CLINICAL PHARMACOLOGY
Mechanism Of Action
Lamivudine is an antiretroviral agent [see Microbiology].
Pharmacokinetics
Pharmacokinetics In Adults
The pharmacokinetic properties of lamivudine have been
studied in asymptomatic, HIV-1-infected adult subjects after administration of
single intravenous (IV) doses ranging from 0.25 to 8 mg per kg, as well as
single and multiple (twice-daily regimen) oral doses ranging from 0.25 to 10 mg
per kg.
The pharmacokinetic properties of lamivudine have also
been studied as single and multiple oral doses ranging from 5 mg to 600 mg per
day administered to HBV-infected subjects.
The steady-state pharmacokinetic properties of the EPIVIR
300-mg tablet once daily for 7 days compared with the EPIVIR 150-mg tablet
twice daily for 7 days were assessed in a crossover trial in 60 healthy
subjects. EPIVIR 300 mg once daily resulted in lamivudine exposures that were
similar to EPIVIR 150 mg twice daily with respect to plasma AUC24,ss; however,
Cmax,ss was 66% higher and the trough value was 53% lower compared with the
150-mg twice-daily regimen. Intracellular lamivudine triphosphate exposures in
peripheral blood mononuclear cells were also similar with respect to AUC24,ss and
Cmax24,ss; however, trough values were lower compared with the 150-mg
twice-daily regimen. Inter-subject variability was greater for intracellular
lamivudine triphosphate concentrations versus lamivudine plasma trough
concentrations.
The pharmacokinetics of lamivudine was evaluated in 12
adult HIV-1-infected subjects dosed with lamivudine 150 mg twice daily in
combination with other antiretroviral agents. The geometric mean (95% CI) for
AUC(0-12) was 5.53 (4.58, 6.67) mcg.h per mL and for Cmax was 1.40 (1.17, 1.69)
mcg per mL.
Absorption And Bioavailability
Absolute bioavailability in 12 adult subjects was 86% ±
16% (mean ± SD) for the 150-mg tablet and 87% ± 13% for the oral solution.
After oral administration of 2 mg per kg twice a day to 9 adults with HIV-1,
the peak serum lamivudine concentration (Cmax) was 1.5 ± 0.5 mcg per mL (mean ±
SD). The area under the plasma concentration versus time curve (AUC) and Cmax increased
in proportion to oral dose over the range from 0.25 to 10 mg per kg.
The accumulation ratio of lamivudine in HIV-1-positive
asymptomatic adults with normal renal function was 1.50 following 15 days of
oral administration of 2 mg per kg twice daily.
Effects Of Food On Oral Absorption
EPIVIR tablets and oral solution may be administered with
or without food. An investigational 25-mg dosage form of lamivudine was
administered orally to 12 asymptomatic, HIV-1-infected subjects on 2 occasions,
once in the fasted state and once with food (1,099 kcal; 75 grams fat, 34 grams
protein, 72 grams carbohydrate). Absorption of lamivudine was slower in the fed
state (Tmax: 3.2 ± 1.3 hours) compared with the fasted state (Tmax: 0.9 ± 0.3
hours); Cmax in the fed state was 40% ± 23% (mean ± SD) lower than in the
fasted state. There was no significant difference in systemic exposure
(AUC∞) in the fed and fasted states.
Distribution
The apparent volume of distribution after IV
administration of lamivudine to 20 subjects was 1.3 ± 0.4 L per kg, suggesting
that lamivudine distributes into extravascular spaces. Volume of distribution
was independent of dose and did not correlate with body weight.
Binding of lamivudine to human plasma proteins is less
than 36%. In vitro studies showed that over the concentration range of 0.1 to
100 mcg per mL, the amount of lamivudine associated with erythrocytes ranged
from 53% to 57% and was independent of concentration.
Metabolism
Metabolism of lamivudine is a minor route of elimination.
In humans, the only known metabolite of lamivudine is the trans-sulfoxide
metabolite (approximately 5% of an oral dose after 12 hours). Serum
concentrations of this metabolite have not been determined. Lamivudine is not
significantly metabolized by cytochrome P450 enzymes.
