Establishing Good Practices for Exposure-Response Analysis of Clinical Endpoints in Drug Development.

This tutorial aims at promoting good practices for exposure-response (E-R) analyses of clinical endpoints in drug development. The focus is on practical aspects of E-R analyses to assist modeling scientists with a process of performing such analyses in a consistent manner across individuals and projects and tailored to typical clinical drug development decisions. This includes general considerations for planning, conducting, and visualizing E-R analyses, and how these are linked to key questions.

The Effects of a GLP-1 Analog on Glucose Homeostasis in Type 2 Diabetes Mellitus Quantified by an Integrated Glucose Insulin Model.

In recent years, several glucagon-like peptide-1 (GLP-1)-based therapies for the treatment of type 2 diabetes mellitus (T2DM) have been developed. The aim of this work was to extend the semimechanistic integrated glucose-insulin model to include the effects of a GLP-1 analog on glucose homeostasis in T2DM patients. Data from two trials comparing the effect of steady-state liraglutide vs. placebo on the responses of postprandial glucose and insulin in T2DM patients were used for model development. The effect of liraglutide was incorporated in the model by including a stimulatory effect on insulin secretion. Furthermore, for one of the trials an inhibitory effect on glucose absorption was included to account for a delay in gastric emptying. As other GLP-1 receptor agonists have similar modes of action, it is believed that the model can also be used to describe the effect of other receptor agonists on glucose homeostasis.

Liraglutide pharmacokinetics and dose-exposure response in Asian subjects with Type 2 diabetes from China, India and South Korea.

AIMS: To investigate the population pharmacokinetics and exposure-response relationship of liraglutide, a human glucagon-like peptide-1 (GLP-1) analogue, in Asian subjects with Type 2 diabetes mellitus. METHODS: Data were derived from a published 16-week, randomized, double-blind, double-dummy, active-controlled, parallel-group trial of liraglutide in China, India and South Korea. The analysis utilized 2061 pharmacokinetic (PK) samples from 605 subjects exposed to liraglutide 0.6, 1.2 or 1.8 mg once daily. Demographic factors (body weight, age, gender, country) of importance for liraglutide clearance were evaluated. An exploratory exposure-response analysis was conducted to investigate effects on glycated haemoglobin (HbA1c) and body weight. RESULTS: Estimated liraglutide exposure (area under the curve; AUC) appeared to increase proportionally with increasing liraglutide dose (0.6-1.8 mg). The covariate analysis confirmed previous findings in a global clinical trial. Body weight was a predictor of liraglutide exposure; compared to a reference subject of 67 kg, exposure was 32% lower for maximum (115 kg) and 54% higher for minimum (37 kg) observed body weights. Gender, age and country had no relevant effect on exposure. Exposure-response analysis supported the use of 1.2mg as maintenance dose with the option of individual dose escalation to 1.8 mg to optimize treatment outcomes. CONCLUSIONS: Exposure appeared to increase proportionally with increasing liraglutide dose in Asian subjects with Type 2 diabetes mellitus. The only PK relevant predictor of exposure was body weight. The exposure-response relationships for HbA1c and body weight in Asian subjects were similar to observations in global populations.

Methods for Predicting Diabetes Phase III Efficacy Outcome From Early Data: Superior Performance Obtained Using Longitudinal Approaches.

The link between glucose and HbA1c at steady state has previously been described using steady-state or longitudinal relationships. We evaluated five published methods for prediction of HbA1c after 26/28 weeks using data from four clinical trials. Methods (1) and (2): steady-state regression of HbA1c on fasting plasma glucose and mean plasma glucose, respectively, (3) an indirect response model of fasting plasma glucose effects on HbA1c, (4) model of glycosylation of red blood cells, and (5) coupled indirect response model for mean plasma glucose and HbA1c. Absolute mean prediction errors were 0.61, 0.38, 0.55, 0.37, and 0.15% points, respectively, for Methods 1 through 5. This indicates that predictions improved by using mean plasma glucose instead of fasting plasma glucose, by inclusion of longitudinal glucose data and further by inclusion of longitudinal HbA1c data until 12 weeks. For prediction of trial outcome, the longitudinal models based on mean plasma glucose (Methods 4 and 5) had substantially better performance compared with the other methods.

