Interspecies Scaling of Biliary Excreted Drugs: A Comparison of Several Methods**The views expressed in this article are those of the author and do not reflect the official policy of the FDA. No official support or endorsement by the FDA is intended or should be inferred

Results from a first-in-human study of dersimelagon, an investigational oral selective MC1R agonist

PURPOSE

To describe outcomes from the first-in-human study of dersimelagon, an investigational oral selective MC1R agonist, under development for the treatment of erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP).

METHODS

In this double-blind, placebo-controlled phase 1 study, the safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple ascending oral doses of dersimelagon in healthy participants were evaluated.

RESULTS

Dersimelagon was generally well tolerated in healthy participants, with the most common TEAEs being lentigo (52.8%) and skin hyperpigmentation (50.0%) after multiple doses. Systemic exposure to dersimelagon in plasma (based on AUC_0-∞ and C_max) increased in a slightly more than dose-proportional manner over the 1- to 600-mg single-dose range. Following multiple doses, dersimelagon was rapidly absorbed (median T_max ranging from 4 to 5 h postdose on days 1 and 14). Mean t_1/2 ranged from 10.56 to 18.97 h on day 14, and the steady state of plasma concentration was generally reached by 5 days of multiple dosing. There were no observable effects of age or race on the PK profile of dersimelagon or its metabolite dersimelagon glucuronide. No treatment-related effects on melanin density (MD) were observed following single doses of dersimelagon; however, after multiple doses, increases in MD were observed in participants receiving 150 and 300 mg dersimelagon.

CONCLUSION

Our study results indicate that dersimelagon is generally well tolerated and demonstrates a generally consistent PK profile across diverse subgroups. Treatment-related increases in MD warrant further investigation in a larger study population and in patients with EPP and XLP.

TRIAL REGISTRATION

A Study to Investigate the Safety, Tolerability and Pharmacokinetics of MT-7117 in Healthy Subjects, NCT02834442, https://clinicaltrials.gov/ct2/show/NCT02834442 , registration began July 2016.

Intestinal Excretion, Intestinal Recirculation, and Renal Tubule Reabsorption Are Underappreciated Mechanisms That Drive the Distribution and Pharmacokinetic Behavior of Small Molecule Drugs

Drug reabsorption following biliary excretion is well-known as enterohepatic recirculation (EHR). Renal tubular reabsorption (RTR) following renal excretion is also common but not easily assessed. Intestinal excretion (IE) and enteroenteric recirculation (EER) have not been recognized as common disposition mechanisms for metabolically stable and permeable drugs. IE and intestinal reabsorption (IR:EHR/EER), as well as RTR, are governed by dug concentration gradients, passive diffusion, active transport, and metabolism, and together they markedly impact disposition and pharmacokinetics (PK) of small molecule drugs. Disruption of IE, IR, or RTR through applications of active charcoal (AC), transporter knockout (KO), and transporter inhibitors can lead to changes in PK parameters. The impacts of intestinal and renal reabsorption on PK are under-appreciated. Although IE and EER/RTR can be an intrinsic drug property, there is no apparent strategy to optimize compounds based on this property. This review seeks to improve understanding and applications of IE, IR, and RTR mechanisms.

Misconceptions and issues regarding allometric scaling during the drug development process

INTRODUCTION

Allometry is the study of size and its consequences. The simple hypothesis of allometric scaling is that all physiological parameters are proportional to body size or body mass. This review examines the development of theory-based allometry or fixed exponents (0.75 and 1.0 for basal metabolic rate and volume, respectively) and the evidence for or against the theory. The main focus of this report is to show the readers that there is enough evidence from experimental data that negate the concept of theory-based allometry in biology, physiology, and pharmacokinetics. Areas covered: In this review, the history of the development of theoretical allometry and the strong evidence against theory-based allometry demonstrated by experimental data is provided. During drug development, allometry is applied to both inter-species (from animals to humans) and intra-species (adults to children) scaling. These two forms of allometric scaling in the context of theory-based allometry are discussed and provide insight on scientific progress that refute theory-based allometry. Expert opinion: Theory-based allometry is a mere theory and experimental data and real-life observations strongly negate the existence of such a theory. Pharmacostatistical and physiological models based on theory-based allometry can be misleading and incorrect because the theory-based allometric exponent 0.75 is not universal. The exponents of allometry are data dependent and are not fixed in the universe.

