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Pharmacokinetic-Pharmacodynamic Modelling of theAntihistaminic (H1) Effect of BilastineNerea Jauregizar,1 Leire de la Fuente,1 Maria Luisa Lucero,2 Ander Sologuren,2 Nerea Leal3 and Monica Rodrguez3

1 PharmaDatum Data Analisis SL, Bermeo, Spain

2 Clinical Department, Laboratorios FAES FARMA SA, Leioa, Spain

3 DynaKin, SL Parque Tecnologico de Bizkaia, Derio, Spain

Abstract Objective: To model the pharmacokinetic and pharmacodynamic relationship of bilastine, a new histamineH

1

receptor antagonist, from single- and multiple-dose studies in healthy adult subjects.

Methods: The pharmacokinetic model was developed from different single-dose and multiple-dose studies.

In the single-dose studies, a total of 183 subjects received oral doses of bilastine 2.5, 5, 10, 20, 50, 100, 120,

160, 200 and 220 mg. In the multiple-dose studies, 127 healthy subjects received bilastine 10, 20, 40, 50, 80,

100, 140 or 200 mg/day as multiple doses during a 4-, 7- or 14-day period.

The pharmacokinetic profile of bilastine was investigated using a simultaneous analysis of all concentration-

time data by means of nonlinear mixed-effects modelling population pharmacokinetic software NONMEM

version 6.1.

Plasma concentrations were modelled according to a two-compartment open model with first-order

absorption and elimination.

For the pharmacodynamic analysis, the inhibitory effect of bilastine (inhibition of histamine-induced

wheal and flare) was assessed on a preselected time schedule, and the predicted typical pharmacokinetic pro-

file (based on the pharmacokinetic model previously developed) was used. An indirect response model was

developed to describe the pharmacodynamic relationships between flare or wheal areas and bilastine plasma

concentrations.

Finally, once values of the concentration that produced 50% inhibition (IC50) had been estimated for wheal

and flare effects, simulations were carried out to predict plasma concentrations for the doses of bilastine 5, 10

and 20 mg at steady state (7296 hours).

Results: A non-compartmental analysis resulted in linear kinetics of bilastine in the dose range studied. Bilastine

was characterized by two-compartmental kinetics with a rapid-absorption phase (first-order absorption rate

constant = 1.50 h-1), plasma peak concentrations were observed at 1 hour following administration and the

maximal response was observed at approximately 4 hours or later. Concerning the selected pharmacodynamic

model to fit the data (type I indirect response model), this selection is attributable to the presence of inhibitory

bilastine plasma concentrations that decrease the input response function, i.e. the production of the skin reac-

tion. This model resulted in the best fit of wheal and flare data. The estimates (with relative standard errors

expressed in percentages in parentheses) of the apparent zero-order rate constant for flare or wheal spontaneousappearance (kin), the first-order rate constant for flare or wheal disappearance (kout) and bilastine IC50 values

were 0.44 ng/mL/h (14.60%), 1.09 h-1 (15.14%) and 5.15 ng/mL (16.16%), respectively, for wheal inhibition, and

11.10 ng/mL/h (8.48%), 1.03 h-1 (8.35%) and 1.25 ng/mL (14.56%), respectively, for flare inhibition.

The simulation results revealed that bilastine plasma concentrations do not remain over the IC50 value

throughout the inter-dose period for doses of 5 and 10 mg. However, with a dose of 20 mg of bilastine

administered every 24 hours, plasma concentrations remained over the IC50 value during the considered period

for the flare effect, and up to 20 hours for the wheal effect.

Conclusion: Pharmacokinetic and pharmacodynamic relationships of bilastine were reliably described with

the use of an indirect response pharmacodynamic model; this led to an accurate prediction of the pharmaco-

dynamic activity of bilastine.

ORIGINAL RESEARCH ARTICLE Clin Pharmacokinet 2009; 48 (8): 543-50312-5963/09/0008-0543/$49.95 2009 Adis Data Information BV. All rights reserve


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Background

Bilastine (F-96221-BM1, p-[2-[4-[1-(2-ethoxyethyl)-2-benz-

imidazolyl]piperidino]ethyl]-a-methylhydratropic acid) is anew histamine H1 receptor antagonist (antihistamine) drug

currently under clinical development by FAES FARMA, SA,

Spain, for the treatment of allergic rhinoconjuntivitis (seasonal

and/or perennial) and urticaria.

The results of in vitro preclinical studies provide evidence

that bilastine has antihistamine activity with high specificity for

H1 receptors and poor or no affinity for other receptors.[1]

The results of the in vivo pharmacological studies conducted

in animal species corroborate those obtained in the in vitro

receptor binding experiments carried out previously. In this

sense, bilastine potently and selectively binds to H1 receptorswith behaviour similar to that of cetirizine and superior to that

of fexofenadine.[2]

Understanding of the pharmacokinetics and pharmaco-

dynamics of this new H1 receptor antagonist provides the ob-

jective basis for selection of an appropriate dose and dosage

interval and the rationale for modification of the dosage regi-

men as needed in special populations, including elderly

patients, and those with hepatic or renal dysfunction.

