Physiologically based pharmacokinetic modelling and in vivo [I]/K(i) accurately predict P-glycoprotein-mediated drug-drug interactions with dabigatran etexilate

Assessing the relative contribution of CYP3A-and P-gp-mediated pathways to the overall disposition and drug-drug interaction of dabigatran etexilate using a comprehensive mechanistic physiological-based pharmacokinetic model

Dabigatran etexilate (DABE) is a clinical probe substrate for studying drug-drug interaction (DDI) through an intestinal P-glycoprotein (P-gp). A recent in vitro study, however, has suggested a potentially significant involvement of CYP3A-mediated oxidative metabolism of DABE and its intermediate monoester BIBR0951 in DDI following microdose administration of DABE. In this study, the relative significance of CYP3A- and P-gp-mediated pathways to the overall disposition of DABE has been explored using mechanistic physiologically based pharmacokinetic (PBPK) modeling approach. The developed PBPK model linked DABE with its 2 intermediate (BIBR0951 and BIBR1087) and active (dabigatran, DAB) metabolites, and with all relevant drug-specific properties known to date included. The model was successfully qualified against several datasets of DABE single/multiple dose pharmacokinetics and DDIs with CYP3A/P-gp inhibitors. Simulations using the qualified model supported that the intestinal CYP3A-mediated oxidation of BIBR0951, and not the gut P-gp-mediated efflux of DABE, was a key contributing factor to an observed difference in the DDI magnitude following the micro-versus therapeutic doses of DABE with clarithromycin. Both the saturable CYP3A-mediated metabolism of BIBR0951 and the solubility-limited DABE absorption contributed to the relatively modest nonlinearity in DAB exposure observed with increasing doses of DABE. Furthermore, the results suggested a limited role of the gut P-gp, but an appreciable, albeit small, contribution of gut CYP3A in mediating the DDIs following the therapeutic dose of DABE with dual CYP3A/P-gp inhibitors. Thus, a possibility exists for a varying extent of CYP3A involvement when using DABE as a clinical probe in the DDI assessment, across DABE dose levels.

Reduced physiologically-based pharmacokinetic model of dabigatran etexilate-dabigatran and its application for prediction of intestinal P-gp-mediated drug-drug interactions

BACKGROUND

Dabigatran etexilate (DABE) has been suggested as a clinical probe for intestinal P-glycoprotein (P-gp)-mediated drug-drug interaction (DDI) studies and, as an alternative to digoxin. Clinical DDI data with various P-gp inhibitors demonstrated a dose-dependent inhibition of P-gp with DABE. The aims of this study were to develop a joint DABE (prodrug)-dabigatran reduced physiologically-based-pharmacokinetic (PBPK) model and to evaluate its ability to predict differences in P-gp DDI magnitude between a microdose and a therapeutic dose of DABE.

METHODS

A joint DABE-dabigatran PBPK model was developed with a mechanistic intestinal model accounting for the regional P-gp distribution in the gastrointestinal tract. Model input parameters were estimated using DABE and dabigatran pharmacokinetic (PK) clinical data obtained after administration of DABE alone or with a strong P-gp inhibitor, itraconazole, and over a wide range of DABE doses (from 375 µg to 400 mg). Subsequently, the model was used to predict extent of DDI with additional P-gp inhibitors and with different DABE doses.

RESULTS

The reduced DABE-dabigatran PBPK model successfully described plasma concentrations of both prodrug and metabolite following administration of DABE at different dose levels and when co-administered with itraconazole. The model was able to capture the dose dependency in P-gp mediated DDI. Predicted magnitude of itraconazole P-gp DDI was higher at the microdose (predicted vs. observed median fold-increase in AUC_+inh/AUC_control (min-max) = 5.88 (4.29-7.93) vs. 6.92 (4.96-9.66) ) compared to the therapeutic dose (predicted median fold-increase in AUC_+inh/AUC_control = 3.48 (2.37-4.84) ). In addition, the reduced DABE-dabigatran PBPK model predicted successfully the extent of DDI with verapamil and clarithromycin as P-gp inhibitors. Model-based simulations of dose staggering predicted the maximum inhibition of P-gp when DABE microdose was concomitantly administered with itraconazole solution; simulations also highlighted dosing intervals required to minimise the DDI risk depending on the DABE dose administered (microdose vs. therapeutic).

