CLINICAL PHARMACOLOGY
Mechanism of Action
Tyzeka is an antiviral drug [see
Microbiology].
Pharmacodynamics
In a randomized, partially single-blinded, placebo and
active-controlled, four-period crossover trial, 53 healthy subjects were
administered Tyzeka 600 mg, a supratherapeutic Tyzeka 1800 mg dose, placebo,
and moxifloxacin 400 mg. After 7 days of dosing, Tyzeka did not prolong the QT
interval. The maximum placebo-adjusted mean (upper 1-side 95% CI) change from
baseline in QTcF on day 7 were 3.4 msec (5.9 msec) for the 600 mg and 4.4 msec
(6.9 msec) for the 1800 mg dosing regimens.
Pharmacokinetics in Adults
The single- and multiple-dose pharmacokinetics of Tyzeka
were evaluated in healthy subjects and in patients with chronic hepatitis B.
Tyzeka pharmacokinetics are similar between both populations.
Absorption and Bioavailability
Following oral administration of Tyzeka 600 mg once-daily
in healthy subjects (n=12), steady state peak plasma concentration (Cmax) was
3.69 ± 1.25 microgram per mL (mean ± SD) which occurred between 1 and 4 hours
(median 2 hours), AUC was 26.1 ± 7.2 microgram * hour per mL (mean ± SD), and
trough plasma concentrations (Ctrough) were approximately 0.2-0.3 microgram per
mL. Steady state was achieved after approximately 5 to 7 days of once-daily
administration with ~1.5-fold accumulation, suggesting an effective half-life
of ~15 hours.
Effects of Food on Oral Absorption
Tyzeka absorption and exposure were unaffected when a
single 600 mg dose was administered with a high-fat (~55 g), high-calorie (~950
kcal) meal. Tyzeka may be taken with or without food.
Distribution
In vitro binding of telbivudine to human plasma proteins
is low (3.3%). After oral dosing, the estimated apparent volume of distribution
is in excess of total body water, suggesting that telbivudine is widely
distributed into tissues. Telbivudine was equally partitioned between plasma
and blood cells.
Metabolism and Elimination
No metabolites of telbivudine were detected following
administration of [14C]-telbivudine in humans. Telbivudine is not a
substrate, or inhibitor of the cytochrome P450 (CYP450) enzyme system.
After reaching the peak concentration, plasma
concentrations of Tyzeka declined in a biexponential manner with a terminal
elimination half-life (T½) of 40-49 hours. Tyzeka is eliminated primarily by
urinary excretion of unchanged drug. The renal clearance of Tyzeka approaches
normal glomerular filtration rate suggesting that passive diffusion is the main
mechanism of excretion. Approximately 42% of the dose is recovered in the urine
over 7 days following a single 600 mg oral dose of Tyzeka. Because renal
excretion is the predominant route of elimination, patients with moderate to
severe renal dysfunction and those undergoing hemodialysis require a dose
regimen adjustment [see DOSAGE AND ADMINISTRATION].
Special Populations
Gender: There are no significant gender-related
differences in Tyzeka pharmacokinetics.
Race: There are no significant race-related
differences in Tyzeka pharmacokinetics.
Pediatrics and Geriatrics: Pharmacokinetic
studies have not been conducted in children or elderly subjects.
Renal Impairment: Single-dose pharmacokinetics of
Tyzeka have been evaluated in subjects (without chronic hepatitis B) with
various degrees of renal impairment (as assessed by creatinine clearance).
Based on the results shown in Table 4, adjustment of the dose regimen for
Tyzeka is recommended in patients with creatinine clearance of less than 50 mL
per min [see DOSAGE AND ADMINISTRATION].
Table 4 : Pharmacokinetic Parameters (mean ± SD) of
Tyzeka in Subjects with Various Degrees of Renal Function
|
Renal Function (Creatinine Clearance in mL/min |
Normal (greater than 80)
(n=8) 600 mg |
Mild (50-80) (n=8) 600 mg
(n=6) 200 mg |
Moderate (30-49)
(n=8) 400 mg |
Severe (less than 30) |
ESRD/Hemodialysis
(n=6) 200 mg |
Cmax (μg/mL) |
3.4 ± 0.9 |
3.2 ± 0.9 |
2.8 ± 1.3 |
1.6 ± 0.8 |
2.1 ± 0.9 |
AUC0-INF (μg•hr/mL) |
28.5 ± 9.6 |
32.5 ± 10.1 |
36.0 ± 13.2 |
32.5 ± 13.2 |
67.4 ± 36.9 |
CLRENAL (L/hr) |
7.6 ± 2.9 |
5.0 ± 1.2 |
2.6 ± 1.2 |
0.7 ± 0.4 |
|
Renally Impaired Subjects on
Hemodialysis: Hemodialysis (up to 4 hours) reduces systemic Tyzeka
exposure by approximately 23%. Following dose regimen adjustment for creatinine
clearance [see DOSAGE AND ADMINISTRATION], no additional dose
modification is necessary during routine hemodialysis. When administered on
hemodialysis days, Tyzeka should be administered after hemodialysis.