Elimination
The majority of lamivudine is eliminated unchanged in
urine by active organic cationic secretion. In 9 healthy subjects given a
single 300-mg oral dose of lamivudine, renal clearance was 199.7 ± 56.9 mL per
min (mean ± SD). In 20 HIV-1-infected subjects given a single IV dose, renal
clearance was 280.4 ± 75.2 mL per min (mean ± SD), representing 71% ± 16% (mean
± SD) of total clearance of lamivudine.
In most single-dose trials in HIV-1-infected subjects,
HBV-infected subjects, or healthy subjects with serum sampling for 24 hours
after dosing, the observed mean elimination half-life (t½) ranged from 5 to 7
hours. In HIV-1-infected subjects, total clearance was 398.5 ± 69.1 mL per min
(mean ± SD). Oral clearance and elimination half-life were independent of dose
and body weight over an oral dosing range of 0.25 to 10 mg per kg.
Specific Populations
Patients With Renal Impairment
The pharmacokinetic properties of lamivudine have been
determined in a small group of HIV-1-infected adults with impaired renal function
(Table 7).
Table 7: Pharmacokinetic Parameters (Mean ± SD) after
a Single 300-mg Oral Dose of Lamivudine in 3 Groups of Adults with Varying
Degrees of Renal Function
Parameter |
Creatinine Clearance Criterion (Number of Subjects) |
>60 mL/min
(n = 6) |
10-30 mL/min
(n = 4) |
<10 mL/min
(n = 6) |
Creatinine clearance (mL/min) |
111 ± 14 |
28 ± 8 |
6 ± 2 |
Cmax (mcg/mL) |
2.6 ± 0.5 |
3.6 ± 0.8 |
5.8 ± 1.2 |
AUC∞ (mcg•h/mL) |
11.0 ± 1.7 |
48.0 ± 19 |
157 ± 74 |
Cl/F (mL/min) |
464 ± 76 |
114 ± 34 |
36 ± 11 |
Tmax was not significantly affected by renal function.
Based on these observations, it is recommended that the dosage of lamivudine be
modified in patients with renal impairment [see DOSAGE AND ADMINISTRATION].
Based on a trial in otherwise healthy subjects with
impaired renal function, hemodialysis increased lamivudine clearance from a
mean of 64 to 88 mL per min; however, the length of time of hemodialysis (4
hours) was insufficient to significantly alter mean lamivudine exposure after a
single-dose administration. Continuous ambulatory peritoneal dialysis and
automated peritoneal dialysis have negligible effects on lamivudine clearance.
Therefore, it is recommended, following correction of dose for creatinine
clearance, that no additional dose modification be made after routine
hemodialysis or peritoneal dialysis.
The effects of renal impairment on lamivudine
pharmacokinetics in pediatric patients are not known.
Patients With Hepatic Impairment
The pharmacokinetic properties of lamivudine have been
determined in adults with impaired hepatic function. Pharmacokinetic parameters
were not altered by diminishing hepatic function. Safety and efficacy of
lamivudine have not been established in the presence of decompensated liver
disease.
Pregnant Women
Lamivudine pharmacokinetics were studied in 36 pregnant
women during 2 clinical trials conducted in South Africa. Lamivudine
pharmacokinetics in pregnant women were similar to those seen in non-pregnant
adults and in postpartum women. Lamivudine concentrations were generally
similar in maternal, neonatal, and umbilical cord serum samples.
Pediatric Patients
The pharmacokinetics of lamivudine have been studied
after either single or repeat doses of EPIVIR in 210 pediatric subjects.
Pediatric subjects receiving lamivudine oral solution (dosed at approximately 8
mg per kg per day) achieved approximately 25% lower plasma concentrations of
lamivudine compared with HIV-1-infected adults. Pediatric subjects receiving
lamivudine oral tablets achieved plasma concentrations comparable to or
slightly higher than those observed in adults. The absolute bioavailability of
both EPIVIR tablets and oral solution are lower in children than adults. The
relative bioavailability of EPIVIR oral solution is approximately 40% lower
than tablets containing lamivudine in pediatric subjects despite no difference in
adults. Lower lamivudine exposures in pediatric patients receiving EPIVIR oral
solution is likely due to the interaction between lamivudine and concomitant
solutions containing sorbitol (such as ZIAGEN). Modeling of pharmacokinetic
data suggests increasing the dosage of EPIVIR oral solution to 5 mg per kg
taken orally twice daily or 10 mg per kg taken orally once daily (up to a
maximum of 300 mg daily) is needed to achieve sufficient concentrations of
lamivudine [see DOSAGE AND ADMINISTRATION]. There are no clinical data
in HIV-1 infected pediatric patients coadministered with sorbitol-containing
medicines at this dose.
