ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Dec. 2011, p. 5914–5922
Copyright © 2011, American Society for Microbiology. All Rights Reserved.
Vol. 55, No. 12
Pharmacokinetics and Safety of Single-Dose Tenofovir Disoproxil
Fumarate and Emtricitabine in HIV-1-Infected Pregnant
Women and Their Infants?
Patricia M. Flynn,1* Mark Mirochnick,2David E. Shapiro,3Arlene Bardeguez,4John Rodman,1†
Brian Robbins,5Sharon Huang,3Susan A. Fiscus,6Koen K. A. Van Rompay,7James F. Rooney,8
Brian Kearney,8Lynne M. Mofenson,9D. Heather Watts,9Patrick Jean-Philippe,10
Barbara Heckman,11Edwin Thorpe, Jr.,12Amanda Cotter,13Murli Purswani,14
and the PACTG 394 Study Team
St. Jude Children’s Research Hospital, Memphis, Tennessee1; Boston University School of Medicine, Boston, Massachusetts2;
Harvard School of Public Health, Boston, Massachusetts3; University of Medicine and Dentistry of New Jersey, Newark,
New Jersey4; University of Nebraska Medical Center, Omaha, Nebraska5; University of North Carolina School of
Medicine, Chapel Hill, North Carolina6; University of California, Davis, California7; Gilead Sciences,
Foster City, California8; PAMA Branch, Eunice Kennedy Shriver National Institute for
Child Health and Development, NIH, Rockville, Maryland9; Henry Jackson Foundation,
Bethesda, Maryland10; Frontier Science & Technology Research Foundation,
Amherst, New York11; University of Tennessee Health Science Center,
Memphis, Tennessee12; University of Miami, Miami, Florida13;
and Bronx-Lebanon Hospital, Bronx, New York14
Received 21 April 2011/Returned for modification 18 June 2011/Accepted 27 August 2011
Tenofovir (TFV) is effective in preventing simian immunodeficiency virus (SIV) transmission in a macaque
model, is available as the oral agent tenofovir disoproxil fumarate (TDF), and may be useful in the prevention
of mother-to-child transmission of human immunodeficiency virus (HIV). We conducted a trial of TDF and
TDF-emtricitabine (FTC) in HIV-infected pregnant women and their infants. Women received a single dose of
either 600 mg TDF, 900 mg TDF, or 900 mg TDF-600 mg FTC at labor onset or prior to a cesarean section.
Infants received no drug or a single dose of TDF at 4 mg/kg of body weight or of TDF at 4 mg/kg plus FTC at
3 mg/kg as soon as possible after birth. All regimens were safe and well tolerated. Maternal areas under the
serum concentration-time curve (AUC) and concentrations at the end of sampling after 24 h (C24) were similar
between the two doses of TDF; the maximum concentrations of the drugs in serum (Cmax) and cord blood
concentrations were higher in women delivering via cesarean section than in those who delivered vaginally (P
? 0.04 and 0.046, respectively). The median ratio of the TFV concentration in cord blood to that in the
maternal plasma at delivery was 0.73 (range, 0.26 to 1.95). Without TDF administration, infants had a median
TFV concentration of 12 ng/ml 12 h after birth. Following administration of a single dose of TDF at 4 mg/kg,
infant TFV concentrations fell below the targeted level, 50 ng/ml, by 24 h postdose. In HIV-infected pregnant
women and their infants, 600 mg of TDF is acceptable as a single dose during labor. Low concentrations at
birth support infant dosing as soon after birth as possible. Rapidly decreasing TFV levels in infants suggest
that multiple or higher doses of TDF will be necessary to maintain concentrations that are effective for viral
Worldwide, the majority of human immunodeficiency virus
(HIV) perinatal transmissions occur during labor and delivery.
Zidovudine (ZDV), as administered in ACTG 076, substan-
tially reduced HIV perinatal transmission (6, 30) but was too
complex and expensive for use in resource-limited settings.
HIVNET 012 demonstrated that single peripartum maternal
and infant nevirapine (NVP) doses can provide effective single-
agent therapy for prevention of mother-to-child transmission
(PMTCT) of HIV in resource-limited areas of the world (13).
This agent appeared optimal because of its strong potency,
easy storage, and oral administration. However, there are con-
cerns over the development of NVP resistance in women and
infants who received this drug alone for prevention of perinatal
transmission (8–11, 27). While development of NVP resistance
can be mitigated by the use of short “tail” regimens in mothers
(5, 21, 34) and the use of triple antiretroviral PMTCT regimens
is becoming widespread, even in the developing world (28),
knowledge about alternative peripartum antiretroviral strate-
gies is needed. This is especially important for women who
register late or not at all for prenatal care or who are diagnosed
in active labor and for their infants, who may benefit from
aggressive intrapartum and postpartum interventions.
