Linking Endogenous Factor Xa Activity, a Biologically Relevant Pharmacodynamic Marker, to Edoxaban Plasma Concentrations and Clinical Outcomes in the ENGAGE AF-TIMI 48 Trial.

BACKGROUND: We previously reported exogenous antifactor Xa (FXa) activity as a pharmacokinetic surrogate marker for edoxaban plasma concentrations. Inhibition of endogenous FXa activity is a more biologically relevant pharmacodynamic measure of edoxaban activity. Here we describe the value of endogenous FXa activity as a pharmacodynamic marker linking edoxaban concentrations and clinical outcomes in the ENGAGE AF-TIMI 48 trial (Effective Anticoagulation With Factor Xa Next Generation in Atrial Fibrillation-Thrombolysis in Myocardial Infarction Study 48). METHODS: In ENGAGE AF-TIMI 48, edoxaban was administered in higher dose (60/30 mg QD) and lower dose (30/15 mg QD) regimens. Both regimens incorporated a 50% dose reduction in patients with characteristics known to increase edoxaban concentration. Pharmacokinetic-pharmacodynamic modeling was performed in a subgroup of 3029 patients who had samples collected for endogenous FXa activity (measured using an assay after endogenous FX was activated with Russell viper venom). RESULTS: Endogenous FXa activity decreased with increasing edoxaban concentrations of ≤440 ng/mL, indicating that inhibition of endogenous FXa activity is saturated above this concentration threshold. Baseline endogenous FXa activity averaged 92.1±20.9% (relative to normal control samples) and was lower with older age, with lower body weight, and in male patients. Model-predicted 24-hour average percentages of inhibition of endogenous FXa activity were 35.8±5.18, 29.1±3.92, 21.9±3.80, and 16.4±2.70 for the higher dose edoxaban regimen 60 mg, dose-reduced higher dose edoxaban regimen 30 mg, lower dose edoxaban regimen 30 mg, and dose-reduced lower dose edoxaban regimen 15 mg groups, respectively. A greater average percentage of inhibition of endogenous FXa activity was associated with a lower incidence of ischemic stroke or systemic embolism and a higher risk of major bleeding ( P<0.001). In a typical subject, the predicted risks for the 10th and 90th percentiles of inhibition of endogenous FXa activity were 1.04% and 0.57% for incidence of ischemic stroke or systemic embolism and 1.35% and 2.33% for major bleeding, respectively. CONCLUSIONS: The extent of inhibition of endogenous FXa activity is influenced by edoxaban dosing and clinical characteristics, and it is associated with both antithrombotic benefit and risk of bleeding. This approach of linking endogenous FXa activity to clinical outcomes may be used to guide dose selection in future clinical trials, monitor patients in certain clinical scenarios, or refine the doses of oral FXa inhibitors in patients who require precise anticoagulation therapy. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov . Unique identifier: NCT00781391.

Evaluating a physiologically based pharmacokinetic model for prediction of omeprazole clearance and assessing ethnic sensitivity in CYP2C19 metabolic pathway.

PURPOSE: The purpose of this study is to evaluate the ethnicity-specific population models in the SimCYP Simulator® for prediction of omeprazole clearance with attention to differences in the CYP2C19 metabolic pathway. METHODS: The SimCYP® models incorporating Caucasian, Chinese, and Japanese population-specific demographic, physiological, and enzyme data were applied to simulate omeprazole pharmacokinetics. Published pharmacokinetic data of omeprazole after intravenous or oral administration in Caucasian, Chinese, and Japanese were used for the evaluation. RESULTS: Following oral administration, the ratio of the predicted to observed geometric mean of omeprazole clearance in Caucasian extensive metabolizers (EMs) was 0.88. The ratios in Chinese EMs were 1.16 and 0.99 after intravenous and oral administration, respectively. The ratios in Japanese EMs were 0.88 and 0.71 after intravenous and oral administration, respectively. Significant differences (2-fold) in the observed oral clearance of omeprazole were identified between Caucasian and Asian (Chinese and Japanese) EMs while the observed oral and intravenous clearances of omeprazole were similar between Chinese and Japanese EMs. Physiologically based pharmacokinetics (PBPK) models within SimCYP accurately predicted the difference in the observed oral clearance between Caucasian and Chinese EMs but overpredicted the difference between Caucasians and Japanese EMs due to under-prediction of oral clearance in Japanese EMs. CONCLUSIONS: The PBPK model within SimCYP adequately predicted omeprazole clearance in Caucasian, Chinese, and Japanese EMs and the 2-fold differences in clearance of omeprazole between Caucasian and Asian EMs. This may lead to early identification of ethnic sensitivity in clearance and the need for different dosing regimens in a specific ethnic group for substrates of CYP2C19 which can support the rational design of bridging clinical trials.

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.

Nilotinib population pharmacokinetics and exposure-response analysis in patients with imatinib-resistant or -intolerant chronic myeloid leukemia.