CONCLUSIONS

This study provides a modelling framework for the evaluation of P-gp inhibitory potential of new molecular entities using DABE as a clinical probe. Simulations of dose staggering and regional differences in the extent of intestinal P-gp inhibition for DABE microdose and therapeutic dose provide model-based guidance for design of prospective clinical P-gp DDI studies.

Risk of Hospitalization With Hemorrhage Among Older Adults Taking Clarithromycin vs Azithromycin and Direct Oral Anticoagulants

IMPORTANCE

Clarithromycin is a commonly prescribed antibiotic associated with higher levels of direct oral anticoagulants (DOACs) in the blood, with the potential to increase the risk of hemorrhage.

OBJECTIVE

To assess the 30-day risk of a hospital admission with hemorrhage after coprescription of clarithromycin compared with azithromycin among older adults taking a DOAC.

DESIGN, SETTING, AND PARTICIPANTS

This population-based, retrospective cohort study was conducted among adults of advanced age (mean [SD] age, 77.6 [7.2] years) who were newly coprescribed clarithromycin (n = 6592) vs azithromycin (n = 18 351) while taking a DOAC (dabigatran, apixaban, or rivaroxaban) in Ontario, Canada, from June 23, 2009, to December 31, 2016. Cox proportional hazards regression was used to examine the association between hemorrhage and antibiotic use (clarithromycin vs azithromycin). Statistical analysis was performed from December 23, 2019, to March 25, 2020.

MAIN OUTCOMES AND MEASURES

Hospital admission with major hemorrhage (upper or lower gastrointestinal tract or intracranial). Outcomes were assessed within 30 days of a coprescription.

RESULTS

Among the 24 943 patients (12 493 women; mean [SD] age, 77.6 [7.2] years) in the study, rivaroxaban was the most commonly prescribed DOAC (9972 patients [40.0%]), followed by apixaban (7953 [31.9%]) and dabigatran (7018 [28.1%]). Coprescribing clarithromycin vs azithromycin with a DOAC was associated with a higher risk of a hospital admission with major hemorrhage (51 of 6592 patients [0.77%] taking clarithromycin vs 79 of 18 351 patients [0.43%] taking azithromycin; adjusted hazard ratio, 1.71 [95% CI, 1.20-2.45]; absolute risk difference, 0.34%). Results were consistent in multiple additional analyses.

CONCLUSIONS AND RELEVANCE

This study suggests that, among adults of advanced age taking a DOAC, concurrent use of clarithromycin compared with azithromycin was associated with a small but statistically significantly greater 30-day risk of hospital admission with major hemorrhage.

Predicted effect of ticagrelor on the pharmacokinetics of dabigatran etexilate using physiologically based pharmacokinetic modeling

Dabigatran etexilate (DABE) is a direct oral anticoagulant (DOAC) and may be combined with ticagrelor, a P2Y₁₂ inhibitor with antiplatelet effects. This combination of antiplatelet drugs and anticoagulants would increases the risk of bleeding in patients. In addition, the potential drug interaction may further increase the risk of bleeding. At present, there is scarce research to clarify the results of the interaction between the two. Therefore, we conducted this study to identify the potential impact of ticagrelor on the pharmacokinetics of DABE using physiologically based pharmacokinetic (PBPK) modeling. The models reasonably predicted the concentration-time profiles of dabigatran (DAB), the transformation form after DABE absorption, and ticagrelor. For pharmacokinetic drug-drug interaction (DDI), exposure to DAB at steady state was increased when co-administrated with ticagrelor. The C_max and AUC_0-t of DAB were raised by approximately 8.7% and 7.1%, respectively. Meanwhile, a stable-state ticagrelor co-administration at 400 mg once-daily increased the C_max and AUC_0-t of DAB by approximately 12.8% and 18.8%, respectively. As conclusions, Ticagrelor slightly increased the exposure of DAB. It is possible to safely use ticagrelor in a double or triple antithrombotic regimen containing DABE, only considering the antithrombotic efficacy, but not need to pay much attention on the pharmacokinetic DDI.

