Investigating Partially Discordant Results in Phase 3 Studies of Aducanumab.

OBJECTIVES: Efficacy and safety results from the EMERGE (NCT02484547) and ENGAGE (NCT02477800) phase 3 studies of aducanumab in early Alzheimer's disease (AD) have been published. In EMERGE, but not in ENGAGE, high-dose aducanumab demonstrated significant treatment effects across primary and secondary endpoints. Low-dose aducanumab results were consistent across studies with non-significant differences versus placebo that were intermediate to the high-dose arm in EMERGE. The present investigation examined data from EMERGE and ENGAGE through post-hoc analyses to determine factors that contributed to discordant results between the high-dose arms of the two studies. DESIGN: EMERGE and ENGAGE were 2 phase 3, randomized, double-blind, placebo-controlled, parallel-group studies. SETTING: EMERGE and ENGAGE were 2 global multicenter studies involving 348 sites in 20 countries. PARTICIPANTS: Participants in EMERGE and ENGAGE were aged 50 to 85 years and had mild cognitive impairment or mild AD dementia with confirmed amyloid pathology. The randomized and dosed population (all randomized patients who received at least one dose of study treatment) included 1638 patients in EMERGE and 1647 in ENGAGE. INTERVENTION: In EMERGE and ENGAGE, participants were randomized to receive low- or high-dose aducanumab or placebo (1:1:1) once every 4 weeks. MEASUREMENTS: In this paper, 4 areas were investigated through post-hoc analyses to understand the discordance in the high-dose arms of the EMERGE and ENGAGE studies: baseline characteristics, amyloid-related imaging abnormalities, non-normality of the data, and dosing/exposure to aducanumab. RESULTS: Post-hoc analyses showed that outcomes in the ENGAGE high-dose group were affected by an imbalance in a small number of patients with extremely rapid progression and by lower exposure to the target dose of 10 mg/kg. These factors were confounded and present in early enrolled patients but were not present in later-enrolled patients who were randomized to the target dosing regimen of 10 mg/kg after titration. Neither baseline characteristics nor amyloid-related imaging abnormalities contributed to the difference in results between the high-dose arms. CONCLUSIONS: Results were consistent across studies in later enrolled patients in which the incidence of rapidly progressing patients was balanced across treatment arms.

Two Randomized Phase 3 Studies of Aducanumab in Early Alzheimer's Disease.

BACKGROUND: Alzheimer's disease is a progressive, irreversible, and fatal disease for which accumulation of amyloid beta is thought to play a key role in pathogenesis. Aducanumab is a human monoclonal antibody directed against aggregated soluble and insoluble forms of amyloid beta. OBJECTIVES: We evaluated the efficacy and safety of aducanumab in early Alzheimer's disease. DESIGN: EMERGE and ENGAGE were two randomized, double-blind, placebo-controlled, global, phase 3 studies of aducanumab in patients with early Alzheimer's disease. SETTING: These studies involved 348 sites in 20 countries. PARTICIPANTS: Participants included 1638 (EMERGE) and 1647 (ENGAGE) patients (aged 50-85 years, confirmed amyloid pathology) who met clinical criteria for mild cognitive impairment due to Alzheimer's disease or mild Alzheimer's disease dementia, of which 1812 (55.2%) completed the study. INTERVENTION: Participants were randomly assigned 1:1:1 to receive aducanumab low dose (3 or 6 mg/kg target dose), high dose (10 mg/kg target dose), or placebo via IV infusion once every 4 weeks over 76 weeks. MEASUREMENTS: The primary outcome measure was change from baseline to week 78 on the Clinical Dementia Rating Sum of Boxes (CDR-SB), an integrated scale that assesses both function and cognition. Other measures included safety assessments; secondary and tertiary clinical outcomes that assessed cognition, function, and behavior; and biomarker endpoints. RESULTS: EMERGE and ENGAGE were halted based on futility analysis of data pooled from the first approximately 50% of enrolled patients; subsequent efficacy analyses included data from a larger data set collected up to futility declaration and followed prespecified statistical analyses. The primary endpoint was met in EMERGE (difference of -0.39 for high-dose aducanumab vs placebo [95% CI, -0.69 to -0.09; P=.012; 22% decrease]) but not in ENGAGE (difference of 0.03, [95% CI, -0.26 to 0.33; P=.833; 2% increase]). Results of biomarker substudies confirmed target engagement and dose-dependent reduction in markers of Alzheimer's disease pathophysiology. The most common adverse event was amyloid-related imaging abnormalities-edema. CONCLUSIONS: Data from EMERGE demonstrated a statistically significant change across all four primary and secondary clinical endpoints. ENGAGE did not meet its primary or secondary endpoints. A dose- and time-dependent reduction in pathophysiological markers of Alzheimer's disease was observed in both trials.