PURPOSE: We evaluated the population pharmacokinetics (PK) and exposure-response relationship of nilotinib in patients with imatinib-resistant or -intolerant chronic myeloid leukemia (CML). METHODS: Concentration data from 493 patients with CML in chronic phase (CML-CP), accelerated phase, or blast crisis were used to perform a population pharmacokinetic analysis using nonlinear mixed-effect modeling. Steady-state nilotinib trough concentrations (Cmin) in individual patients were estimated from the population PK model for correlation with the efficacy and safety variables. Exposure-efficacy analysis was performed in patients with CML-CP, whereas exposure-safety analysis was performed in all patients who had both nilotinib PK data and efficacy/safety measures available. RESULTS: Baseline demographics and CML disease phase did not significantly affect nilotinib PK. Patients with a lower Cmin had significantly longer time to complete cytogenetic response (P = 0.010), longer time to major molecular response (P = 0.012), shorter time to progression (TTP; P = 0.009), and a trend toward lower response rates vs. patients with higher Cmin. A joint effect of prognostic risk score and Cmin on TTP was significant (P < 0.001). Nilotinib Cmin was also associated with the occurrence of all-grade elevations in total bilirubin (P < 0.001) and lipase (P = 0.002) levels. CONCLUSIONS: When tolerability allows, adherence to the nilotinib dose (400 mg twice daily) in order to maintain sufficient Cmin is important in maximizing the efficacy of nilotinib in patients with imatinib-resistant or -intolerant CML.

Omeprazole limited sampling strategies to predict area under the concentration-time curve ratios: implications for cytochrome P450 2C19 and 3A phenotyping.

PURPOSE: To develop a limited sampling strategy (LSS) to predict area under the concentration-time curve (AUC) ratios of omeprazole (AUC(OPZ)) to its metabolites 5-hydroxyomeprazole (AUC(5OH)) and omeprazole sulfone (AUC(SUL)) as phenotyping parameters for cytochrome P450 (CYP) 2C19 and 3A. METHODS: Data were obtained from 37 (4 women) Caucasian, Chinese, and Korean healthy adults from three published studies. The AUC(OPZ), AUC(5OH), and AUC(SUL) were calculated via noncompartmental analysis. Observed AUC(OPZ, OBS)/AUC(5OH, OBS) and AUC(OPZ, OBS)/AUC(SUL, OBS) were determined. Plasma concentrations of omeprazole, 5-hydroxyomeprazole, and omeprazole sulfone at 1, 1.5, 2, 3, 4, 6, and 8 h post-dose were used to generate limited sampling strategy (LSS) models to predict AUC(OPZ,PRE)/AUC(5OH,PRE) and AUC(OPZ,PRE/)AUC(SUL,PRE). Bias and precision were assessed via percentage mean prediction error (%MPE) and percentage mean absolute error (%MAE), with acceptable limits being <15%. RESULTS: For CYP2C19, the AUC(OPZ,OBS)/AUC(5OH,OBS) was [mean ± standard deviation (SD)] 2.10 ± 1.63. Five LSS models of AUC(OPZ,PRE)/AUC(5OH,PRE) were generated, but none met the bias or precision criteria. Upon stratification by CYP2C19 genotype and ethnicity, a three-timepoint (at 1, 2, and 4 h) LSS model accurately predicted AUC(OPZ)/AUC(5OH) in Caucasian CYP2C19*1/*1 subjects. For CYP3A, AUC(OPZ,OBS)/AUC(SUL,OBS) (mean ± SD) was 1.79 ± 0.67. All LSS models had unacceptable %MAE, even when stratified by CYP2C19 genotype and ethnicity. CONCLUSIONS: A LSS model to predict AUC(OPZ)/AUC(5OH), and thus CYP2C19 activity, was generated for Caucasian CYP2C19*1/*1 subjects. However, additional model validation is needed prior to general use. LSS models to predict AUC(OPZ)/AUC(SUL), and thus CYP3A activity, were not possible, even upon stratification by CYP2C19 genotype and ethnicity.

Population pharmacokinetic and exposure-response analysis of nilotinib in patients with newly diagnosed Ph+ chronic myeloid leukemia in chronic phase.

PURPOSE: We investigated the population pharmacokinetics and exposure-response relationship of nilotinib in patients with newly diagnosed chronic myeloid leukemia (CML) in chronic phase. METHODS: Nilotinib was given at 300 mg or 400 mg twice daily. Serum concentration data (sparse and full pharmacokinetic profiles) were obtained from 542 patients over 12 months. A population pharmacokinetic analysis was performed using nonlinear mixed-effect modeling. Exposure-response relationships were explored graphically or using logistic regression models. RESULTS: Nilotinib concentrations were stable over 12 months. Patients in the 400 mg twice-daily arm had an 11.5% higher exposure than did those in the 300 mg twice-daily arm, and the relative bioavailability of nilotinib 400 mg twice daily was 0.84 times that of 300 mg twice daily. Patient demographics did not significantly affect nilotinib pharmacokinetics. The occurrence of all-grade total bilirubin elevation was significantly higher in patients with higher nilotinib exposure, and a positive correlation was also observed between nilotinib exposure and QTcF change on electrocardiograms from baseline. There was no significant relationship between nilotinib exposure and major molecular response at 12 months. CONCLUSIONS: There is a less than proportional dose-exposure relationship between nilotinib 300 mg and 400 mg twice-daily doses. Blood level testing is unlikely to play an important role in the general management of patients with newly diagnosed CML treated with nilotinib.