Assessing Potential Drug-Drug Interactions Between Dabigatran Etexilate and a P-Glycoprotein Inhibitor in Renal Impairment Populations Using Physiologically Based Pharmacokinetic Modeling

Plasma concentrations of dabigatran, an active principle of prodrug dabigatran etexilate (DABE), are increased by renal impairment (RI) or coadministration of a P‐glycoprotein inhibitor. Because the combined effects of drug–drug interactions and RI have not been evaluated by means of clinical studies, the decision of DABE dosing for RI patients receiving P‐glycoprotein inhibitors is empirical at its best. We conducted virtual drug–drug interactions studies between DABE and the P‐glycoprotein inhibitor verapamil in RI populations using physiologically based pharmacokinetic modeling. The developed physiologically based pharmacokinetic model for DABE and dabigatran was used to predict trough dabigatran concentrations in the presence and absence of verapamil in virtual RI populations. The population‐based physiologically based pharmacokinetic model provided the most appropriate dosing regimen of DABE for likely clinical scenarios, such as drug–drug interactions in this RI population based on available knowledge of the systems changes and in the absence of actual clinical studies.

Warfarin vs. apixaban in nonvalvular atrial fibrillation, and analysis by concomitant antiarrhythmic medication use: A national retrospective study

BACKGROUND

No real-world data exist on outcomes in patients on anticoagulants and concomitant antiarrhythmic medications. This study aims to compare the safety and effectiveness of apixaban and warfarin, first in patients with nonvalvular atrial fibrillation (NVAF) and then in patients on concurrent antiarrhythmic medications.

METHODS

A retrospective cohort study was conducted using a large US electronic medical record database (2012-2016). Patients with NVAF on warfarin or apixaban were included. The primary endpoint was a composite of stroke (ischemic or hemorrhagic) or systemic embolism. The primary safety endpoint was major bleeding (ISTH definition). Patients were matched using propensity scoring. Univariate survival analyses were conducted by using the log-rank test and Kaplan-Meier survival curves. A subgroup analysis was conducted to assess outcomes on patients on concurrent antiarrhythmic medications.

RESULTS

A total of 332 100 patients with NVAF were identified, and 20 378 were included in the propensity-matching analysis. No baseline differences were seen in age, comorbidities, or CHA 2 DS 2-VASc score. The primary endpoint occurred in 122 (1.2%) patients on apixaban compared to 166 (1.63%) on warfarin (hazard ratio, 0.84; 95% confidence interval [CI], 0.79-0.88). Major bleeding occurred at a lower rate in the apixaban group (n = 600, 5.89%) compared to warfarin (n = 887, 8.71%) (odds ratio, 0.65; 95% CI, 0.58-0.73). In patients on concurrent antiarrhythmic medications (n = 2498), there was no difference in thrombotic (1.04% vs. 1.37%; P = 0.42) or bleeding events (5.29% vs. 6.89%; P = 0.08).

CONCLUSION

Apixaban was associated with reduced stroke/systemic embolism and bleeding when compared with warfarin. No difference was seen in thrombotic or bleeding events in patients on concurrent antiarrhythmic medications.

Drug interactions between direct-acting oral anticoagulants and calcineurin inhibitors during solid organ transplantation: considerations for therapy

Introduction: There is a high incidence of venous thromboembolism (VTE) in solid organ transplant recipients. The safety and efficacy of direct-acting oral anticoagulants (DOAC) have been well established in clinical practice for the prevention and treatment of VTE in broad populations. However, the management of VTE in the setting of solid organ transplantation remains a challenge to clinicians due to limited evidence of DOAC usage with calcineurin inhibitors. Areas covered: The current literature available on the pharmacokinetic-pharmacodynamic interaction between DOACs and calcineurin inhibitors is presented. A comprehensive review was undertaken using PubMed, Embase, drug product labeling, and drug product review conducted by the US Food and Drug Administration using Drugs@FDA. The potential for mitigation strategies and clinical management using extant knowledge is explored. Expert opinion: Immunosuppression therapy is necessary to prevent graft rejection by the host. The sparsity of data together with the lack of well-designed prospective studies of DOAC use in solid organ transplant recipients presents a unique challenge to clinicians in determining the clinical relevance of possible drug interactions. Existing evidence suggests that with attention to concomitant drug use and renal function, the co-administration of DOACs and calcineurin inhibitors is safe and effective.