The in vivo test in which inhibition of the histamine-

induced skin wheal and flare reactions is measured has been

extensively used to study the antihistaminic activity of several H1receptor antagonists.[3-7] As was recently stated, this test may not

be a valid surrogate measure for antihistaminic clinical efficacy

and should not be used to compare different antihistamines.[8]

However, it establishes the order of magnitude of the clinically

efficacious dose. Indeed, phase III studies of bilastine have shown

that the selected clinically efficacious regimen of 20 mg once daily

was in accordance with the conclusions of phase I studies. [9]

Little pharmacokinetic and pharmacodynamic modelling has

been performed for antihistaminic agents. For most drugs, the

relationship between exposure and effect is nonlinear and plasma

drug concentrations cannot usually be (directly) related to the

drug effect.[10] In the case of antihistaminic drugs, both the effectcompartment models for norebastine and levocabastine[7]and the

indirect response models for mizolastine[11] and cetirizine[12] have

been applied to account for the lag between peak plasma drug

concentrations and pharmacodynamic effects.

In the present study, plasma drug concentration-time pro-

files of single and multiple oral doses of bilastine given to

healthy subjects were described using an appropriate popula-

tion pharmacokinetic model. The pharmacodynamic effect of

bilastine was modelled by means of a physiological indirect

response model (using the pharmacokinetic model previously

developed). The estimated pharmacokinetic and pharmaco

dynamic parameters of the model are summarized in this article

Methods

Subjects and Study Design

A total of 310 healthy adult subjects (248 males an

62 females) were included in the study. All participants gav

signed informed consent, and ethical approval was obtained

from the Queens University Research Ethics Committe

(Belfast, Northern Ireland), the Northern Ireland Phase

Research Ethics Committee from the Office for Researc

Ethics Committees Northern Ireland (Belfast, Norther

Ireland) or the Ethical Committee for Clinical Research oSanta Creu i Sant Pau Hospital (Barcelona, Spain).

Bilastine plasma concentration-time data were availabl

from 12 studies and antihistamine activity was quantified in

two of these studies; all of the studieswere part of a phase I tria

Study design details are summarized in table I. [13-18] All of th

available data were analysed simultaneously.

Blood samples from studies 1 and 2 were drawn at th

following sampling times: predose (0 hour) and at 0.5, 1, 1.5, 2

2.5, 3, 3.5, 4, 6, 8, 12, 16, 24, 36, 48, 72 and 96 hours post-dose

Blood samples from studies 4, 5, 7, 8, 9 and 10 were collected a

the same sampling times but only up to 48 hours post-dose andup to 72 hours post-dose for studies 11 and 12. Studies 3, 6 an

10 were multiple-dose studies where samples were available o

day 1 (samples were collected up to 24 hours post-dose) betwee

96 and 144 hours for study 10, between 168 and 216 hours fo

study 6 and on day 14 (240288 hours) for study 3.

The antihistaminic activity of bilastine was evaluated b

using the effect measurements (wheal and flare) from studie

4 and 5. The inhibitory effect of bilastine (inhibition of histamine

induced wheal and flare) was assessed at a preselected tim

schedule: predose and at 1.5, 4, 8, 12 and 24 hours post-dose.

Pharmacokinetics

Blood samples (7 mL) from a suitable antecubital vein wer

collected into green-top/sodium heparin Vacutainer tube

predose and at different post-dose timepoints. Plasma sample

were separated by centrifugation (approximately 2500 rpm 1

minutes at 41C), split into two aliquots and stored in clearl

labelled containers in a freezer set at or below -201C unt

shipment to MDS Pharma Services in Zurich, Switzerland, fo

analysis.

544 Jauregizar et a

2009 Adis Data Information BV. All rights reserved. Clin Pharmacokinet 2009; 48 (


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Bilastine concentrations were determined in heparinized hu-

man plasma by a validated liquid chromatography-tandem mass

spectrometry (LC-MS/MS) method using a solid-phase extrac-

tion procedure. In brief, using 3-mL disposable glass tubes,

500mL of each plasma sample was spiked with internal standard(100mL of 500ng/mL of trandolapril in water) and combined

with 300mL of Millipore water and 100mL of 1% (v/v) aqueous

trifluoroacetic acid. The sample was vortex-mixed and

centrifuged for 1 minute at 3000 rpm. Solid-phase extraction

cartridges (Isolute C8, EC; Biotage AB, Uppsala, Sweden) were

solvated subsequently with 2 mL of methanol and 2 mL of 0.1%

(v/v) aqueous trifluoroacetic acid. Samples were applied quanti-

tatively, washed with 2 mL of 0.1% (v/v) aqueous trifluoroacetic

acid and eluted with 2 mL of 5 mM ammonium acetate in 90%

(v/v) aqueous methanol. The eluent was evaporated using a

vacuum centrifuge (SpeedVac; Savant Instruments, Lif

Sciences International, Runcorn, UK) and the residue wa

reconstituted in 200mL of mobile phase (1% [v/v] formic acid i

50% [v/v] aqueous acetonitrile), vortex-mixed for 1 minute an

transferred into a polypropylene auto sampler vial.LC-MS/MS analysis was performed using a Perkin-Elme