Effects of CYP2D6*10, CYP3A5*3, CYP1A2*1F, and ABCB1 C3435T polymorphisms on the pharmacokinetics of flecainide in healthy Chinese subjects.

BACKGROUND: Although flecainide is thought to be meta-bolized predominantly by cytochrome P450 (CYP) 2D6, it shows pharmacokinetic interactions with drugs, such as verapamil and digoxin, which may suggest other CYP pathways or ATP-binding cassette (ABC) transporters might be involved. This study evaluated effects of common polymorphisms in Chinese in CYP2D6, CYP3A5, CYP1A2, and ABCB1 on flecainide pharmacokinetics. METHODS: Single oral 100-mg doses of flecainide were given to 15 healthy male Chinese subjects who were genotyped for the CYP2D6*2, *5, *10, CYP3A5*3, CYP1A2*1F and ABCB1 C1236T, G2677T/A, and C3435T polymorphisms. RESULTS: There was no significant difference in the pharmacokinetics of flecainide among CYP2D6 (mainly involving *10) genotypes. The CYP3A5*3/*3 subjects (n=8) had a 26% higher systemic exposure (AUC0-∞) and 17% lower apparent oral clearance of flecainide than the combined group of CYP3A5*1/*1 (n=6) and CYP3A5*1/*3 (n=1) subjects (p<0.05). Subjects homozygous for CYP1A2*1F tended to have lower systemic exposure and increased clearance of flecainide compared to those with CYP1A2*1A/1F in subjects with at least one CYP2D6 variant allele. CONCLUSIONS: The disposition of flecainide appeared to be influenced by the CYP3A5*3 and possibly the CYP1A2*1F polymorphisms, particularly in subjects with CYP2D6 variant alleles.

Effects of nilotinib on single-dose warfarin pharmacokinetics and pharmacodynamics: a randomized, single-blind, two-period crossover study in healthy subjects.

BACKGROUND AND OBJECTIVE: Nilotinib (Tasigna®), a highly selective and potent BCR-ABL tyrosine kinase inhibitor, is approved for the treatment of chronic myeloid leukaemia in the chronic phase (CML-CP) and the accelerated phase (CML-AP) in patients resistant or intolerant to prior therapy, including imatinib. Nilotinib has shown competitive inhibition of cytochrome P450 enzyme (CYP) 2C9 in vitro, but its effect on CYP2C9 activity in humans is unknown. This study evaluated the effects of nilotinib on the pharmacokinetics and pharmacodynamics of warfarin, a sensitive CYP2C9 substrate, in healthy subjects. METHODS: Twenty-four subjects (six female, 18 male, aged 21-65 years) were enrolled to receive a single oral dose of warfarin 25 mg with either a single oral dose of nilotinib 800 mg or matching placebo (all administered 30 minutes after consumption of a high-fat meal) in a crossover design. Serial blood samples were collected post-dose for determining serum concentrations of nilotinib and plasma concentrations of S- and R-warfarin. Prothrombin time (PT) and international normalized ratio (INR) values were determined as pharmacodynamic measures of warfarin activity. CYP2C9 genotyping was performed in all subjects using TaqMan® assay. RESULTS: Sixteen subjects were identified as CYP2C9 extensive metabolizers (EMs) and eight as intermediate metabolizers (IMs). There were no CYP2C9 poor metabolizers. Pharmacokinetic parameters of S- and R-warfarin were similar between the two treatments (warfarin + nilotinib vs warfarin alone) in both the EM and the IM groups. The geometric mean ratios (90% CIs) for the maximum concentration in plasma (C(max)) and area under the concentration-time curve from time zero to infinity (AUC(∞)) of S-warfarin in plasma in all subjects were 0.98 (0.95, 1.02) and 1.03 (0.99, 1.07), respectively, and for R-warfarin 1.00 (0.96, 1.04) and 1.02 (0.99, 1.04), respectively. Mean ratios for the maximum observed value and AUC from time zero to the last sampling time for PT were 1.00 (0.96, 1.04) and 1.00 (0.98, 1.02), respectively, and for the maximum observed value for INR and the AUC from time zero to the last sampling time for INR were 1.00 (0.97, 1.03) and 1.00 (0.99, 1.01), respectively. Mean ± SD serum nilotinib C(max) was 1872 ± 560 ng/mL, which is comparable to steady-state C(max) in CML and gastrointestinal stromal tumour patients receiving twice-daily 400 mg doses. Adverse events observed following either treatment were generally consistent with the known safety profiles of both drugs, and no new safety issues were observed. CONCLUSION: The study results demonstrate that nilotinib has no effect on single-dose warfarin pharmacokinetics and pharmacodynamics. This implies that nilotinib is unlikely to inhibit CYP2C9 activity in human subjects. These findings suggest that warfarin and nilotinib may be used concurrently as needed.

