Quantifying and Communicating Uncertainty in Preclinical Human Dose-Prediction.

Human dose-prediction is fundamental for ranking lead-optimization compounds in drug discovery and to inform design of early clinical trials. This tutorial describes how uncertainty in such predictions can be quantified and efficiently communicated to facilitate decision-making. Using three drug-discovery case studies, we show how several uncertain pieces of input information can be integrated into one single uncomplicated plot with key predictions, including their uncertainties, for many compounds or for many scenarios, or both.

Model-based drug discovery: implementation and impact.

Model-based drug discovery (MBDDx) aims to build and continuously improve the quantitative understanding of the relation between drug exposure (target engagement) efficacy and safety, to support target validation; to define compound property criteria for lead optimization and safety margins; to set the starting dose; and to predict human dose and scheduling for clinical candidates alone, or in combination with other medicines. AstraZeneca has systematically implemented MBDDx within all drug discovery programs, with a focused investment to build a preclinical modeling and simulation capability and an in vivo information platform and architecture, the implementation, impact and learning of which are discussed here.

The pharmacokinetics and hepatic disposition of repaglinide in pigs: mechanistic modeling of metabolism and transport.

The predictive power of using in vitro systems in combination with physiologically based pharmacokinetic (PBPK) modeling to elucidate the relative importance of metabolism and carrier-mediated transport for the pharmacokinetics was evaluated using repaglinide as a model compound and pig as the test system. Repaglinide was chosen as model drug as previous studies in humans have shown that repaglinide is subject to both carrier-mediated influx to the liver cells and extensive hepatic metabolism. A multiple sampling site model in pig was chosen since it provides detailed in vivo information about the liver disposition.

Optimal experimental design for assessment of enzyme kinetics in a drug discovery screening environment.

A penalized expectation of determinant (ED)-optimal design with a discrete parameter distribution was used to find an optimal experimental design for assessment of enzyme kinetics in a screening environment. A data set for enzyme kinetic data (V(max) and K(m)) was collected from previously reported studies, and every V(max)/K(m) pair (n = 76) was taken to represent a unique drug compound. The design was restricted to 15 samples, an incubation time of up to 40 min, and starting concentrations (C(0)) for the incubation between 0.

Measurement of unbound drug exposure in brain: modeling of pH partitioning explains diverging results between the brain slice and brain homogenate methods.

Currently used methodology for determining unbound drug exposure in brain combines measurement of the total drug concentration in the whole brain in vivo with estimation of brain tissue binding from one of two available in vitro methods: equilibrium dialysis of brain homogenate and the brain slice uptake method. This study of 56 compounds compares the fraction of unbound drug in brain (f(u,brain)), determined using the brain homogenate method, with the unbound volume of distribution in brain (V(u,brain)), determined using the brain slice method. Discrepancies were frequent and were primarily related to drug pH partitioning, attributable to the preservation of cellular structures in the slice that are absent in the homogenate.

Hepatic disposition of ximelagatran and its metabolites in pig; prediction of the impact of membrane transporters through a simple disposition model.

Purpose: The double prodrug, ximelagatran, is bioconverted, via the intermediates ethylmelagatran and N-hydroxymelagatran, to the direct thrombin inhibitor, melagatran. The primary aim of this study was to investigate the hepatic metabolism and disposition of ximelagatran and the intermediates in pig. A secondary aim was to explore a simple in vitro methodology for quantitative investigations of the impact of membrane transporters on the disposition of metabolized drugs.

Structure-brain exposure relationships in rat and human using a novel data set of unbound drug concentrations in brain interstitial and cerebrospinal fluids.

New experimental methodologies were applied to measure the unbound brain-to-plasma concentration ratio (K(p,uu,brain)) and the unbound CSF-to-plasma concentration ratio (K(p,uu,CSF)) in rats for 43 structurally diverse drugs. The relationship between chemical structure and K(p,uu,brain) was dominated by hydrogen bonding. Contrary to popular understanding based on the total brain-to-plasma concentration ratio (logBB), lipophilicity was not a determinant of unbound brain exposure.

Improved measurement of drug exposure in the brain using drug-specific correction for residual blood.