Hepatic Impairment: The pharmacokinetics of
Tyzeka following a single 600 mg dose have been studied in subjects (without
chronic hepatitis B) with various degrees of hepatic impairment. There were no
changes in Tyzeka pharmacokinetics in hepatically impaired subjects compared to
unimpaired subjects. Results of these studies indicate that no dosage
adjustment is necessary for patients with hepatic impairment.
Drug Interactions
Drug-drug interaction studies
show that lamivudine, adefovir dipivoxil, cyclosporine, pegylated interferon
alfa2a, and tenofovir disoproxil fumarate do not alter Tyzeka pharmacokinetics.
In addition, Tyzeka does not alter the pharmacokinetics of lamivudine, adefovir
dipivoxil, cyclosporine, or tenofovir disoproxil fumarate. No definitive
conclusion could be drawn regarding the effects of Tyzeka on the
pharmacokinetics of pegylated interferon alfa-2a due to the high
inter-individual variability of pegylated interferon alfa-2a concentrations. At
concentrations up to 12 times that in humans, telbivudine did not inhibit in
vitro metabolism mediated by any of the following human hepatic microsomal
cytochrome P450 (CYP) isoenzymes known to be involved in human medicinal
product metabolism: 1A2, 2C9, 2C19, 2D26, 2E1, and 3A4. Based on the above
results and the known elimination pathway of telbivudine, the potential for
CYP450-mediated interactions involving telbivudine with other medicinal
products is low.
Microbiology
Mechanism of Action
Telbivudine is a synthetic
thymidine nucleoside analogue with activity against HBV DNA polymerase. It is
phosphorylated by cellular kinases to the active triphosphate form, which has
an intracellular half-life of 14 hours. Telbivudine 5'-triphosphate inhibits
HBV DNA polymerase (reverse transcriptase) by competing with the natural
substrate, thymidine 5'-triphosphate. Incorporation of telbivudine
5'-triphosphate into viral DNA causes DNA chain termination. Telbivudine is an
inhibitor of both HBV first strand (EC50 value = 1.3 ±
1.6 micromolar) and second
strand synthesis (EC50 value = 0.2 ± 0.2 micromolar). Telbivudine
5'-triphosphate at concentrations up to 100 micromolar did not inhibit human
cellular DNA polymerases α, β, or γ. No appreciable
mitochondrial toxicity was observed in HepG2 cells treated with telbivudine at
concentrations up to 10 micromolar.
Antiviral Activity
The antiviral activity of
telbivudine was assessed in the HBV-expressing human hepatoma cell line 2.2.15,
as well as in primary duck hepatocytes infected with duck hepatitis B virus.
The concentration of telbivudine that effectively inhibited 50% of viral DNA
synthesis (EC50) in both systems was approximately 0.2 micromolar. The anti-HBV
activity of telbivudine was additive with adefovir in cell culture, and was not
antagonized by the HIV NRTIs didanosine and stavudine. Telbivudine was not
antagonistic to the anti-HIV activity of abacavir, didanosine, emtricitabine,
lamivudine, stavudine, tenofovir, or zidovudine. Transient reductions in HIV-1
RNA have been seen in some patients after administration of telbivudine in the
absence of antiretroviral therapy. The clinical significance of these
reductions has not been determined.
Resistance
Trial NV-02B-007 (007 GLOBE)
In an as-treated analysis of
the Phase III global registration trial, 59% (251/429) of treatment-naïve
HBeAg-positive and 89% (202/227) of treatment-naïve HBeAg-negative subjects
receiving Tyzeka 600 mg once daily achieved undetectable serum HBV DNA levels
(less than 300 copies per mL) by Week 52. Of those who continued treatment
beyond Week 52, 58% (243/418) and 85% (190/224) of HBeAg-positive and
HBeAg-negative Tyzeka recipients, respectively, had undetectable HBV DNA at
Week 104 (or at the end of dosing in treatment Year 2).