Tenofovir (TFV), a potent inhibitor of retroviral transcrip-
tase, has demonstrated significant prophylactic efficacy against
simian immunodeficiency virus (SIV) infection in macaques, a
* Corresponding author. Mailing address: St. Jude Children’s Re-
search Hospital, Department of Infectious Disease, 262 Danny
Thomas Place, Mailstop 600, Memphis, TN 38105-2794. Phone: (901)
595-2338. Fax: (901) 595-5068. E-mail: firstname.lastname@example.org.
?Published ahead of print on 6 September 2011.
primate model of AIDS, in multiple studies, including a peri-
natal transmission model (32, 35, 36, 38–40). In addition, the
emergence in reverse transcriptase (RT) of the K65R substi-
tution mutation, the main mutation associated with TDF re-
sistance, occurs infrequently (31). An understanding of the
disposition of these agents in pregnant women and the transfer
to their fetuses is an essential first step in determining a role in
PMTCT. The availability of tenofovir disoproxil fumarate
(TDF), an oral prodrug of TFV, supports the investigation of
tenofovir as a potential agent for use in PMTCT. TDF is
currently approved for the treatment of HIV infection as part
of a combination antiretroviral therapy (cART) at a dose of
300 mg once daily and is also available as the fixed drug
combination tenofovir-emtricitabine (TDF-FTC; Truvada),
coformulated with 200 mg emtricitabine (FTC). PACTG 394
was developed to determine the safety, tolerance, and phar-
macokinetics (PK) of TDF, administered either as a single
agent or as TDF-FTC in HIV-infected pregnant women and
their infants. The findings of this study complement those of
the ANRS 12109 (14–16, 33, 34) and HPTN 057 (23, 24) trials,
studies that administered TDF to pregnant women and their
infants in various dosing regimens and employed complemen-
tary analysis techniques.
MATERIALS AND METHODS
Study population. HIV-infected pregnant women at ?34 weeks of gestation
were recruited at clinical trial sites in the United States and Puerto Rico. Women
and their infants were allowed to receive any antiretroviral agents, except TDF,
as part of a PMTCT regimen. They were excluded from participation if they had
serious illness, laboratory results indicating grade 3 or higher underlying toxicity
(based on the Division of AIDS 1994 Toxicity Table, available at http://rsc.tech
_of_Adult_Pediatric_Adverse_Events.pdf), a creatinine clearance of ?70 ml/min
/1.73 m2, or urine protein levels of ?300 mg/24 h. They were also excluded if they
had clinical or sonographic evidence of fetal growth retardation or major
congenital anomalies, use of highly nephrotoxic drugs, or therapeutic use of
heparin. Breast-feeding was not permitted.
Study procedures. Two groups of mothers administered TDF in dosages of 600
mg and 900 mg were initially planned for the study. Dose escalation from a dose
of 600 mg TDF in the first group to 900 mg TDF in the second group was
dependent on preestablished safety and PK criteria. Safety criteria to increase
the dose (or for any dose to be considered safe) required that there were no
life-threatening toxicities and that the incidence of non-life-threatening toxicities
(grade 3 or 4) was ?30%, as well as that no adverse pregnancy or neonatal
outcomes could be attributable to study treatment. PK criteria to escalate the
maternal dose included median TFV concentrations in either cord blood or
infants at 24 h of life of less than 50 ng/ml, the typical 24-h trough concentration
in adults receiving TDF therapeutically (4). The maternal area under the serum
concentration-time curve (AUC) was also required to be ?1.5 times the value for
nonpregnant adults given a single 600-mg dose (2). In the first group, no TDF or
FTC was administered to infants. The infant dose and the timing of postdelivery
dosing were determined by PK findings in the initial group of women and infants
studied. In all groups, infants received standard ZDV prophylaxis until 6 weeks
In the first group, women received a single oral dose of 600 mg TDF, admin-
istered as two 300-mg TDF tablets, with two ounces of milk or nutritional
supplement at the onset of active labor or 4 to 8 h prior to scheduled delivery by
cesarean section. All women received standard intravenous ZDV prophylaxis.
The women’s PK samples were obtained predose, at 1, 2, 4, 8, 12, and 24 h
postdose, and at the time of delivery. Cord blood and infant samples were
collected at 12, 24, and 36 h of life. Accrual continued until 10 evaluable
mother/infant pairs were enrolled. An evaluable pair was defined as a mother
and infant with a complete set of PK evaluations, with infant delivery occurring
between 2 and 24 h after the maternal dosing of TDF. In this group, a minimum
of five women were expected to deliver vaginally.