Atacicept in relapsed/refractory multiple myeloma or active Waldenström's macroglobulinemia: a phase I study.

BACKGROUND: Advanced multiple myeloma (MM) and Waldenström's macroglobulinemia (WM) are incurable B-cell malignancies. This is the first full clinical report of atacicept, a fusion protein that binds to and neutralises the B-cell survival factors, B-lymphocyte stimulator (BLyS) and A proliferation-inducing ligand (APRIL), in MM and WM. METHODS: In this open-label phase-I study, 16 patients with advanced disease (12 MM, 4 WM) received one cycle of five once-weekly subcutaneous injections of atacicept (2, 4, 7 or 10 mg kg(-1)). Patients with stable disease after cycle 1 entered an extension study (either two additional cycles (2, 4 and 7 mg kg(-1) cohorts) or 15 consecutive weekly injections of atacicept 10 mg kg(-1)). RESULTS: Atacicept was well tolerated, systemically and locally; the maximum tolerated dose was not identified. Of 11 patients with MM who completed initial treatment, five patients were progression-free after cycle 1 and four patients were progression-free after extended therapy. Of four patients with WM, three patients were progression-free after cycle 1. Consistent with atacicept's mechanism of action, polyclonal immunoglobulin isotypes and total B cells were reduced. Bone-marrow density, myeloma cell numbers and plasma concentrations of soluble CD138 also decreased. CONCLUSION: Atacicept is well tolerated in patients with MM and WM, and shows clinical and biological activity consistent with its mechanism of action.

Modelling and simulation of variability and uncertainty in toxicokinetics and pharmacokinetics.

Two important methodological issues within the framework of the variability and uncertainty analysis of toxicokinetic and pharmacokinetic systems are discussed: (i) modelling and simulation of the existing physiologic variability in a population; and (ii) modelling and simulation of variability and uncertainty when there is insufficient or not well defined (e.g. small sample, semiquantitative, qualitative and vague) information available. Physiologically based pharmacokinetic models are especially suited for separating and characterising the physiologic variability from the overall variability and uncertainty in the system. Monte Carlo sampling should draw from multivariate distributions, which reflect all levels of existing dependencies in the intact organism. The population characteristics should be taken into account. A fuzzy simulation approach is proposed to model variability and uncertainty when there is semiquantitative, qualitative and vague information about the model parameters and their statistical distributions cannot be defined reliably.

Empirical versus mechanistic modelling: comparison of an artificial neural network to a mechanistically based model for quantitative structure pharmacokinetic relationships of a homologous series of barbiturates.