The pharmacokinetics of lamivudine dosed once daily in
HIV-1-infected pediatric subjects aged 3 months through 12 years was evaluated
in 3 trials (PENTA-15 [n = 17], PENTA 13 [n = 19], and ARROW PK [n = 35]). All
3 trials were 2-period, crossover, open-label pharmacokinetic trials of
twice-versus once-daily dosing of abacavir and lamivudine. These 3 trials
demonstrated that once-daily dosing provides similar AUC0-24 to twice-daily
dosing of lamivudine at the same total daily dose when comparing the dosing
regimens within the same formulation (i.e., either the oral solution or the
tablet formulation). The mean Cmax was approximately 80% to 90% higher with
lamivudine once-daily dosing compared with twice-daily dosing.
Table 8: Pharmacokinetic Parameters (Geometric Mean
[95% CI]) after Repeat Dosing of Lamivudine in 3 Pediatric Trials
Age Range |
Trial (Number of Subjects) |
ARROW PK
(n = 35) |
PENTA-13
(n = 19) |
PENTA-15
(n = 17)a |
3-12 years |
2-12 years |
3-36 months |
Formulation |
Tablet |
Solutionb and Tabletc |
Solutionb |
Parameter |
Once Daily |
Twice Daily |
Once Daily |
Twice Daily |
Once Daily |
Twice Daily |
C max (mcg/mL) |
3.17 (2.76, 3.64) |
1.80 (1.59, 2.04) |
2.09 (1.80, 2.42) |
1.11 (0.96, 1.29) |
1.87 (1.65, 2.13) |
1.05 (0.88, 1.26) |
AUC (0-24) (mcg•h/mL) |
13.0 (11.4, 14.9) |
12.0 (10.7, 13.4) |
9.80 (8.64, 11.1) |
8.88 (7.67, 10.3) |
8.66 (7.46, 10.1) |
9.48 (7.89, 11.4) |
a n = 16 for PENTA-15 Cmax. b Solution was
dosed at 8 mg per kg per day.
c Five subjects in PENTA-13 received lamivudine tablets. |
Distribution of lamivudine into cerebrospinal fluid (CSF)
was assessed in 38 pediatric subjects after multiple oral dosing with
lamivudine. CSF samples were collected between 2 and 4 hours postdose. At the
dose of 8 mg per kg per day, CSF lamivudine concentrations in 8 subjects ranged
from 5.6% to 30.9% (mean ± SD of 14.2% ± 7.9%) of the concentration in a
simultaneous serum sample, with CSF lamivudine concentrations ranging from 0.04
to 0.3 mcg per mL.
Limited, uncontrolled pharmacokinetic and safety data are
available from administration of lamivudine (and zidovudine) to 36 infants aged
up to 1 week in 2 trials in South Africa. In these trials, lamivudine clearance
was substantially reduced in 1-week-old neonates relative to pediatric subjects
(aged over 3 months) studied previously. There is insufficient information to
establish the time course of changes in clearance between the immediate
neonatal period and the age-ranges over 3 months old [see ADVERSE REACTIONS].
Geriatric Patients
The pharmacokinetics of lamivudine after administration
of EPIVIR to subjects over 65 years have not been studied [see Use In Specific
Populations].
Male And Female Patients
There are no significant or clinically relevant gender
differences in lamivudine pharmacokinetics.
Racial Groups
There are no significant or clinically relevant racial
differences in lamivudine pharmacokinetics.
Drug Interaction Studies
Effect Of Lamivudine On The Pharmacokinetics Of Other
Agents
Based on in vitro study results, lamivudine at
therapeutic drug exposures is not expected to affect the pharmacokinetics of
drugs that are substrates of the following transporters: organic anion
transporter polypeptide 1B1/3 (OATP1B1/3), breast cancer resistance protein
(BCRP), P-glycoprotein (P-gp), multidrug and toxin extrusion protein 1 (MATE)1,
MATE2-K, organic cation transporter 1 (OCT)1, OCT2, or OCT3.