A unified strategy in selection of the best allometric scaling methods to predict human clearance based on drug disposition pathway

1. It is critical to develop a unified strategy to select the best allometric scaling (AS) method for a given group of drugs. 2. A total of 446 drugs with known human CL_iv, clear disposition pathway and animal (rat, dog, monkey) CL_iv were analyzed. All drugs were stratified based on their disposition pathway, liver extraction ratio (ER_H) and ratios of unbound clearance to renal glomerular filtration rate (R_GFR). Up to 22 AS methods were applied and compared in prediction of human CL_iv to each group of drugs. 3. AS methods that give the best prediction of human CL_iv, were identified for drugs primarily eliminated through liver with a fraction of renal elimination (f_renal) within 0.3-0.5 or ER_H > 0.3, where human CL_iv of more than 80% or 90% drugs could be accurately (within 2- or 3-fold error) predicted. For drugs with ER_H < 0.3, acceptable accuracy could be achieved by a two species method TS_R,D resulting more than 60% or 75% drugs were predicted within 2- or 3-fold error. 4. By stratified analysis of drugs, according to their disposition pathway and organ extraction ratio, a unified strategy was developed to select the best AS method in prediction of human CL_iv.

Neutrophil maturation rate determines the effects of dipeptidyl peptidase 1 inhibition on neutrophil serine protease activity

Background and Purpose

Neutrophil serine proteases (NSPs) are activated by dipeptidyl peptidase 1 (DPP1) during neutrophil maturation. The effects of neutrophil turnover rate on NSP activity following DPP1 inhibition was studied in a rat pharmacokinetic/pharmacodynamic model.

Experimental Approach

Rats were treated with a DPP1 inhibitor twice daily for up to 14 days; NSP activity was measured in onset or recovery studies, and an indirect response model was fitted to the data to estimate the turnover rate of the response.

Key Results

Maximum NSP inhibition was achieved after 8 days of treatment and a reduction of around 75% NSP activity was achieved at 75% in vitro DPP1 inhibition. Both the rate of inhibition and recovery of NSP activity were consistent with a neutrophil turnover rate of between 4–6 days. Using human neutrophil turnover rate, it is predicted that maximum NSP inhibition following DPP1 inhibition takes around 20 days in human.

Conclusions and Implications

Following inhibition of DPP1 in the rat, the NSP activity was determined by the amount of DPP1 inhibition and the turnover of neutrophils and is thus supportive of the role of neutrophil maturation in the activation of NSPs. Clinical trials to monitor the effect of a DPP1 inhibitor on NSPs should take into account the delay in maximal response on the one hand as well as the potential delay in a return to baseline NSP levels following cessation of treatment.

Role of enterohepatic recirculation in drug disposition: cooperation and complications

Enterohepatic recirculation (EHC) concerns many physiological processes and notably affects pharmacokinetic parameters such as plasma half-life and AUC as well as estimates of bioavailability of drugs. Also, EHC plays a detrimental role as the compounds/drugs are allowed to recycle. An in-depth comprehension of this phenomenon and its consequences on the pharmacological effects of affected drugs is important and decisive in the design and development of new candidate drugs. EHC of a compound/drug occurs by biliary excretion and intestinal reabsorption, sometimes with hepatic conjugation and intestinal deconjugation. EHC leads to prolonged elimination half-life of the drugs, altered pharmacokinetics and pharmacodynamics. Study of the EHC of any drug is complicated due to unavailability of the apposite model, sophisticated procedures and ethical concerns. Different in vitro and in vivo methods for studies in experimental animals and humans have been devised, each having its own merits and demerits. Involvement of the different transporters in biliary excretion, intra- and inter-species, pathological and biochemical variabilities obscure the study of the phenomenon. Modeling of drugs undergoing EHC has always been intricate and exigent models have been exploited to interpret the pharmacokinetic profiles of drugs witnessing multiple peaks due to EHC. Here, we critically appraise the mechanisms of bile formation, factors affecting biliary drug elimination, methods to estimate biliary excretion of drugs, EHC, multiple peak phenomenon and its modeling.

