Population Pharmacokinetic Modeling of the Enterohepatic Recirculation of Fimasartan in Rats, Dogs, and Humans

Prediction of Compound Plasma Concentration-Time Profiles in Mice Using Random Forest

Pharmacokinetic (PK) parameters such as clearance (CL) and volume of distribution (Vd) have been the subject of previous in silico predictive models. However, having information of the concentration over time profile explicitly can provide additional value like time above MIC or AUC, etc., to understand both the efficacy and safety-related aspects of a compound. In this work, we developed machine learning models for plasma concentration-time profiles after both i.v. and p.o. dosing for a series of 17 in-house projects. For explanatory variables, MACCS Keys chemical descriptors as well as in silico and experimental in vitro PK parameters were used. The predictive accuracy of random forest (RF), message passing neural network, 2-compartment models using estimated CL and Vdss, and an average model (as a control experiment) was investigated using 5-fold cross-validation (5-fold CV) and leave-one-project-out validation (LOPO-V). The predictive accuracy of RF in 5-fold CV for i.v. and p.o. plasma concentration-time profiles was the best among the models studied, with an RMSE for i.v. dosing at 0.08, 1, and 8 h of 0.245, 0.474, and 0.462, respectively, and an RMSE for p.o. dosing at 0.25, 1, and 8 h of 0.500, 0.612, and 0.509, respectively. Furthermore, by investigating the importance of the in vitro PK parameters using the Gini index, we observed that the general prior knowledge in ADME research was reflected well in the respective feature importance of in vitro parameters such as predicted human Vd (hVd) for the initial distribution, mouse intrinsic CL and unbound fraction of mouse plasma for the elimination process, and Caco2 permeability for the absorption process. Also, this model is the first model that can predict twin peaks in the concentration-time profile much better than a baseline compartment model. Because of its combination of sufficient accuracy and speed of prediction, we found the model to be fit-for-purpose for practical lead optimization.

The Role of "Physiologically Based Pharmacokinetic Model (PBPK)" New Approach Methodology (NAM) in Pharmaceuticals and Environmental Chemical Risk Assessment

Physiologically Based Pharmacokinetic (PBPK) models are mechanistic tools generally employed in the pharmaceutical industry and environmental health risk assessment. These models are recognized by regulatory authorities for predicting organ concentration-time profiles, pharmacokinetics and daily intake dose of xenobiotics. The extension of PBPK models to capture sensitive populations such as pediatric, geriatric, pregnant females, fetus, etc., and diseased populations such as those with renal impairment, liver cirrhosis, etc., is a must. However, the current modelling practices and existing models are not mature enough to confidently predict the risk in these populations. A multidisciplinary collaboration between clinicians, experimental and modeler scientist is vital to improve the physiology and calculation of biochemical parameters for integrating knowledge and refining existing PBPK models. Specific PBPK covering compartments such as cerebrospinal fluid and the hippocampus are required to gain mechanistic understanding about xenobiotic disposition in these sub-parts. The PBPK model assists in building quantitative adverse outcome pathways (qAOPs) for several endpoints such as developmental neurotoxicity (DNT), hepatotoxicity and cardiotoxicity. Machine learning algorithms can predict physicochemical parameters required to develop in silico models where experimental data are unavailable. Integrating machine learning with PBPK carries the potential to revolutionize the field of drug discovery and development and environmental risk. Overall, this review tried to summarize the recent developments in the in-silico models, building of qAOPs and use of machine learning for improving existing models, along with a regulatory perspective. This review can act as a guide for toxicologists who wish to build their careers in kinetic modeling.