LC system combined with a Sciex API 3000 mass spectromete

equipped with a Turbo Ion Spray source (GenTech Scientific

Inc., Arcade, NY, USA). A 10 mL-aliquot of the reconstitute

sample was injected using a reverse phase column (Water

SymmetryShield RP18, 3.5 mm 2.1 50 mm; Waters Corpo

ration, Milford, MA, USA) at a temperature of 501C and

constant mobile phase flow of 0.15 mL/minute. The retentio

times were 0.7 minutes for bilastine and 0.9 minutes fo

trandolapril. Mass transitions of 464-272 for bilastine an

Table I. Summary of phase I clinical studies, evaluating the pharmacokinetics of bilastine (BIL), included in the pharmacokinetic database. The pharmaco

dynamic database was created with data from studies 4 and 5

Study

number

Description Dosing regimen No. of healthy

adult subjects

1 Double-blind, ascending, single-dose study to evaluate the safety, tolerability and

pharmacokinetics of BIL

SOD: 5, 10, 50 and

100mg

36

2 Pharmacokinetic study to assess the single-dose bioavailability of BIL under fed and

fasted conditions

SOD: 20 mg 12

3[13] Randomized, multiple-dose study to evaluate the safety and tolerability and pharmacokinetics

of BIL at escalating doses

MOD: 10, 20, 50 and

100mg/day for 14 days

36

4[14] Randomized, single-dose, placebo-controlled, four-period crossover study to evaluate the

safety and tolerability, pharmacokinetics and antihistaminic activity of BIL at five dose levels

compared with cetirizine

SOD: 2.5, 5, 10, 20

and 50 mg

21

5[15] Open-label study to assess the effects of age and gender on the pharmacokinetics and

pharmacodynamics of BIL

SOD: 20 mg 32

6 Randomized, double-blind, crossover, placebo- and positive standard-controlled, single-centre

clinical trial for evaluation of CNS effects of BIL at different doses after single and repeat

oral administration

MOD: 20, 40 and

80mg/day for 7 days

20

7[16] Pharmacokinetic and safety study evaluating the potential interaction of erythromycin and BIL

under steady-state conditions

SOD: 20 mg 24

8 Pharmacokinetic and safety study evaluating the potential interaction of ketoconazole and BIL

under steady-state conditions

SOD: 20 mg 24

9[17] Randomized, double-blind, placebo-controlled, sequential group study to evaluate the safety,

tolerability and pharmacokinetics of single, ascending doses of BIL and of multiple doses of BIL

SOD: 120, 160, 200

and 220 mg

MOD: 140 and

220mg/day for 7 days

54

10 Randomized, multiple-dose, double-blind, five-way crossover study of the ECG effects

of bilastine

MOD: 20 and 100 mg/day

for 4 days

30

11 Randomized, open-label, two-way crossover study to evaluate the effect of grapefruit juice on

the single-dose pharmacokinetics of BIL

SOD: 20 mg 11

12[18] Randomized, open-label, two-way crossover study to evaluate the effect of diltiazem on the

single-dose pharmacokinetics of BIL

SOD: 20 mg 11

CNS = central nervous system; ECG =electrocardiographic; MOD=multiple oral doses; SOD= single oral dose.

PK/PD Modelling of Bilastine 54



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431-234 for trandolapril were selected for quantification in

multiple-reaction monitoring mode.

Signal quantification was performed by the peak area ratio.

The assay was validated over a linear range (0.2200 ng/mL).The lower limit of quantification was 0.2 ng/mL.

Antihistamine Activity

Antihistamine activity was evaluated by measuring the sur-

face areas of skin wheals and flares for 24 hours. In each

treatment period, histamine skin-prick tests (100 mg/mL his-

tamine in normal saline) were performed on the back of the

subject at the following timepoints: predose and at 1.5, 4, 8, 12

and 24 hours post-dose. At each timepoint, two skin-prick tests

were performed on matching sites on opposing sides of the

spine. Ten minutes after each skin-prick test, the wheal and

flare areas induced by histamine were outlined directly on the

back with a green marker and a red marker, respectively, and

transferred onto acetate tracing paper using permanent marker

pens. Calculation of the wheal and flare areas was performed

manually. An average area of the two sites for each timepoint

was calculated and used for analysis. Post-treatment, histamine

time-response (wheal and flare areas expressed in square cen-

timetres) curves were constructed.