Characterization of preclinical in vitro and in vivo pharmacokinetics properties for KBP-7018, a new tyrosine kinase inhibitor candidate for treatment of idiopathic pulmonary fibrosis

KBP-7018 is a novel selective tyrosine kinase inhibitor with potential for the treatment of idiopathic pulmonary fibrosis. The objective of this study was to characterize the preclinical pharmacokinetics of KBP-7018 in vitro and in vivo, and then to assess the likelihood of developing KBP-7018 as a clinical candidate. The systemic clearance (CL) of KBP-7018 was relatively low in rodents and monkeys with a value of less than 30% of hepatic blood flow, while it was high in dogs. The steady-state volume of distribution (V_ss) ranged from 1.51 L/kg to 4.65 L/kg across the species tested. The maximum concentration (C_max) of KBP-7018 occurred at 0.25–6 hours after oral dosing, and the bioavailability was moderate (21%–68%). The human CL (~20% of hepatic blood flow) and V_ss (1.6–5.3 L/kg) were predicted by allometric scaling method and together with the other modeling methods indicated low metabolism and acceptable half-time (4.8–19.3 hours) in vivo. Overall, the preclinical data make it amenable to further oral solid dosage from design for the upcoming Phase I trials in human.

Cross-Species Differences in the Preclinical Pharmacokinetics of CT7758, an α4β1/α4β7 Integrin Antagonist

CT7758, a carboxylate containing α4β1/α4/β7 integrin antagonist, was characterized for its pharmacokinetic profile in various in vitro and in vivo assays in support of clinical development. The oral bioavailability of CT7758 was 4% in mice, 2% in rats, 7-55% in dogs, and 0.2% in cynomolgus monkeys. The low bioavailability in rodents and monkey results from low intestinal absorption as evidenced by a low fraction absorbed in the rat portal vein model (3%), low-to-medium permeability in Caco-2 cells (≤1.3 × 10(-6) cm/s) with evidences of polarized efflux, and high polar surface area (104 Å). In rodents and cynomolgus monkeys, the total plasma clearance was moderate to high (≥50% hepatic blood flow QH) and associated with a short elimination half-life (≤1 hour). This contrast with the dog data which showed a much lower clearance (6% QH) and a longer t1/2 (2.4 hours). The volume of distribution (Vz) also varied significantly across species with value of 5.5, 2.8, 0.24, and 0.93 l/kg in mouse, rat, dog, and cynomolgus monkey, respectively. In vitro assays demonstrated that active hepatic uptake accounted for most of the in vivo clearance and was the source of the large species variability. In vitro uptake assays predicted a total plasma clearance in humans in the low range (33% QH), a finding subsequently confirmed in the clinic. Assays in OAPT1B1-transfected cells demonstrated active uptake transport through this transporter. The prospect of limited absorption in human prompted the synthesis an ethyl ester prodrug, CDP323, which demonstrated higher in vitro permeability, increased oral bioavailability, as well as efficient in vivo release of its active moiety CT7758.