Predictiveness of the Human-CYP3A4-Transgenic Mouse Model (Cyp3aXAV) for Human Drug Exposure of CYP3A4-Metabolized Drugs

The extrapolation of drug exposure between species remains a challenging step in drug development, contributing to the low success rate of drug approval. As a consequence, extrapolation of toxicology from animal models to humans to evaluate safe, first-in-human (FIH) doses requires high safety margins. We hypothesized that a human-CYP3A4-expressing transgenic (Cyp3aXAV) mouse is a more predictive model for human drug exposure of CYP3A4-metabolized small-molecule drugs. Population pharmacokinetic models based on wild-type (WT) and Cyp3aXAV mouse pharmacokinetic data of oral lorlatinib, brigatinib, ribociclib and fisogatinib were allometrically scaled and compared to human exposure. Extrapolation of the Cyp3aXAV mouse model closely predicted the observed human exposure for lorlatinib and brigatinib with a 1.1-fold and 1.0-fold difference, respectively, compared to a 2.1-fold and 1.9-fold deviation for WT-based extrapolations of lorlatinib and brigatinib, respectively. For ribociclib, the extrapolated WT mouse model gave better predictions with a 1.0-fold deviation compared to a 0.3-fold deviation for the extrapolated Cyp3aXAV mouse model. Due to the lack of a human population pharmacokinetic model for fisogatinib, only median maximum concentration ratios were calculated, resulting in ratios of 1.0 and 0.6 for WT and Cyp3aXAV mice extrapolations, respectively. The more accurate predictions of human exposure in preclinical research based on the Cyp3aXAV mouse model can ultimately result in FIH doses associated with improved safety and efficacy and in higher success rates in drug development.

Analytical method development and validation for simultaneous estimation of Fimasartan Potassium Trihydrate and Cilnidipine in synthetic mixture by HPLC for the treatment of hypertension stage-II

Background

A specific, accurate, precise, robust, and cost-effective HPLC method was developed and validated for quantitative analysis of Fimasartan Potassium Trihydrate and Cilnidipine in fixed-dose combination. The isocratic elution was accomplished by Symmetry C18 column (150 mm × 4.6 mm, 5 µm) at 25 °C. Mobile phase composition is Methanol: Acetonitrile: Potassium Dihydrogen Phosphate buffer (pH 3) (60:05:35%v/v/v) at a flow rate of 1.0 mL/min, injection volume 20 µL with DAD detection at 240 nm.

Result

Fimasartan Potassium Trihydrate and Cilnidipine were eluted with retention time 2.65 min and 5.51 min respectively. This method was validated as per ICH guideline (Q2 R1). The calibration plots were over the concentration range of 15–90 μg/mL and 2.5–15 μg/mL for Fimasartan Potassium Trihydrate and Cilnidipine with correlation coefficient 0.9992 and 0.9989 respectively. Accuracy was obtained between 99.51–101.65% and 100.06–101.20% for Fimasartan Potassium Trihydrate and Cilnidipine respectively. LOD were found to be 0.97 μg/mL and 0.57 μg/mL and LOQ were found to be 2.95 μg/mL and 1.75 μg/mL for Fimasartan Potassium Trihydrate and Cilnidipine respectively.

Conclusion

The results showed that the developed method is reliable for the routine analysis for simultaneous determination of Fimasartan Potassium Trihydrate and Cilnidipine.

Pharmacokinetics, distribution, and excretion of sodium oligomannate, a recently approved anti-Alzheimer's disease drug in China

The National Medical Products Administration has authorized sodium oligomannate for treating mild-to-moderate Alzheimer's disease. In this study, an LC-MS/MS method was developed and validated to quantitate sodium oligomannate in different biomatrices. The plasma pharmacokinetics, tissue distribution, and excretion of sodium oligomannate in Sprague-Dawley rats and beagle dogs were systematically investigated. Despite its complicated structural composition, the absorption, distribution, metabolism, and excretion profiles of the oligosaccharides in sodium oligomannate of different sizes and terminal derivatives were indiscriminate. Sodium oligomannate mainly crossed the gastrointestinal epithelium through paracellular transport following oral administration, with very low oral bioavailability in rats (0.6%–1.6%) and dogs (4.5%–9.3%). Absorbed sodium oligomannate mainly resided in circulating body fluids in free form with minimal distribution into erythrocytes and major tissues. Sodium oligomannate could penetrate the blood-cerebrospinal fluid (CSF) barrier of rats, showing a constant area under the concentration-time curve ratio (CSF/plasma) of approximately 5%. The cumulative urinary excretion of sodium oligomannate was commensurate with its oral bioavailability, supporting that excretion was predominantly renal, whereas no obvious biliary secretion was observed following a single oral dose to bile duct-cannulated rats. Moreover, only 33.7% (male) and 26.3% (female) of the oral dose were recovered in the rat excreta within 96 h following a single oral administration, suggesting that the intestinal flora may have ingested a portion of unabsorbed sodium oligomannate as a nutrient.