Data Analysis

The first step was to perform a non-compartmental analysis of

the data in order to evaluate linearity or non-linearity of the

kinetics. The computational method used to measure areas was

the trapezoidal rule. The analysis was performed simultaneously

at the different dose levels. This analysis was carried out with the

use of WinNonlin software (Pharsight Corporation, Cary, NC,

USA). The estimated parameters for the different doses were

compared by analysis of variance (ANOVA) with theuseof SPPS

software version 14 (SPPS, Inc., Chicago, IL, USA).

Afterwards, a population approach was used and the strat-

egy was as follows: the pharmacokinetic model was built firstand, using the typical disposition characteristics of bilastine, a

pharmacodynamic model describing the drug effect was

then developed. All analyses were performed with nonlinear

mixed-effects modelling software NONMEM version 6.1

(Globomax LLC, Ellicott City, MD, USA).[19]

For each of the pharmacokinetic or pharmacodynamic

analyses, a basic population model was proposed. Based on a

model that describes mean population and individual tenden-

cies, observations are expressed as follows (equation 1):

OBSij fyi; D;tj eij Eq: 1

where OBSij is the jth observation (bilastine plasma concen

tration or the measured wheal or flare effect) in the ith ind

vidual, f represents the structural model, yi represents the set o

parameters (pharmacokinetic or pharmacodynamic) for thith individual, D is the administered dose, tj is the time at whic

the jth observation was recorded and eij represents the residua

shift of the observation from model predictions; eij are random

variables assumed to be symmetrically distributed around 0

with variance denoted by s2. Although, in the previous expres

sion, an additive model was used to relate observations t

predictions, different models (i.e. the constant coefficient o

variation [CV] slope/intercept) were also explored.

For each of the elements ofyI, the following model was use

(equation 2):

Pi P eZiP Eq: 2

This equation represents an exponential model to describ

interindividual variability in the model parameters. Pi denote

the individual parameter estimated forthe ith individual, P is th

typical value of the parameter estimated for the population an

Zi is the interindividual error for the ith individual, i.e. th

difference between the estimated value of P and the typica

value of P for the population. The random variable Zi is as

sumed to be symmetrically distributed around 0 with varianc

of O. Other models that were compared were the additiv

model (constant variance) and the proportional model (th

constant CV).

Different pharmacokinetic models (in the absence of co

variates) were fitted to the available data. The selection criteri

used in the model-building and selection process include

the minimum value of the objective function provided b

NONMEM defined as -2 times log of maximum likelihood a

a measure of goodness of fit, the Akaike Information Criterio

(the value that is used to compare hierarchical and non

hierarchical models with the same weighting scheme) and othe

population-parameter values including standard errors of th

estimates, the CV and confidence intervals. Residual plots ma

also be used as diagnostic tools. In this sense, weighted annon-weighted residuals versus predicted concentrations and ver

sus time were analysed since shaped patterns in these plots ma

indicate problems with the error model (variance or weighting) o

with the structural model. Other plots that were examined in

cluded predicted versus observed concentration plots, as well a

predicted and observed concentrations versus time.

Individual concentration-time profiles were obtained b

post hoc Bayesian estimation using model parameters that ha

been previously obtained. Bayesian estimates of the individua

pharmacokinetic parameters were obtained by standar

546 Jauregizar et a



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methods with the estimated values of the population fixed- and

random-effect parameters.

Visual predictive checks (VPCs) were used as a way to visua-

lize how well the model predicted the profile and the vari-ability, assuming perfect precision (no uncertainty). VPCs were

developed by simulating 5000 individual concentration-time

profiles for the selected therapeutic dose (20 mg of bilastine

given once daily), taking population estimates of fixed effects

and sampling from random effects distribution to obtain indi-

vidual profile prediction. Random draws from residual error

distribution were added to each predicted value.

Evaluation of the Relationship between Covariates

and Model Parameters

Theinfluence of covariates on themodel structural parameters

was first assessed by plotting individual empirical Bayesian esti-

mates of parameters versus all of the preselected potential co-

variates including demographic data (age, bodyweight, height

and sex), biochemical data (serum albumin, creatinine, bilirrubin,

g-glutamyltransferase [GGT], aspartate aminotransferase [AST],

alkaline phosphatase and blood urea nitrogen [BUN] con-

centrations) and vital signs (pulse).

Initially, plots of the interindividual variabilities of phar-

macokinetic parameters versus each analysed covariate, as well

as weighted residuals versus covariates, were analysed. Then a

statistical analysis of covariates was carried out and the sta-

tistically significant covariates were included in the base model

by stepwise regressions with an inclusion criterion of p 0.05.

Once the covariates to be included in the model were

selected, this model with covariates was statistically compared

with the base model.

In the final model selection process, all of the described

issues were considered, as well as the standard error of esti-

mates, the extent of interindividual variability, and the corre-

lation matrix of parameters and diagnostic plots (including

covariance among parameters and distribution histograms).

Pharmacokinetic Model

A compartmental analysis showed that a two-compartment

model with first-order absorption and elimination best de-

scribed the kinetics of bilastine after oral administration.

