Pregnancy-Related Effects on Lamivudine Pharmacokinetics in a
Population Study with 228 Women
Sihem Benaboud,a,b,cJean Marc Tréluyer,a,b,c,dSaik Urien,a,bStéphane Blanche,eNaim Bouazza,a,b,cHélène Chappuy,a,c,e
Elisabeth Rey,dEmmanuelle Pannier,fGhislaine Firtion,fOdile Launay,a,f,gand Déborah Hirta,b,c
Université Paris Descartes, Paris, Francea; Unité de Recherche Clinique Cochin/Necker, AP-HP, Paris, Franceb; CIC Inserm 0901, Paris, Francec; Service de Pharmacologie
Clinique, AP-HP, Groupe Hospitalier Paris Centre, Paris, Franced; Hôpital Necker Enfants Malades, Université Paris-Descartes, Paris, Francee; AP-HP, Groupe Hospitalier Paris
Centre, Service de Gynécologie-Obstétrique, and Groupe Hospitalier Paris Centre, Maternité Port Royal, Paris, Francef; and AP-HP, Groupe Hospitalier Paris Centre, Pôle de
Médecine, CIC de Vaccinologie Cochin Pasteur, Paris, Franceg
ral drugs to prevent transmission to their newborns, compared
with 9% in 2004 (8a). After zidovudine, the nucleoside reverse
transcriptase inhibitor used most frequently during pregnancy is
lamivudine (3TC), due to its favorable safety, tolerability, and
pregnancy category C drug.
Physiological changes associated with pregnancy can lead to
significant variations in pharmacokinetics (PK) (modified ab-
sorption, distribution, and elimination) (2). Two studies on 3TC
PK in HIV-infected pregnant women have been reported: one on
the day of delivery (12) and the other at the 38th week of preg-
nancy and 1 week postpartum (14). Those studies concluded that
of pregnancy. However, lamivudine is eliminated predominantly
plasma flow and glomerular filtration occur shortly after concep-
tion and persist throughout the second trimester (6). The impact
Drug studies during delivery are restricted to single maternal
plasma samples with umbilical blood samples obtained at time of
because it does not take into account the delay between the last
drug administration and the sampling time. Indeed, the placental
transfer of 3TC has been described in one study by the ratio be-
tween cord blood and maternal concentrations at delivery, and it
ccording to the latest United Nations Joint Programme on
HIV/AIDS estimates (8a), 15.7 million women are infected
varied from a negligible value, due to fetal concentrations below
the limit of quantification (LOQ), up to 742%, with a median of
centrations and estimated 3TC amniotic fluid accumulation by a
fluid-to-mother plasma concentration ratio at delivery ranging
from 0.26 to 133.3.
In this work, a population pharmacokinetic study was per-
mother to fetus using a fetus-to-mother exposure ratio, and (iii)
estimate the accumulation of 3TC into the amniotic fluid and
estimate the fetal elimination of 3TC into this compartment.
MATERIALS AND METHODS
Patients. The population included nonpregnant women, pregnant
women, and women on the day of delivery receiving oral lamivudine for
centrations were monitored on a routine basis. A lamivudine tablet was
Received 18 March 2011 Returned for modification 16 August 2011
Accepted 17 October 2011
Published ahead of print 21 November 2011
Address correspondence to Sihem Benaboud,
Copyright © 2012, American Society for Microbiology. All Rights Reserved.
aac.asm.org 0066-4804/12/$12.00 Antimicrobial Agents and Chemotherapyp. 776–782
and samplings, time of dosing, body weight (BW), age, and weeks of
gestation were carefully recorded.
Analytical method. Lamivudine was measured in a 100-?l plasma
sample by high-performance liquid chromatography. An internal stan-
dard was used. Lamivudine was extracted by solid-phase extraction on a
Bond Elut C18column and separated on a Satisfaction C8Plus column
(250 by 3 mm) with a gradient of solvent A (water with 0.01% trifluoro-
acetic acid, 2% methanol, and 3% acetonitrile) and solvent B (acetoni-
trile), as follows: 50% solvent A and 50% solvent B for 30 min, 90%
solvent A and 10% solvent B for 30 min, and 98% solvent A and 2%
solvent B for 30 min. The UV absorbance at 270 nm was used for the
detection of 3TC. The limit of quantification (LOQ) was 0.02 mg/liter.