Effect of multidrug resistance gene-1 (ABCB1) polymorphisms on the single-dose pharmacokinetics of cloxacillin in healthy adult Chinese men.

BACKGROUND: Plasma concentrations of cloxacillin have been found to vary as much as 20-fold among individuals receiving the same oral dose. There is evidence that cloxacillin may be a substrate for P-glycoprotein, suggesting that polymorphisms in the ABCB1 gene may be a contributing factor to the observed variability in plasma cloxacillin concentrations. OBJECTIVE: This study investigated the effect of ABCB1 polymorphisms on the pharmacokinetic profile of cloxacillin in healthy subjects. METHODS: A single oral dose of cloxacillin 500 mg was administered to healthy Chinese male subjects under fasting conditions. Serial blood and urine samples were collected for up to 6 hours after administration. A high-performance liquid chromatography method was used to determine plasma cloxacillin pharmacokinetics and urinary excretion. A polymerase chain reaction technique was used for genotyping of 3 single nucleotide polymorphisms (SNPs) of the ABCB1 gene: exon 12 C1236T, exon 21 G2677T/A, and exon 26 C3435T. Cloxacillin pharmacokinetic parameters and urinary excretion were then compared according to genotype and haplotype groups. RESULTS: The study included 18 healthy Chinese male subjects who ranged in age from 21 to 26 years, had a mean weight ranging from 55.6 to 70.6 kg, and had normal renal function at baseline (mean [SD] serum creatinine, 93.4 [11.0] micromol/L). Plasma concentrations of cloxacillin were generally lower in the group carrying the 1236CC genotype (n = 3) compared with those carrying the 1236CT genotype (n = 9) or the 1236TT genotype (n = 6). Compared with the other groups, carriers of the 1236CC genotype had a significantly lower mean Cmax (-53%; P = 0.013) and AUC(0-infinity) (-40%; P = 0.044), and a significantly higher mean apparent oral clearance (35%; P = 0.013). They also had significantly lower urinary excretion of cloxacillin over 6 hours (-52%; P = 0.027). There were no significant differences in cloxacillin t(1/2) or renal clearance between the 3 C1236T genotypes, nor was the G2677T or C3435T SNP associated with any significant changes in the cloxacillin pharmacokinetic profile. Among subjects with 1 of the 3 major haplotype pairs, those carrying the CGC/CGC pair had a significantly lower C(max) (P = 0.017), AUC (P = 0.032), and urinary excretion of cloxacillin (P = 0.026) compared with those carrying the CGC/TGC and TTT/TTT pairs. CONCLUSIONS: In this small population of healthy Chinese men, the C1236T variant of ABCB1 appeared to be an important contributor to interindi-vidual differences in plasma cloxacillin exposure, most likely through an effect on oral absorption rather than on disposition. Studies of multiple doses in larger sample sizes are needed to confirm these findings.

Edoxaban Versus Warfarin in Patients With Atrial Fibrillation and History of Liver Disease.

BACKGROUND: Patients with liver disease have increased risk of thrombosis and bleeding but are typically excluded from trials of direct oral anticoagulant agents. OBJECTIVES: This study evaluated the pharmacokinetics (PK), pharmacodynamics (PD), clinical efficacy and safety of edoxaban versus warfarin in patients with atrial fibrillation (AF) and history of liver disease. METHODS: ENGAGE AF-TIMI 48 (Effective Anticoagulation With Factor Xa Next Generation in Atrial Fibrillation-Thrombolysis In Myocardial Infarction Study 48) was a randomized, double-blind trial comparing edoxaban with warfarin in patients with AF followed for 2.8 years. History of liver disease was defined as investigator-reported liver disease or >2-fold transaminase elevation at randomization. The primary efficacy and safety endpoints of stroke or systemic embolic event (SSEE) and major bleeding were assessed stratified by history of liver disease. PK/PD assessments of edoxaban included endogenous and extrinsic factor Xa activity and edoxaban concentration. RESULTS: Among 21,105 patients, 1,083 (5.1%) had a history of liver disease; they had a higher prevalence of many comorbidities. The adjusted risks of SSEE were similar (adjusted hazard ratio [HRadj]: 0.90; 95% confidence interval [CI]: 0.67 to 1.22; p = 0.50), but major bleeding was more common in patients with liver disease (HRadj: 1.38; 95% CI: 1.10 to 1.74; p = 0.005). There were no significant differences in PK/PD assessment of edoxaban in patients with versus without liver disease. The HRs for higher-dose edoxaban versus warfarin for SSEE were 0.86 (95% CI: 0.73 to 1.01) in patients without and 1.11 (95% CI: 0.54 to 2.30) with liver disease (p for interaction [pint] = 0.47), major bleeding 0.80 (95% CI: 0.70 to 0.91) in patients without and 0.91 (95% CI: 0.56 to 1.47) with liver disease (pint = 0.63). There were no significant differences in hepatic adverse events between the 2 treatment groups. CONCLUSIONS: Among patients with AF receiving oral anticoagulation, bleeding, but not thromboembolic events, was increased in patients with liver disease. A history of liver disease did not alter the relative efficacy and safety of edoxaban compared with warfarin. Hepatic adverse events were similar between edoxaban and warfarin.