In the second group, women received 900 mg TDF, administered as three TDF
tablets, and infants received 4 mg/kg of body weight of a TDF suspension
(investigational new drug [IND] number 68947) as soon as possible after deliv-
ery. TDF for oral suspension is an investigational product and consists of a white
to off-white powder that is constituted with water to yield a TDF suspension with
a concentration of 20 mg/ml. The PK samples for women in the second group
were obtained as for the first group. Infant PK samples were obtained predose
and at 4, 12, 24, and 36 h postdose. Cord blood was also collected. A maximum
of 10 evaluable mother/infant pairs was to be included in this group, with no
restrictions on mode of delivery.
Following a protocol amendment, a third group of women received a single
dose of 900 mg TDF-600 mg FTC, administered as three tenofovir-emtricitabine
tablets, and infants received a single dose of 4 mg/kg of the TDF suspension and
3 mg/kg of an FTC solution as soon as possible after delivery. The PK sampling
was the same as for the second group. A minimum of 6 evaluable mother/infant
pairs was targeted for this third group, and the maximum for the second group
was modified to include 6 evaluable mother/infant pairs to achieve a total of 10
to 12 evaluable mother/infant pairs in the second and third groups combined.
TDF, TDF-FTC, and FTC were provided by Gilead Sciences.
Women were followed until 12 weeks postpartum. Those with a detectable
virus level (?1,000 copies/ml) at labor and delivery or 1, 6, and/or 12 weeks
postpartum were subjected to viral resistance testing. If targeted TFV resistance
mutations were detected, repeat assessments were performed over 1 year. Infants
were followed until 2 years of age. Mother and infant adverse events were
monitored by the study team on biweekly or monthly teleconference calls, during
which the final relationship of the study drugs to the outcome was determined.
All women and infants exposed to TDF, tenofovir-emtricitabine, or FTC in this
study were evaluated for safety.
Informed consent was obtained from all mothers, and the study and all sub-
sequent amendments were approved by each clinical trial site’s institutional
review board before implementation.
Laboratory procedures. TFV and FTC concentrations were measured by
Gilead Sciences using a validated liquid chromatography/mass spectrometry (LC/
MS) assay as previously described (20). The analytic laboratory conforms to
international standards of good laboratory practices (GLP) and GLP-like anal-
yses for clinical samples and is overseen by Gilead Sciences, Inc. Briefly, samples
were deproteinized using methanol with an internal standard added (lamivudine
[3TC] for FTC and adefovir for TFV). After extraction, the analytes were
resolved using isocratic reverse-phase chromatography and detected using mass
spectrometry with lower limits of 5 ng/ml for FTC and 10 ng/ml for TFV. The
selected reaction-monitoring (SRM) mode was used with atmospheric pressure
chemical ionization (APCI) with positive polarity. The ion transitions were 288
3 176 m/z for TFV, 248 3 130 m/z for FTC, 274 3 162 m/z for adefovir, and 230
3 112 m/z for 3TC. Inter- and intra-assay performance, as determined during
validation, had a precision percent coefficient of variation (%CV) of ?13% and
an accuracy within 16% (20). The viral loads were measured using the Roche
UltraSensitive Monitor assay, version 1.5 (Roche Molecular Diagnostics, Pleas-
anton, CA). Bulk sequencing for the detection of resistance mutations was
performed using the Siemens Trugene HIV-1 genotyping assay. Viral loads and
genotyping were performed at the University of North Carolina at Chapel Hill
laboratory, which was certified by the Division of AIDS Virology Quality Assur-
ance program for both viral load and genotyping assays. For the sensitive real-
time PCR resistance assays, HIV-1 genomic RNA from the blood plasma sam-
ples was extracted using Qiagen BioRobot M48 from 200 ?l patient plasma and
tested at the Centers for Disease Control and Prevention in Atlanta, GA. A
region of the HIV-1 template that included nucleotide 58 to nucleotide 777 of
the gene for RT was amplified by RT-PCR as previously described (17, 18). The
RNA samples were tested for two mutations in RT, K65R and K70E, using
established assay cutoffs equivalent to 0.4% to 1% of the mutant virus, which are
above the background reactivity observed when testing wild-type virus.