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ADME profiles of sodium oligomannate oligosaccharides were indiscriminate.

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An LC-MS/MS method was developed and validated for the ADME study of sodium oligomannate.

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Sodium oligomannate was absorbed through paracellular transport with very low BA.

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Approximately 5% of sodium oligomannate penetrated the blood–CSF barrier of rats.

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The absorbed drug was excreted through the kidney; unabsorbed drug was excreted in feces.

Enteric reabsorption processes and their impact on drug pharmacokinetics

Enteric reabsorption occurs when a drug is secreted into the intestinal lumen and reabsorbed into the systemic circulation. This distribution process is evidenced by multiple peaks in pharmacokinetic profiles. Commonly, hepatobiliary drug secretion is assumed to be the underlying mechanism (enterohepatic reabsorption, EHR), neglecting other possible mechanisms such as gastric secretion (enterogastric reabsorption, EGR). In addition, the impact of drug reabsorption on systemic clearance, volume of distribution and bioavailability has been a subject of long-standing discussions. In this work, we propose semi-mechanistic pharmacokinetic models to reflect EHR and EGR and compare their respective impact on primary pharmacokinetic parameters. A simulation-based analysis was carried out considering three drug types with the potential for reabsorption, classified according to their primary route of elimination and their hepatic extraction: (A) hepatic metabolism-low extraction; (B) hepatic metabolism-intermediate/high extraction; (C) renal excretion. Results show that an increase in EHR can significantly reduce the clearance of drugs A and B, increase bioavailability of B drugs, and increase the volume of distribution for all drugs. Conversely, EGR had negligible impact in all pharmacokinetic parameters. Findings provide background to explain and forecast the role that this process can play in pharmacokinetic variability, including drug-drug interactions and disease states.

Intestinal absorption and hepatic elimination of drugs in high-fat high-cholesterol diet-induced non-alcoholic steatohepatitis rats: exemplified by simvastatin

BACKGROUND AND PURPOSE

Altered drug pharmacokinetics is a significant concern in non-alcoholic steatohepatitis (NASH) patients. Although high-fat high-cholesterol (HFHC) diet-induced NASH (HFHC-NASH) rats could simulate the typical dysregulation of cholesterol in NASH patients, experimental investigation on the altered drug pharmacokinetics in this model are limited. Thus, the present study comprehensive investigates the nature of such altered pharmacokinetics using simvastatin as the model drug.

EXPERIMENTAL APPROACH

Pharmacokinetic profiles of simvastatin and its active metabolite simvastatin acid together with compartmental pharmacokinetic modelling were used to identify the key factors involved in the altered pharmacokinetics of simvastatin in HFHC-NASH rats. Experimental investigations via in situ single-pass intestinal perfusion and intrahepatic injection of simvastatin were carried out. Histology, Ces1 activities and mRNA/protein levels of Oatp1b2/CYP2c11/P-gp in the small intestine/liver of healthy and HFHC-NASH rats were compared.

KEY RESULTS

Reduced intestinal absorption and more extensive hepatic elimination in HFHC-NASH rats resulted in less systemic exposures of simvastatin/simvastatin acid. In the small intestine of HFHC-NASH rats, thicker intestinal wall with more collagen fibres, increased Ces1 activity and up-regulated P-gp protein decreased the permeability of simvastatin, accelerated the hydrolysis of simvastatin and promoted the efflux of simvastatin acid respectively. In the liver of HFHC-NASH rats, higher hepatic P-gp expression accelerated the hepatic elimination of simvastatin.