Population pharmacokinetic modeling. The pharmacokinetics of
3TC in women, cord blood, and amniotic fluid were studied sequentially
as follows: (i) the pharmacokinetics of 3TC in adult women were investi-
and the corresponding parameters were estimated, but the woman pa-
rameters were fixed; (iii) amniotic fluid was connected to the model,
fixing woman and cord blood parameters; and (iv) all the parameters of
the integrated model, woman plus cord blood plus amniotic fluid, were
For the women’s data, one- and two-compartment models were
tested. For cord blood concentrations, two models were tested: an addi-
tional compartment linked to the mother compartment and an effect
compartment linked by first-order processes to the maternal circulation
(Fig. 1). For amniotic fluid concentrations, several models were investi-
by a fixed swallowing flow constant (kSF) (calculated as kSF? 500 ml/24
h/amniotic fluid volume [1 liter]) (16) and an estimated first-order con-
stant of the fetal rate of elimination into the amniotic compartment.
Lamivudine concentrations below the LOQ were set to half of the LOQ
(3). Several error models were investigated (i.e., multiplicative and addi-
tive error models) to describe residual variability. An exponential model
was used for intersubject variability (ISV). Only significant ISVs in phar-
macokinetic parameters were retained.
The covariates tested were women’s body weight on the day of sam-
pling, women’s age, labor status, and pregnancy status.
The effect of each patient covariate was systematically tested via gen-
eralized additive modeling on the basic model.
ing to the following equation using CL, for example: CL ? ?CL?
tient with the median covariate value and ?CO
factor for the continuous covariate. When a covariate was missing, it was
set to the median value from all the other women.
Delivery was considered a binary covariate, and its influence was
tested as follows: CL ? ?CL???DEL
and 0 is otherwise and where ?DEL
between clearance and gestational age,
CL ? ?CL???
, where ?CLis the typical value of clearance for a pa-
CLis the estimated influential
CL?DEL, where DEL equals 1 for delivery
CLis the estimated influential factor for
where PREG equals 1 if pregnant and 0 is otherwise and ?GA
mated influential factor for pregnancy, and
CLis the esti-
CL??CL? (1 ? PREG ? [e(??1· GA)? e(??2· GA)])
and ?1and ?2are the estimated influential factors for pregnancy, and (ii)
first trimester of pregnancy (TR1), second trimester (TR2), and third
A covariate was retained if its effect was biologically plausible; it pro-
duced a reduction in the Bayesian information criterion (BIC) and a re-
duction in the variability of the pharmacokinetic parameter, assessed by
the associated intersubject variability.
An intermediate model with all significant covariates was obtained.
A backward elimination phase was finally performed by deleting each
covariate from the intermediate model to obtain the final model.
Population pharmacokinetic analysis. Data were analyzed by using
the nonlinear mixed-effect modeling software program Monolix, ver-
sion 31s (http://wfn.software.monolix.org) (9, 11). Parameters were
estimated by computing the maximum likelihood estimator of the
parameters without any approximation of the model (no lineariza-
tion) using the stochastic approximation expectation maximization
(SAEM) algorithm combined with an MCMC (Markov chain Monte
Carlo) procedure. The number of MCMC chains was fixed to 10 for all
estimations. The BIC was used to test different hypotheses regarding
the final model and covariate effect on the pharmacokinetic parame-
ter(s). Diagnostic graphics and other statistics were obtained by using
the R program. Simulated lamivudine profiles and observed data were
compared by a visual predictive check in order to validate the model.
The vector of pharmacokinetic parameters from 1,000 patients was
simulated by using the final model. The 5th, 50th, and 95th percentiles
of the simulated concentrations at each time were then overlaid onto
the observed concentration data by using the R program, and a visual
inspection was performed.
lated. Maternal and fetal 3TC areas under the curve (AUCs) were derived
from the estimated individual PK parameters, and the ratio between fetal
FIG1 Population pharmacokinetic model for the simultaneous prediction of
lamivudine concentrations in the mother, cord, and amniotic fluid. A two-
compartment model with first-order absorption and elimination best de-
scribed maternal data. For concentrations in cord blood, an effect compart-
ment is linked to the maternal plasma compartment by a first-order process.