Pharmacokinetic and statistical analysis. Noncompartmental pharmacoki-
netic parameters were calculated using two commercial computer programs,
WinNonlin (Pharsight Corp., Palo Alto, CA) and Microsoft Excel (Redmond,
WA). The maximum concentration (Cmax), time to maximum concentration
(tmax), and concentration at the end of sampling (24 h) (C24) were determined by
inspection of concentration-time curves. The area under the serum concentra-
tion-time curve (AUC) was calculated by the trapezoidal rule. Terminal elimi-
nation half-lives (t1/2s) were determined by a weighted least-squares fitting of the
terminal elimination phase of the concentration-time curves. As a measure of
placental transfer, the median ratio of the TFV concentration in cord blood to
that in the maternal plasma at delivery (CB/M TFV concentration ratio) was
calculated using the maternal TFV plasma concentration obtained within 90 min
of delivery and the measured cord blood concentration. The Wilcoxon rank sum
test was used for a comparison of PK parameters by group using SAS version 9.1
VOL. 55, 2011TENOFOVIR AND FTC PK IN PREGNANT WOMEN AND INFANTS5915
software (SAS Institute, Inc., Cary, NC), with a two-sided P value of ?0.05
considered to indicate statistical significance.
Three groups of women and their infants were included in
the study. Following review of the safety and PK findings in
group 1, maternal dose escalation was warranted based on
unacceptable infant concentrations at 24 h of life. Group 2
included women and their infants who received TDF only, and
group 3 included those who received both TDF and FTC. The
characteristics of women who received the study drug and their
infants are shown in Table 1. Fifteen women were enrolled in
group 1, and 14 received the study drug. The subject who did
not receive the study drug was not considered further. One
woman had only one sample with detectable TFV at 8 h after
dosing and was excluded from the PK analysis. In addition, two
women delivered more than 24 h after the dose of TDF and
one woman delivered within 2 h after the dose of TDF. These
3 women, but not their infants, completed PK evaluations and
are included in the PK analysis. Thus, there are 13 women and
10 infants from group 1 included in the PK analysis.
Nine women were enrolled in group 2. Two mother/infant
pairs were excluded from PK analysis, one where the mother
developed a medical complication before the study drug was
administered and the second where the mother received a
commercial preparation of the study drug instead of the study
product, and neither she nor her infant had PK sampling per-
formed. The second woman and her infant are included in
safety but not PK evaluations. Thus, seven women and their
infants in group 2 were included in the PK analysis.
Nine women were enrolled in group 3. One woman was
discovered to be in false labor and was discharged following
study drug administration with no PK sampling performed.
However, her infant received the study drug and completed PK
sampling following birth. Also in group 3, one infant received
TDF only. This resulted in eight women and nine infants being
included in the TFV PK analysis in group 3.
Tenofovir pharmacokinetics. Maternal PK parameters for
TFV are shown in Table 2, and maternal TFV levels over the
24-h sampling period are depicted in Fig. 1. Values for PK
parameters for groups 2 and 3 (900 mg TDF alone and 900 mg
TDF in combination with FTC, respectively) were similar and
were therefore combined. No statistically significant differ-
ences in AUC, Cmax, t1/2, tmax, C24, or concentration at delivery
were observed between the 600-mg and 900-mg groups. In the
entire cohort, the Cmaxwas greater in women who delivered via
cesarean section than in those who delivered vaginally (P ?
0.04). Substantial interpatient variability was seen with both
Cord blood concentrations are shown in Table 3. The me-
dian cord blood concentration was 76 ng/ml in group 1 (600
mg) and 68 ng/ml in groups 2 and 3 (900 mg), demonstrating
similar concentrations regardless of maternal dose (P ? 0.5).
Higher cord blood concentrations were observed in infants
delivered via cesarean section than in infants delivered vagi-
nally (P ? 0.046). For the entire study population, the CB/M
concentration ratio was 0.73 (range, 0.26 to 1.95). The rela-
tionship between the time from maternal dose to delivery and
the CB/M concentration ratio is presented graphically in Fig. 2
for the entire study population.
In group 1, the infant TFV concentrations at all measured
time points (12, 24, and 36 h of life) were below the 50-ng/ml
TABLE 1. Characteristics of mothers who received the study drug and their infants
Characteristic of mothers or infantsd
Value (range) for:
Median age (yr)
Median viral load (log10copies/ml)
Median wt (kg)
Median time from dose to delivery (h)
No. who delivered vaginally
No. who received background ART that was:
23.5 (19–44) 27.5 (19–37) 26 (22–37)
Median birth wt (kg)
Median gestational age (wk)
Median time from birth to study drug dose (h)
aGroup 1 consisted of mothers (n ? 14) given 600 mg TDF.
bGroup 2 consisted of mothers (n ? 8) given 900 mg TDF and infants (n ? 8) given 4 mg/kg TDF.
cGroup 3 consisted of mothers (n ? 9) given 900 mg TDF and 600 mg FTC and infants (n ? 9) given 4 mg/kg TDF and 3 mg/kg FTC.
dPI, protease inhibitor; NNRTI, nonnucleoside reverse transcriptase inhibitor; NRTI, nucleoside reverse transcriptase inhibitor. All NNRTI-based regimens
contained nevirapine. All NRTI-based regimens consisted of zidovudine, lamivudine, and abacavir. The “other” ART regimen contained efavirenz and lopinavir-
en ? 7.