Longitudinal Modeling of the Relationship Between Mean Plasma Glucose and HbA1c Following Antidiabetic Treatments.

Late-phase clinical trials within diabetes generally have a duration of 12-24 weeks, where 12 weeks may be too short to reach steady-state glycated hemoglobin (HbA1c). The main determinant for HbA1c is blood glucose, which reaches steady state much sooner. In spite of this, few publications have used individual data to assess the time course of both glucose and HbA1c, for predicting HbA1c. In this paper, we present an approach for predicting HbA1c at end-of-trial (24-28 weeks) using glucose and HbA1c measurements up to 12 weeks. The approach was evaluated using data from 4 trials covering 12 treatment arms (oral antidiabetic drug, glucagon-like peptide-1, and insulin treatment) with measurements at 24-28 weeks to evaluate predictions vs. observations. HbA1c percentage was predicted for each arm at end-of-trial with a mean prediction error of 0.14% [0.01;0.24]. Furthermore, end points in terms of HbA1c reductions relative to comparator were accurately predicted. The proposed model provides a good basis to optimize late-stage clinical development within diabetes.CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e82; doi:10.1038/psp.2013.58; advance online publication 30 October 2013.

Pharmacokinetics and allometric scaling of levormeloxifene, a selective oestrogen receptor modulator.

The pharmacokinetics of a new selective oestrogen receptor modulator levormeloxifene was investigated in mice, rats, cynomolgus monkeys and humans by compartmental pharmacokinetics. Levormeloxifene was administered as an oral solution in all studies. Allometric scaling was used to predict human pharmacokinetic parameters and the performance of the approach was evaluated. Mean values of clearance confounded by F(CL/F) were 0.073, 0.29, 3.18 and 2.4 l/h in mice, rats, monkeys and humans, respectively. Values of distribution volume at steady state confounded by F(V(ss)/F) were 0.073 and 7.5 l in mice and rats. In monkeys, values of the central volume F(V(c)/F) and volume at steady state F(V(ss)/F) were 28.9 and 57.9 l, respectively. In humans, values of V(c)/F and V(ss)/F were 106 and 587 l, respectively. Predicted CL/F and V(ss)/F showed a linear relationship when plotted vs BW on a log-log scale; for CL/F, r was 0.95-0.98 and for V(ss)/F, r was 0.99. Using allometric scaling the predicted human V(ss)/F deviated 3-fold from the experimentally determined values. Observed values of CL/F deviated 21-25 fold from the predicted, the latter depending on the scaling method. Confidence intervals for the predicted parameters showed major lack of precision for all the allometric scaling methods.

Population pharmacokinetics of tiagabine in epileptic patients on monotherapy.

A retrospective study of the population pharmacokinetics of tiagabine was performed from sparse data collected in a multicentre clinical trial in patients with newly diagnosed partial seizures. The purpose was to estimate the inter patient variability and to study the influence of various demographic, environmental and pathophysiological parameters on the pharmacokinetics of tiagabine in patients on monotherapy. A total of 593 plasma concentrations from 130 patients dosed with 2.5, 5, 7.5 or 10 mg tiagabine twice daily were used for modelling. A one-compartment open model with first-order absorption and elimination was fitted to the concentration-time data using the NONMEM program. Selection of covariates was initially performed using stepwise linear regression analyses. The selected covariates were incorporated in the population model and the importance of each covariate was investigated by means of backwards elimination. A one-compartment model with first-order absorption and elimination adequately described the tiagabine concentration-time profile. The apparent clearance as well as the apparent volume of distribution were both significantly correlated to body height in a nonlinear relationship. No other demographic, environmental or clinical chemical parameters were identified as covariates although only a few pathological values of the latter were present in the data. The mean values of CL/f was 6.10 l/h, of V/f was 62.0 l and of k(a) was 1.25 h(-1) for a subject of 170-cm height. The population half-life was 5.72 h. The apparent clearance and volume of distribution of tiagabine in epilepsy patients on monotherapy were both dependent on body height. Prospective studies are required in order to reveal if dose adjustments based on body height will result in improved therapeutic outcome.

Impact of quinidine on plasma and cerebrospinal fluid concentrations of codeine and morphine after codeine intake.