A mechanism-based population pharmacokinetic model for characterizing time-dependent pharmacokinetics of midostaurin and its metabolites in human subjects.

BACKGROUND AND OBJECTIVE: Midostaurin, a novel potent inhibitor of protein kinase C enzyme and class III receptor tyrosine kinases, including Fms-like tyrosine kinase-3 (FLT3) and c-KIT, shows time-dependent pharmacokinetics in human subjects, presumably due to enzyme auto-induction. The purpose of this study was to develop a mechanism-based population pharmacokinetic model to describe the plasma concentration profiles of midostaurin and its metabolites and to characterize the time course of auto-induction. SUBJECTS AND METHODS: Data from 37 diabetic patients who received oral doses of midostaurin (25 mg twice daily, 50 mg twice daily or 75 mg twice daily) for 28 days were analysed using nonlinear mixed-effects modelling. The structural model included a gut compartment for drug input and central and peripheral compartments for midostaurin, with drug output from the central compartment to either of two compartments for the midostaurin metabolites CGP62221 and CGP52421. Different enzyme induction sub-models were evaluated to account for the observed time-dependent decrease in midostaurin concentrations. RESULTS: An enzyme turnover model, with CGP62221 formation (CL(1)) being a linear process but CGP52421 formation (CL(2)) being inducible, was found to be most appropriate. In the pre-induced state, CL(1) and CL(2) of midostaurin were determined to be 1.47 L/h and 0.501 L/h, respectively. At the end of 28 days of dosing, CL(2) was increased by 5.2-, 6.6- and 6.9-fold in the 25 mg, 50 mg and 75 mg groups, respectively, resulting in a 2.1- to 2.5-fold increase in total clearance of midostaurin. The final model estimated a mean maximum fold of induction (E(max)) of 8.61 and a concentration producing 50% of the E(max) (EC(50)) of 1700 ng/mL (approximately 2.9 micromol/L) for CGP52421-mediated enzyme induction. CONCLUSIONS: The population pharmacokinetic model that was developed was able to describe the time-dependent pharmacokinetic profiles of midostaurin and its auto-induction mechanism. Thus it may be useful for designing an appropriate dosage regimen for midostaurin. The unique feature of this model included a precursor compartment that was able to capture the time delays of auto-induction. The use of such precursor extension in the model may be applicable to other drugs showing long time delays in enzyme auto-induction.

Dose- and time-dependent pharmacokinetics of midostaurin in patients with diabetes mellitus.

Midostaurin is a novel potent inhibitor of both protein kinase C and the major receptor for vascular endothelial growth factor involved in angiogenesis, presenting a rationale for its use in diabetic retinopathy. This study evaluated the safety and pharmacokinetics of midostaurin following multiple oral doses of midostaurin for 28 days at 4 dose levels (25 mg bid, 50 mg bid, 75 mg bid, 75 mg tid), as well as a single oral 100-mg dose in patients with diabetes mellitus (n = 9-13 per dose cohort). Pharmacokinetic parameters were determined on days 1 and 28 based on the plasma concentrations of midostaurin and its metabolites, CGP62221 and CGP52421. The plasma exposures (C(max) and AUC(0-tau)) of midostaurin and metabolites increased less than proportionally over the dose range of 25 to 100 mg, showing a 2.2-fold increase after the first dose. Midostaurin concentrations increased during the first 3 to 6 days of dosing, then declined with time (by 30%-50%) until a steady state was achieved, representing an average accumulation factor (R) of 1.7. CGP62221 showed a similar concentration-time pattern as midostaurin (R = 2.5), but CGP52421 accumulated significantly (R = 18.8). A high-fat meal was found to significantly increase the C(max) and AUC(0-12 h) of midostaurin by 1.5-fold (P = .04) and 1.8-fold (P = .01), respectively, compared with taking the drug after an overnight fast. Midostaurin administered at 50 to 225 mg/day appeared to be generally safe in this group of patients. The most common treatment-related adverse events (eg, loose stools, nausea, vomiting, and headache) were found to be dose related, and the frequency increased markedly above the 150-mg/day dose level.