Effect Of Other Agents On The Pharmacokinetics Of Lamivudine
Lamivudine is a substrate of MATE1, MATE2-K, and OCT2 in
vitro. Trimethoprim (an inhibitor of these drug transporters) has been shown to
increase lamivudine plasma concentrations. This interaction is not considered
clinically significant as no dose adjustment of lamivudine is needed.
Lamivudine is a substrate of P-gp and BCRP; however,
considering its absolute bioavailability (87%), it is unlikely that these
transporters play a significant role in the absorption of lamivudine.
Therefore, coadministration of drugs that are inhibitors of these efflux
transporters is unlikely to affect the disposition and elimination of
lamivudine.
Interferon Alfa
There was no significant pharmacokinetic interaction
between lamivudine and interferon alfa in a trial of 19 healthy male subjects [see
WARNINGS AND PRECAUTIONS].
Ribavirin
In vitro data indicate ribavirin reduces phosphorylation
of lamivudine, stavudine, and zidovudine. However, no pharmacokinetic (e.g.,
plasma concentrations or intracellular triphosphorylated active metabolite
concentrations) or pharmacodynamic (e.g., loss of HIV-1/HCV virologic
suppression) interaction was observed when ribavirin and lamivudine (n = 18),
stavudine (n = 10), or zidovudine (n = 6) were coadministered as part of a
multi-drug regimen to HIV-1/HCV co-infected subjects [see WARNINGS AND
PRECAUTIONS].
Sorbitol (Excipient)
Lamivudine and sorbitol solutions were coadministered to
16 healthy adult subjects in an open-label, randomized-sequence, 4-period,
crossover trial. Each subject received a single 300-mg dose of lamivudine oral
solution alone or coadministered with a single dose of 3.2 grams, 10.2 grams,
or 13.4 grams of sorbitol in solution. Coadministration of lamivudine with
sorbitol resulted in dose-dependent decreases of 20%, 39%, and 44% in the AUC(0-24),
14%, 32%, and 36% in the AUC(∞), and 28%, 52%, and 55% in the Cmax; of
lamivudine, respectively.
Trimethoprim/Sulfamethoxazole
Lamivudine and TMP/SMX were coadministered to 14
HIV-1-positive subjects in a single-center, open-label, randomized, crossover
trial. Each subject received treatment with a single 300-mg dose of lamivudine
and TMP 160 mg/SMX 800 mg once a day for 5 days with concomitant administration
of lamivudine 300 mg with the fifth dose in a crossover design.
Coadministration of TMP/SMX with lamivudine resulted in an increase of 43% ±
23% (mean ± SD) in lamivudine AUC∞, a decrease of 29% ± 13% in lamivudine
oral clearance, and a decrease of 30% ± 36% in lamivudine renal clearance. The
pharmacokinetic properties of TMP and SMX were not altered by coadministration
with lamivudine. There is no information regarding the effect on lamivudine
pharmacokinetics of higher doses of TMP/SMX such as those used in treat PCP.
Zidovudine
No clinically significant alterations in lamivudine or
zidovudine pharmacokinetics were observed in 12 asymptomatic HIV-1-infected
adult subjects given a single dose of zidovudine (200 mg) in combination with
multiple doses of lamivudine (300 mg every 12 hours).
Microbiology
Mechanism Of Action
Lamivudine is a synthetic nucleoside analogue.
Intracellularly, lamivudine is phosphorylated to its active 5'-triphosphate
metabolite, lamivudine triphosphate (3TC-TP). The principal mode of action of
3TC-TP is inhibition of HIV-1 reverse transcriptase (RT) via DNA chain
termination after incorporation of the nucleotide analogue.
Antiviral Activity
The antiviral activity of lamivudine against HIV-1 was
assessed in a number of cell lines including monocytes and fresh human
peripheral blood lymphocytes (PBMCs) using standard susceptibility assays. EC50
values were in the range of 0.003 to 15 microM (1 microM = 0.23 mcg per mL).