OBJECTIVE: The analgesic effect of codeine depends on its O-demethylation to morphine via sparteine oxygenase (CYP2D6) in the liver and presumably also via this enzyme in the CNS. We studied the ability of quinidine, which is a potent inhibitor of CYP2D6, to penetrate the blood brain barrier and its possible impact on codeine O-demethylation in CNS. METHODS: The study comprised 16 extensive and one poor metaboliser of sparteine, who underwent spinal anaesthesia for urinary tract surgery or examination. Eight patients were given an oral dose of 125 mg codeine and 9 patients (including the poor metaboliser) were given 200 mg quinidine 2 h before the same dose of codeine. Plasma and spinal fluid samples were collected 2 h after codeine intake. RESULTS: Free concentrations of quinidine were 11-times lower in cerebrospinal fluid than in plasma, and ranged from 9-15 nmol.l-1. Morphine concentrations were significantly lower in patients pre-treated with quinidine, both in plasma (median 1.45 nmol.l-1, range 0.74-1.95 nmol.l-1 vs 9.86 nmol.l-1, range 4.59-28.4 nmol.l-1) and in cerebrospinal fluid (0.23, 0.16-0.61 nmol.l-1 vs 3.63, 0.6-8.09 nmol.l-1). The morphine/codeine concentration ratio in plasma (3.07 x 10 (-3), 1.68-3.68 x 10 (-3) vs 19.87 x 10 (-3), 9.87-66.22 x 10 (-3) and in cerebrospinal fluid (0.83 d 10 (-3), 0.58-1.45 x 10 (-3) vs 7.19 x 10 (-3), 2.03-17.7 x 10 (-3) was also lower. The morphine/codeine concentration ratios were significantly lower in cerebrospinal fluid both without and with quinidine, but the difference between the plasma and spinal fluid ratio was significantly smaller with quinidine than without (p = 0.0002). CONCLUSION: Quinidine penetrates the blood brain barrier poorly, but quinidine pre-treatment leads to pronounced lowering of the cerebrospinal fluid concentration of morphine after codeine intake. However, the O-demethylation of codeine in CNS may not be totally blocked by quinidine.

Comparison of sandwich enzyme-linked immunoadsorbent assay and radioimmunoassay for determination of exogenous glucagon-like peptide-1(7-36)amide in plasma.

A sensitive sandwich enzyme-linked immunoadsorbent assay (ELISA) for determination of exogenous glucagon-like peptide-1(7-36)amide (GLP-1(7-36)amide) in plasma samples from pharmacokinetic studies is described. The assay employs an N-terminally directed antibody and a C-terminally directed antibody. The ELISA has a working range from 10 to 500 pmol l-1, and can be applied to plasma samples from humans, dogs, pigs, minipigs, cats, rabbits, and rats. The assay was compared to a validated radioimmunoassay (RIA), employing an antibody directed against the mid-region of GLP-1. After s.c. administration of GLP-1(7-36)amide, the plasma immunoreactivity of GLP-1 (P-GLP-1-IR) measured by ELISA was markedly lower than P-GLP-1-IR measured by RIA. After HPLC fractionation of plasma samples with subsequent RIA and ELISA analyses of the fractions, this difference was shown to be due to cross reaction with biologically inactive fragments of GLP-1(7-36)amide in the RIA but not in the ELISA.

Pen injected apomorphine against off phenomena in late Parkinson's disease: a double blind, placebo controlled study.

The effect, therapeutic dose range, and pharmacokinetics of apomorphine, given as subcutaneous injections by a single use pen, were evaluated in the treatment of off phenomena in 22 patients with idiopathic Parkinson's disease. At study entry a placebo controlled apomorphine test was performed, and apomorphine doses were then individually titrated (mean 3.4 (range 0.8-6.0) mg) and compared with placebo in a double blind cross over phase. With apomorphine compared with placebo the mean daily duration of off periods was reduced by 51% as assessed by the patients and by 58% as assessed by the staff. The severity of off periods was also significantly reduced. The effect was unchanged after a maintenance phase of eight weeks. At study termination 13 of 14 patients were able to inject themselves and 11 of 14 patients found that their feeling of freedom had increased. The most common adverse events were nausea, subcutaneous nodules, and increased frequency of involuntary movements. Pharmacokinetics were linear and did not change with repeat dosing. The tmax ranged from five to 45 minutes (16 patients). It is concluded that pen injected apomorphine is a valuable treatment for patients with advanced Parkinson's disease with on-off phenomena.