Amniotic fluid concentrations were linked to the fetal compartment via the
fetal swallowing flow and fetal elimination rate constant. kadenotes the ab-
sorption rate constant, CL denotes the maternal elimination clearance from
partment, Q denotes the maternal intercompartmental clearance, Vpdenotes
the volume of the peripheral maternal compartment, kMFdenotes maternal-
to-fetal rate constant, kFMdenotes the fetal-to-maternal rate constant, and keF
denotes the fetal elimination rate constant.
Pregnancy-Related Lamivudine Pharmacokinetics
February 2012 Volume 56 Number 2aac.asm.org 777
and maternal area under the concentration-time curve from 0 to 24 h
(AUC0–24) values was calculated.
fluid and cord blood concentrations was calculated. Amniotic fluid and
fetal 3TC areas under the curve were derived from the estimated individ-
ual PK parameters, and the ratio between amniotic fluid and fetal
AUC0–24values was calculated.
Demographic data. Data from 228 women were available for the
3TC pharmacokinetic evaluation. Table 1 summarizes the pa-
Populationpharmacokinetics.A total of 387 concentrations
from women and 125 cord blood and 44 amniotic fluid con-
centrations were used for the pharmacokinetic analysis: a total
of 171 samples were obtained during pregnancy (9 in the first
trimester, 55 in the second trimester, and 105 in the third tri-
mester), 128 were obtained on the day of delivery, and 88 were
obtained after pregnancy. The range of sampling times was 0.2
to 37 h after the dose. Sampling times higher than 30 h were
reported for women on the day of delivery. Eighteen maternal
concentrations, two cord blood concentrations, and one amni-
otic fluid concentration were lower than the LOQ, so they were
set to half of the LOQ. All plasma samples were collected at
steady state. Eleven body weights were missing, so they were set
to the median body weight value. A two-compartment model
with first-order absorption and elimination best described the
women’s data. The effect compartment satisfactorily described
cord blood concentrations. Amniotic fluid concentrations
were best described as a compartment connected to the fetal
compartment via fetal swallowing flow (16) and first-order fe-
tal elimination; the differential equations used are presented in
the appendix. Estimated parameters of the model were the ma-
ternal absorption rate constant (ka), maternal elimination
clearance (CL), maternal central volume of distribution (Vc),
maternal intercompartmental clearance (Q), maternal periph-
eral volume of distribution (Vp) maternal-to-fetal rate con-
stant (kMF), fetal-to-maternal rate constant (kFM), and fetal
elimination rate constant (keF). Since 3TC was administered
orally, CL/F, Vc/F, Q/F, and Vp/F were apparent parameters,
where F is the unknown bioavailability. The fetal swallowing
flow constant was calculated as follows: 500 ml/24 h/amniotic
fluid volume (1 liter) (16). The available data were not suffi-
cient to estimate intersubject variability for ka, Q/F, Vp/F, kMF,
kFM, and keF, and fixing the variance of these random effects to
zero did not increase the BIC value. Variabilities were thus
estimated for CL/F and Vc/F. The residual variabilities were
best described by a proportional error model.
Body weight and age had no significant effect on the appar-
ent clearance and apparent volume of distribution of 3TC. De-
livery had no significant effect on CL/F, so parturient women
had the same clearance as that of nonpregnant women. Preg-
clearance rate than nonpregnant women. Figure 2 represents
individual clearances of lamivudine as a function of gestational
age, showing the increase in the rate of clearance during preg-
clearance could not be established, probably because of a lack
of plasma samples obtained in the first trimester of pregnancy.
Figure 3 displays observed and predicted plasma concentra-
TABLE 1 Characteristics of HIV-infected women (n ? 228)
No. of patients
(no. of samples)
Median age (yr)
Median body wt
Median gestational age
Women in labor
FIG 2 Individual women’s lamivudine clearances (liter/h) as a function of gestational age (weeks).
Benaboud et al.
aac.asm.orgAntimicrobial Agents and Chemotherapy
tions of 3TC as a function of time for the women, the cord
blood, and the amniotic fluid compartments.
Evaluation and validation. The final model performance was
appreciated by comparing population predicted and individual
predicted concentrations to observed plasma concentrations and
population weighted residuals versus predicted concentrations
and versus time for 3TC (not shown).
small percent relative standard errors (RSE%). The visual predic-
tive check (Fig. 4) confirmed that the average prediction matched
the observed concentrations, and the variability was well esti-
Maternal and fetal exposure to 3TC and placental transfer.