The median EC50 values of lamivudine were 60 nM (range: 20 to 70 nM), 35 nM
(range: 30 to 40 nM), 30 nM (range: 20 to 90 nM), 20 nM (range: 3 to 40 nM), 30
nM (range: 1 to 60 nM), 30 nM (range: 20 to 70 nM), 30 nM (range: 3 to 70 nM),
and 30 nM (range: 20 to 90 nM) against HIV-1 clades A-G and group O viruses (n
= 3 except n = 2 for clade B) respectively. The EC50 values against HIV-2
isolates (n = 4) ranged from 0.003 to 0.120 microM in PBMCs. Lamivudine was not
antagonistic to all tested anti-HIV agents. Ribavirin (50 microM) used in the
treatment of chronic HCV infection decreased the anti-HIV-1 activity of
lamivudine by 3.5-fold in MT-4 cells.
Resistance
Lamivudine-resistant variants of HIV-1 have been selected
in cell culture. Genotypic analysis showed that the resistance was due to a
specific amino acid substitution in the HIV-1 reverse transcriptase at codon
184 changing the methionine to either valine or isoleucine (M184V/I).
HIV-1 strains resistant to both lamivudine and zidovudine
have been isolated from subjects. Susceptibility of clinical isolates to
lamivudine and zidovudine was monitored in controlled clinical trials. In
subjects receiving lamivudine monotherapy or combination therapy with
lamivudine plus zidovudine, HIV-1 isolates from most subjects became
phenotypically and genotypically resistant to lamivudine within 12 weeks.
Genotypic And Phenotypic Analysis Of On-Therapy HIV-1
Isolates From Subjects With Virologic Failure
Trial EPV20001
Fifty-three of 554 (10%) subjects enrolled in EPV20001
were identified as virological failures (plasma HIV-1 RNA level greater than or
equal to 400 copies per mL) by Week 48. Twenty-eight subjects were randomized
to the lamivudine once-daily treatment group and 25 to the lamivudine
twice-daily treatment group. The median baseline plasma HIV-1 RNA levels of
subjects in the lamivudine once-daily group and lamivudine twice-daily group
were 4.9 log10 copies per mL and 4.6 log10 copies per mL, respectively.
Genotypic analysis of on-therapy isolates from 22
subjects identified as virologic failures in the lamivudine once-daily group
showed that isolates from 8 of 22 subjects contained a treatment-emergent
lamivudine resistance-associated substitution (M184V or M184I), isolates from 0
of 22 subjects contained treatment-emergent amino acid substitutions associated
with zidovudine resistance (M41L, D67N, K70R, L210W, T215Y/F, or K219Q/E), and
isolates from 10 of 22 subjects contained treatment-emergent amino acid
substitutions associated with efavirenz resistance (L100I, K101E, K103N, V108I,
or Y181C).
Genotypic analysis of on-therapy isolates from subjects
(n = 22) in the lamivudine twice-daily treatment group showed that isolates
from 5 of 22 subjects contained treatment-emergent lamivudine resistance
substitutions, isolates from 1 of 22 subjects contained treatment-emergent
zidovudine resistance substitutions, and isolates from 7 of 22 subjects
contained treatment-emergent efavirenz resistance substitutions.
Phenotypic analysis of baseline-matched on-therapy HIV-1
isolates from subjects (n = 13) receiving lamivudine once daily showed that
isolates from 7 of 13 subjects showed an 85-to 299-fold decrease in
susceptibility to lamivudine, isolates from 12 of 13 subjects were susceptible
to zidovudine, and isolates from 8 of 13 subjects exhibited a 25-to 295-fold
decrease in susceptibility to efavirenz.
Phenotypic analysis of baseline-matched on-therapy HIV-1
isolates from subjects (n = 13) receiving lamivudine twice daily showed that
isolates from 4 of 13 subjects exhibited a 29-to 159-fold decrease in
susceptibility to lamivudine, isolates from all 13 subjects were susceptible to
zidovudine, and isolates from 3 of 13 subjects exhibited a 21-to 342-fold
decrease in susceptibility to efavirenz.
Trial EPV40001
Fifty subjects received lamivudine 300 mg once daily plus
zidovudine 300 mg twice daily plus abacavir 300 mg twice daily and 50 subjects
received lamivudine 150 mg plus zidovudine 300 mg plus abacavir 300 mg all
twice-daily. The median baseline plasma HIV-1 RNA levels for subjects in the 2
groups were 4.79 log10 copies per mL and 4.83 log10 copies per mL,
respectively. Fourteen of 50 subjects in the lamivudine once-daily treatment
group and 9 of 50 subjects in the lamivudine twice-daily group were identified
as virologic failures.