Effects of imatinib (Glivec) on the pharmacokinetics of metoprolol, a CYP2D6 substrate, in Chinese patients with chronic myelogenous leukaemia.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: Imatinib, a tyrosine kinase inhibitor, exhibits a competitive inhibition on the CYP450 2D6 isozyme with a K(i) value of 7.5 microm. However, the clinical significance of the inhibition and its relevance to 2D6 polymorphisms have not been evaluated. The pharmacokinetics of imatinib have been well studied in Caucasians, but not in a Chinese population. Metoprolol, a CYP2D6 substrate, has different clearances among patients with different CYP2D6 genotypes. It is often used as a CYP2D6 probe substrate for clinical drug-drug interaction studies. WHAT THIS STUDY ADDS: Co-administration of imatinib at 400 mg twice daily increased the plasma AUC of metoprolol by approximately 23% in 20 Chinese patients with chronic myeloid leukaemia (CML), about 17% increase in CYP2D6 intermediate metabolizers (IMs) (n = 6), 24% in extensive metabolizers (EMs) (n = 13), and 28% for the subject with unknown 2D6 status (n = 1) suggesting that imatinib has a weak to moderate inhibition on CYP2D6 in vivo. * The clearance of imatinib in Chinese patients with CML showed no difference between CYP2D6 IMs and EMs, and no major difference from Caucasian patients with CML based on data reported in the literature. AIMS To investigate the effect of imatinib on the pharmacokinetics of a CYP2D6 substrate, metoprolol, in patients with chronic myeloid leukaemia (CML). The pharmacokinetics of imatinib were also studied in these patients. METHODS: Patients (n = 20) received a single oral dose of metoprolol 100 mg on day 1 after an overnight fast. On days 2-10, imatinib 400 mg was administered twice daily. On day 8, another 100 mg dose of metoprolol was administered 1 h after the morning dose of imatinib 400 mg. Blood samples for metoprolol and alpha-hydroxymetoprolol measurement were taken on study days 1 and 8, and on day 8 for imatinib. RESULTS: Of the 20 patients enrolled, six patients (30%) were CYP2D6 intermediate metabolizers (IMs), 13 (65%) extensive metabolizers (EMs), and the CYP2D6 status in one patient was unknown. In the presence of 400 mg twice daily imatinib, the mean metoprolol AUC was increased by 17% in IMs (from 1190 to 1390 ng ml(-1) h), and 24% in EMs (from 660 to 818 ng ml(-1) h). Patients classified as CYP2D6 IMs had an approximately 1.8-fold higher plasma metoprolol exposure than those classified as EMs. The oral clearance of imatinib was 11.0 +/- 2.0 l h(-1) and 11.8 +/- 4.1 l h(-1) for CYP2D6 IMs and EMs, respectively. CONCLUSIONS: Co-administration of a high dose of imatinib resulted in a small or moderate increase in metoprolol plasma exposure in all patients regardless of CYP2D6 status. The clearance of imatinib showed no difference between CYP2D6 IMs and EMs.

Uninterrupted administration of edoxaban vs vitamin K antagonists in patients undergoing atrial fibrillation catheter ablation: Rationale and design of the ELIMINATE-AF study.

Patients with atrial fibrillation (AF) are at an approximately 0.5% to 3% increased risk of thromboembolism during and immediately after catheter ablation. Treatment guidelines recommend periprocedural oral anticoagulation plus unfractionated heparin during ablation. Rivaroxaban and dabigatran are the only non-vitamin K oral anticoagulants for which there are randomized controlled trials assessing uninterrupted anticoagulation in patients undergoing catheter ablation of AF. Edoxaban, a direct factor Xa inhibitor, is noninferior vs warfarin for the prevention of stroke or systemic embolism with less major bleeding in patients with nonvalvular AF. The ELIMINATE-AF (Evaluation of Edoxaban Compared With VKA in Subjects Undergoing Catheter Ablation of Nonvalvular Atrial Fibrillation) trial is a multinational, multicenter, prospective, randomized, open-label, parallel-group, blinded-endpoint evaluation (PROBE) study to assess the safety and efficacy of once-daily edoxaban 60 mg (30 mg in patients indicated for a dose reduction) vs vitamin K antagonists (VKA) in patients with nonvalvular AF undergoing catheter ablation (http://www.ClinicalTrials.gov: NCT02942576). A total of 560 patients are planned for randomization to edoxaban or VKA (2:1 ratio) to obtain 450 patients fully compliant with the protocol. Patients will complete 21 to 28 days of anticoagulation prior to the ablation and a 90-day post-ablation period. The primary efficacy endpoint is the composite of all-cause death, stroke, and major bleeding. The primary safety endpoint is major bleeding. A magnetic resonance imaging substudy will assess the incidence of silent cerebral lesions post-ablation. ELIMINATE-AF will define the efficacy and safety of edoxaban for uninterrupted oral anticoagulation during catheter ablation of AF.

Variability in renal clearance of substrates for renal transporters in chinese subjects.