5916FLYNN ET AL.ANTIMICROB. AGENTS CHEMOTHER.
target. At 12 h of life, the median TFV concentration was 12
ng/ml. In groups 2 and 3, infants received TDF at a median of
5.5 h of life (range, 1.8 to 11.1 h). Median infant TFV concen-
trations following the dose are shown in Fig. 3. At the time of
TDF dosing, the median TFV concentration in the infants was
29 ng/ml (range, 0 to 91 ng/ml) and was below the targeted
minimum concentration of 50 ng/ml in 9 of 15 infants. The
median tmaxwas 4 h (range, 4 to 24 h), and the median Cmax
was 101 ng/ml (range, 40 to 621 ng/ml) (Table 4 ). The Cmax
was less than 50 ng/ml in 3 of 16 infants. By 24 h after dosing,
the median TFV concentration was 46 ng/ml (range, 17 to 120
Emtricitabine pharmacokinetics. PK samples from all eight
women who received TDF-FTC and from 6 of their infants
were evaluable. None of the study mothers received emtricit-
abine as part of their cART regimen. Infants were dosed with
FTC at a median of 5.3 h of life (range, 1.5 to 7.7 h). FTC PK
parameters for mothers and infants are presented in Table 5.
TFV resistance. The viral load measurements for 19 women
were greater than 1,000 copies/ml in 23 samples over the
course of the study. One woman had a K65R mutation at
baseline; no new K65R or K70E mutations were detected in
any of the study samples when tested either by bulk sequencing
or in a sensitive real-time PCR assay.
Safety and tolerance. The mothers and infants tolerated the
study drug well. There were multiple adverse events reported,
mostly consisting of laboratory abnormalities considered unre-
lated to the study agents. There was one grade 3 hemoglobin
value for an infant that was thought to possibly be related to
the drawing of blood for the study. There were no grade 4
events or adverse maternal or neonatal outcomes. There were
no HIV MTCT cases in this study.
This study demonstrates that TDF administration at the
time of active labor can achieve TFV concentrations that can
suppress HIV replication and can have potential utility for the
prevention of HIV MTCT. Although substantial interpatient
variability exists, we have confirmed that TDF doses of 600 mg
administered during labor result in TFV exposure consistent
with that of the standard 300-mg doses used in treatment of
HIV-infected nonpregnant adults and achieve targeted levels
in most women and in cord blood (2, 29). We saw no further
increase in TFV AUC, C24, or cord blood concentration when
the TDF dose was increased to 900 mg, either as TDF alone or
as TDF coformulated with FTC. Although the number of sub-
jects was modest, these data suggest that increasing the intra-
partum TDF dose to 900 mg does not significantly increase
TFV exposure in mother or infant. This was unexpected, be-
cause the TFV Cmaxand AUC were dose proportional follow-
ing single doses of TDF between 75 mg and 600 mg (2). This
confirms that 600 mg should be the recommended TDF dose
for intrapartum use (14). We also identified that women de-
livering via cesarean section had increased TFV Cmaxcom-
pared to those of women delivering vaginally. Many of the
cesarean sections performed on women in this study were
planned, and women did not enter active labor. It is possible
that TDF absorption may be impaired during active labor. The
clinical significance of this difference is not known. However,
TABLE 2. TFV PK parametersa
Value (range) for mothers receivingb:
300 mg TDF dailyc
600 mg TDF
900 mg TDF
All women (n ? 13)
Delivering by cesarean
section (n ? 7)
vaginally (n ? 6)
All women (n ? 15)
Delivering by cesarean
section (n ? 6)
vaginally (n ? 9)
Median TFV AUC
(ng ? h/ml)
15.9 (3.3–187.6) (n ? 12)
19.1 (3.3–187.6) (n ? 6)
16.9 (10.2–33.7) (n ? 13)
19.1 (14–22.8) (n ? 6)
14.2 (10.2–33.7) (n ? 7)
at delivery (ng/ml)d
78 (0–252) (n ? 10)
72 (48–237) (n ? 5)
83 (0–252) (n ? 5)
109 (0–381) (n ? 13)
157 (101–381) (n ? 6)
80 (0–150) (n ? 7)
aObserved following 600-mg and 900-mg TDF administration in HIV-infected pregnant women and 300-mg, steady-state, daily doses in nonpregnant, HIV-infected patients.
bExceptions to the stated numbers of women are noted.
cRanges shown are based on steady-state PK parameters following dosing with 300 mg daily over 12 to 48 weeks of continuous dosing (19).
dMaternal concentrations at delivery were obtained within 90 min of delivery.