Physiologically based pharmacokinetic modelling of acute digoxin toxicity and the effect of digoxin-specific antibody fragments

CONTEXT

Recommended doses of digoxin-specific antibody fragments (digoxin-Fab) for treatment of acute digoxin poisoning are pharmacokinetically unsubstantiated and theoretically excessive. Physiologically based pharmacokinetic (PBPK) modelling creates clinical simulations which are closely related to physiological and pharmacokinetic behaviour. This paper details the formulation of a PBPK model of digoxin and explores its use as a simulation tool for acute digoxin toxicity and its management.

MATERIALS AND METHODS

A PBPK model of digoxin was constructed and validated for acute digoxin poisoning management by comparing simulations with observed individual acute overdose patients. These simulations were compared with standard two-compartment PK model simulations.

RESULTS

PBPK model simulations showed good agreement with post-absorption plasma concentrations of digoxin measured in 6 acute overdose patients. PBPK predictions were accurate to 1.5-fold or less of observed clinical values, proving to be more accurate than two-compartment simulations of the same patients which produced up to a 4.9-fold change.

CONCLUSIONS

Compared to conventional two-compartment modelling, PBPK modelling is superior in generating realistic simulations of acute digoxin toxicity and the response to digoxin-Fab. Simulation capacity provides realistic, continuous data which has the potential to substantiate alternative, less expensive, and safer digoxin-Fab dosing strategies for the treatment of acute digoxin toxicity.

Assessment of Pharmacokinetic Drug-Drug Interactions in Humans: In Vivo Probe Substrates for Drug Metabolism and Drug Transport Revisited

Pharmacokinetic parameters of selective probe substrates are used to quantify the activity of an individual pharmacokinetic process (PKP) and the effect of perpetrator drugs thereon in clinical drug-drug interaction (DDI) studies. For instance, oral caffeine is used to quantify hepatic CYP1A2 activity, and oral dagibatran etexilate for intestinal P-glycoprotein (P-gp) activity. However, no probe substrate depends exclusively on the PKP it is meant to quantify. Lack of selectivity for a given enzyme/transporter and expression of the respective enzyme/transporter at several sites in the human body are the main challenges. Thus, a detailed understanding of the role of individual PKPs for the pharmacokinetics of any probe substrate is essential to allocate the effect of a perpetrator drug to a specific PKP; this is a prerequisite for reliably informed pharmacokinetic models that will allow for the quantitative prediction of perpetrator effects on therapeutic drugs, also in respective patient populations not included in DDI studies.

Physiological based pharmacokinetic modeling to estimate in vivo Ki of ketoconazole on renal P-gp using human drug-drug interaction study result of fesoterodine and ketoconazole

This study was conducted to estimate in vivo inhibition constant (Ki) of ketoconazole on renal P-glycoprotein (P-gp) using human drug-drug interaction (DDI) study result of fesoterodine and ketoconazole. Fesoterodine is a prodrug which is extensively hydrolyzed by non-specific esterases to the active metabolite 5-hydroxymethyl tolterodine (5-HMT). 5-HMT is then further metabolized via Cytochrome P450 (CYP) 2D6 and CYP3A4. It is reported that 5-HMT is a substrate of P-gp whereas fesoterodine is not. Renal clearance of 5-HMT is approximately two-times greater than renal glomerular filtration rate. This suggests the possibility that renal clearance of 5-HMT involves secretion by P-gp. Utilizing the available pharmacokinetic characteristics of fesoterodine and 5-HMT, we estimated in vivo Ki of ketoconazole on P-gp at kidney based on DDI study data using physiologically-based pharmacokinetic approach. The estimated in vivo Ki of ketoconazole for hepatic CYP3A4 (6.64 ng/mL) was consistent with the reported values. The in vivo Ki of ketoconazole for renal P-gp was successfully estimated as 2.27 ng/mL, which was notably lower than reported in vitro 50% inhibitory concentration (IC₅₀) values ranged 223-2440 ng/mL due to different condition between in vitro and in vivo.