NONMEM subroutine ADVAN4, TRANS4 was used. The

schematic illustration in figure 1 assumes first-order absorp-

tion, where ka denotes the first-order absorption rate constant.

This figure shows schematically the time-course of the drug

in the central compartment (compartment 1) and peripheral

compartment (compartment 2) after administration of an ora

dose. The drug is eliminated from the central compartment

where CL denotes drug clearance, and on the other hand, it i

distributed from the central to the peripheral compartmentQ being the inter-compartmental clearance. Hence, V1 and V

denote the central compartment volume of distribution and th

peripheral compartment volume of distribution, respectively.

Model building and final analysis were performed usin

NONMEM with the first-order conditional estimatio

(FOCE) method. After completing the model-building proces

for the totality of plasma concentration-time data from th

11 studies (single- and multiple-dose studies), population esti

mates of the fixed effects (y) as well as their relative standar

errors (ESy), expressed in percentages, were obtained.

Individual concentration-time profiles were obtained byposhoc Bayesian estimation using the model parameters that ha

been previously obtained. Bayesian estimates of individua

pharmacokinetic parameters were obtained by standar

methods, with estimated values of the population fixed- and

random-effect parameters.

Pharmacodynamic Model

In order to obtain estimates of the pharmacodynami

properties of bilastine, the entire population pharmacokinetic

were estimated separately and the empirical parameter est

mates, conditional on those subjects with pharmacodynami

kin

1V1

2V2

ka

kout R

D

CL

Q

3 Pharmacodynamics

Pharmacokinetics

Inhibition

Fig. 1. Schematic presentation of the pharmacokinetic-pharmacodynam

model that best fitted the data (i.e. plasma concentration and wheal and flar

data) on the time-course of the drug in the central compartment (compartmen

1) and the peripheral compartment (compartment 2) after administration of a

oral dose (D). The specified indirect response model is a type I model o

inhibition of response build-up model; observed effects were coded as dat

from compartment 3. CL=apparent total body clearance of the drug from

plasma; ka= first-order absorption rate constant; kin= zero-order rate consta

for productionof response; kout= first-orderrate constant for lossof response

Q = intercompartmental clearance; R = response; V1= central compartme

volume of distribution; V2=peripheral compartment volume of distribution.




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measurements, were used to drive the turnover model in

$DES. In this sequential pharmacokinetic-pharmacodynamic

modelling, the corresponding (proportional) sigma for the

pharmacokinetic parameter was fixed to the pharmacokineticmodel estimate. This approach reduced run times drastically

when compared with simultaneous fitting, which was very time

intensive and did not converge.

A physiological indirect response model with inhibition of

response production[11] was used to describe bilastine pharma-

codynamics. A schematic illustration of the indirect response

model is presented in figure 1.

In the population pharmacokinetic-pharmacodynamicmodel,

the following differential equations defining the indirect res-

ponse model were additionally introduced (equations 3 and 4):

EFF IC50IC50 A1

Eq: 3

dA3

dt kin EFF kout A3 Eq: 4

where EFF corresponds to the effect.

The specified indirect response model is a type I model or

inhibition of response build-up model, where k in is the zero-

order constant for response production, while kout represents

the first-order constant for loss of response. IC50 can be

defined as the drug concentration that achieves 50% of

maximum inhibition. Note that in the NONMEM data file,

the observed wheal or flare effects were coded as data from

compartment 3 [A(3)].

Initial values for the pharmacodynamic parameters of k in,

kout, IC50 and maximum inhibition (Imax) were estimated as

follows: kout was set to log2 divided by the effect half-life,

roughly estimated from the data; kin was calculated taking into

account that the baseline value of the response (the observed

baseline value at time 0) equals k in/kout; the IC50 was set to the

plasma concentration corresponding to the time of maximum

effect; and Imax was set to 1.

The FOCE method was applied in the pharmacokinetic-

pharmacodynamic modelling process.

Simulations

Finally, computer simulations were carried out with the aim

of selecting the optimal dose and dosing regimen of bilastine.

The selected times to perform the simulations were between 72

and 96 hours, i.e. those corresponding to day 4 in a multiple-

dose regimen. This time selection was based on the value of the

elimination half-life obtained previously, and simulated con-

centrations were at steady state. Mean plasma concentration-

time profiles of bilastine were simulated for daily doses of

5, 10 and 20 mg. IC50 values, estimated separately for whea

and flare, were used as thresholds for dose selection via simu

lation. Proposed dosing regimens should maintain the con

centration levels within the thresholds during the entire regimeinterval.

Results

Pharmacokinetic Study

The non-compartmental pharmacokinetic analysis reveale

that bilastine presents linear pharmacokinetics in the studie

dose range (2.5220 mg/day). Both the maximum concentra

tion and the area under the plasma concentration-time curv

(AUC) of bilastine increased proportionally to the administered doses. The terminal elimination half-life as well as th

other pharmacokinetic parameters of bilastine remained con

stant over the entire studied dosing range. The ANOVA wit

Scheffe post hoc confirmed that the pharmacokinetics of bi

lastine are linear in the dose range of 2.5220 mg/day.