VOL. 55, 2011TENOFOVIR AND FTC PK IN PREGNANT WOMEN AND INFANTS5917
since TFV exposure in the infant seems to be determined more
by infant than maternal dosing, the significance is expected to
As predicted by animal models, substantial amounts of TFV
cross the placenta. Studies of pregnant rhesus monkeys dem-
onstrated fetal/maternal TFV ratios of 17% and 60% following
daily subcutaneous doses and a single dose administered to
near-term macaques, respectively (32, 38). Although TFV
crossed the placenta well in our subjects, with a CB/M TFV
concentration ratio of 0.73, 4 of 10 infants in group 1 and 5 of
15 infants in groups 2 and 3 failed to exceed the target con-
centration of 50 ng/ml in cord blood. In previous studies of
intrapartum administration of nevirapine and tenofovir, the
time between maternal dosing and delivery played an impor-
tant role in determining fetal exposure to a maternally admin-
istered drug (14, 16, 22). Hirt et al. and the TEmAA ANRS
12109 Study Group recommend repeat dosing of women with
an additional 600 mg TDF if more than 12 h have elapsed since
dosing and the woman has not yet delivered the infant (14, 34).
Pharmacokinetic findings from repeat dosing in two women
have demonstrated concentrations comparable to those in
women who had received a single dose as well as no significant
safety issues (16, 34).
A very surprising finding in our study, corroborated by oth-
ers, is the very rapid decline in infant TFV concentrations
immediately after birth (14, 16, 23). Infant rhesus monkeys
demonstrate a 65% decrease in the clearance of TFV, which is
thought to be due to immature renal function and which sug-
gests that TFV elimination would also be decreased in neo-
nates (37). In contrast, elimination of transplacentally acquired
TFV appeared brisk in our newborns in group 1, with no infant
having a TFV concentration above 14 ng/ml by 12 h of life.
Based on these findings of rapid decline of infant TFV con-
centrations after birth in the first group studied, we opted to
dose infants as soon as possible after delivery in the second and
third groups. Despite this plan, TDF was administered to in-
fants in our study at a median of 5.5 h of life due to practical
reasons. If TDF is to be given to infants as part of a successful
TABLE 3. Cord blood TFV PK parameters
Value (range) for infants of mothers receivinga:
600 mg TDF 900 mg TDF
All infants (n ? 10)
section (n ? 5)
vaginally (n ? 5)
All infants (n ? 15)
section (n ? 6)
vaginally (n ? 9)
No. with cord
of ?50 ng/ml
CB/M TFV ratio
76 (0–309)94 (41–223)64 (0–309) 68 (0–224) 110 (68–224)49 (0–114)
0.78 (0.35–1.95) (n ? 9)0.94 (0.57–1.95)0.76 (0.35–1.62) (n ? 4)0.63 (0.26–0.84) (n ? 12) 0.71 (0.59–0.84)0.63 (0.26–0.79) (n ? 6)
aObserved following 600-mg and 900-mg TDF administration in HIV-infected pregnant women. Exceptions to the stated numbers of infants are noted.
FIG. 1. Median maternal TFV concentrations following a single dose of 600 mg or 900 mg TDF. Vertical bars represent interquartile ranges
(IQRs), and the numbers along the bottom are the numbers of available data points at each time point for each dose level.
5918 FLYNN ET AL.ANTIMICROB. AGENTS CHEMOTHER.
PMTCT regimen, infant dosing should be given sooner after
birth in order to maintain targeted levels for viral suppression.
The optimal length of time necessary to maintain targeted
levels for viral suppression in newborns remains unknown.
However, based on nevirapine pharmacokinetics in newborns
(25) and recent data from the HPTN 040/PACTG 1043 trial,
where 1 to 2 weeks of additional antiretroviral agents was
added to the standard 6 weeks of ZDV in infants born to
women who received no antepartum therapy, resulting in re-
duced transmission (26), a minimum of 1 to 2 weeks seems
Differential clearance of plasma TFV has been observed
between doses administered as parenteral TFV and doses ad-
ministered as oral TDF. In macaques, the plasma half-life of
subcutaneous TFV was 3.9 h, compared to 15.3 h for TDF.