CONCLUSION AND IMPLICATIONS

Altered histology, Ces1 activity and P-gp expression in the small intestine/liver were identified to be the major contributing factors leading to less systemic exposure of drugs in HFHC-NASH rats, which may be applicable to NASH patients.

Delay differential equations for the description of Irbesartan pharmacokinetics: A population approach to model absorption complexities leading to dual peaks

Irbesartan is a poorly soluble BCS class II compound with weak acidic properties. After oral administration, dual peaks are noted in its concentration (C) - time (t) profile, a phenomenon that may be attributed to enterohepatic recirculation, gastric emptying and/or other absorption complexities related to its pH- and buffer capacity-dependent dissolution behavior. A population pharmacokinetic model, encompassing delay differential equations, was found the most appropriate approach to describe dual peaks in irbesartan's C-t profiles. Parameters estimated were: the absorption rate constant in the central compartment (ka = 0.304 h^-1), the constant time delay between the administration and the absorption (T=1.68 h), the apparent volume of distribution of the central (V1/F = 13.8 L) and peripheral (V2/F = 85.8 L) compartment, the apparent clearance from the central compartment (CL/F = 13.5 L/h), and the inter-compartmental clearance (Q/F = 17.7 L/h). Using simulations, it was made evident that changing the time delay results in significant changes of peak plasma concentrations but not of its blood pressure-lowering effect. In conclusion, delay differential equations may be useful to model dual peaks arising from absorption complexities, while changes of the time delay that reflect physiological processes that take place before absorption may have significant implications in proving bioequivalence.

Physiologically Relevant In Vitro-In Vivo Correlation (IVIVC) Approach for Sildenafil with Site-Dependent Dissolution

This study aimed to establish a physiologically relevant in vitro-in vivo correlation (IVIVC) model reflecting site-dependent dissolution kinetics for sildenafil based on population-pharmacokinetic (POP-PK) modeling. An immediate release (IR, 20 mg) and three sustained release (SR, 60 mg) sildenafil tablets were prepared by wet granulation method. In vitro dissolutions were determined by the paddle method at pH 1.2, 4.5, and 6.8 media. The in vivo pharmacokinetics were assessed after oral administration of the prepared IR and SR formulations to Beagle dogs (n = 12). The dissolution of sildenafil from SR formulations was incomplete at pH 6.8, which was not observed at pH 1.2 and pH 4.5. The relative bioavailability was reduced with the decrease of the dissolution rate. Moreover, secondary peaks were observed in the plasma concentration-time curves, which may result from site-dependent dissolution. Thus, a POP-PK model was developed to reflect the site-dependent dissolution by separately describing the dissolution and absorption processes, which allowed for estimation of the in vivo dissolution of sildenafil. Finally, an IVIVC was established and validated by correlating the in vitro and in vivo dissolution rates. The present approach may be applied to establish IVIVC for various drugs with complex dissolution kinetics for the development of new formulations.

Liquid Chromatography-Tandem Mass Spectrometry of Desoxo-Narchinol a and Its Pharmacokinetics and Oral Bioavailability in Rats and Mice

Desoxo-narchinol A is one of the major active constituents from Nardostachys jatamansi, which has been reported to possess various pharmacological activities, including anti-inflammatory, antioxidant, and anticonvulsant activity. A simple and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of desoxo-narchinol A in two different biological matrices, i.e., rat plasma and mouse plasma, using sildenafil as an internal standard (IS). The method involved simple protein precipitation with acetonitrile and the analyte was separated by gradient elution using 100% acetonitrile and 0.1% formic acid in water as a mobile phase. The MS detection was performed with a turbo electrospray in positive ion mode. The lower limit of quantification was 10 ng/mL in both rat and mouse plasma. Intra- and inter-day accuracies were in the ranges of 97.23-104.54% in the rat plasma and 95.90-110.11% in the mouse plasma. The precisions were within 8.65% and 6.46% in the rat and mouse plasma, respectively. The method was applied to examine the pharmacokinetics of desoxo-narchinol A, and the oral bioavailability of desoxo-narchinol A was 18.1% in rats and 28.4% in mice. The present results may be useful for further preclinical and clinical studies of desoxo-narchinol A.