5-Fluororacil-Induced Gastrointestinal Damage Impairs the Absorption and Anticoagulant Effects of Dabigatran Etexilate

Fluoropyrimidines, including 5-fluororacil (5-FU), cause gastrointestinal damage in the clinical setting and might affect the gastrointestinal absorption of concomitantly administered drugs. We aimed to evaluate the effects of fluoropyrimidine-induced gastrointestinal damage on the pharmacokinetics and pharmacodynamics of dabigatran etexilate (DABE), an anticoagulant, in rats with gastrointestinal damage induced by the repeated oral administration of 5-FU. Rats were administered DABE orally or dabigatran (DAB), an active moiety of DABE, intravenously. The plasma DAB concentration was determined using liquid chromatography-tandem mass spectrometry. The activated partial thromboplastin time (APTT) was measured before and 30 min after the administration of each drug, and the APTT ratio was calculated. In 5-FU-treated rats, the maximum plasma concentration, the area under the concentration-time curve of DAB after the oral administration of DABE, and the oral bioavailability of DABE were significantly decreased to 18.3%, 22.9%, and 16.3% of the respective control values. The 5-FU-treated rats' APTT ratio was also significantly lower than the control value. Fluoropyrimidine-induced gastrointestinal damage might reduce the plasma concentration of DAB by impairing DABE absorption and might attenuate the anticoagulant effects of DABE in the clinical setting.

Does type 2 diabetes affect the on-treatment levels of direct oral anticoagulants in patients with atrial fibrillation?

AIMS

Type 2 diabetes (T2D) is connected with several abnormalities in haemostasis; and with higher risk of stroke and systemic embolism in patients with non-valvular atrial fibrillation (NV-AF). However, it is recently unknown whether T2D affects the activity of direct oral anticoagulants (DOACs). The aim of this study was to determine the impact of T2D on DOACs activity in patients with NV-AF.

METHODS

This pilot prospective study enrolled totally 65 patients with NV-AF (20 dabigatran-treated, 110 mg/twice daily; 28 rivaroxaban-treated, 15 mg/daily; 17 apixaban-treated, 5 mg/twice daily). 25 patients had T2D (8 dabigatran-treated, 11 rivaroxaban-treated, and 6 apixaban-treated). DOAC activity was tested with Hemoclot® Thrombin Inhibitor assay in dabigatran-treated patients, and with factor Xa-calibrated anti-Xa chromogenic analysis in rivaroxaban- and apixaban-treated patients prior and two hours after drug administration.

RESULTS

There were no significant differences in dabigatran baseline (62.1 ± 8.0 vs. 51.8 ± 38.9 ng/ml, p = .76) and 2-h-post-drug-administration (91.7 ± 57.2 vs. 72.2 ± 33.2 ng/ml, p = .48) activity comparing T2D and non-diabetic patients. Similarly, no significant differences were found in rivaroxaban baseline (35.9 ± 22.5 vs. 55.3 ± 45.1 ng/ml, p = .19) and 2-h-post-drug-administration (145.7 ± 74.1 vs. 202.6 ± 135.0 ng/ml, p = .22) anti-Xa activity. In addition, no significant differences were present in apixaban baseline (96.0 ± 54.5 vs. 63.9 ± 36.8 ng/ml, p = .24) and 2-h-post-drug-administration (151.0 ± 78.3 vs. 151.7 ± 59.1 ng/ml, p = .98) anti-Xa activity between T2D and non-diabetic patients.

CONCLUSIONS

This pilot study did not detect differences in DOACs activity according to T2D status in patients with NV-AF.