Halothane anesthesia enhances the effect of dopamine uptake inhibition on interstitial levels of striatal dopamine.

The anesthetic, isoflurane, has been shown to potentiate the ability of the dopamine (DA)-uptake inhibitor, nomifensine, to increase the brain interstitial dopamine level ([DA]e). Since the effect of the more commenly used anesthetic, halothane, on this system is unknown, we determined [DA]e by microdialysis in the striatum of rats, conscious or anesthetized with halothane, in the presence of the more selective DA uptake inhibitor, vanoxerine (GBR 12909), or the DA releaser, d-amphetamine. Basal [DA]e was not changed by halothane. However, in halothane-anesthetized rats, the vanoxerine (3 mg/kg i.v.)-induced DA response increased severalfold compared to the response in conscious rats. The initial peak response to d-amphetamine (1 mg/kg i.v.) did not change, but the late response (1-3 h after injection) was augmented in anesthetized rats. Halothane is believed to increase firing of DA neurons in the substantia nigra and, hence, to release striatal DA. We hypothesize that [DA]e is maintained at a normal level during the increased firing by equally increased activity of the DA transporter. However, when the DA transporter is blocked by vanoxerine, the increased DA release is unimpaired and [DA]e rises.

Nonlinear multiple-dose pharmacokinetics of the dopamine reuptake inhibitor vanoxerine.

The human pharmacokinetics of vanoxerine (GBR 12909) were studied in 14 normal subjects with a multiple-dose regimen. In a crossover design, each subject received daily oral doses of 25, 75, and 125 mg for 14 days at each dose level with washout periods of 7 days duration. Drug concentrations in serum during and after dosing were estimated by an HPLC method sensitive to 2 nmol/L (corresponding to 1.04 ng/mL). Drug accumulation was observed during dosing at the two highest dose levels, but near steady-state conditions were attained within 9-11 days of dosing. Estimates of steady-state concentrations all showed statistically significant deviations from dose linearity in the form of disproportionately higher concentrations at higher dose levels than expected from drug concentrations in serum at lower doses. The nonlinear pharmacokinetics was most likely due to increasing bioavailability with dose. The mean elimination half-lives were 53.5 and 66.0 h at 75 and 125 mg/day, respectively, in accordance with the observed time to reach near steady-state conditions. These estimates were higher than previous estimates in less extensive studies.

Combined reversed phase and anion exchange solid phase extraction for the assay of the neuroprotectant NBQX in human plasma and urine.

A combination of reversed phase and anion exchange solid phase extraction (SPE) was investigated for the liquid chromatographic assay of the neuroprotectant agent NBQX in human plasma and urine. Reversed phase SPE alone using a variety of phases failed to yield sufficiently pure extracts for the assay of plasma in the low ng/mL concentration range using UV detection. However, using Bond Elut Certify II SPE columns containing a mixture of reversed phase and anion exchange functionalities markedly improved the purity of plasma extracts. Furthermore, a change of detector wavelength from UV (294 nm) to the visible region (380 nm) removed some minor interfering peaks originating from plasma. Using optimized SPE conditions with an extraction recovery of 92.3% and a high performance liquid chromatographic procedure with Lichrospher C18 as the stationary phase, the lower limit of quantitation in human plasma was 2 ng/mL (corresponding to 0.75 ng injected on-column). Intra-assay coefficients of variation ranged from 9.6% at 2 ng/mL to 1.3% at 10 ng/mL. A similar SPE procedure was applied to human urine with acceptable recovery (88.3%), but an analytical column of different selectivity (Chromspher B C18) was necessary in order to avoid interference from the urine. The limit of quantitation for the urine assay was 25 ng/mL and the intra-assay precision ranged from 4.6% at 25 ng/mL to 2.2% at 500 ng/mL.

Food intake increases the relative oral bioavailability of vanoxerine.