The aim of the current study was to compare the predictive performance of a mechanistically based model and an empirical artificial neural network (ANN) model to describe the relationship between the tissue-to-unbound plasma concentration ratios (Kpu's) of 14 rat tissues and the lipophilicity (LogP) of a series of nine 5-n-alkyl-5-ethyl barbituric acids. The mechanistic model comprised the water content, binding capacity, number of the binding sites, and binding association constant of each tissue. A backpropagation ANN with 2 hidden layers (33 neurons in the first layer, 9 neurons in the second) was used for the comparison. The network was trained by an algorithm with adaptive momentum and learning rate, programmed using the ANN Toolbox of MATLAB. The predictive performance of both models was evaluated using a leave-one-out procedure and computation of both the mean prediction error (ME, showing the prediction bias) and the mean squared prediction error (MSE, showing the prediction accuracy). The ME of the mechanistic model was 18% (range, 20 to 57%), indicating a tendency for overprediction; the MSE is 32% (range, 6 to 104%). The ANN had almost no bias: the ME was 2% (range, 36 to 64%) and had greater precision than the mechanistic model, MSE 18% (range, 4 to 70%). Generally, neither model appeared to be a significantly better predictor of the Kpu's in the rat.

Recombinant factor VIII Fc fusion protein: extended-interval dosing maintains low bleeding rates and correlates with von Willebrand factor levels.

BACKGROUND: Routine prophylaxis with replacement factor VIII (FVIII) - the standard of care for severe hemophilia A - often requires frequent intravenous infusions (three or four times weekly). An FVIII molecule with an extended half-life could reduce infusion frequency. The A-LONG study established the safety, efficacy and prolonged pharmacokinetics of recombinant FVIII Fc fusion protein (rFVIIIFc) in previously treated adolescents and adults with severe hemophilia A. OBJECTIVE: In this post hoc analysis, we investigated the relationship between subjects' prestudy (FVIII) and on-study (rFVIIIFc) regimens. METHODS: We analyzed two subgroups of subjects: prior prophylaxis and on-study individualized prophylaxis (n = 80), and prior episodic treatment and on-study weekly prophylaxis (n = 16). Subjects' prestudy dosing regimens and bleeding rates were compared with their final rFVIIIFc regimens and annualized bleeding rates (ABRs) in the last 3 months on-study. Dosing regimen simulations based on population pharmacokinetics models for rFVIII and rFVIIIFc were performed. RESULTS: As compared with their prestudy regimen, 79 of 80 (98.8%) subjects on individualized rFVIIIFc prophylaxis decreased their infusion frequency. Overall ABRs were low, with comparable factor consumption. Longer dosing intervals, including 5-day dosing, were associated with higher baseline von Willebrand factor antigen levels. Simulated dosing regimens predicted a greater proportion of subjects with steady-state FVIII activity trough levels of ≥ 1 IU dL(-1) (1%) with rFVIIIFc than with equivalent rFVIII regimens. CONCLUSION: These results suggest that patients on rFVIIIFc prophylaxis can reduce their infusion frequency as compared with their prior FVIII regimen while maintaining low bleeding rates, affording more patients trough levels of ≥ 1 IU dL(-1) than with rFVIII products requiring more frequent dosing regimens.

Pharmacokinetics and immunoglobulin response of subcutaneous and intravenous atacicept in patients with systemic lupus erythematosus.

Atacicept, a recombinant fusion protein of the TACI receptor and human IgG, is an inhibitor of B-Lymphocyte Stimulator (BLyS) and APRIL, potent stimulators of B cell maturation, proliferation, and survival. Pharmacokinetics (PKs) and biological activity of intravenous (iv) and subcutaneous (sc) atacicept are described here for patients with systemic lupus erythematosus in two randomized, double-blind, placebo-controlled, Phase Ib studies. Study 1: Six cohorts of eight patients received sc atacicept (single dose: 0.3, 1, 3, or 9 mg/kg; four weekly doses: 1 or 3 mg/kg), or placebo (3:1 ratio). Study 2: Four cohorts of six patients received iv atacicept (single dose: 3, 9, or 18 mg/kg; multiple dose: 2 x 9 mg/kg), or matching placebo (5:1 ratio). PK profiles were determined through serum atacicept and atacicept-BLyS complex, and biological activity through IgA, IgG, and IgM levels. PK profiles of atacicept were influenced by saturable binding between atacicept and its ligands, and were consistent and predictable across doses and regimens. Atacicept's biological activity was compatible with its presumed mechanism of action. Bioavailability was approximately 30-40% following sc or iv administration and similar doses yielded similar biological activity irrespective of administration route. This observation may have a mechanistic foundation and may inform dosing regimen design for future studies.