Scaling and systems biology for integrating multiple organs-on-a-chip

Coupled systems of in vitro microfabricated organs-on-a-chip containing small populations of human cells are being developed to address the formidable pharmacological and physiological gaps between monolayer cell cultures, animal models, and humans that severely limit the speed and efficiency of drug development. These gaps present challenges not only in tissue and microfluidic engineering, but also in systems biology: how does one model, test, and learn about the communication and control of biological systems with individual organs-on-chips that are one-thousandth or one-millionth of the size of adult organs, or even smaller, i.e., organs for a milliHuman (mHu) or microHuman (μHu)? Allometric scaling that describes inter-species variation of organ size and properties provides some guidance, but given the desire to utilize these systems to extend and validate human pharmacokinetic and pharmacodynamic (PK/PD) models in support of drug discovery and development, it is more appropriate to scale each organ functionally to ensure that it makes the suitable physiological contribution to the coupled system. The desire to recapitulate the complex organ-organ interactions that result from factors in the blood and lymph places a severe constraint on the total circulating fluid (~5 mL for a mHu and ~5 μL for a μHu) and hence on the pumps, valves, and analytical instruments required to maintain and study these systems. Scaling arguments also provide guidance on the design of a universal cell-culture medium, typically without red blood cells. This review presents several examples of scaling arguments and discusses steps that should ensure the success of this endeavour.

Probe ADME and test hypotheses: a PATH beyond clearance in vitro-in vivo correlations in early drug discovery

INTRODUCTION

In vitro cytochrome P450 (CYP450) metabolic profiling is pursued extensively to optimize drug properties. Still, the in vivo clearance of half of all new chemical entities (NCEs) remains poorly predicted by CYP450 metabolism, based on Novartis rat pharmacokinetic data. The conventional route to illuminating key drivers of in vivo clearance beyond hepatic metabolism is, frequently, the process of elimination, a time-consuming and sometimes resource-intensive practice. A more nimble and efficient diagnosis of drug clearance is imperative to support today's chemistry optimization.

AREAS COVERED

This article reviews in vitro-in vivo clearance correlation (IVIVC) analysis of drugs and NCEs including in silico advances, in vitro opportunities for clearance characterization and guidance for proper interpretation of clearance data. Potential mechanisms for under- and overestimation of in vivo clearance obtained from in vitro approaches are reviewed. The article offers insight into a practical PATH (Probe ADME and Test Hypotheses) for discovery data analysis that can enrich IVIVC development and guide more efficient use of the ADME-PK toolbox.

EXPERT OPINION

In vitro hepatic CYP450 stability measurements remain the most practical way to triage for high metabolic liabilities. Clearance is a complex process involving multiple mechanisms and many factors tend to be overlooked in routine correlation analyses. Equilibrium protein binding, intrinsic permeability and ionization may yield insight into distribution-limited clearance. In addition, hydrophobic character and transporter interaction can be valuable in diagnosing dominant clearance pathways. An integrated ADME approach to clearance interrogation is expected to help refine the in vitro-in silico strategies that guide medicinal chemistry.

Applications of human pharmacokinetic prediction in first-in-human dose estimation

Quantitative estimations of first-in-human (FIH) doses are critical for phase I clinical trials in drug development. Human pharmacokinetic (PK) prediction methods have been developed to project the human clearance (CL) and bioavailability with reasonable accuracy, which facilitates estimation of a safe yet efficacious FIH dose. However, the FIH dose estimation is still very challenging and complex. The aim of this article is to review the common approaches for FIH dose estimation with an emphasis on PK-guided estimation. We discuss 5 methods for FIH dose estimation, 17 approaches for the prediction of human CL, 6 methods for the prediction of bioavailability, and 3 tools for the prediction of PK profiles. This review may serve as a practical protocol for PK- or pharmacokinetic/pharmacodynamic-guided estimation of the FIH dose.

