and 1.6-fold increase in CL/F, respectively), weight (33.4?L larger apparent volume of distribution per kilogram), and co-administration of chemotherapy (0.6-fold lower apparent volume of distribution).

Conclusion

We developed a prediction basis for mean posaconazole concentrations in AML/MDS patients. Patient weight, presence of diarrhea, and concomitant medication (chemotherapy and pantoprazole) showed significant effects on posaconazole exposure. Corresponding adjustments of the starting dose according to the presence of diarrhea and during the co-administration of chemotherapy or proton-pump inhibitors appear justified before therapeutic drug monitoring results are available. Further investigation of the interaction between different chemotherapeutic regimens and posaconazole is warranted.     

Assessment of interaction potential of AZD2066 using in vitro metabolism tools, physiologically based pharmacokinetic modelling and in vivo cocktail data

Purpose

Static and dynamic (PBPK) prediction models were applied to estimate the drug–drug interaction (DDI) risk of AZD2066. The predictions were compared to the results of an in vivo cocktail study. Various in vivo measures for tolbutamide as a probe agent for cytochrome P450 2C9 (CYP2C9) were also compared.

Methods

In vitro inhibition data for AZD2066 were obtained using human liver microsomes and CYP-specific probe substrates. DDI prediction was performed using PBPK modelling with the SimCYP simulator? or static model. The cocktail study was an open label, baseline, controlled interaction study with 15 healthy volunteers receiving multiple doses of AD2066 for 12 days. A cocktail of single doses of 100 mg caffeine (CYP1A2 probe), 500 mg tolbutamide (CYP2C9 probe), 20 mg omeprazole (CYP2C19 probe) and 7.5 mg midazolam (CYP3A probe) was simultaneously applied at baseline and during the administration of AZD2066. Bupropion as a CYP2B6 probe (150 mg) and 100 mg metoprolol (CYP2D6 probe) were administered on separate days. The pharmacokinetic parameters for the probe drugs and their metabolites in plasma and urinary recovery were determined.

Results

In vitro AZD2066 inhibited CYP1A2, CYP2B6, CYP2C9, CYP2C19 and CYP2D6. The static model predicted in vivo interaction with predicted AUC ratio values of >1.1 for all CYP (except CYP3A4). The PBPK simulations predicted no risk for clinical relevant interactions. The cocktail study showed no interaction for the CYP2B6 and CYP2C19 enzymes, a possible weak inhibition of CYP1A2, CYP2C9 and CYP3A4 activities and a slight inhibition (29 %) of CYP2D6 activity. The tolbutamide phenotyping metrics indicated that there were significant correlations between CL_form and AUC_TOL, CL, Ae_met and LnTOL_24h. The MR_Ae in urine showed no correlation to CL_form.

Conclusions

DDI prediction using the static approach based on total concentration indicated that AZD20066 has a potential risk for inhibition. However, no DDI risk could be predicted when a more in vivo-like dynamic prediction method with the PBPK with SimCYP? software based on early human PK data was used and more parameters (i.e. free fraction in plasma, no DDI risk) were taken into account. The clinical cocktail study showed no or low risks for clinical relevant DDI interactions. Our findings are in line with the hypothesis that the dynamic prediction method predicts DDI in vivo in humans better than the static model based on total plasma concentrations.     

Effect of glycyrrhizin on the activity of CYP3A enzyme in humans

Background

Glycyrrhizin is a major ingredient of licorice which is widely used in the treatment of various diseases such as chronic hepatitis. Licorice or glycyrrhizin has been shown to alter the activity of CYP3A in rodents. The influence of glycyrrhizin on CYP3A has not been elucidated in humans.

Objective

To investigate the effects of repeated glycyrrhizin ingestion on the oral pharmacokinetics of midazolam, a probe drug for CYP3A activity in humans.