Genotypic analysis of on-therapy HIV-1 isolates from
subjects (n = 9) in the lamivudine once-daily treatment group showed that
isolates from 6 subjects had an abacavir and/or lamivudine
resistance-associated substitution M184V alone. On-therapy isolates from
subjects (n = 6) receiving lamivudine twice daily showed that isolates from 2
subjects had M184V alone, and isolates from 2 subjects harbored the M184V substitution
in combination with zidovudine resistance-associated amino acid substitutions.
Phenotypic analysis of on-therapy isolates from subjects
(n = 6) receiving lamivudine once daily showed that HIV-1 isolates from 4
subjects exhibited a 32-to 53-fold decrease in susceptibility to lamivudine.
HIV-1 isolates from these 6 subjects were susceptible to zidovudine.
Phenotypic analysis of on-therapy isolates from subjects
(n = 4) receiving lamivudine twice daily showed that HIV-1 isolates from 1
subject exhibited a 45-fold decrease in susceptibility to lamivudine and a
4.5-fold decrease in susceptibility to zidovudine.
Pediatrics
Pediatric subjects receiving lamivudine oral solution
concomitantly with other antiretroviral oral solutions (abacavir,
nevirapine/efavirenz, or zidovudine) in ARROW developed viral resistance more
frequently than those receiving tablets. At randomization to once-daily or
twice-daily dosing of EPIVIR plus abacavir, 13% of subjects who started on
tablets and 32% of subjects who started on solution had resistance
substitutions. The resistance profile observed in pediatrics is similar to that
observed in adults in terms of the genotypic substitutions detected and
relative frequency, with the most commonly detected substitutions at M184 (V or
I) [see Clinical Studies].
Cross-Resistance
Cross-resistance has been observed among nucleoside
reverse transcriptase inhibitors (NRTIs). Lamivudine-resistant HIV-1 mutants
were cross-resistant in cell culture to didanosine (ddI). Cross-resistance is
also expected with abacavir and emtricitabine as these select M184V
substitutions.
Clinical Studies
The use of EPIVIR is based on the results of clinical
trials in HIV-1-infected subjects in combination regimens with other
antiretroviral agents. Information from trials with clinical endpoints or a
combination of CD4+ cell counts and HIV-1 RNA measurements is included below as
documentation of the contribution of lamivudine to a combination regimen in
controlled trials.
Adult Subjects
Clinical Endpoint Trial
NUCB3007 (CAESAR) was a multicenter, double-blind,
placebo-controlled trial comparing continued current therapy (zidovudine alone
[62% of subjects] or zidovudine with didanosine or zalcitabine [38% of
subjects]) to the addition of EPIVIR or EPIVIR plus an investigational
non-nucleoside reverse transcriptase inhibitor (NNRTI), randomized 1:2:1. A
total of 1,816 HIV-1-infected adults with 25 to 250 CD4+ cells per mm³ (median
= 122 cells per mm³) at baseline were enrolled: median age was 36 years, 87%
were male, 84% were nucleoside-experienced, and 16% were therapy-naive. The
median duration on trial was 12 months. Results are summarized in Table 9.
Table 9: Number of Subjects (%) with at Least One
HIV-1 Disease Progression Event or Death
Endpoint |
Current Therapy
(n = 460) |
EPIVIR plus Current Therapy
(n = 896) |
EPIVIR plus an NNRTIa plus Current Therapy
(n = 460) |
HIV-1 progression or death |
90 (19.6%) |
86 (9.6%) |
41 (8.9%) |
Death |
27 (5.9%) |
23 (2.6%) |
14 (3.0%) |
a An investigational non-nucleoside reverse
transcriptase inhibitor not approved in the United States. |
Surrogate Endpoint Trials
Dual Nucleoside Analogue Trials
Principal clinical trials in the initial development of
lamivudine compared lamivudine/zidovudine combinations with zidovudine
monotherapy or with zidovudine plus zalcitabine. These trials demonstrated the
antiviral effect of lamivudine in a 2-drug combination. More recent uses of
lamivudine in treatment of HIV-1 infection incorporate it into multiple-drug
regimens containing at least 3 antiretroviral drugs for enhanced viral
suppression.