Pharmacological and Non-pharmacological Treatments for Stroke Prevention in Patients with Atrial Fibrillation

Atrial fibrillation (AF) is associated with significant risk of stroke and other thromboembolic events, which can be effectively prevented using oral anticoagulation (OAC) with either vitamin K antagonists (VKAs) or non-VKA oral anticoagulants (NOACs) dabigatran, rivaroxaban, apixaban, or edoxaban. Until recently, VKAs were the only available means for OAC treatment. NOACs had similar efficacy and were safer than or as safe as warfarin with respect to reduced rates of hemorrhagic stroke or other intracranial bleeding in the respective pivotal randomized clinical trials (RCTs) of stroke prevention in non-valvular AF patients. Increasing “real-world” evidence on NOACs broadly confirms the results of the RCTs. However, individual patient characteristics including renal function, age, or prior bleeding should be taken into account when choosing the OAC with best risk–benefit profile. In patients ineligible for OACs, surgical or interventional stroke prevention strategies should be considered. In patients undergoing cardiac surgery for other reasons, the left atrial appendage excision, ligation, or amputation may be the best option. Importantly, residual stumps or insufficient ligation may result in even higher stroke risk than without intervention. Percutaneous left atrial appendage occlusion, although requiring minimally invasive access, failed to demonstrate reduced ischemic stroke events compared to warfarin. In this review article, we summarize current treatment options and discuss the strengths and major limitations of the therapies for stroke risk reduction in patients with AF.

Physiologically based pharmacokinetic and pharmacodynamic modeling in cancer drug development: status, potential and gaps

INTRODUCTION

Modeling and simulation have become important means of answering questions relevant to the development of a drug, making it possible to assess risks early and to reduce costs. Physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) models contribute to a comprehensive understanding of the drug, covering specific questions from early discovery through lifecycle management stages. As for other disease areas, in oncology, PBPK and PD models are important topics that remain to be addressed.

AREAS COVERED

This review describes current PBPK and PD approaches, their applicability in drug development in general and specifically in the area of oncology. It discusses the current status and then focuses on key challenges and the potential for future use. It provides cases in which modeling currently cannot answer the questions and assesses the requirements to close gaps for PBPK/PD in oncology.

EXPERT OPINION

PBPK/PD models have led to improvements in identifying risks and reducing costs during the drug development process. Nevertheless, there is a lot of potential, where more rigorous integration of biological knowledge and specific experimental design would result in a more comprehensive biological picture. Ideally, such approaches would reveal the extent to which preclinical work can be extrapolated to clinical settings, thus enabling reliable prediction and, ultimately, reducing failed trials in clinical oncology.

Physiologically Based Pharmacokinetic (PBPK) Modeling and Simulation Approaches: A Systematic Review of Published Models, Applications, and Model Verification

Modeling and simulation of drug disposition has emerged as an important tool in drug development, clinical study design and regulatory review, and the number of physiologically based pharmacokinetic (PBPK) modeling related publications and regulatory submissions have risen dramatically in recent years. However, the extent of use of PBPK modeling by researchers, and the public availability of models has not been systematically evaluated. This review evaluates PBPK-related publications to 1) identify the common applications of PBPK modeling; 2) determine ways in which models are developed; 3) establish how model quality is assessed; and 4) provide a list of publically available PBPK models for sensitive P450 and transporter substrates as well as selective inhibitors and inducers. PubMed searches were conducted using the terms "PBPK" and "physiologically based pharmacokinetic model" to collect published models. Only papers on PBPK modeling of pharmaceutical agents in humans published in English between 2008 and May 2015 were reviewed. A total of 366 PBPK-related articles met the search criteria, with the number of articles published per year rising steadily. Published models were most commonly used for drug-drug interaction predictions (28%), followed by interindividual variability and general clinical pharmacokinetic predictions (23%), formulation or absorption modeling (12%), and predicting age-related changes in pharmacokinetics and disposition (10%). In total, 106 models of sensitive substrates, inhibitors, and inducers were identified. An in-depth analysis of the model development and verification revealed a lack of consistency in model development and quality assessment practices, demonstrating a need for development of best-practice guidelines.