A Gallbladder-Based Enterohepatic Circulation Model for Pharmacokinetic Studies

BACKGROUND AND OBJECTIVES

Strategies for modeling the enterohepatic circulation (EHC) process reported in the literature vary; however, gallbladder-based models currently provide the best physiological representation of the process. Regardless, the addition of a gallbladder to the model does not fully depict the physiology of EHC. A more physiological gallbladder-based EHC model is needed. This model should take into account a physiological representation of the bile secretion, gallbladder filling and emptying, the duration of gallbladder emptying, and irregular mealtimes. Considering all of these factors, the objectives of the present analysis were to propose a gallbladder-based EHC model and then to use that model to perform sensitivity analyses evaluating the effect of the extent of EHC on the pharmacokinetic profile and noncompartmental analysis (NCA) calculations.

METHODS

A gallbladder-based model that describes the EHC process was developed and used to perform determinant simulations assuming various degrees of EHC. Next, these simulations were compared to evaluate the effect of the EHC on the pharmacokinetic profiles of orally administered drugs. The influence of the EHC process on the NCA calculations was determined while assuming two sampling schemes that differed in the times at which sampling was performed in relation to meal times.

RESULTS

The presence of EHC results in nonlinearity in the system and changes the pharmacokinetic profile, affecting the maximum concentration (C_max), time to C_max (T_max), and half-life estimates. Comparison of the results obtained using the two sampling schemes for a drug undergoing various degrees of EHC demonstrated a significant influence of the selected sampling times on the NCA estimations. Bias in the NCA calculations was also dependent on the sampling times used.

CONCLUSION

Caution should be taken when designing clinical studies for drugs that undergo EHC. It may be essential to consider the timing of meals when planning pharmacokinetic studies and defining sampling times. The period over which samples are taken needs to be extended as compared to that traditionally used with other drugs. Future studies that attempt to identify the best sampling strategies in the presence of EHC are needed.

Regional Absorption of Fimasartan in the Gastrointestinal Tract by an Improved in situ Absorption Method in Rats

The aim of the present study was to assess the regional absorption of fimasartan by an improved in situ absorption method in comparison with the conventional in situ single-pass perfusion method in rats. After each gastrointestinal segment of interest was identified, fimasartan was injected into the starting point of each segment and the unabsorbed fimasartan was discharged from the end point of the segment. Blood samples were collected from the jugular vein to evaluate the systemic absorption of the drug. The relative fraction absorbed (F_abs,relative) values in the specific gastrointestinal region calculated based on the area under the curve (AUC) values obtained after the injection of fimasartan into the gastrointestinal segment were 8.2% ± 3.2%, 23.0% ± 12.1%, 49.7% ± 11.5%, and 19.1% ± 11.9% for the stomach, duodenum, small intestine, and large intestine, respectively, which were comparable with those determined by the conventional in situ single-pass perfusion. By applying the fraction of the dose available at each gastrointestinal segment following the oral administration, the actual fraction absorbed (F′_abs) values at each gastrointestinal segment were estimated at 10.9% for the stomach, 27.1% for the duodenum, 40.7% for the small intestine, and 5.4% for the large intestine, which added up to the gastrointestinal bioavailability (F_X·F_G) of 84.1%. The present method holds great promise to assess the regional absorption of a drug and aid to design new drug formulations.