The authors evaluated the inter- and intraindividual variability in the renal clearance of substrates of organic anion transporters (OAT) or organic cation transporters (OCT) using repeated drug application procedures. Two OAT substrates (ampicillin and cephalexin) and 2 OCT substrates (famotidine and metformin) were selected. Each drug was administered orally twice to healthy subjects, with sample sizes ranging from 12 to 28 (using bioequivalent formulations of each drug). The inter-(delta(inter)) and intrasubject (delta(intra)) variances in renal clearance were estimated based on analysis of variance, and the genetic contribution (r(GC)) was calculated as (delta(inter - intra))/delta(inter). The renal clearances of ampicillin, cephalexin, famotidine, and metformin averaged 5.21 (range, 2.87-11.20), 3.01 (range, 1.50-3.82), 4.96 (range, 2.84-8.17), and 9.44 (range, 5.66-15.43) mL/min/kg, with mean intraindividual coefficients of variation of 17.7%, 7.3%, 13.5%, and 9.0% and r(GC) values of 0.75, 0.89, 0.81, and 0.93, respectively. These high r(GC) values suggest a potential significant genetic contribution by the renal OATs and OCTs in Chinese subjects. Further studies in a larger population are needed to confirm the importance of these results as well as to identify specific genetic variants in these transporters responsible for such variability.

Population pharmacokinetics of cyclosporine in chinese cardiac transplant recipients.

STUDY OBJECTIVE: To characterize the population pharmacokinetics of cyclosporine in Chinese patients undergoing cardiac transplantation and to identify the demographic and clinical covariates affecting cyclosporine clearance. DESIGN: Population pharmacokinetic analysis using data from a retrospective chart review. SETTING: Specialty hospital in Hong Kong for treatment of cardiac and pulmonary diseases. PATIENTS: Thirty-eight Chinese adult patients (mean age 46 yrs) who had undergone routine cyclosporine therapeutic drug monitoring after cardiac transplantation between January 1, 1991, and December 31, 2003. MEASUREMENTS AND MAIN RESULTS: Data regarding dosing, demographics, clinical laboratory values, and concurrent drugs were collected retrospectively. Data were included if patients had blood cyclosporine concentrations determined for at least 12 weeks after transplantation; an average of 18 blood samples/patient were collected. Population modeling was performed using a one-compartment linear model with first-order absorption and elimination. Various demographic and clinical covariates were tested for their significant effects on the apparent oral clearance (Cl/F) of cyclosporine. The stability of the final population model was evaluated by using the bootstrap resampling method. Statistically significant associations were observed between Cl/F and each of the following covariates: body weight (BW), use of diltiazem (DIL), and hematocrit value (HCT). The final model was Cl/F=5.00*(1-DIL)+365/HCT+(0.144*BW). The interindividual variabilities of Cl/F and apparent volume of distribution were 14.5% and 40.2%, respectively. The mean parameter estimates obtained from bootstrap analyses were highly consistent with those obtained with the original data set. CONCLUSION: The estimated Cl/F values of cyclosporine in our Chinese cardiac transplant recipients appeared to be similar to those reported for Caucasian cardiac transplant recipients. Thus, our data provide support that a cyclosporine dosage regimen similar to that in Caucasian patients may be needed in Chinese cardiac transplant recipients. However, further studies are required to determine the optimum cyclosporine dosage regimen in the Chinese population.

Population pharmacokinetic modeling and simulation for assessing renal impairment effect on the pharmacokinetics of mirogabalin.

A population pharmacokinetic model was developed to describe plasma concentrations of mirogabalin and lactam metabolite, obtained following a single oral dose of 5 mg mirogabalin to subjects with varying degrees of renal function.A 2-compartment model was used for both mirogabalin and lactam metabolite. Body weight was a significant covariate on volume of distribution of mirogabalin and lactam metabolite, whereas creatinine clearance significantly affected both renal and nonrenal clearance of mirogabalin. The total clearance of mirogabalin was decreased by 25%, 54%, and 76% in subjects with mild, moderate, and severe renal impairment, respectively, relative to normal controls. Simulation results showed that in comparison with the normal renal function group receiving mirogabalin 15 mg once or twice daily, dose reduction by 50% or 75% in subjects with moderate or severe renal impairment would produce similar AUCss values, but 37%-43% or 28%-32% lower Cmax,ss of mirogabalin. Predicted mirogabalin AUCss was 26% higher, whereas Cmax,ss was similar in subjects with mild renal impairment compared with those having normal renal function taking the same dose. Results support a dose reduction by 50% or 75% in subjects with moderate or severe renal impairment. No dose adjustment seemed necessary for subjects with mild renal impairment.

CYP2C9, but not CYP2C19, polymorphisms affect the pharmacokinetics and pharmacodynamics of glyburide in Chinese subjects.