After completing the model-building process for the totalit

of the plasma concentration-time data from the different stud

ies (single- and multiple-dose studies), population estimates o

the fixed effects (y) as well as their ESy values, expressed i

percentages, were obtained and are presented in table II. Thes

standard errors denote the precision in parameter estimation

concluding with an acceptable precision in estimation (


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shown) and high residual values that increased with predicted

concentrations were observed. This situation led to a cone-

shaped plot, suggesting the use of a weighting factor. The

addition of a weight factor helped to overcome this effect. In

fact, as the cone shape disappeared, residual values declined

considerably, and residual distribution became random around

the 0 line. In conclusion, this variance model is suitable. Addi-

tionally, the time-course profiles of non-weighted and weighted

residuals were studied (data not shown). The adequacy of the

weighting scheme was again demonstrated. Residual values

were acceptable, as well as random distribution of residual

around the 0 line throughout the analysed time range.

The VPC for the 20 mg dose is shown in figure 4.

Pharmacodynamic Study

The results of the population pharmacokinetic-pharmaco

dynamic modelling for wheal and flare effects are summarized

in table III. These ESy values are related to estimation preci

sion, which were quite acceptable (14.60%, 15.14% and 16.16%

for kin, kout and IC50, respectively).

Model parameter Z values, expressed as CV%, are als

presented in this table. It can be observed that the IC50 wa

associated with a higher interindividual variability than th

other parameters.Intra-individual variability (e) had a value of 0.011

(ESy= 6.28%). As a result of the error model that was selecte

(additive error), this e is defined as a standard deviation (in

contrast to the CV% in the pharmacokinetic model) and ac

counts for model mis-specification or measurement erro

Hence, the obtained value is acceptable, as it is of the sam

order as the available wheal effects.

The model-predicted individual effect on histamine-induce

wheal as a function of time was in close proximity to th

time-course profile of the observed effects (figure 5). A simila

congruence was observed for flare inhibition (figure 6).

Pharmacodynamic parameter final estimates and their ES

values for flare are also presented in table III. kin values wer

different for flare and wheal; this can be explained by the fact tha

Table II. Population pharmacokinetic-model fit to plasma concentration-

time data from all available studies. Population pharmacokinetic-parameter

estimates (with relative standard errorsa [ESy] expressed as %) and inter-

individual variability expressed as the percentage of the coefficient of varia-tion (CV [%])

Parameter Estimate y (ESy) CV% (ESy)

CL (L/h) 18.1 (1.8) 29.0 (8.7)

V1 (L) 59.2 (2.2) 35.4 (9.6)

Q (L/h) 1.59 (3.9) 56.5 (10.3)

V2 (L) 30.2 (5.1) 73.1 (9.6)

ka (h-1) 1.50 (3.2) 35.4 (16.9)

s (%) [ESy] 28.6 (6.1)

a The relative standard error is the standard error divided by the parameter

estimate.

CL=

apparent total body clearance of the drug from plasma; ka=

first-orderabsorption rate constant; Q=apparent intercompartmental clearance;

V1= central compartment volume of distribution; V2=peripheralcompartment

volume of distribution.

0

1000

2000

3000

4000

5000

6000

7000

8000

0 2000 4000 6000 8000

Observed concentration (ng/mL)

Population-predictedco

ncentration(ng/mL)

Fig. 2. Population-predicted concentrations vs observed concentrations with the line of identity.




8/13

flare areas were larger than wheal areas. The kout value was ap-

proximately 1 h-1 for both wheal and flare, and the IC50 values

(5.15 ng/mL for wheal and 1.25 ng/mL for flare) were lower for

flare than for wheal by a ratio of approximately 4 and were low

compared with the bilastine concentrations obtained after oral

administration.

Finally, the results of simulations of plasma concentrations

corresponding to doses of 5, 10 and 20 mg and for a preselected

time schedule that ranged from 72 to 96 hours were analysed

(figure 7). The time selection was carried out under th

assumption of being at steady state. Taking into account tha

the estimated IC50 values for wheal and flare effects wer

5.15 ng/mL and 1.25ng/mL, respectively, bilastine plasm

concentrations reached after a dose of 20 mg remained over th

IC50 value for the flare effect throughout the entire inter-dos

period (24 hours). Bilastine plasma concentrations decrease

to less than the mean estimated IC50 value for the whea

effect between 20 and 24 hours only. This means that th

0

1000

2000

3000

4000

5000

6000

7000

8000

0 1000 2000 3000 4000 5000 6000 7000 8000

Observed concentration (ng/mL)

Individual-predictedconcentration(ng/mL)

Fig. 3. Individual-predicted concentrations vs observed concentrations with the line of identity.