Methods

Sixteen healthy adult male subjects were enrolled in a two-phase randomized crossover design. In each phase the volunteers received placebo or glycyrrhizin for 14 days. On the 15th day, midazolam was administered and blood samples were obtained to determine midazolam plasma concentrations. Bioequivalence was assessed by determining geometric mean ratios (GMRs) and 90% confidence intervals (90% CI).

Results

The geometric mean (geometric coefficient of variation) for the $ {\hbox{AU}}{{\hbox{C}}_{0 - \infty }} $ of midazolam in the placebo group was 196.4 ng·h/ml (30.3%) and after glycyrrhizin treatment, 151.3 ng·h/ml (34.7%). The GMRs and 90% CI for $ {\hbox{AU}}{{\hbox{C}}_{0 - \infty }} $ and C_max of midazolam in the presence/absence of glycyrrhizin were 0.77 (0.70, 0.89) and 0.83 (0.74, 1.01), respectively. The 90% CI for $ {\hbox{AU}}{{\hbox{C}}_{0 - \infty }} $ and C_max for the GMR of glycyrrhizin over placebo were both out of the no-effect boundaries of 0.80–1.25.

Conclusions

Administration of glycyrrhizin resulted in a modest induction of CYP3A that was clinically relevant according to the bioequivalence analysis.     

Effects of vercirnon on the activity of CYP3A4, CYP2C19 and CYP2C8 enzymes and BCRP and OATP1B1 transporters using probe substrates

Purpose

Vercirnon is a CCR9 chemokine receptor antagonist being developed for the treatment of Crohn’s disease. As a variety of concomitant medications are often required for the treatment of Crohn’s disease, it is important to characterise the drug interaction profile of vercirnon. To confirm the results of previous in vitro inhibition studies, this study assessed the in vivo effect of vercirnon on the activity of cytochrome P450 enzymes (CYP3A4, CYP2C19 and CYP2C8) and drug transport proteins (BCRP and OATP1B1) using probe substrates.

Methods

This was an open-label, single-sequence, repeat-dose study conducted in 24 healthy adult subjects. On days 1–4, subjects received probe substrates (midazolam, pioglitazone, omeprazole and rosuvastatin; in that order), followed by administration of vercirnon 500 mg twice daily (BID) on days 5–14. On days 11–14, in addition to vercirnon 500 mg BID, subjects also received probe substrates as on days 1–4. Blood samples were collected for pharmacokinetic analysis of probe substrates, vercirnon and two of its metabolites.

Results

Geometric least-squares mean ratios (90 % confidence interval) of area under the concentration-time curve from time zero to infinity for probe administered with vercirnon (test) compared with probe alone (reference) for midazolam, pioglitazone, omeprazole and rosuvastatin were 0.92 (0.85, 0.99), 1.01 (0.95, 1.07), 0.99 (0.76,1.31) and 0.98 (0.88, 1.09), respectively.

Conclusions

Co-administration of probe substrates midazolam, pioglitazone, omeprazole, and rosuvastatin following repeat dosing of vercirnon 500 mg BID demonstrated vercirnon had no clinically significant effect on CYP3A4, CYP2C8, CYP2C19 enzyme activity or BCRP or OATP1B1 transporter activity.     

Influence of UDP-glucuronosyltransferase polymorphisms on valproic acid pharmacokinetics in Chinese epilepsy patients

Purpose

The aim of this study was to investigate the genetic polymorphisms of UGT1A3, UGT1A6, and UGT2B7 in Chinese epilepsy patients and their potential influence on the pharmacokinetics of valproic acid (VPA).

Methods

The genetic architectures of UGT1A3, UGT1A6, and UGT2B7 in 242 epilepsy patients were detected by DNA sequencing and PCR-restriction fragment length polymorphism. Steady-state plasma concentrations of VPA in 225 patients who had received VPA (approx. 250–1,000?mg/day) for at least 2 weeks were determined and associated with UGT polymorphisms.