Dose Regimen Comparison Surrogate Endpoint Trials In Therapy-Naive
Adults
EPV20001 was a multicenter, double-blind, controlled
trial in which subjects were randomized 1:1 to receive EPIVIR 300 mg once daily
or EPIVIR 150 mg twice daily, in combination with zidovudine 300 mg twice daily
and efavirenz 600 mg once daily. A total of 554 antiretroviral treatment-naive
HIV-1-infected adults enrolled: male (79%), white (50%), median age of 35
years, baseline CD4+ cell counts of 69 to 1,089 cells per mm³ (median = 362
cells per mm³), and median baseline plasma HIV-1 RNA of 4.66 log10 copies per
mL. Outcomes of treatment through 48 weeks are summarized in Figure 1 and Table
10.
Figure 1: Virologic Response through Week 48, EPV20001a,b
(Intent-to-Treat)
a Roche AMPLICOR HIV-1 MONITOR.
b Responders at each visit are subjects who had achieved and
maintained HIV-1 RNA less than 400 copies per mL without discontinuation by
that visit.
Table 10: Outcomes of Randomized Treatment through 48
Weeks (Intent-to-Treat)
Outcome |
EPIVIR 300 mg Once Daily plus RETROVIR plus Efavirenz
(n = 278) |
EPIVIR 150 mg Twice Daily plus RETROVIR plus Efavirenz
(n = 276) |
Respondera |
67% |
65% |
Virologic failureb |
8% |
8% |
Discontinued due to clinical progression |
<1% |
0% |
Discontinued due to adverse events |
6% |
12% |
Discontinued due to other reasonsc |
18% |
14% |
a Achieved confirmed plasma HIV-1 RNA less
than 400 copies per mL and maintained through 48 weeks.
b Achieved suppression but rebounded by Week 48, discontinued due to
virologic failure, insufficient viral response according to the investigator,
or never suppressed through Week 48.
c Includes consent withdrawn, lost to follow-up, protocol violation,
data outside the trial-defined schedule, and randomized but never initiated
treatment. |
The proportions of subjects with HIV-1 RNA less than 50
copies per mL (via Roche Ultrasensitive assay) through Week 48 were 61% for
subjects receiving EPIVIR 300 mg once daily and 63% for subjects receiving
EPIVIR 150 mg twice daily. Median increases in CD4+ cell counts were 144 cells
per mm³ at Week 48 in subjects receiving EPIVIR 300 mg once daily and 146 cells
per mm³ for subjects receiving EPIVIR 150 mg twice daily.
A small, randomized, open-label pilot trial, EPV40001,
was conducted in Thailand. A total of 159 treatment-naive adult subjects (male
32%, Asian 100%, median age 30 years, baseline median CD4+ cell count 380 cells
per mm³, median plasma HIV-1 RNA 4.8 log10 copies per mL) were enrolled. Two of
the treatment arms in this trial provided a comparison between lamivudine 300
mg once daily (n = 54) and lamivudine 150 mg twice daily (n = 52), each in
combination with zidovudine 300 mg twice daily and abacavir 300 mg twice daily.
In intent-to-treat analyses of 48-week data, the proportions of subjects with
HIV-1 RNA below 400 copies per mL were 61% (33 of 54) in the group randomized
to once-daily lamivudine and 75% (39 of 52) in the group randomized to receive
all 3 drugs twice daily; the proportions with HIV-1 RNA below 50 copies per mL
were 54% (29 of 54) in the once-daily lamivudine group and 67% (35 of 52) in
the all-twice-daily group; and the median increases in CD4+ cell counts were
166 cells per mm³ in the once-daily lamivudine group and 216 cells per mm³ in
the all-twice-daily group.
Pediatric Subjects
Clinical Endpoint Trial
ACTG300 was a multicenter, randomized, double-blind trial
that provided for comparison of EPIVIR plus RETROVIR (zidovudine) with
didanosine monotherapy. A total of 471 symptomatic, HIV-1-infected
therapy-naive (less than or equal to 56 days of antiretroviral therapy)
pediatric subjects were enrolled in these 2 treatment arms. The median age was 2.7
years (range: 6 weeks to 14 years), 58% were female, and 86% were non-white.