An exploratory dose-escalating study investigating the safety, tolerability, pharmacokinetics and pharmacodynamics of intravenous atacicept in patients with systemic lupus erythematosus.

Atacicept, a recombinant fusion protein containing the extracellular, ligand-binding portion of the transmembrane activator and calcium modulator and cyclophilin-ligand interactor receptor, and the Fc portion of human immunoglobulin (Ig) G, is designed to block the activity of B-lymphocyte stimulator and a proliferation-inducing ligand, and may have utility as a treatment for B-cell-mediated diseases, such as systemic lupus erythematosus (SLE). This Phase Ib study investigated the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics of intravenous (i.v.) atacicept in patients with mild-to-moderate SLE. Patients (n = 24) were randomised (5:1) to receive atacicept (single dose: 3, 9 or 18 mg/kg; or multiple dose: 2 x 9 mg/kg) or matching placebo. Patients were followed for 6 weeks after dosing (9 weeks in the 2 x 9 mg/kg cohort). Local tolerability of atacicept was comparable with that of placebo, with only mild injection-site reactions reported with atacicept. Atacicept i.v. was generally well tolerated, both systemically and locally, in patients with mild-to-moderate SLE. Atacicept displayed non-linear PK, which was predictable across doses and between single and repeat doses. The biological activity of atacicept was demonstrated by its marked effect in reducing B-cells and Ig levels in patients with SLE. This supports the utility of this therapeutic approach in the treatment of autoimmune diseases, such as SLE.

Atacicept in patients with rheumatoid arthritis: results of a multicenter, phase Ib, double-blind, placebo-controlled, dose-escalating, single- and repeated-dose study.

OBJECTIVE: Atacicept is a recombinant fusion protein that binds and neutralizes B lymphocyte stimulator and a proliferation-inducing ligand. The purpose of this study was to investigate the tolerability, pharmacokinetics, and pharmacodynamics of atacicept treatment in patients with rheumatoid arthritis (RA) and to collect exploratory data on clinical outcomes. METHODS: In this multicenter, phase Ib, randomized, placebo-controlled, dose-escalating trial, 73 patients were enrolled into 6 escalating-dose cohorts. Patients received atacicept or placebo as single doses (70, 210, or 630 mg) or as repeated doses given at 2-week intervals (3 doses of 70 mg, 3 doses of 210 mg, or 7 doses of 420 mg), followed by 10 weeks of trial assessments, with a followup assessment at 3 months after the final dose. RESULTS: Atacicept was well tolerated, with few differences between treatment groups and no obvious safety concerns. The pharmacokinetics profile was nonlinear, but was consistent and predictable across all doses and regimens. Treatment-related decreases in immunoglobulin (particularly IgM) and rheumatoid factor levels were evident, and a clear decrease in anti-citrullinated protein antibodies was observed in the cohort that received 7 doses of 420 mg. The B cell response was biphasic, with an initial transient increase (dominated by memory B cells) followed by a dose-related decrease (dominated by mature B cells). Clinical assessments showed trends toward improvement with the 3-month treatment. Little effect on the erythrocyte sedimentation rate or C-reactive protein levels was seen. CONCLUSION: Atacicept was well tolerated both systemically and locally. The results demonstrated that the biologic activity of atacicept was consistent with its mechanism of action.

A WWW resource for physiologically based modelling in pharmacokinetics, pharmacodynamics, toxicology and risk assessment.