Additionally, TDF administration resulted in higher concen-
trations of the active metabolite TFV-diphosphate (TFV-DP)
in peripheral blood mononuclear cells (7). Because infants in
groups 2 and 3 were exposed to circulating TFV via the pla-
centa and received TDF orally, their pharmacokinetic param-
eters likely represent a combination of both parenteral- and
oral-administration PK patterns. This also suggests that de-
spite low plasma concentrations following oral administration
of TDF, substantial intracellular concentrations of the active
metabolite TFV-DP may be present. TFV-DP was assessed by
Hirt et al. in 20 cord blood specimens following maternal
intrapartum dosing of 600 mg and in 22 infants 10 to 45 h old
following a dose of 13 mg/kg of TDF suspension (16). Only 2
of the cord blood specimens had quantifiable TFV-DP present,
but the infant concentrations were comparable to those in
adults at steady state. Although there was no sampling between
birth and the assessment 10 to 45 h after infant dosing, a lag in
the appearance of TFV-DP is proposed. The role of TFV-DP
concentrations in adult pre- and postexposure prophylaxis reg-
imens is under investigation and may provide additional insight
Our study is one of the first to report the pharmacokinetics
of infant dosing with TDF in the first week of life. After
receiving 4 mg/kg at a median of 5.5 h after birth, these infants
had low TFV AUC and Cmax(but similar t1/2) compared to
those of uninfected adults receiving standard 300-mg doses
(19, 29) as well as to those of the mothers in the current study
who received 600 mg or 900 mg during labor. By 24 h after the
dose, the median infant concentration was 46 ng/ml, which is
below the 50-ng/ml target. These data suggest that a larger
infant dose will be needed to maintain infant TFV concentra-
tions above the target concentration in the first days of life.
Hirt et al. had proposed an infant dose of 13 mg/kg based on
a simulation of data from maternal intrapartum TDF doses
and the washout of transplacentally acquired drugs from in-
fants (14). They have recently reported their findings using a
population PK approach (16). The median infant TFV AUCs
and Cmaxwere approximately twice those seen with our
4-mg/kg dose (3,730 versus 1,841 ng ? h/ml and 290 versus 101
ng/ml, respectively). Additionally, the safety of this dose in
infants seems acceptable (34). A clinical study using a 6-mg/kg
FIG. 2. Comparison of CB/M TFV concentration ratios and the intervals between maternal doses and deliveries.
VOL. 55, 2011 TENOFOVIR AND FTC PK IN PREGNANT WOMEN AND INFANTS5919
dose with repeated dosing is under way (24), and findings from
this study will help determine the optimal infant TDF dosing
Eight of our study mothers also received 600-mg intrapar-
tum doses of FTC in the form of TDF-FTC, the fixed-dose
combination of TDF and FTC. FTC PK parameters in these
subjects were compared to those seen in non-HIV-infected
adults receiving standard FTC doses of 200 mg; the AUC was
increased by roughly 40%, while the Cmax, C24, and t1/2were
similar (29). However, the FTC AUC, Cmax, and C24values in
our subjects were similar to those seen following intrapartum
400-mg doses in another study (15). This similarity suggests
that intrapartum administration of 2 TDF-FTC tablets, which
provide 600 mg TDF and 400 mg FTC, should provide an
exposure to both drugs that is equivalent to that seen in non-
pregnant adults receiving standard doses of 300 mg TDF and
200 mg FTC.
The median CB/M FTC concentration ratio was 0.85, con-
firming that transfer of FTC from mother to infant is substan-
tial (3, 15). Our data are the first to describe FTC pharmaco-
kinetics following administration to neonates. We chose a
conservative dose of 3 mg/kg, one-half of the usual pediatric
dose of 6 mg/kg (41). The FTC AUC in our infants exceeded
that seen following 200-mg doses in uninfected adults and
120-mg/m2doses in HIV-infected children, while the Cmaxwas
FIG. 3. Median infant TFV concentrations following a single 4-mg/kg dose administered shortly after birth. Vertical bars represent IQRs. The
dashed line represents a TFV concentration of 50 ng/ml, the targeted C24concentration. The numbers along the bottom are the numbers of
available data points at each testing time.
TABLE 4. Infant TFV PK parametersa
Value (range) for
all infants (n ? 16)
Median TFV AUC (ng ? h/ml)....................................1,841 (883–7,931)
Median Cmax(ng/ml) .................................................... 101 (40–621)
Median tmax(h) .............................................................
aObserved following 4-mg/kg TDF administration to infants.
bn ? 14.
TABLE 5. Maternal, cord blood, and infant FTC PK
parameters in group 3a
PK parameterValue (range)
Mothers (600 mg FTC) (n ? 8)
Median FTC AUC (ng ? h/ml).........................13,794 (5,322–36,268)
Median Cmax(ng/ml) ......................................... 1,795 (393–4,820)
Median tmax(h) ..................................................
Median concn at delivery (ng/ml)....................
Cord blood (n ? 8)
Median amount of cord blood (ng/ml) ...........
CB/M FTC ratio.................................................