BACKGROUND: Although cytochrome P450 (CYP) 2C9 was thought to be the main pathway for glyburide (INN, glibenclamide) metabolism in vivo, studies in vitro indicated that CYP2C19 had a more dominant effect. This study investigated the relative influence of CYP2C9 and CYP2C19 genotypes on the pharmacokinetics and pharmacodynamics of glyburide in Chinese subjects. METHODS: Three groups of healthy male Chinese subjects (n=6 per group) were enrolled, as follows: group I, CYP2C9*1/*1 and CYP2C19 extensive metabolizers (EMs); group II, CYP2C9*1/*1 and CYP2C19 poor metabolizers (PMs); and group III, CYP2C9*1/*3 and CYP2C19 EMs. Subjects received single oral doses of 5 mg glyburide. Multiple blood samples were collected, and the plasma glyburide concentrations were determined by an HPLC method. The plasma glucose and insulin concentrations were also measured up to 2 hours after dosing. RESULTS: No significant differences in glyburide pharmacokinetics were observed between CYP2C19 EM and PM subjects who had the CYP2C9*1/*1 genotype (group I versus group II). Their respective values for area under the plasma concentration-time curve from time 0 to infinity (AUC0-infinity) and elimination half-life (t1/2) were 0.46+/-0.13 microg.h/mL versus 0.57+/- 0.11 microg.h/mL (P=.569) and 2.09+/-0.22 hours versus 2.24+/- 0.27 hours (P=.721). However, significant increases in AUC(0-infinity) (125% and 82%; P=.008 and .024, respectively) and t1/2 (71% and 60%; P=.003 and .007, respectively) were observed when CYP2C9*1/*3 subjects (group III) were compared with CYP2C9*1/*1 subjects in group I or II. Blood glucose reductions at 2 hours after dosing were 41.8%, 23.9%, and 27.7% in groups I, II, and III, respectively (P=.029), and hypoglycemia developed in 3 of 6 CYP2C9*1/*3 carriers and 2 of 12 CYP2C9*1/*1 carriers. CONCLUSION: CYP2C9, but not CYP2C19, polymorphism appears to exert a dominant influence on glyburide pharmacokinetics and pharmacodynamics in vivo. Further studies in diabetic patients with long-term dosing are warranted to confirm these findings.

Pharmacogenetics and herb-drug interactions: experience with Ginkgo biloba and omeprazole.

OBJECTIVE: Ginkgo biloba was found to exert a significant inductive effect on CYP2C19 activity. This study was designed to investigate the potential herb-drug interaction between G. biloba and omeprazole, a widely used CYP2C19 substrate, in subjects with different CYP2C19 genotypes. METHODS: Eighteen healthy Chinese subjects previously genotyped for CYP2C19 were selected. All subjects received a single omeprazole 40 mg at baseline and then at the end of a 12-day treatment period with G. biloba (140 mg, bid). Multiple blood samples were collected over 12 h, and 24 h urine was collected post omeprazole dosing. Plasma and urine concentrations of omeprazole and its metabolites, 5-hydroxyomeprazole and omeprazole sulfone, were determined, and their pharmacokinetics calculated non-compartmentally. RESULTS: Plasma concentrations of omeprazole and omeprazole sulfone were significantly decreased, and 5-hydroxyomeprazole significantly increased following G. biloba administration in comparison to baseline. A significant decrease in the ratio of area under the plasma concentration-time curve (AUC) of omeprazole to 5-hydroxyomeprazole was observed in the homozygous extensive metabolizers, heterozygous extensive metabolizers, and poor metabolizers, respectively. The decrease was greater in PMs than EMs. No significant changes in the AUC ratios of omeprazole to omeprazole sulfone were observed. Renal clearance of 5-hydroxyomeprazole was significantly decreased after G. biloba, but the change was not significantly different among the three genotype groups. CONCLUSION: Our results show that G biloba can induce omeprazole hydroxylation in a CYP2C19 genotype-dependent manner and concurrently reduce the renal clearance of 5-hydroxyomeprazole. Co-administration of G. biloba with omeprazole or other CYP2C19 substrates may significantly reduce their effect, but further studies are warranted.

A modified two-portion absorption model to describe double-peak absorption profiles of ranitidine.

BACKGROUND: The pharmacokinetics of oral drugs exhibiting double peaks cannot be adequately described by using conventional compartmental models. OBJECTIVE: To propose and evaluate a modified two-portion absorption model based on physiological and biopharmaceutical considerations to describe the double-peak concentration-time curve of ranitidine. MODEL DESIGN: The proposed model assumes that oral ranitidine is absorbed sequentially in two portions due to delayed gastric emptying, and thus includes a gut compartment in addition to the central and peripheral compartments. METHODS: Validation of the model was performed with respect to structural identifiability, parameter estimability and model applicability. Using initial estimates of parameters obtained from previous intravenous data, the model was used to fit oral ranitidine data from six subjects who manifested clear double-peak concentration-time profiles as well as from six subjects who showed irregular but apparent single-peak concentration-time curves. RESULTS: Based on goodness-of-fit criteria, the model fitted well for both double-peak and single-peak concentration-time curves of ranitidine (for the two groups: weighted residual sum of squares, 0.044 +/- 0.027 and 0.054 +/- 0.036; correlation between observed and model predicted concentrations, 0.995 +/- 0.003 and 0.995 +/- 0.005). Simulation studies with concentrations generated with 10% normally distributed random error showed that all model fitted parameters had good accuracy and reasonable precision. The mean percentage bias ranged from -7.0 to 28.6%, and the coefficient of variance was within 30% for the majority of parameters compared with the theoretical values. CONCLUSION: The modified two-portion absorption model may afford a useful approach to characterise the absorption phase and estimate pharmacokinetic parameters for drugs with two absorption peaks.