A major challenge associated with the determination of the unbound brain-to-plasma concentration ratio of a drug (K(p,uu,brain)), is the error associated with correction for the drug in various vascular spaces of the brain, i.e., in residual blood.

Development of a high-throughput brain slice method for studying drug distribution in the central nervous system.

New, more efficient methods of estimating unbound drug concentrations in the central nervous system (CNS) combine the amount of drug in whole brain tissue samples measured by conventional methods with in vitro estimates of the unbound brain volume of distribution (V(u,brain)). Although the brain slice method is the most reliable in vitro method for measuring V(u,brain), it has not previously been adapted for the needs of drug discovery research. The aim of this study was to increase the throughput and optimize the experimental conditions of this method.

Methodologies to assess brain drug delivery in lead optimization.

In the area of lead optimization for potential CNS-active drugs in medicinal chemistry, there is a great need for experimental methodologies that can generate data relevant to estimates of free (unbound) drug exposure within the CNS. The methods chosen have to be efficient and have to measure a pharmacologically relevant entity. The lack of methods for generating such data is probably linked with the lack of successful lead optimization strategies within CNS drug discovery.

Early integration of pharmacokinetic and dynamic reasoning is essential for optimal development of lead compounds: strategic considerations.

The aims of this report are firstly to raise awareness among kineticists and pharmacologists as to why pharmacokinetic-pharmacodynamic (PKPD) integration is essential for target validation (TV), optimizing development of lead compounds (lead generation [LG] and lead optimization [LO]) and scaling these to human. A related aim is to demonstrate strategic examples of PKPD collaborations that have improved the planning, execution and evaluation of experiments in primary and safety pharmacology. Examples include design of TV studies, design and data 'pruning' of PKPD studies in LO, analysis of data with marginal and substantial temporal (time) differences between exposure and response, design of safety pharmacology studies, assessment of safety margin and assessment of uncertainties in predictions of first dose in human.

The multiple depletion curves method provides accurate estimates of intrinsic clearance (CLint), maximum velocity of the metabolic reaction (Vmax), and Michaelis constant (Km): accuracy and robustness evaluated through experimental data and Monte Carlo simulations.

The use of multiple depletion curves for the estimation of maximum velocity of the metabolic reaction (V(max)), the Michaelis constant (K(m)), and intrinsic clearance (CL(int)) was thoroughly evaluated by means of experimental data and through a series of Monte Carlo simulations. The enzyme kinetics of seven compounds were determined using the multiple depletion curves method (MDCM), the traditional initial formation rate of metabolite method (IFRMM), and the "in vitro t(1/2)" method, and the parameter estimates that were derived from the three methods were compared. The impact of a change in enzyme activity during the incubation period on the parameter estimates and the possibility to correct for this were also investigated.

Prediction of drug tissue to plasma concentration ratios using a measured volume of distribution in combination with lipophilicity.

One of the drug specific parameters needed in physiologically based pharmacokinetic (PBPK) models is the tissue to plasma drug concentration ratios (K(p) values). The aim of this study was to develop an empirical method for predicting K(p) values using a preclinically determined in vivo volume of distribution, in combination with descriptors for drug lipophilicity. Pharmacokinetic data in laboratory animals for a wide range of drug compounds were collected.

In vitro methods for estimating unbound drug concentrations in the brain interstitial and intracellular fluids.

Concentrations of unbound drug in the interstitial fluid of the brain are not rapidly measured in vivo. Therefore, measurement of total drug levels, i.e.

Regional intestinal absorption and biliary excretion of fluvastatin in the rat: possible involvement of mrp2.

The first purpose of this study was to investigate the in vivo absorption, biliary secretion, and first-pass effect of fluvastatin following regional intestinal dosing in the rat. We also examined the membrane transport mechanisms and made in silico predictions of the relative importance of various intestinal regions to the human absorption of fluvastatin. Fluvastatin was administered intravenously (2, 10, and 20 micromol/kg) and into the duodenum (1.

Metabolic stability for drug discovery and development: pharmacokinetic and biochemical challenges.