Table 3 summarizes the apparent clearance and area under the
curve (AUC) obtained after a 300-mg daily dose of 3TC in this
study with patients split into three groups, nonpregnant
results of previous studies with adults (7, 15, 17). On the day of
delivery, the median delay between the administration of 3TC
to the mothers and delivery was 7.5 h (minimum to maximum
[min-max], 0.7 to 37 h). At delivery, the median observed cord
blood and maternal concentrations were 0.342 mg/liter (min-
max, 0.01 to 1.31 mg/liter) and 0.289 mg/liter (min-max, 0.01
to 1.66 mg/liter), respectively. The median observed cord
blood concentration-to-maternal concentration ratio was 1.22
(range, 0.32 to 21.8). The predicted median maternal 3TC
AUC0–24was 12.50 mg · h/liter (min-max, 8.81 to 23.58 mg ·
FIG 3 (Left) Observed and model-predicted lamivudine concentrations versus time in nonpregnant women (open circles and thin line) and pregnant women
(line) concentrations in amniotic fluid. Asterisks indicate concentrations lower than the LOQ.
TABLE 2 Population pharmacokinetic parameters of lamivudine from
the final modela
Model and parameterEstimated value (RSE%)
aRSE%, percent relative standard error; ka, absorption rate constant; CL/F, maternal
apparent elimination clearance from the central compartment; Vc/F, apparent central
volume of distribution; Q/F, intercompartmental clearance; Vc/F, apparent peripheral
volume of distribution; kMF, maternal-to-fetal rate constant; kFM, fetal-to-maternal rate
constant; keF, fetus elimination rate constant; ?PREG, effect of pregnancy on CL/F; ?,
residual variability estimates (proportional error model); ?, interindividual variability
Pregnancy-Related Lamivudine Pharmacokinetics
February 2012 Volume 56 Number 2aac.asm.org 779
h/liter), given that the maternal pharmacokinetic variability
for the 0- to 24-h fetal exposure period varied from 7.59 to
20.30 mg · h/liter. Placental transfer was estimated by the ratio
between fetal and maternal 3TC AUCs for 24 h (4). The pre-
dicted fetal-to-maternal AUC0–24ratio was 0.86.
Amniotic fluid accumulation. At delivery, the median ob-
served amniotic fluid concentrations were 1.80 mg/liter (min-
max, 0.01 to 3.21 mg/liter). The median observed amniotic fluid-
values was 2.9.
In the present work, the pharmacokinetics of lamivudine in
women, cord blood, and amniotic fluid were satisfactorily de-
servations support the validity of this model: (i) in women, cord
blood, and amniotic fluid, the population predicted concentra-
tions were well correlated with the observed concentrations, and
(ii) the population model was validated with the visual predictive
checks (VPC) method. Moreover, pharmacokinetic parameters
obtained from our population model were close to the values re-
ported in previous studies (Table 3). The fetal elimination rate
constant estimated with these amniotic fluid data is close to the
elimination rate constant calculated with another PK model for
neonates and children (5).
Moodley et al. previously reported 3TC pharmacokinetics
in women at week 38 of pregnancy and 1 week after delivery
lamivudine disposition (14). In our study, we analyzed 3TC
pharmacokinetics not only in late pregnancy but also from
week 6 to week 39 of gestation, during labor, and after preg-
nancy. We observed that the rate of lamivudine clearance was
about 22% higher in women during pregnancy. Lamivudine is
FIG 4 Evaluation of the final model by comparison between the 5th (dash line), 50th (solid line), and 95th (dashed line) percentiles obtained from 1,000
simulations and the observed data (open circles) for lamivudine concentrations in women (left) and cord blood (right). Asterisks indicate concentrations lower
than the LOQ.
TABLE 3 Median apparent clearances and areas under the curve after a 300-mg daily dose of 3TC
Value reported by:
Yuen et al.a
Moore et al.b
Heald et al.c
Pregnant NonpregnantIn labor
AUC0–24(mg · h/liter)
aSee reference 17.
bSee reference 15.
cSee reference 7.