Prediction of human oral plasma concentration-time profiles using preclinical data: comparative evaluation of prediction approaches in early pharmaceutical discovery

BACKGROUND AND OBJECTIVES

Empirically based methods remain one of our tools in human pharmacokinetic predictions. The Dedrick approach and the steady-state plasma drug concentration (C(ss))-mean residence time (MRT) approach are based on the assumption that concentration-time profiles are similar among species, including man, and that curves derived from a variety of animal species can be superimposed after mathematical transformation. In the Dedrick approach the transformation is based on the slope and intercept of the allometric relationship. The C(ss)-MRT approach is based on the implementation of measured animal and predicted human MRT and dose/volume of distribution at steady state (V(ss)). The aims of the present study were to compare the predictive performance of concentration-time profiles obtained by these approaches, to evaluate the prediction of individual pharmacokinetic parameters by these approaches and to further refine these approaches incorporating the experience from our previous work.

METHODS

A retrospective analysis using 35 proprietary compounds developed at Johnson & Johnson Pharmaceutical Research and Development was conducted to compare the accuracies of the Dedrick and C(ss)-MRT approaches for predicting oral concentration-time profiles and pharmacokinetic parameters in man. In the first step, input for the transformation was based on simple allometry. Then we assessed whether both methods could be fine-tuned by systematically incorporating correction factors (maximum life span potential, brain weight and plasma protein binding), depending on the interspecies relationship. In addition, for the C(ss)-MRT approach, we used formulas based on multivariate regression analysis as input for the transformation.

RESULTS

Inclusion of correction factors significantly improved the profile predictability for the Dedrick and C(ss)-MRT approaches. This was mainly linked to an improved prediction of terminal elimination half-life (t(½)), MRT and the ratio between the maximum plasma concentration and the concentration at the last observed time point (C(max)/C(last)). No significant differences were observed between the Dedrick approach with correction factors, the C(ss)-MRT approach with correction factors and the C(ss)-MRT approach, based on the regression equations.

CONCLUSIONS

Based on the dataset evaluated in this study, we demonstrated that human plasma concentration-time profiles and pharmacokinetic parameters could be predicted with the Dedrick and C(ss)-MRT approaches and that if correction factors were implemented, the predictions improved significantly. With the requirement of only a limited preclinical in vivo pharmacokinetic dataset, these empirical methods could offer potential in the early stages of drug discovery.

Important clinical syndromes associated with liver disease

Several clinical syndromes can develop in many different liver diseases. They are important to understanding the clinical manifestations of hepatobiliary diseases. The signs, diagnostic procedures, and specific diseases associated with these syndromes are discussed.

Pharmacokinetic allometric scaling of antibodies: application to the first-in-human dose estimation

The objectives of this study are: (i) to evaluate the predictive performance of interspecies scaling for antibodies to predict clearance, volume of distribution at steady state, and half-life in humans from animal data and (ii) to estimate first-in-human dose based on the predicted human clearance. Four methods were used to predict clearance in humans: (1) clearance versus body weight (simple allometry), (2) the product of clearance and maximum life-span potential (MLP) versus body weight, (3) the product of clearance and brain weight versus body weight, and (4) the application of a fixed exponent of 0.75. Based on the predicted human clearance, six methods were used to estimate the first-in-human dose. The predicted pharmacokinetic parameters and the estimated first-in-human dose of antibodies were compared with the observed human values. The results of the study indicated that the clearance of antibodies can be predicted with reasonable accuracy in humans and a good estimate of first human dose can be obtained from the predicted human clearance.

Prediction of human pharmacokinetics-biliary and intestinal clearance and enterohepatic circulation