Metabolic stability refers to the susceptibility of compounds to biotransformation in the context of selecting and/or designing drugs with favourable pharmacokinetic properties. Metabolic stability results are usually reported as measures of intrinsic clearance, from which secondary pharmacokinetic parameters such as bioavailability and half-life can be calculated when other data on volume of distribution and fraction absorbed are available. Since these parameters are very important in defining the pharmacological and toxicological profile of drugs as well as patient compliance, the pharmaceutical industry has a particular interest in optimising for metabolic stability during the drug discovery and development process.

Pharmacokinetics and pharmacodynamics of ximelagatran, a novel oral direct thrombin inhibitor, in young healthy male subjects.

Objectives: Ximelagatran is a novel, oral direct thrombin inhibitor designed to overcome the low and variable oral absorption of melagatran, its active form. The pharmacokinetics and pharmacodynamics of ximelagatran following single and repeated oral administration were investigated. The primary objectives were to determine the dose linearity and reproducibility of melagatran exposure and the influence of food intake.

Absorption, distribution, metabolism, and excretion of ximelagatran, an oral direct thrombin inhibitor, in rats, dogs, and humans.

The absorption, metabolism, and excretion of the oral direct thrombin inhibitor, ximelagatran, and its active form, melagatran, were separately investigated in rats, dogs, and healthy male human subjects after administration of oral and intravenous (i.v.) single doses.

The direct thrombin inhibitor melagatran and its oral prodrug H 376/95: intestinal absorption properties, biochemical and pharmacodynamic effects.

Unlabelled: Suboptimal gastrointestinal absorption is a problem for many direct thrombin inhibitors. The studies presented herein describe the new oral direct thrombin inhibitor H 376/95, a prodrug with two protecting residues added to the direct thrombin inhibitor melagatran. Absorption properties in vitro: H 376/95 is uncharged at intestinal pH while melagatran is charged.

Pharmacokinetics and arteriovenous differences in clevidipine concentration following a short- and a long-term intravenous infusion in healthy volunteers.

Background: Clevidipine is an ultra-short-acting calcium antagonist developed for reduction and control of blood pressure during cardiac surgery. The objectives of the current study were to determine the pharmacokinetics of clevidipine after 20-min and 24-h intravenous infusions, and to determine the relation between the arterial and venous concentrations and the hemodynamic responses to clevidipine in healthy volunteers.

Methods: Four volunteers received clevidipine for 20 min, and eight subjects were administered clevidipine intravenously for 24 h at two different dose rates.

Stereoselective metabolism by human liver CYP enzymes of a substituted benzimidazole.

H 259/31 is a substituted benzimidazole developed as a structural analog of omeprazole. Metabolites of H 259/31 formed in human liver microsomes were identified by using the synthetic reference compounds and liquid chromatography/mass spectrometry. The predominant metabolic pathways found include oxidation of the sulfoxide to sulfone, oxidative O-dealkylation of the cyclopropylmethoxy group to the corresponding pyridone and aromatic hydroxylation to give the phenolic derivative.

Animal pharmacokinetics of inogatran, a low-molecular-weight thrombin inhibitor with potential use as an antithrombotic drug.

Pharmacokinetics, excretion, and metabolism of inogatran, a low-molecular-weight thrombin inhibitor, were studied in the rat, dog, and cynomolgus monkey. After intravenous administration the half-life was short in all three animal species, due to a small volume of distribution and a relatively high clearance. At doses of 0.

The protective action of chlormethiazole against ischaemia-induced neurodegeneration in gerbils when infused at doses having little sedative or anticonvulsant activity.

1. The effect of chlormethiazole administration on delayed neuronal death in gerbil hippocampus following transient global ischaemia has been examined. Chlormethiazole was administered either intraperitoneally or by intravenous infusion with either the dose or the time of infusion varied.

A comparison between the semisimultaneous and the stable isotope techniques for bioavailability estimation of terbutaline in humans.

A recently proposed bioavailability estimation procedure, the "semisimultaneous" method, in which the test and reference dose administrations are separated by a short time interval and total concentrations are analyzed, was compared with the stable isotope method for precision and accuracy. By administering isotope-labeled (reference) and unlabeled (test) terbutaline in a semisimultaneous fashion, the bioavailability could be determined with both methods at the same time. The extent and rate of bioavailability of oral terbutaline was determined in eight healthy volunteers by use of both model fitting, AUC methods, and deconvolution.