Infants (3 mg/kg FTC) (n ? 6)
Median FTC AUC (ng ? h/ml).........................17,852 (9,525–22,898)
Median Cmax(ng/ml) ......................................... 1,068 (769–1,538)
Median tmax(h) ..................................................
aObserved after administration of three tablets of TDF-FTC (900 mg TDF
plus 600 mg FTC in mothers and 4 mg/kg TDF plus 3 mg/kg FTC in infants).
5920 FLYNN ET AL.ANTIMICROB. AGENTS CHEMOTHER.
lower in our infants (29, 41). However, our sampling schedule
may have resulted in an underestimation of the Cmax, as our
first sample was collected 4 h after the dose but the FTC tmax
averages 1.5 h in older infants and children (41). The median
t1/2in our neonates was 9.2 h, similar to that observed in older
children and adults (29, 41). Our data suggest that an FTC
dose of 3 mg/kg as soon as possible after birth provides FTC
exposure that exceeds the average in vitro FTC 90% inhibitory
concentration (IC90) for wild-type HIV-1 virus replication of
51 ng/ml for at least 24 h after the dose. A smaller dose of 2
mg/kg may be adequate for prophylaxis of HIV MTCT in
neonates, consistent with the recommendation from a simula-
tion of neonatal FTC dosing (15).
In summary, TDF, alone or with FTC, at doses of 600 mg
and 900 mg, was safe and well tolerated in HIV-infected
women both in active labor and prior to a cesarean section and
resulted in TFV exposure similar to that seen in HIV-infected
persons taking 300 mg TDF daily. No significant maternal or
infant adverse events, including the development of new 65R
or 70E mutations, were observed with the administration of
TDF to pregnant women. Maternal FTC administration was
also well tolerated, and FTC exposure with 600-mg intrapar-
tum doses was greater than that seen with 200-mg doses in
nonpregnant adults and children but not different than that
seen with 400-mg intrapartum doses. Based on these data, we
recommend intrapartum TDF dosing of 600 mg, with 400 mg
FTC recommended if the fixed-dose combination product is
used. Infant doses of 4 mg/kg TDF resulted in targeted TFV
concentrations, but these concentrations were not maintained
over 24 h, suggesting that TDF should be given to infants
immediately after birth and that doses higher than the 4 mg/kg
used in this study and/or more frequent dosing intervals will be
required to maintain targeted TFV levels in the first days of
Overall support for the International Maternal Pediatric Adolescent
AIDS Clinical Trials (IMPAACT) Group was provided by the Na-
tional Institute of Allergy and Infectious Diseases (NIAID) (grant U01
AI068632), the Eunice Kennedy Shriver National Institute of Child
Health and Human Development (NICHD), and the National Insti-
tute of Mental Health (NIMH) (grant AI068632). This work was
supported by the Statistical and Data Analysis Center at the Harvard
School of Public Health under National Institute of Allergy and In-
fectious Diseases cooperative agreement number 5 U01 AI41110 with
the Pediatric AIDS Clinical Trials Group (PACTG) and cooperative
agreement number 1 U01 AI068616 with the IMPAACT Group. Sup-
port for the sites was provided by the NIAID and the NICHD Inter-
national and Domestic Pediatric and Maternal HIV Clinical Trials
Network, funded by NICHD (contract number N01-DK-9-001/
The content is solely the responsibility of the authors and does not
necessarily represent the official views of the NIH.
Gilead Sciences, Inc., provided the study drugs TDF, tenofovir-
emtricitabine (Truvada), and FTC and performed the drug concentra-
We thank Kimberly Hudgens for assistance with protocol develop-
ment and management. We would also like to acknowledge Jeff John-
son and Jonathan Lipscomb from the Centers for Disease Control and
Prevention for performing the sensitive real-time PCR resistance as-
The following clinical trial sites and personnel participated in the
conduct of this study: at San Juan City Hospital, Elvia Perez-Hernan-
dez, Antonio Rodriguez-Mimoso, Midnela Acevedo-Flores, and Luis
Marquez-Babilonia; at the Regional Medical Center at Memphis, Ed-
win M. Thorpe, Jr., and Nina K. Sublette; at the New Jersey Medical
School, Arry Dieudonne, Charmane Calilap-Bernardo, Juliette John-
son, and Lisa Monti; at St. Jude Children’s Research Hospital, Kath-
erine Knapp, Nehali Patel, Jill Utech, and Sandra J. Boyd; at the
Children’s Hospital of Michigan, Ernestine Brown, Tamika Watson,
and Theodore B. Jones; at Bronx-Lebanon Hospital, Mahboobullah
Mirza-Baig, Mavis Dummitt, Stefan Hagmann, and Murli Purswani;
and at the University of Miami, Amanda Cotter, Gwendolyn B. Scott,
Erika Lopez, and Sergio Jordan.
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