The main objective was to evaluate and propose methods for predicting biliary clearance (CL(bile)) and enterohepatic circulation (EHC) of intact drugs in man. Another aim was to evaluate to role of intestinal drug secretion and propose a method for prediction of intestinal secretion CL (CL(i)). Animal data poorly predict the CL and CL(bile) of biliary excreted drugs, and the suggested molecular weight threshold for bile excretion as the dominant elimination route does not seem to hold. Active transport, low metabolic intrinsic CL (CL(int)) and, as an approximation, permeability (P(e)) less than that of metoprolol is required for substantial CL(bile) to occur. The typical EHC plasma concentration vs time profile (multiple peaks) is demonstrated for many low metabolic CL(int)-compounds with efflux and moderate to high intestinal P(e) and fraction absorbed. Physiologically-based in-vitro to in-vivo (PB-IVIV) methodology with in-vitro intrinsic CL(bile)-data obtained with sandwich-cultured human hepatocytes has generated 2- and 5-fold underpredictions for two compounds with intermediate to high CL(bile). This is despite not considering the unbound fraction. Possible explanations include low transporter activity and diffusion limitations in the in-vitro experiments. Intestinal reabsorption and EHC were also neglected in these predictions and in-vivo CL(bile) estimations. The sandwich model and these reference data are still very useful. Consideration of an empirical scaling factor and a newly developed approach that accounts for intestinal reabsorption and EHC could potentially lead to improved PB-IVIV predictions of CL(bile). Apparently, no attempts have been made to predict CL(i). Elimination via the intestinal route does not appear to be of great importance for the few compounds with available data, but could be equally as important as bile excretion. Net secretion in-vitro P(e) and newly estimated in-vivo intrinsic CL(i) data for digoxin and rosuvastatin could be useful for approximation of CL(i) of other compounds.

Identification of interspecies difference in efflux transporters of hepatocytes from dog, rat, monkey and human

The large interspecies differences of hepatobiliary transport present a challenge for the allometric prediction of human biliary excretion for drug candidates primarily cleared via hepatobiliary secretion. In the present study, we determined the metabolic stabilities of common fluorescent substrates of hepatobiliary efflux transporters and developed a rapid efflux assay to determine the functional activities of MRP/Mrp, BCRP/Bcrp and P-gp in hepatocytes of four species. The specificities of transporter-mediated dye efflux were confirmed by selective transporter inhibitors. Among tested species, transporter-specific dye efflux kinetics was consistent between freshly isolated and cryopreserved hepatocytes. Hepatocyte elimination half-lives of MRP/Mrp substrates GS-MF and calcein were observed in the rank order of human>monkey>dog>rat. The fourfold higher MRP/Mrp substrate efflux rate of rat hepatocytes compared to human is likely due to the species-specific functional differences of MRP2/Mrp2 expressed on the canalicular membrane. We also observed efficient BCRP-mediated pheophorbide A (PhA) efflux by human and dog hepatocytes, while PhA extrusion in monkey and rat hepatocytes appeared limited. P-gp function measured by DiOC2(3) efflux was minimal in hepatocytes of all origins and no significant species differences were detected. Our results demonstrated marked differences in hepatocyte MRP/Mrp and BCRP/Bcrp activities across species, indicating that they may contribute to the species differences of in vivo hepatobiliary excretion. These results also suggest the potential utility of primary hepatocytes, either fresh or cryopreserved, as an in vitro model to predict interspecies differences in the biliary transport of MRP/Mrp and BCRP/Bcrp substrates.

Animal models of BMAA neurotoxicity: a critical review

Of all the molecules reported to have toxicological effects, BMAA (beta-methylamino alanine) stands out as having the most checkered past. In the late 1960's it was reported to be a toxic component of the cycad flour consumed by Chamorros on Guam which caused the high incidence of amyotrophic lateral sclerosis (ALS) in Guam, that was associated with a Parkinson's disease-like dementia complex (ALS-PDC). However, because ALS-PDC is a slow onset disease, manifesting itself as long as 30 years following exposure to the putative neurotoxin, and only acute toxic effects of BMAA were observed in animal studies, interest in BMAA waned. A seminal study by Spencer et al., in 1987 showing neurological impairments with long-term BMAA-fed monkeys revived the hypothesis that BMAA could cause ALS-PDC. However, the amounts of BMAA used in that study were viewed as being the equivalent of a person consuming their body weight of cycad flour every day. Again, the BMAA hypothesis was discarded. Recently a third iteration of the BMAA hypothesis has been proposed. It is based on the discovery of a novel dietary source of BMAA via biomagnification of BMAA in flying foxes, once consumed in great amounts by Chamorros. Also, reports that BMAA can be incorporated into plant and animal proteins, a heretofore unrecognized dietary source of BMAA, further solidified this new hypothesis. However, once again this hypothesis has its detractors and it remains controversial. This manuscript critically evaluates in vivo studies directed at establishing an animal model of BMAA-induced ALS-PDC and their implications for this hypothesis.