Pharmacokinetics and Anti-Gastric Ulceration Activity of Oral Administration of Aceclofenac and Esomeprazole in Rats

This study examined the effects of esomeprazole on aceclofenac pharmacokinetics and gastrointestinal complications in rats. Aceclofenac alone, or in combination with esomeprazole, was orally administered to male Sprague-Dawley rats. Plasma concentrations of aceclofenac, its major metabolite diclofenac, and esomeprazole were simultaneously determined by a novel liquid chromatography-tandem mass spectrometry method. Gastrointestinal damage was determined by measuring ulcer area and ulcer lesion index of the stomach. Oral administration of aceclofenac induced significant gastric ulceration, which was inhibited by esomeprazole administration. Following concurrent administration of aceclofenac and esomeprazole, overall pharmacokinetic profiles of aceclofenac and metabolic conversion to diclofenac were unaffected by esomeprazole. Aceclofenac metabolism and pharmacokinetics were not subject to significant food effects, whereas bioavailability of esomeprazole decreased in fed compared to fasting conditions. In contrast, the pharmacokinetics of aceclofenac and esomeprazole were significantly altered by different dosing vehicles. These results suggest that co-administration of esomeprazole with aceclofenac may reduce aceclofenac-induced gastrointestinal complications without significant pharmacokinetic interactions. The optimal combination and clinical significance of the benefits of the combination of aceclofenac and esomeprazole need to be further evaluated.

On the population pharmacokinetics and the enterohepatic recirculation of total ezetimibe

Ezetimibe is a potent cholesterol absorption inhibitor, with an erratic pharmacokinetic (PK) profile, attributed to an extensive enterohepatic recirculation (EHC). The aim of this study was to develop a population PK model able to adequately characterize the complex distribution processes of total ezetimibe. The analysis was performed on the individual concentration-time data obtained from 28 healthy subjects who participated in a bioequivalence study comparing two oral ezetimibe formulations. The population PK analysis was performed using nonlinear mixed effect modeling, where different EHC models were developed and evaluated for their performance. Total ezetimibe pharmacokinetics was best described by a four-compartment model featuring EHC through the inclusion of an additional gallbladder compartment, which was assumed to release drug at specific time-intervals consistent with food intake. The final PK model was able to adequately estimate the population pharmacokinetic parameters and to allow for a formal characterization of the pharmacokinetic profile and the secondary peaks due to enterohepatic recirculation.

On the pharmacokinetics of two inhaled budesonide/formoterol combinations in asthma patients using modeling approaches

Dry powder inhalers containing the budesonide/formoterol combination have currently a well-established position among other inhaled products. Even though their efficacy mainly depends on the local concentrations of the drug they deliver within the lungs, their safety profile is directly related to their total systemic exposure. The aim of the present investigation was to explore the absorption and disposition kinetics of the budesonide/formoterol combination delivered via two different dry powder inhalers in asthma patients. Plasma concentration-time data were obtained from a single-dose, crossover bioequivalence study in asthma patients. Non-compartmental and population compartmental approaches were applied to the available datasets. The non-compartmental analysis allowed for an initial characterization of the primary pharmacokinetic (PK) parameters of the two inhaled drugs and subsequently the bioequivalence assessment of the two different dry powder inhalers. The population pharmacokinetic analysis further explored the complex absorption and disposition characteristics of the two drugs. In case of inhaled FOR, a five-compartment PK model including an enterohepatic re-circulation process was developed. For inhaled BUD, the incorporation of two parallel first-order absorption rate constants (fast and slow) for lung absorption in a two-compartment PK model emphasized the importance of pulmonary anatomical features and underlying physiological processes during model development. The role of potential covariates on the variability of the PK parameters was also investigated.