To answer the challenges of physiologically based (PB) modelling and to enhance the research efforts in this area, a WWW site (http:/(/)www.capkr.man.ac.uk) was launched at The Centre for Applied Pharmacokinetic Research, School of Pharmacy and Pharmaceutical Sciences, University of Manchester. The site provides instant access to all the resources (data, methodology and tools), necessary to start a PB modelling study. The contents include PB modelling databases and knowledgebases, software resources, glossaries of terms, symbols and notation, and discussion groups on PB modelling and related topics. The overall aim of the WWW site is to reduce the time and the effort necessary to develop a PB model and to provide a forum for exchange of ideas between the scientists involved in the field. According to our evaluation, using the information available may reduce the duration of a typical PB modelling exercise from at least a couple of months to not more than a couple of weeks. The site's contents is targeted both to scientists with a general interest in pharmacokinetic models, and to researchers undertaking specific PB modelling projects. An additional benefit is the standardization of the procedures, rules, and data-sets, which improves the comparability of the results achieved.

Sensitivity analysis of pharmacokinetic and pharmacodynamic systems: I. A structural approach to sensitivity analysis of physiologically based pharmacokinetic models.

Based on a frequency response approach to the sensitivity analysis of pharmacokinetic models, the concept of structural sensitivity is introduced. The core of this concept is the factorization of the system sensitivity into two multipliers. The first one, called structural sensitivity index, has an analytical form, which depends solely on the structure and connectivity of the system and does not depend on the drug administered or the factor perturbed. The second multiplier, the parameter sensitivity index, depends on the drug properties, the tissue of interest and the parameter perturbed, but is largely independent of the structure of the system. The structural and parametric sensitivity indices can be evaluated and analyzed separately. The most important feature of the proposed approach is that the conclusions drawn from the analysis of the structural sensitivity index are valid across all mammalian species, as the latter share a common anatomical and physiological structure. The concept of structural sensitivity is illustrated on the commonly used structure of the whole body physiologically based pharmacokinetic models by showing that the factorization of the sensitivity carried out arises naturally from the mechanism of the distribution of perturbations throughout the organism. The concept of structural sensitivity has interesting practical implications. It enables the formal proof of relationships and facts that have been observed previously. Moreover, the conclusions drawn introduce in fact a ranking of the tissues or subsystems with respect to their impact on the model outputs. From this ranking, direct recommendations regarding the design of experiments for whole-body physiologically based pharmacokinetic models are derived.

Accumulation profiles during quasi-uniform multiple dosing regimens.

An extension of the plasma area method of Chiou to the evaluation of accumulation profiles during quasi-uniform multiple dosing regimens (i.e., regimens with varying doses and/or dosing intervals within a certain time period which are repeated in the successive periods throughout the administration course) is presented. The derivations show, that the equations for the accumulation and steady state curves during quasi-uniform multiple dosing are similar or identical to these for the uniform multiple dosing case, if the constant time interval in the latter is replaced by the constant time period in the former. The equations derived can be used for rapid estimation of the time, required to reach a prespecified fraction of quasi steady state plasma level during quasi-uniform multiple dosing.

[An evaluation of Visidex test strips in the blood sugar control of diabetics]. / Otsenka na test-lentichki Visidex pri kruvnozakharen kontrol na diabetitsi.

The test stripes Visidex for visual evaluation of glycemia were tested clinically. The results were compared with a reference laboratory method for blood sugar measurement. A correlation coefficient of r = 0.971 with 74% coincidence in the same glycemic interval was found. The test stripes are suitable for blood sugar self-control in domestic conditions.

Quantitative structure-pharmacokinetics relationships: II. A mechanistically based model to evaluate the relationship between tissue distribution parameters and compound lipophilicity.