Cardiovascular pharmacogenomics: current status and future directions

Drugs are widely used and highly effective in the treatment of heart disease. Nevertheless, in some instances, even drugs effective in a population display lack of efficacy or adverse drug reactions in individual patients, often in an apparently unpredictable fashion. This review summarizes the genomic factors now known to influence variability in responses to widely used cardiovascular drugs such as clopidogrel, warfarin, heparin and statins. Genomic approaches being used to discover new pathways in common cardiovascular diseases and thus potential new targets for drug development are described. Finally, the way in which this new information is likely to be used in an electronic medical record environment is discussed.

Physiologically based pharmacokinetic modeling of impaired carboxylesterase-1 activity: effects on oseltamivir disposition

BACKGROUND AND OBJECTIVE

Human carboxylesterase-1 (CES1) is an enzyme that is primarily expressed in the liver, where it plays an important role in the metabolism of many commonly used medications. Ethanol (alcohol)-mediated inhibition of CES1 and loss-of-function polymorphisms in the CES1 gene can markedly reduce this enzyme's function. Such alterations in CES1 activity may have important effects on the disposition of substrate drugs. The aim of this study is to develop a physiologically based pharmacokinetic (PBPK) model to predict changes in CES1 substrate drug exposure in humans with CES1 activity impaired by ethanol or loss-of-function CES1 genetic polymorphisms.

METHODS

The antiviral drug oseltamivir, an ethyl ester prodrug that is rapidly converted in vivo to the active metabolite oseltamivir carboxylate (OSC) by CES1 was used as a probe drug for CES1 activity. Oseltamivir PBPK models integrating in vitro and in vivo data were developed and refined. Then the changes in oseltamivir and OSC exposure in humans with CES1 impaired by ethanol or polymorphisms were simulated using a PBPK model incorporating in vitro inhibition and enzyme kinetic data. Model assumptions were verified by comparison of simulations with observed and published data. A sensitivity analysis was performed to gain a mechanistic understanding of the exposure changes of oseltamivir and OSC.

RESULTS

The simulated changes in oseltamivir and OSC exposures in humans with CES1 impaired by ethanol or polymorphism were similar to the observed data. The observed exposures to oseltamivir were increased by 46 and 37 % for the area under the plasma concentration-time curve from time zero to 6 h (AUC6) and from time zero to 24 h (AUC24), respectively, with co-administration of ethanol 0.6 g/kg. In contrast, only a slight change was observed in OSC exposure. The simulated data show the same trend as evidenced by greater change in exposures to oseltamivir (27 and 26 % for AUC(6) and AUC(24), [corrected] respectively) than OSC (≤6 %).

CONCLUSIONS

The PBPK model of impaired CES1 activity correctly predicts observed human data. This model can be extended to predict the effects of drug interactions and other factors affecting the pharmacokinetics of other CES1 substrate drugs.

The functional influences of common ABCB1 genetic variants on the inhibition of P-glycoprotein by Antrodia cinnamomea extracts

Antrodia cinnamomea is a traditional healthy food that has been demonstrated to possess anti-inflammatory, antioxidative, and anticacer effects. The purpose of this study was to evaluate whether the ethanolic extract of A. cinnamomea (EEAC) can affect the efflux function of P-glycoprotein (P-gp) and the effect of ABCB1 genetic variants on the interaction between EEAC and P-gp. To investigate the mechanism of this interaction, Flp-In™-293 cells stably transfected with various genotypes of human P-gp were established and the expression of P-gp was confirmed by Western blot. The results of the rhodamine 123 efflux assay demonstrated that EEAC efficiently inhibited wild-type P-gp function at an IC50 concentration of 1.51 ± 0.08 µg/mL through non-competitive inhibition. The IC50 concentrations for variant-type 1236T-2677T-3435T P-gp and variant-type 1236T-2677A-3435T P-gp were 5.56 ± 0.49 µg/mL and 3.33±0.67 µg/mL, respectively. In addition, the inhibition kinetics of EEAC also changed to uncompetitive inhibition in variant-type 1236T-2677A-3435T P-gp. The ATPase assay revealed that EEAC was an ATPase stimulator and was capable of reducing verapamil-induced ATPase levels. These results indicate that EEAC may be a potent P-gp inhibitor and higher dosages may be required in subjects carrying variant-types P-gp. Further studies are required to translate this basic knowledge into clinical applications.