Benaboud et al.
aac.asm.org Antimicrobial Agents and Chemotherapy
The rate of renal clearance of lamivudine is higher than the
glomerular filtration rate (GFR), which implies that lamivu-
dine is actively secreted into the renal tubule (8). In pregnancy,
the GFR and effective renal plasma flow increase to levels 50%
to 80% above levels for nonpregnant women (2, 6). This in-
crease occurs shortly after conception and persists throughout
the second trimester (6). A decrease in the GFR during the last
3 weeks of pregnancy was also reported previously, reaching
postpartum values by the last week of pregnancy (2). In our
study, the increased clearance in pregnant women can be ex-
plained by these physiological changes in the GFR during preg-
nancy. The description of clearance as a function of gestational
age probably failed because of the lack of concentration data in
the first trimester, when the increase in the GFR occurs. Tubu-
lar secretion is dependent on saturable membrane transport
proteins. Very little is known regarding the effect of pregnancy
on tubular secretion and/or reabsorption (2).
was relatively close to data reported previously for nonpregnant
adults (Table 3), and no dosage adjustment seems to be necessary
to reach the adult AUC value.
Few data on 3TC placental transfer have been reported. A pre-
vious study by Mandelbrot et al. described placental transfer by a
simple cord blood-to-maternal concentration ratio, which is
highly variable, from a negligible value up to 742% (12). In our
study, from one sample at delivery (at various times after drug
administration) for each mother-cord pair, we were able to assess
the maternal and cord blood concentration profiles over time.
Placental transfer could be estimated as a fetal-to-maternal drug
exposure ratio, which was estimated to be 86%.
The high 3TC amniotic fluid concentration can be ex-
plained as follows: 3TC diffuses from the maternal blood to
fetal blood through the placenta, the fetal kidney removes 3TC
from fetal blood and concentrates it in urine, and fetal mictu-
rition causes the rise in the concentration of 3TC in amniotic
fluid. 3TC returns from amniotic fluid to fetal blood mainly
because of fetal swallowing, and the larger part of this 3TC will
again be excreted by the kidney into the amniotic compart-
ment. This mechanism is satisfactorily described by our model
and seems to be applicable to other substances cleared mainly
by kidney, as was described previously for para-amino-
hippurate (1). This model allowed us to estimate the capacity
for fetal elimination into the amniotic fluid compartment. We
could also draw the 3TC PK profile for the amniotic fluid and
thus express the accumulation into this compartment via an
exposition constant ratio of 3. The high 3TC amniotic fluid
concentrations may have clinical implications for the fetus,
either beneficial or detrimental. Indeed, the lamivudine swal-
lowed may account for an oral loading dose for the fetus; it can
also be protective against concomitant exposure to infectious
HIV by the oral route. On the other hand, the potential toxicity
of perinatal exposure to nucleoside analogs may be of concern.
In conclusion, maternal, fetal, and amniotic fluid lamivudine
pharmacokinetics were accurately described by the proposed
by 22% in pregnant women compared to nonpregnant or partu-
values reported previously for nonpregnant adults, no dose ad-
justment should be needed. Maternal-to-fetal transfer was as-
sessed by using an exposure ratio that was about 86%. The fetal
elimination rate constant of 3TC for the amniotic fluid was esti-
mated to be 0.181 h?1. The accumulation in the amniotic fluid
compartment expressed as an AUC ratio was 3.
The differential system connected with the model depicted in Fig.
1 is as follows:
dG ⁄ dt ? ?ka· G
where G ? D at t ? 0,
dA1⁄ dt ? ka· G ? k21· A2? (k12? k10) · A1
where A1? 0 at t ? 0,
dA2⁄ dt ? k12· A1? k21· A2
where A2? 0 at t ? 0,
dA3⁄ dt ? kMF· A1? kFM· A3? keF· A3? kSF· A4
where A3? 0 at t ? 0, and
dA4⁄ dt ? keF· A3? kSF· A4
where A4? 0 at t ? 0.
G, A1, A2, A3, and A4correspond to the amounts of 3TC in the
gut compartment, the maternal central compartment, the mater-
nal peripheral compartment, the fetal compartment, and the am-
niotic fluid compartment, respectively.
k10equals CL/Vc, k12equals Q/Vc, k21equals Q/Vp, and kSF
and intercompartmental clearance, respectively; Vcand Vpindi-
cate the volume of the central and peripheral maternal compart-
ments, respectively; kMFdenotes the maternal-to-fetal rate con-
stant; kFMindicates the fetal-to-maternal rate constant; and keF
denotes the fetal elimination rate constant.
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