Genotypic analysis of paired
baseline and treatment failure isolates from 181 evaluable subjects with
amplifiable HBV DNA and greater than or equal to 16 weeks of Tyzeka treatment
showed that the rtM204I/V substitution was associated with virologic failure
(HBV DNA greater than or equal to 1,000 copies per mL) and virologic rebound
(HBV DNA greater than or equal to 1 log10 increase above nadir). The rtM204I/V
substitution was detectable in isolates from 78% (142/181) of evaluable
subjects, and was frequently found with substitutions rtL80I/V and rtL180M. The
rtM204I/V substitution was found infrequently with rtV27A, rtL82M, rtV173L,
rtT184I/S, rtA200V, rtL229F/V/W, and rtR289K substitutions. The HBV of 16
subjects developed rtA181S/T amino acid substitutions while receiving Tyzeka. Eight
of these 16 subjects had outgrowth of HBV expressing an rtM204I/V substitution
without the rtA181 substitution and 1 subject's HBV had both the rtM204I and
rtA181T substitutions.
Trial CLDT600A2303
After 2 years of Tyzeka
monotherapy in the 007 GLOBE trial, 77% (505/656) of subjects entered the
open-label CLDT600A2303 extension trial to continue Tyzeka for up to 2
additional years, including 349 subjects who had undetectable levels of HBV DNA
and 156 subjects who were viremic at entry. The rtM204I/V substitution was
detectable in the virus from 83% (39/47) of the subjects losing viral
suppression and having evaluable genotypic data. Of evaluable viremic subjects
entering the extension, 25/33 (76%) developed rtM204I/V substitutions. Overall,
64 subjects developed genotypic resistance to Tyzeka with evidence of emerging
rtM204I/V substitutions during the 2 years of Tyzeka treatment in this
extension trial.
Subjects with higher baseline
viral load had higher rates of genotypic resistance to Tyzeka, while subjects
who achieved HBV DNA levels less than 300 copies per mL at Week 24 had lower
rates of genotypic resistance to Tyzeka. The cumulative frequency of genotypic
resistance (emergence of the rtM204I/V substitution) to Tyzeka in nucleos(t)ide
treatment-naïve subjects was 7% and 22% at Weeks 52 and 104 of the controlled
007 GLOBE trial, and 30% and 35% at Weeks 156 and 208 of the open-label
extension trial (CLDT600A2303), respectively (Table 5).
One-hundred-sixty-seven
subjects (25% of those in the 007 GLOBE trial) were treated with Tyzeka
according to current dosing recommendations [see INDICATIONS AND USAGE].
Eighty-four percent (140/167) of these subjects qualified at 24 weeks for
continued Tyzeka treatment (HBV DNA less than 300 copies per mL). Retrospective
calculation of the cumulative rate of genotypic resistance to Tyzeka for this
subgroup of subjects was 0%, 3%, 12%, and 16% at Weeks 52, 104, 156, and 208,
respectively (Table 5).
Table 5 : Cumulative Rates
of Genotypic Resistance to Tyzeka through Week 208
Trial |
|
Cumulative genotypic resistance rate1 |
Overall study population |
Subjects treated with Tyzeka according to current dosing recommendations2 |
NV-02B-007 (007 GLOBE trial) |
Week 52 |
7% |
0% |
Week 104 |
22% |
3% |
CLDT600A2303 (104-week extension trial) |
Week 156 |
30% |
12% |
Week 208 |
35% |
16% |
1The cumulative rates of genotypic resistance to Tyzeka were
calculated using the formula previously described by Pawlotsky et al. (2008).
2Tyzeka dosing recommendations are provided in this Package Insert
[see INDICATIONS AND USAGE and DOSAGE AND ADMINISTRATION]. |
Cross-Resistance
Cross-resistance has been
observed among HBV nucleos(t)ide analogues. In cell-based assays,
lamivudineresistant HBV strains expressing either the rtM204I substitution or
the rtL180M/rtM204V double substitution had greater than or equal to 1,000-fold
reduced susceptibility to telbivudine. Telbivudine retained wild-type
phenotypic activity (1.2-fold reduction) against HBV expressing rtM204V alone.
Most subjects (92%, 155/169) whose virus developed lamivudine
resistance-associated substitutions (rtM204I/V) during 2 years of lamivudine
treatment in the 007 GLOBE trial remained viremic (HBV DNA greater than 300
copies per mL) after up to 2 years of Tyzeka monotherapy in the CLDT600A2303
extension trial, including 91% (50/55) of the subjects with the rtM204V
substitution.