The tissue-to-unbound plasma distribution coefficients (Kpus) of 14 rat tissues after i.v. administration of nine 5-n-alkyl-5-ethyl barbituric acids, determined in a previous study, were used to identify a model of the relationship between tissue distribution and lipophilicity of the homologs, expressed in terms of their octanol to water partition ratio, P. Based on mechanistic considerations and assumptions, the parameter model was expressed as Kpu tau = fw.tau [1 + a tau (nPt.tau)Pb tau], where fw.tau is the tissue water content. (nPt. tau) is the binding capacity of the tissue, n is the number of the binding sites, a tau and b tau are the parameters of the relationship Ka tau = a tau Pb tau; and Ka tau is the binding association constant of each tissue. The parameter model was linearized and fitted to the predetermined Kpu values, yielding correlation coefficients ranging between .940 and .997. The predictive performance of the parameter model was evaluated using a leave-one-out procedure with subsequent computation of the mean prediction error (ME = measurement of the prediction bias) and the square root of the mean squared prediction error (RMSE = measurement of the prediction accuracy). The ME varied between -22.48 and 61.14%, indicating a slight tendency for overpredicting. The RMSE was between 24.73 and 102% for the individual tissues across the different homologs; and between 28.33 and 85.2% for the individual homologs across the different tissues. The apparently high Kpu prediction errors, when translated through the low sensitivity of the barbiturate whole-body physiologically based pharmacokinetic model, established previously, leads to predicted tissue concentration-time profiles within 5 to 20% of the original ones. Therefore, it is concluded, that the identified mechanistically based model is a good predictor of the tissue-to-unbound Kpus in the rat tissues.

Physiologically based pharmacokinetic modeling of a homologous series of barbiturates in the rat: a sensitivity analysis.

Sensitivity analysis studies the effects of the inherent variability and uncertainty in model parameters on the model outputs and may be a useful tool at all stages of the pharmacokinetic modeling process. The present study examined the sensitivity of a whole-body physiologically based pharmacokinetic (PBPK) model for the distribution kinetics of nine 5-n-alkyl-5-ethyl barbituric acids in arterial blood and 14 tissues (lung, liver, kidney, stomach, pancreas, spleen, gut, muscle, adipose, skin, bone, heart, brain, testes) after i.v. bolus administration to rats. The aims were to obtain new insights into the model used, to rank the model parameters involved according to their impact on the model outputs and to study the changes in the sensitivity induced by the increase in the lipophilicity of the homologues on ascending the series. Two approaches for sensitivity analysis have been implemented. The first, based on the Matrix Perturbation Theory, uses a sensitivity index defined as the normalized sensitivity of the 2-norm of the model compartmental matrix to perturbations in its entries. The second approach uses the traditional definition of the normalized sensitivity function as the relative change in a model state (a tissue concentration) corresponding to a relative change in a model parameter. Autosensitivity has been defined as sensitivity of a state to any of its parameters; cross-sensitivity as the sensitivity of a state to any other states' parameters. Using the two approaches, the sensitivity of representative tissue concentrations (lung, liver, kidney, stomach, gut, adipose, heart, and brain) to the following model parameters: tissue-to-unbound plasma partition coefficients, tissue blood flows, unbound renal and intrinsic hepatic clearance, permeability surface area product of the brain, have been analyzed. Both the tissues and the parameters were ranked according to their sensitivity and impact. The following general conclusions were drawn: (i) the overall sensitivity of the system to all parameters involved is small due to the weak connectivity of the system structure; (ii) the time course of both the auto- and cross-sensitivity functions for all tissues depends on the dynamics of the tissues themselves, e.g., the higher the perfusion of a tissue, the higher are both its cross-sensitivity to other tissues' parameters and the cross-sensitivities of other tissues to its parameters; and (iii) with a few exceptions, there is not a marked influence of the lipophilicity of the homologues on either the pattern or the values of the sensitivity functions. The estimates of the sensitivity and the subsequent tissue and parameter rankings may be extended to other drugs, sharing the same common structure of the whole body PBPK model, and having similar model parameters. Results show also that the computationally simple Matrix Perturbation Analysis should be used only when an initial idea about the sensitivity of a system is required. If comprehensive information regarding the sensitivity is needed, the numerically expensive Direct Sensitivity Analysis should be used.