0

100

200

300

400

500

600

700

800

900

1000

0 2 4 6 8 10 12 14 16 18 20 22 24

Time (h)

Bilastineplasm

aconcentration(ng/mL)

Observed concentrationMedian predicted interquartile

95% predicted interval

Fig. 4. Predicted and observedconcentration-time profiles of bilastine after a single oral doseof 20 mg. The simulations usedfixed effects point estimates an

were performed across, between and within subject variability.

550 Jauregizar et a



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main part of the antihistaminic activity lasts nearly for the

entire duration between two once daily dosing intervals.

However, for doses of 5 and 10 mg, plasma drug concentra-

tions were below the wheal IC50 value for a few hours before

administration of the next dose (10 hours for a 10 mg dose

and 16 hours for a 5 mg dose). Hence it can be concluded

that the optimal dosing regimen for bilastine is 20 mg every

24 hours.

Discussion

The purpose of this study was to characterize the relation-

ship between the pharmacokinetics and the antihistaminic ac-

tivity of bilastine in healthy adult subjects. This is importantnot

only to establish adequate dosage regimens,[20] but also

to understand the actual mechanism of action involved in the

in-vivo drug effect.[21]

In this study, the pharmacokinetics and pharmacodynamics

of bilastine after oral administration were studied using thepopulation pharmacokinetic-pharmacodynamic approach. The

non-compartmental pharmacokinetic analysis revealed that

bilastine displays linear pharmacokinetics in the studied dose

range.

Bilastine was characterized by two-compartmental kinetics

with a rapid-absorption phase (ka= 1.50 h-1); peak plasma

concentrations were observed at 1 hour following oral admin-

istration and the elimination half-life was approximately

14 hours. Bilastine and most orally administered new H1receptor antagonists are well absorbed and appear to be

extensively distributed into body tissues; many are highly pro

tein bound. Most new H1 receptor antagonists do not accu

mulate in tissues during repeated administration.[3] The sam

result was observed for bilastine: according to the ratio of thAUC obtained from multiple-dose studies (i.e. the accumula

tion ratio between the AUC from 312 to 336 hours and th

AUC from 0 to 24 hours = 1) [results not shown], it can b

inferred that bilastine does not undergo accumulation after th

studied dosing regimens.

The effect of bilastine on raw wheal and flare areas, ex

pressed as square centimetres, was modelled. Measurement o

wheal and flare skin reactions to assess the pharmacodynamic

of antihistaminic drugs has been extensively used. [4,10,11,22-24]

Little pharmacokinetic and pharmacodynamic modellin

has been performed for antihistaminic agents. The mechanismof action of bilastine corresponds to an inhibition of build-up

turnover pharmacodynamic model,[25,26] and this model wa

successfully applied in this study. In fact, indirect respons

models have been successfully used to describe the pharmaco

dynamics of antihistaminic drugs such as mizolastine[10] an

cetirizine.[12]

In this study, the peak plasma concentration was rapidl

reached in approximately 1 hour and the maximal respons

was observed later at approximately 4 hours or longer. Here

the measurement site is the skin; therefore, the observe

delay could be attributed to diffusion to the skin of the anti

histamine. The indirect-effect model intrinsically addresses thi

delay.[20]

The pharmacokinetic-pharmacodynamic model that wa

developed showed good performance in describing both th

mean population tendency and individual effect profiles. Th

0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30

Time (h)

Predictedandobservedwhealareas(cm

2)

Observed wheal effect

Predicted wheal effect

Fig. 5. Predicted and observed wheal effects vs time for individuals wh

participated in study 5.

Table III. Pharmacokinetic-pharmacodynamic population model fit of the

wheal and flare effects

Parameter kin

[ng/mL/h]

kout

[h-1]

IC50

[ng/mL]

Wheal

Estimatea 0.44 (14.60) 1.09 (15.14) 5.15 (16.16)

Zb 29.36 (32.95) 14.04 (81.22) 55.95 (45.05)

Flare

Estimatea 11.10 (8.48) 1.03 (8.35) 1.25 (14.56)

Zb 24.02 (45.41) 26.98 (26.65) 65.65 (29.93)

a Values are expressed as estimate (%ESy). The ESy is the standard error

divided by the parameter estimate.

b Values are expressed as %CV (%ES).

g = interindividual variability;ES = standard error; ESh= relative standarderror

of the pharmacodynamic parameter; IC50= estimated concentration produ-cing 50% inhibition; kin= zero-order rate constant for production of response;

kout= first-order rate constant for loss of response.




10/13

pharmacodynamic parameters had reasonable estimates. Dif-

ferences in kin values for flare and wheal, as well as lower IC50values for flare than for wheal, have also been observed with

mizolastine,[11] cetirizine[12] and other antihistaminic drugs in

an analysis in which an effect compartment model was used. [7]

When using typical pharmacokinetic parameters, the inter-

individual variability associated with pharmacodynamic

parameters is likely to be overestimated, since variability of

the absorption and disposition processes is also involved.

However, the estimates of variability were not extremely

high: 29.36% for kin, 14.04% for kout and 55.95% for IC50 forthe

wheal effect; and 24.02%, 26.98% and 65.65%, respectively,

for the flare effect.