The mean baseline CD4+ cell count was 868 cells per mm³ (mean: 1,060 cells per
mm³ and range: 0 to 4,650 cells per mm³ for subjects aged less than or equal to
5 years; mean: 419 cells per mm³ and range: 0 to 1,555 cells per mm³ for
subjects aged over 5 years) and the mean baseline plasma HIV-1 RNA was 5.0 log10
copies per mL. The median duration on trial was 10.1 months for the subjects receiving
EPIVIR plus RETROVIR and 9.2 months for subjects receiving didanosine
monotherapy. Results are summarized in Table 11.
Table 11: Number of Subjects (%) Reaching a Primary
Clinical Endpoint (Disease Progression or Death)
Endpoint |
EPIVIR plus RETROVIR
(n = 236) |
Didanosine
(n = 235) |
HIV-1 disease progression or death (total) |
15 (6.4%) |
37 (15.7%) |
Physical growth failure |
7 (3.0%) |
6 (2.6%) |
Central nervous system deterioration |
4 (1.7%) |
12 (5.1%) |
CDC Clinical Category C |
2 (0.8%) |
8 (3.4%) |
Death |
2 (0.8%) |
11 (4.7%) |
Once-Daily Dosing
ARROW (COL105677) was a 5-year randomized, multicenter
trial which evaluated multiple aspects of clinical management of HIV-1
infection in pediatric subjects. HIV-1-infected, treatment-naïve subjects aged
3 months to 17 years were enrolled and treated with a first-line regimen
containing EPIVIR and abacavir, dosed twice daily according to World Health
Organization recommendations. After a minimum of 36 weeks on treatment,
subjects were given the option to participate in Randomization 3 of the ARROW
trial, comparing the safety and efficacy of once-daily dosing with twice-daily
dosing of EPIVIR and abacavir, in combination with a third antiretroviral drug,
for an additional 96 weeks. Of the 1,206 original ARROW subjects, 669
participated in Randomization 3. Virologic suppression was not a requirement
for participation: at baseline for Randomization 3 (following a minimum of 36
weeks of twice-daily treatment), 75% of subjects in the twice-daily cohort were
virologically suppressed, compared with 71% of subjects in the once-daily
cohort.
The proportion of subjects with HIV-1 RNA of less than 80
copies per mL through 96 weeks is shown in Table 12. The differences between
virologic responses in the two treatment arms were comparable across baseline
characteristics for gender and age.
Table 12: Virologic Outcome of Randomized Treatment at
Week 96a (ARROW Randomization 3)
Outcome |
EPIVIR plus Abacavir Twice-Daily Dosing
(n = 333) |
EPIVIR plus Abacavir Once-Daily Dosing
(n = 336) |
HIV-1 RNA <80 copies/mLb |
70% |
67% |
HIV-1 RNA ≥80 copies/mLc |
28% |
31% |
No virologic data |
|
|
Discontinued due to adverse event or death |
1% |
<1% |
Discontinued study for other reasonsd |
0% |
<1% |
Missing data during window but on study |
1% |
1% |
a Analyses were based on the last observed
viral load data within the Week 96 window.
b Predicted difference (95% CI) of response rate is -4.5% (-11% to
2%) at Week 96.
c Includes subjects who discontinued due to lack or loss of efficacy
or for reasons other than an adverse event or death, and had a viral load value
of greater than or equal to 80 copies per mL, or subjects who had a switch in
background regimen that was not permitted by the protocol.
d Other includes reasons such as withdrew consent, loss to follow-up,
etc. and the last available HIV-1 RNA less than 80 copies per mL (or missing). |
Analyses by formulation demonstrated the proportion of
subjects with HIV-1 RNA of less than 80 copies per mL at randomization and Week
96 was higher in subjects who had received tablet formulations of EPIVIR and
abacavir (75% [458/610] and 72% [434/601]) than in those who had received
solution formulation(s) (with EPIVIR solution given at weight band-based doses
approximating 8 mg per kg per day) at any time (52% [29/56] and 54% [30/56]),
respectively [see WARNINGS AND PRECAUTIONS]. These differences were
observed in each different age group evaluated.