Educating the diabetes care professionals in eastern Europe: a Bulgarian experience.

The first educational course for 30 medical doctors and 16 nurses, engaged in outpatient diabetes care in Bulgaria, was carried out with the aim of assessing the existing level of knowledge of diabetes, to implement a training programme matching the assessed needs, and to evaluate the efficiency of the education delivered. The initial level of knowledge was assessed by an anonymous pre-test questionnaire on general issues of diabetes care. After 5 days of training, a post-test questionnaire was administered which included more specific questions on matters that had been taught during the course. The results of the pre-test showed that, on average, 60.3 +/- 20.6 (SD) % of the doctors and 50.5 +/- 25.0% of the nurses gave correct answers. The results of the post-test were significantly improved (73.5 +/- 20.6% for the doctor and 70.8 +/- 23.5% for the nurses), although the post-test questionnaire had been expertly evaluated as more complex and specific. The analysis of the results allowed us to draw general conclusions regarding the educational needs, the optimal structure, and implementation of such training courses in the specific conditions of Bulgaria. Some of the results and conclusions might be useful for other countries from Central and Eastern Europe in their efforts to promote successful diabetes education programmes.

Quantitative structure-pharmacokinetics relationships: I. Development of a whole-body physiologically based model to characterize changes in pharmacokinetics across a homologous series of barbiturates in the rat.

As part of an overall program to develop a framework for evaluating the contribution of structural and physicochemical properties to pharmacokinetics, the distribution kinetics of nine 5-n-alkyl-5-ethyl barbituric acids in arterial blood and 14 tissues (lung, liver, kidney, stomach, pancreas, spleen, gut, muscle, adipose, skin, bone, heart, brain, testes) was examined after i.v. bolus administration in rats. The barbituric acids studied form a true homologous series; therefore any differences in pharmacokinetics, noted between congeners, can be directly linked to the increase in lipophilicity, resulting from the addition of a methylene group. A whole-body physiologically based pharmacokinetic model has been developed, assuming most of the tissues to be well-stirred compartments. Brain and testes, in which distribution for the lower homologues was permeability rate-limited, were represented by two compartments. For each homologue, the model parameters have been optimized, using the tissue concentration-time data. The initial distribution processes in the system were very rapid, making it quite stiff, and essentially over before the first samples were taken. A progressively increasing redistribution from lean tissues into adipose on ascending the homologous series was observed, characterized by a tendency for a progressive decrease in the magnitude of the concentration-time profiles for some of the lean and well-perfused tissues, an increase in the adipose concentration-time profile, and an increase in the time to reach the maximum adipose concentration. A shift from permeability rate limitation to perfusion rate limitation of the distribution processes for brain and testes, as well as an increase in the intrinsic hepatic clearance and decrease in the renal clearance with the increase of lipophilicity of the homologues, were quantified. An increase in the total unbound volume of distribution on ascending the homologous series was also observed. Muscle was found to be the major drug depot at steady state, accounting for approximately 50% of the total unbound volume of distribution, regardless of the lipophilicity of the homologue; the unbound volume of distribution of adipose increases more than 10-fold with the increase of lipophilicity.

Modeling and stimulation for clinical trial design involving a categorical response: a phase II case study with naratriptan.