HBV encoding the adefovir
resistance-associated substitution rtA181V showed 3- to 5-fold reduced
susceptibility to telbivudine in cell culture. The rtA181S and rtA181T
substitutions conferred 2.7- and 3.5-fold reductions in susceptibility to
telbivudine, respectively. The rtA181T substitution is associated with
decreased clinical response in subjects with HBV treated with adefovir and
entecavir. HBV encoding the adefovir resistance-associated substitution rtN236T
remained susceptible to telbivudine.
Clinical Studies
Clinical Experience in
Nucleoside-Naïve Adults
The safety and efficacy of
long-term (104-week) Tyzeka treatment were evaluated in one active-controlled,
clinical trial (NV-02B-007 GLOBE Trial) that included 1,367 subjects with
chronic hepatitis B and a smaller supportive trial (NV-02B-015) that included
332 subjects. Subjects were 16 years of age or older, with chronic hepatitis B,
evidence of HBV infection with viral replication (HBsAg-positive,
HBeAg-positive or HBeAg-negative, HBV DNA detectable by a PCR assay), and
elevated ALT levels greater than or equal to 1.3 x ULN, no evidence of hepatic
decompensation, and chronic inflammation on liver biopsy compatible with
chronic viral hepatitis.
NV-02B-007 GLOBE Trial
The Week 52 and Week 104
results of the 007 GLOBE trial are summarized below.
The 007 GLOBE trial was a Phase
III, randomized, double-blind, multinational trial of Tyzeka 600 mg once daily
compared to lamivudine 100 mg once daily for a treatment period of 104 weeks in
1,367 (n= 680 Tyzeka; n=687 lamivudine) nucleoside-naïve chronic hepatitis B
HBeAg-positive and HBeAg-negative subjects. The primary data analysis was
conducted after all subjects had reached Week 52.
HBeAg-positive Subjects: (n= 458 Tyzeka; n= 463 lamivudine) The mean age of subjects
was 32 years, 74% were male, 82% were Asian, 12% were Caucasian, and 6% had
previously received alfa-interferon therapy. At baseline, subjects had a mean
Knodell Necroinflammatory Score greater than or equal to 7; mean serum HBV DNA
as measured by Roche COBAS Amplicor® PCR assay was 9.52 log10 copies
per mL; and mean serum ALT was 153 IU per L. Pre- and post-liver biopsy samples
were adequate for 86% of subjects.
HBeAg-negative Subjects: (n=222 Tyzeka; n= 224
lamivudine)The mean age of subjects was 43 years, 77% were male, 65% were
Asian, 23% were Caucasian, and 11% had previously received alfa-interferon
therapy. At baseline, subjects had a mean Knodell Necroinflammatory Score
greater than or equal to 7; mean serum HBV DNA as measured by Roche COBAS
Amplicor® PCR assay was 7.54 log10 copies per mL; and mean serum ALT
was 140 IU per L. Pre- and post-liver biopsy samples were adequate for 92% of
subjects.
Clinical Results
Clinical and virologic efficacy
endpoints were evaluated separately in the HBeAg-positive and HBeAg-negative
subject populations.
The primary endpoint of
Therapeutic Response at Week 52 was a composite endpoint requiring suppression
of HBV DNA to less than 5 log10 copies per mL in conjunction with either loss
of serum HBeAg or ALT normalization. Key secondary endpoints included
histologic response, ALT normalization, and measures of virologic response.
At Week 52, in HBeAg-positive
subjects, 75% of Tyzeka subjects and 67% of lamivudine subjects had a
Therapeutic Response; in HBeAg-negative subjects, 75% of Tyzeka subjects and
77% of lamivudine subjects had a Therapeutic Response.
Analysis of the histological
response at Week 52 is shown in Table 6.