Each of 12 healthy male subjects received single oral doses of 100 mg vanoxerine (GBR 12909), a dopamine reuptake inhibitor with potential antidepressant activity, on three different occasions (fasting, after a low-fat meal and after a high-fat meal) according to a randomized, cross-over design. The mean tmax value increased from 0.82 h after fasting to 1.44 h after a low-fat meal and to 2.46 h after a high-fat meal. Only modest food effects were seen on mean Cmax values (55 nM, 52 nM and 84 nM, after fasting, after the low-fat meal and after the high-fat meal, respectively) but values of AUC up to the last measurable concentration (AUC(0,t)) increased by 76% (from 110 to 194 nM h) after the low-fat meal and by 255% (from 110 to 391 nM h) after the high-fat meal compared with fasting. All of these effects were statistically significant except for the differences in tmax and Cmax between fasting and the low-fat meal. The mechanism of these changes is unclear, but it seems likely that food may lower the first-pass metabolism of vanoxerine, as has been shown for other lipophilic basic drugs.

Superiority of sandwich ELISA over competitive RIA for the estimation of ANP-270, an analogue of human atrial natriuretic factor.

ANP-270 is a 26 amino acid analogue of naturally occurring atrial natriuretic factor (ANF) which it was anticipated would be of value for the treatment of congestive heart failure and acute renal failure. Two sensitive assays--a radioimmunoassay (RIA) and a sandwich enzyme linked immunosorbent assay (ELISA)--were developed and validated for use in clinical investigations. The RIA utilized a single C terminal monoclonal antibody whereas two monoclonal antibodies directed against different epitopes were used for the ELISA. The two assays were comparable with respect to sensitivity and precision, but assay results obtained on samples from normal volunteers dosed intravenously with ANP-270 differed widely. Thus, in one volunteer the elimination half-life was estimated to be 123 min using RIA results but 6 min using the ELISA results. By reversed phase liquid chromatographic fractionation of plasma extracts followed by RIA and ELISA, these discrepancies were shown to be due to fragments of ANP-270 cross-reacting in the RIA but not in the ELISA. Consequently, the sandwich ELISA was the method of choice for estimating this compound in plasma.

Human pharmacokinetics of an analogue of atrial natriuretic factor.

The pharmacokinetics of ANP-270, a 26 amino acid analogue of alpha human natriuretic factor (alpha-hANF) with a prolonged effect on isolated arterial preparations, has been studied in 40 healthy males, in a double-blind placebo controlled investigation. Placebo or ANP-270 0.3, 1.5 or 3.0 micrograms/kg were given by intravenous bolus injection, each to groups of 10 subjects. Blood samples were assayed for ANP-270 by a specific sandwich ELISA. The disappearance of ANP-270 from plasma followed a two-compartment decay, with mean distribution and elimination half-lives of 2.6 min (n = 30) and 10.6 min (n = 20), respectively. These estimates were similar to those obtained by other investigators for alpha-hANF. Their brevity explains the lack of a prolonged effect of ANP-270 in vivo compared to alpha-hANF.

Column liquid chromatographic assay of the dopamine reuptake inhibitor vanoxerine (GBR 12909) in human serum.

A method for the assay of the dopamine reuptake inhibitor vanoxerine (GBR 12909, I) in human serum is described. Serum was diluted in urea (8 M) and extracted using C18 extraction columns. Compound I was eluted from the columns using methanol containing 1% (v/v) ammonia. The extracts were analysed by high-performance liquid chromatography with fluorescence detection. The limit of quantitation was 2 nM, corresponding to 1.04 ng/ml. Validation of the method showed acceptable recovery, accuracy, precision and specificity. The method has been used for drug assay in several clinical studies of the pharmacokinetics and therapeutic efficacy of compound I.

Immunoturbidimetry of serum C-reactive protein in low concentration of polyethylene glycol.

A simple, rapid immunoturbidimetric assay for determination of serum C-reactive protein is presented. In order to obtain constant sample blank values within a few minutes we found it necessary to use a low concentration (10 g/L) of polyethylene glycol 6000 in contrast to the commonly used 40 g/L PEG solution. The sensitivity of the assay presented is 7 mg/L; within-run and between-run CVs ranged respectively from 1.4% to 2.4% and from 2.1% to 5.5%. Results obtained with the proposed method correlate well with radial immunodiffusion.