PURPOSE: The overall aim of the present study was to investigate retrospectively the feasibility and utility of model-based clinical trial simulation as applied to the clinical development of naratriptan with effect measured on a categorical scale. METHODS: A PK-PD model for naratriptan was developed by using information gathered from previous naratriptan and sumatriptan preclinical and clinical trials. The phase IIa naratriptan data were used to check the PK-PD model in its ability to describe future data. A further PK-PD model was developed by using the phase IIa naratriptan data, and a phase IIb trial was designed by simulation with the use of Matlab. The design resulting from clinical trial simulation was compared with that derived by using D-optimal design. RESULTS: The PK-PD model showed reasonable agreement with the data observed in the phase IIa naratriptan clinical trial. Clinical trial simulation resulted in a design with four or five arms at 0 mg, 2.5 and/or 5 mg, 10 mg, and 20 mg, PD measurements to be taken at 0, 2, and 4 or 6 h and at least 150 patients per arm. A sub-D-optimal design resulted in two dosing arms at 0 and 10 mg and PD measurements to be taken at 1 and 2 h. CONCLUSIONS: Clinical trial simulation is a useful tool for the quantitative assessment of the influence of the controllable factors and is the only tool for the quantitative assessment of the uncontrollable factors on the power of a clinical trial.

Lumping of whole-body physiologically based pharmacokinetic models.

Lumping is a common pragmatic approach aimed at the reduction of whole-body physiologically based pharmacokinetic (PBPK) model dimensionality and complexity. Incorrect lumping is equivalent to model misspecification with all the negative consequences to the subsequent model implementation. Proper lumping should guarantee that no useful information about the kinetics of the underlying processes is lost. To enforce this guarantee, formal standard lumping procedures and techniques need to be defined and implemented. This study examines the lumping process from a system theory point of view, which provides a formal basis for the derivation of principles and standard procedures of lumping. The lumping principle in PBPK modeling is defined as follows: Only tissues with identical model specification, and occupying identical positions in the system structure should be lumped together at each lumping iteration. In order to lump together parallel tissues, they should have similar or close time constants. In order to lump together serial tissues, they should equilibrate very rapidly with one another. The lumping procedure should include the following stages: (i) tissue specification conversion (when tissues with different model specifications are to be lumped together); (ii) classification of the tissues into classes with significantly different kinetics, according to the basic principle of lumping above; (iii) calculation of the parameters of the lumped compartments; (iv) simulation of the lumped system; (v) lumping of the experimental data; and (vi) verification of the lumped model. The use of the lumping principles and procedures to be adopted is illustrated with an example of a commonly implemented whole-body physiologically based pharmacokinetic model structure to characterize the pharmacokinetics of a homologous series of barbiturates in the rat.

Tissue distribution and physiologically based pharmacokinetics of antisense phosphorothioate oligonucleotide ISIS 1082 in rat.

The aim of this study was to develop a whole body physiologically based model of the pharmacokinetics (PBPK) of the phosphorothioate oligonucleotide (PS-ODN) ISIS 1082 in vivo. Rats were administered an intravenous (i.v.) bolus dose of ISIS 1082 (10 mg/kg plus 3H tracer), and arterial blood and tissues were taken at specific times up to 72 hours. Radioactivity was measured in all samples. The parent compound was determined specifically in blood and tissues at 90 minutes and in liver and kidney also at 24 hours, using capillary gel electrophoresis (CGE). A whole body PBPK model was fitted to the combined blood and tissue radioactivity data using nonlinear regression analysis. CGE analysis indicated that the predominant species in plasma and all tissues is ISIS 1082, together with some n-1 and n-2 metabolites. Total radioactivity primarily reflects these species. The whole body model successfully described temporal events in all tissues. However, to adequately model the experimental data, all tissues had to be partitioned into vascular and extravascular spaces to accommodate the relatively slow distribution of ISIS 1082 out of blood because of a permeability rate limitation. ISIS 1082 distributes extensively into tissues, but the relative affinity varies enormously, being highest for kidney and liver and lowest for muscle and brain. A whole body PBPK model with a permeability rate limited tissue distribution was developed that adequately described events in both blood and tissue for an oligonucleotide. This model has the potential not only to characterize the events in individual tissues throughout the body for such compounds but also to scale across animal species, including human.