Results

The allelic distribution of UGT1A3 in our Chinese epilepsy patients was significantly different from that in healthy subjects based on reference data. The standardized trough plasma concentration (C_S) of VPA was much lower in our patients with the UGT1A3*5 variant than in the wild type carriers (3.24?±?1.05 vs. 4.68?±?1.24?μg·kg·mL^-1·mg^-1, P?Conclusion Our results suggest that UGT1A3*5 may be an important determinant of individual variability in the pharmacokinetics of VPA and that it may be necessary to increase VPA dose for UGT1A3*5 carriers to ensure its therapeutic range of 50–100?μg/mL.     

Pharmacokinetics of dolutegravir in HIV-seronegative subjects with severe renal impairment

Purpose

Dolutegravir (DTG), an unboosted HIV integrase inhibitor (INI), is metabolized by UGT1A1 and to a minor extent by CYP3A. Renal elimination of unchanged DTG is very low (< 1 %). As renal impairment may affect pharmacokinetics (PK), even for drugs primarily metabolized or secreted in bile, this study investigated the effect of renal impairment on the PK of DTG.

Methods

This was an open-label, single-dose study of oral DTG 50 mg administered to subjects with severe renal impairment (creatinine clearance [CLcr] <30 mL/min; not on dialysis) and to healthy controls (CLcr >90 mL/min) matched for gender, age and body mass index (8 subjects per group). Serial PK samples were collected up to 72 h post-dose for determination of DTG and DTG-glucuronide (DTG-Gluc) concentrations in plasma. DTG unbound fraction in plasma was determined at 3 and 24 h. PK parameters were determined by non-compartmental methods and compared between groups by analysis of covariance.

Results

DTG was well tolerated with a low incidence of Grade 1 adverse events. DTG PK parameters showed significant overlap between groups. DTG mean exposure was lower in subjects with severe renal impairment compared to healthy, matched subjects: AUC(0-∞) and Cmax were 40 % and 23 % lower, while mean DTG-Gluc was increased. Renal impairment did not affect DTG fraction unbound in plasma.

Conclusions

The modest reductions in mean PK exposures for DTG and increases for DTG-Gluc in the severe renal impairment group are not considered clinically significant. DTG does not require dose adjustment in patients with renal impairment.     

Translational PK�CPD modelling of molecular target modulation for the AMPA receptor positive allosteric modulator Org 26576

Introduction

The ??-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor potentiator Org 26576 represents an interesting pharmacological tool to evaluate the utility of glutamatergic enhancement towards the treatment of psychiatric disorders. In this study, a rat?Chuman translational pharmacokinetic?Cpharmacodynamic (PK?CPD) model of AMPA receptor modulation was used to predict human target engagement and inform dose selection in efficacy clinical trials.

Methods

Modelling and simulation was applied to rat plasma and cerebrospinal fluid (CSF) pharmacokinetic and pharmacodynamic measurements to identify a target concentration (EC₈₀) for AMPA receptor modulation. Human plasma pharmacokinetics was determined from 33 healthy volunteers and eight major depressive disorder patients. From four out of these eight patients, CSF PK was also determined. Simulations of human CSF levels were performed for several doses of Org 26576.

Results

Org 26576 (0.1?C10?mg/kg, i.v.) potentiated rat hippocampal AMPA receptor responses in an exposure-dependant manner. The rat plasma and CSF PK data were fitted by one-compartment model each. The rat CSF PK?CPD model yielded an EC₈₀ value of 593?ng/ml (90% confidence interval 406.8, 1,264.1). The human plasma and CSF PK data were simultaneously well described by a two-compartment model. Simulations showed that in humans at 100?mg QD, CSF levels of Org 26576 would exceed the EC₈₀ target concentration for about 2?h and that 400?mg BID would engage AMPA receptors for 24?h.

Conclusion

The modelling approach provided useful insight on the likely human dose?Cmolecular target engagement relationship for Org 26576. Based on the current analysis, 100 and 400?mg BID would be suitable to provide ??phasic?? and ??continuous?? AMPA receptor engagement, respectively.     