Characterization and evaluation of a self-microemulsifying drug delivery system containing tectorigenin, an isoflavone with low aqueous solubility and poor permeability

The purpose of this study was to characterize and evaluate tectorigenin-loaded self-microemulsifying drug delivery system (TG-SMEDDS), a previously studied preparation, and further confirm the improvement of TG in solubility and bioavailability. The appearance of TG-SMEDDS was clear and transparent, with good mobility. The microemulsion formed by TG-SMEDDS was globular, edge smooth, clear-cut, and distribution homogeneous under transmission electron microscope. The stability studies revealed that TG-SMEDDS remained stable at room temperature for at least 3 months. TG-SMEDDS showed excellent dissolution behavior that more than 90% of TG was released in only 5 min. The in situ intestinal perfusion studies indicated enhancement of absorption in four tested intestinal segments, and the main absorption site of TG was changed to duodenum. In addition, TG-SMEDDS showed significantly higher Cmax and AUC values (11-fold and 5-fold higher values, respectively; P < 0.05) than TG, and the absolute oral bioavailability of TG-SMEDDS was 56.33% (5-fold higher than that of crude TG). What's more, the AUC0-t of crude TG and TG-SMEDDS in bile duct non-ligation rats were 6.05 and 2.80 times, respectively, than that in bile duct ligation rats, indicating the existence of enterohepatic circulation and the secretion of bile could significantly affect the absorption of TG. Further studies showed that even the bile duct was ligation, TG-SMEDDS can still keep a better oral bioavailability (179.67%, compared with crude TG in the bile duct non-ligation rats). Therefore, our study implies that SMEDDS containing TG could be an effective strategy for the oral administration of TG.

Characterizing the time-course of antihypertensive activity and optimal dose range of fimasartan via mechanism-based population modeling

Fimasartan is a novel angiotensin II receptor blocker. Our aims were to characterize the time-course of the antihypertensive activity of fimasartan via a new population pharmacokinetic/pharmacodynamic model and to define its optimal dose range. We simultaneously modelled all fimasartan plasma concentrations and 24-h ambulatory blood pressure monitoring (ABPM) data from 39 patients with essential hypertension and 56 healthy volunteers. Patients received placebo, 20, 60, or 180mg fimasartan every 24h for 28days and healthy volunteers received placebo or 20 to 480mg as a single oral dose or as seven doses every 24h. External validation was performed using data on 560 patients from four phase II or III studies. One turnover model each was used to describe diastolic and systolic blood pressure. The input rates into these compartments followed a circadian rhythm and were inhibited by fimasartan. The average predicted (observed) diastolic blood pressure over 24-h in patients decreased by 10.1±7.5 (12.6±9.2; mean±SD)mmHg for 20mg, 14.2±7.0 (15.1±9.3) mmHg for 60mg, and 15.9±6.8 (11.5±9.9)mmHg for 180mg daily relative to placebo. The model explained the saturation of antihypertensive activity by counter-regulation at high fimasartan concentrations. Drug effect was maximal at approximately 23ng/mL fimasartan for diastolic and 12ng/mL for systolic blood pressure. The proposed mechanism-based population model characterized the circadian rhythm of ABPM data and the antihypertensive effect of fimasartan. After internal and external model validation, 30 to 60mg oral fimasartan given once daily was predicted as optimal dose range.

Decreased potency of fimasartan in liver cirrhosis was quantified using mixed-effects analysis

Fimasartan is a nonpeptide angiotensin II receptor blocker. In a previous study that compared the pharmacokinetics (PK) of fimasartan between patients with hepatic impairment (cirrhosis) and healthy subjects, the exposure to fimasartan was found to be higher in patients, but the decrease of blood pressure (BP) was not clinically significant in those with moderate hepatic impairment. The aims of this study were to develop a population PK-pharmacodynamic (PD) model of fimasartan and to evaluate the effect of hepatic function on BP reduction by fimasartan using previously published data. A 2-compartment linear model with mixed zero-order absorption followed by first-order absorption with a lag time adequately described fimasartan PK, and the effect of fimasartan on BP changes was well explained by the inhibitory sigmoid function in the turnover PK-PD model overlaid with a model of circadian rhythm (NONMEM version 7.2). According to our PD model, the lower BP responses in hepatic impairment were the result of the increased fimasartan EC₅₀ in patients, rather than from a saturation of effect. This is congruent with the reported pathophysiological change of increased plasma ACE and renin activity in hepatic cirrhosis.