Table 6 : Histological
Improvement and Change in Ishak Fibrosis Score at Week 52 (007 GLOBE Trial)
|
HBeAg-positive (n=797) |
HBeAg-negative (n=417) |
Tyzeka 600 mg
(n=399)1 |
Lamivudine 100 mg
(n=398)1 |
Tyzeka 600 mg
(n=205)1 |
Lamivudine 100 mg
(n=212)1 |
Histologic Response2 |
Improvement |
69% |
60% |
69% |
68% |
No Improvement |
19% |
26% |
23% |
25% |
Missing Week 52 Biopsy |
12% |
15% |
8% |
7% |
Ishak Fibrosis Score3 |
Improvement |
41% |
46% |
48% |
44% |
No Change |
39% |
32% |
34% |
43% |
Worsening |
9% |
7% |
10% |
5% |
Missing Week 52 Biopsy |
12% |
15% |
8% |
7% |
1Subjects with greater than or equal to one dose of trial
drug with evaluable baseline liver biopsies and baseline Knodell Necroinflammatory
Score greater than or equal to 2
2Histologic Response defined as greater than or equal to 2 point
decrease in Knodell Necroinflammatory Score from baseline with no worsening of
the Knodell Fibrosis Score
3For Ishak Fibrosis Score, improvement defined as greater than or
equal to a 1-point reduction in Ishak Fibrosis Score from baseline to Week 52 |
Subjects were eligible to
continue blinded treatment to Week 104. In the ITT population, 624/680 (92%)
Tyzeka recipients and 599/687 (87%) lamivudine recipients completed trial
treatment to Week 104. At Week 104, in HBeAg-positive subjects, 63% of Tyzeka subjects
and 48% of lamivudine subjects had a Therapeutic Response, while in
HBeAg-negative subjects 78% of Tyzeka subjects and 66% of lamivudine subjects
had a Therapeutic Response.
Selected virologic,
biochemical, and serologic outcome measures at Weeks 52 and 104 are shown in
Table 7.
Table 7 : Virological,
Biochemical and Serologic Endpoints at Weeks 52 and 104 (007 GLOBE Trial)
Response Parameter |
HBeAg-positive
(n=921) |
HBeAg-negative
(n=446) |
Tyzeka 600 mg
(n=458) |
Lamivudine 100 mg
(n=463) |
Tyzeka 600 mg
(n=222) |
Lamivudine 100 mg
(n=224) |
Week 52 |
Week 104 |
Week 52 |
Week 104 |
Week 52 |
Week 104 |
Week 52 |
Week 104 |
Mean HBV DNA Reduction from Baseline (log10 copies/mL) ± SEM1 |
-6.45 (0.11) |
-5.74 (0.15) |
-5.54 (0.11) |
-4.42 (0.15) |
-5.23 (0.13) |
-5.00 (0.15) |
-4.40 (0.13) |
-4.17 (0.16) |
% Subjects HBV DNA undetectable by PCR |
60% |
56% |
40% |
39% |
88% |
82% |
71% |
57% |
ALT Normalization2 |
77% |
70% |
75% |
62% |
74% |
78% |
79% |
70% |
HBeAg Seroconversion3 |
23% |
30% |
22% |
25% |
NA |
NA |
NA |
NA |
HBeAg Loss3 |
26% |
35% |
23% |
29% |
NA |
NA |
NA |
NA |
1Roche COBAS Amplicor® Assay (LLOQ less than or equal to 300
copies/mL).
2ALT normalization assessed only in subjects with ALT greater than
ULN at baseline.
3HBeAg seroconversion and loss assessed only in subjects with
detectable HBeAg at baseline. |
Subjects who achieved
non-detectable HBV DNA levels at 24 weeks were more likely to undergo e-antigen
seroconversion, achieve undetectable levels of HBV DNA, normalize ALT, and were
less likely to develop resistance at one and two years.
NV-02B-015 Trial
The efficacy results of the 007
GLOBE trial were supported by results of trial NV-02B-015. This was a Phase
III, randomized, double-blind, trial of Tyzeka 600 mg once daily compared to
lamivudine 100 mg once daily for a treatment period of 104 weeks in 332 (n=167
Tyzeka; n=165 lamivudine) nucleoside-naïve chronic hepatitis B HBeAg-positive
and HBeAg-negative Chinese subjects. The primary efficacy endpoint was serum
HBV DNA reduction from baseline. In this trial, the composite endpoint
Therapeutic Response was a key secondary endpoint. Histological response was
not assessed as an outcome measure in this trial.
Clinical Results
Among HBeAg-positive subjects
(n=147 Tyzeka; n=143 lamivudine) results for key endpoints at Week 104 included
Therapeutic Response (66% vs. 41%), mean HBV DNA reduction (-5.47 vs. -3.97 log10
copies per mL), HBV DNA PCR negativity (58% vs. 34%), ALT normalization (73%
vs. 59%), HBeAg loss (40% vs. 28%) and HBeAg seroconversion (29% vs. 20%), for Tyzeka
and lamivudine, respectively. Because the number of HBeAg-negative subjects in
this trial was small (n=42), definitive conclusions could not be drawn
regarding efficacy outcomes in this subpopulation.