Edoxaban population pharmacokinetics and exposure–response analysis in patients with non-valvular atrial fibrillation

Purpose

The aim of this study was to evaluate the population pharmacokinetics (PK) and exposure–response relationship of edoxaban in patients with non-valvular atrial fibrillation (AF).

Methods

Concentration data from 1,134 subjects in 11 clinical studies (eight phase I, one phase II, and two phase III) were used to perform a population PK analysis, including estimation of the bioavailability and quantification of the effects of P-glycoprotein (P-gp) inhibitors as well as renal impairment on edoxaban PK. The potential relationship between edoxaban PK exposure and incidence of bleeding events was explored based on data from 893 AF patients.

Results

Absolute bioavailability of edoxaban was estimated as 58.3 %. With oral dosing of edoxaban, co-administration of various P-gp inhibitors significantly increased edoxaban bioavailability and decreased volume of distribution (V ₂), resulting in a predicted increase of 33–77 % in area under the curve (AUC) and 65–104 % in C _max. A much smaller increase was seen in edoxaban concentration at 24 h post-dose (C ₂₄, ?24 to 38 %), due to decreased V ₂ and shortened elimination half-life. With IV dosing of edoxaban, co-administration of the P-gp inhibitor quinidine decreased both edoxaban clearance (CL) and V ₂, resulting in an increase of 32 % in AUC and 66 % in C ₂₄. Creatinine clearance was a significant covariate on renal clearance, whereas age and body weight significantly affected nonrenal clearance. Model-predicted steady state C _min was slightly higher, but AUC was comparable for patients who had severe renal impairment and received edoxaban 15 mg once daily (QD) versus patients who had normal renal function or mild renal impairment and received edoxaban 30 mg QD. Exposure–response analysis suggested that edoxaban C _min and country/region are significantly associated with the incidence of bleeds.

Conclusions

The model provided reasonable estimation with regard to the absolute bioavailability of edoxaban, the magnitude of change in edoxaban exposure upon co-administration of P-gp inhibitors, and the impact of renal impairment on edoxaban clearance. Analysis results supported a 50 % dose reduction scheme for subjects with severe renal impairment. Further confirmation will be sought by incorporating clinical safety and efficacy information from larger phase III trials.     

Effect of the ethinylestradiol/levonorgestrel combined oral contraceptive on the activity of cytochrome P4503A in obese women

AIM(S)

While it is known that CYP3A4/5 activity is decreased with combined oral contraceptive (COC) use and obesity suppresses CYP expression, the combined effects of obesity and COC use on CYP3A4/5 activity are unclear. Therefore, our aim was to examine the effect of COC usage on CYP3A4/5 activity in obese women.

METHODS

Thirty-four, obese (body mass index, BMI > 30 kg m⁻²) women of reproductive age (18–35 years old) were placed on a COC pill containing 20 µg ethinylestradiol/100 µg levonorgestrel for 21 days starting at the onset of menses. A midazolam pharmacokinetic study was conducted prior to initiation and after 21 days of COC treatment. Serial blood samples were collected and plasma concentrations of midazolam were measured using liquid chromatography tandem mass spectrometry. Pharmacokinetic parameters were estimated using a non-compartmental method.

RESULTS

Midazolam clearance, a surrogate measure of CYP3A4/5 activity, was significantly decreased upon COC use (63.3 l h⁻¹vs. 53.9 l h⁻¹, P < 0.05). A median decrease of 5.6 l h⁻¹ (95% CI −4.1, 13.3 l h⁻¹) was observed. However, the magnitude of change was similar to that reported in women with normal BMI.

CONCLUSIONS

Although we hypothesized that obesity might amplify the impact on CYP3A4/5 activity in COC users, we found that this was not the case. This finding is reassuring regarding potential additional drug−drug interactions in obese COC users as CYP3A4/5 is a major enzyme in the metabolism of many marketed drugs.