The NONMEM run, by itself, estimated population

mean values and variances of parameter values within such a

population, as well as residual error variance. Populatio

means were then used as a priori estimates for individual pos

hoc parameters by the Bayesian analysis in every iteration o

minimizing the objective function. The population mixedeffects approach with Bayesian analysis is a powerful tool fo

accounting for interindividual variability and, hence, allowin

for the description of the time-course of the antihistamini

effect for each individual. These results demonstrate tha

pharmacokinetic-pharmacodynamic analysis, as stated b

Levy,[20] can reflect the actual mechanism of action involved in

the pharmacological response of a given drug.

Finally, with the use of the population-pharmacokineti

model, computer simulations were performed to obtain bilas

tine plasma concentrations at steady state after the adminis

tration of 5, 10 or 20 mg once daily. Bilastine concentrationreached after a dose of 20 mg are over the IC50 value for th

flare effect throughout the entire inter-dose period (24 hours)

Such concentrations decreased to less than the mean estimate

IC50 value for wheal between 20 and 24 hours only. This implie

that the main part of the antihistaminic activity lasts nearly fo

the entire duration between two once-daily dosing intervals

which suggests that the optimal dosing regimen for bilastine i

20 mg every 24 hours. Pharmacokinetic and pharmacodynami

relationships of bilastine were reliably described with the use o

a physiological indirect response model; this led to an accurat

prediction of bilastine pharmacodynamic activity. Further

more, although this model has no predictive value for de

termining the clinical superiority of one antihistaminic dru

over another, it provides relevant information regarding which

drug dosages, based on the drug concentration-response i

terms of the rate and duration of inhibition, could be anti

cipated to be below the desired pharmacodynamic response an

1

10

100

1000

0 12 24 36 48 60 72 84 96

Time (h)

Simulatedbilastine

plasma

concentration(ng

/mL)

IC50 of wheal effect

IC50 of flare effect

Fig. 7. Simulation of population mean bilastine plasma concentrations corresponding to four consecutive 20 mg doses and, thus, being at steady state. Th

estimated concentration producing 50% inhibition (IC50) values for wheal and flare effects (5.15 ng/mL and 1.25 ng/mL, respectively) are also shown. Plasm

concentrations of bilastine after a dose of 20 mg are over the IC50 value for the flare effect throughout the inter-dose period (24 hours).

10

0

10

20

30

0 10 20 30

Time (h)

Predictedandobservedflareareas(cm

2)

Observed flare effect

Predicted flare effect

Fig. 6. Predicted and observed flare effects vs time for individuals who

participated in study 5.

552 Jauregizar et a



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which dosage should be the potential candidate for further

development in clinical trials. This should be determined on the

basis of more clinically relevant endpoints.[26]

Conclusion

Bilastine displayed linear pharmacokinetics in the studied

dose range (2.5220 mg/day). The population-pharmacokinetic

model that resulted in the best fit of plasma concentration-time

data was a two-compartmental model with first-order absorp-

tion and elimination. No significant relationship could be

detected between pharmacokinetic parameters and any of the

covariates that were analysed (age, bodyweight, height, sex,

serum albumin, creatinine, bilirubin, GGT, AST, BUN and

alkaline phosphatase concentrations, as well as pulse). Ingeneral, no covariate had a substantial role in explaining the

variability of the model parameters.

The pharmacokinetic-pharmacodynamic model that yielded

the best fit of time-effect data was a type I indirect response

model, also known as a model for inhibition of response pro-

duction. In fact, the selected population model fits success-

fully both wheal-and flare-effect data. The estimated IC50values were 5.15 ng/mL for the wheal effect and 1.25 ng/mL

for the flare effect. Therefore, with 20 mg of bilastine given

every 24 hours, plasma drug concentrations at steady state

would be maintained over the IC50 value (to inhibit thewheal and flare effects) throughout almost the entire dosing

interval.

Acknowledgements

The authors would like to thank Deirdre McLaverty and A.J. Stewart

(MDS Pharma Services Belfast, Northern Ireland), and M.J. Barbanoj,

R.M. Antonijoan and C. Garca-Gea (Centre dInvestigacio de Medica-

ments, Institut de Recerca de lHospital de la Santa Creu i Sant Pau,

Barcelona, Spain) as the principalinvestigators of the different studies. The

authors received no funding forthe conduct of this study.Nerea Jauregizar

and Leire de la Fuente are employees of Pharma Datum Data Ana lisis SL;

Nerea Leal and Mo nica Rodrguez are employees of DynaKin; andM. Luisa Lucero and Ander Sologuren are employees of FAES FARMA

SA The authors have no other conflicts of interest that are directly relevant

to the content of this study.

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Correspondence: Ms M. Luisa Lucero, FAES FARMA SA, Maxim

Aguirre 14, 48940, Leioa (Vizcaya), Spain.

E-mail: [email protected]

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