Interspecies Prediction of Human Drug Clearance Based on Scaling Data from One or Two Animal Species

A data-driven approach was adopted to derive new one- and two-species-based methods for predicting human drug clearance (CL) using CL data from rat, dog, or monkey (n = 102). The new one-species methods were developed as CL(human)/kg = 0.152 x CL(rat)/kg, CL(human)/kg = 0.410 x CL(dog)/kg, and CL(human)/kg = 0.407 x CL(monkey)/kg, referred to as the rat, dog, and monkey methods, respectively. The coefficient of the monkey method (0.407) was similar to that of the monkey liver blood flow (LBF) method (0.467), whereas the coefficients of the rat method (0.152) and dog method (0.410) were considerably different from those of the LBF methods (rat, 0.247; dog, 0.700). The new rat and dog methods appeared to perform better than the corresponding LBF methods, whereas the monkey method and the monkey LBF method showed improved predictability compared with the rat and dog one-species-based methods and the allometrically based "rule of exponents" (ROE). The new two-species methods were developed as CL(human) = a(rat-dog) . W (human)(0.628) (referred to as rat-dog method) and CL(human) = a(rat-monkey) . W (human)(0.650) (referred to as rat-monkey method), where a(rat-dog) and a(rat-monkey) are the coefficients obtained allometrically from the corresponding two species. The predictive performance of the two-species methods was comparable with that of the three-species-based ROE. Twenty-six Wyeth compounds having data from mouse, rat, dog, monkey, and human were used to test these methods. The results showed that the rat, dog, monkey, rat-dog, and rat-monkey methods provided improved predictions for the majority of the compounds compared with those for the ROE, suggesting that the use of three or more species in an allometrically based approach may not be necessary for the prediction of human exposure.

Preclinical pharmacokinetics and interspecies scaling of ragaglitazar, a novel biliary excreted PPAR dual activator

Allometric scaling has been used as an effective tool for the prediction of human pharmacokinetic parameters. Allometry has been a useful approach for the analysis of compounds that are eliminated unchanged in the urine and/or exhibit similar metabolic patterns across species. However, it has been a challenging issue to correctly predict human pharmacokinetic parameters for drugs that are eliminated intact and/or as conjugates in the bile. Ragaglitazar is a novel, non-thiazolidinedione peroxisome proliferator-activated receptor (PPAR) alpha- and gamma-agonist. In our investigation, preclinical pharmacokinetic data on ragaglitazar were gathered for several animal species (mice, rats, rabbits and dogs). Ragaglitazar when administered orally has shown a low clearance rate (Cl/F; < 5% of hepatic blood flow) in mice, rats and rabbits and a moderately high Cl/F in dogs (> 15% of hepatic blood flow). A qualitative estimation of rat bile has unequivocally confirmed the elimination of ragaglitazar in the bile. The human pharmacokinetic data are also indicative of the involvement of enterohepatic biliary recycling. In order to predict key parameters such as Cl/F and volume of distribution (V/F), simple allometry was the approach adopted at the onset. Although V/F scaled adequately, it failed to accurately predict human Cl/F. Therefore, standard correction factors such as maximum life span potential (MLP) and brain weight were also included. Although such modifications improved the linearity (r2 > 0.9), they failed to predict the investigated values. Further incorporation of correction factors particularly relevant to biliary excreted drugs improved the prediction of these values. Interestingly, the exclusion of dog data from the interspecies scaling considerably improved the prediction of both Cl/F and V/F.