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Safety and antiviral activity of emtricitabine (FTC) for the treatment of chronic hepatitis B infection: A two-year study
  Journal of Hepatology
July 2005
This manuscript is dedicated to Dr Steven Sacks for his significant contributions to this trial and the treatment of hepatitis B
Robert G. Gish1, Huy Trinh1, Nancy Leung2, Francis K.L. Chan2, Michael W. Fried3, Teresa L. Wright4, Chia Wang5, Jane Anderson6, Elsa Mondou6, Andrea Snow6, Jeff Sorbel6, Franck Rousseau6, Lawrence Corey7
Received 3 September 2004; received in revised form 14 December 2004; accepted 1 February 2005 published online 11 April 2005.
Background/Aims: The aim of this study was to evaluate long term safety and antiviral activity of different doses of emtricitabine given once daily to patients chronically infected with hepatitis B.
Methods: Eligible patients were randomized in a double-blind, parallel study to evaluate 25, 100 or 200mg once daily doses of emtricitabine for 48 weeks. Patients were then followed for an additional 48 weeks on open-label 200mg emtricitabine. Serum HBV DNA, ALT, and hepatitis B serology were measured at regular intervals over the 2 years. Resistance surveillance was performed after 1 and 2 years on viremic samples, i.e. >4700copies/mL.
Emtricitabine was well tolerated and produced a dose proportional antiviral
response. After 2 years, 53% of the patients had serum HBV DNA ≦4700copies/mL, 33% seroconverted to anti-HBe and 85% had normal ALT.
Eighteen percent of the patients who had received 200mg emtricitabine for 2 years developed resistance mutations.
Genotypic analysis of the HBV polymerase was performed on serum samples with HBV DNA >4700copies/mL at week 56 (or week 48). A majority of these HBV DNA levels were increasing above their nadir or had reached and remained at an intermediate level. The 1 year incidence of mutations associated with resistance to emtricitabine (rtM204I/V with or without the rtL180M and rtV173L) were 16, 12 and 9% for dose groups 25, 100, and 200mg, respectively
Conclusions: Emtricitabine was well tolerated and demonstrated a potent antiviral response for up to 2 years in patients with chronic hepatitis B infection. Based on these data, 200mg emtricitabine once daily was chosen as the optimal dose for future hepatitis B studies.
Baseline characteristics
The three dose groups were similar with regard to demographics and baseline characteristics. Patients participating in this study who were nucleoside experienced were patients who had participated in Study FTCB-101 (2 months of emtricitabine monotherapy).
Virologic response
The primary endpoint, AAUCMB for log10 HBV DNA through week 48 showed a statistically significant difference between treatment groups (P=0.003). A numerically greater proportion of patients in the 200mg dose group achieved HBV DNA levels ≦4700copies/mL by week 48 (55% versus 39% and 38% in the 100 and 25mg dose groups, respectively).
Serologic response
Of the 77 patients who were HBeAg positive at baseline, a similar serological response was observed across dose groups with about 23% of the patients having seroconverted to anti-HBe. One patient in the 200mg treatment group lost HBsAg by week 48.
Biochemical response
A summary of ALT results show that although there were numerically more patients in the 25mg treatment arm who had normal ALT values at baseline, by week 48 the majority of patients, irrespective of dose group, had normal ALT values (87%), including those patients with abnormal values at baseline. No dose response relationship was observed. Numerically, a greater proportion of patients treated with 200mg emtricitabine QD for 48 weeks (52% for the 200mg group), achieved the composite endpoint, i.e. HBV DNA levels ≦4700copies/mL and normal ALT values.
Virology, serology and ALT
At week 48, all patients were treated with 200mg emtricitabine QD. At the end of Year 2, sustained virologic and biochemical response was observed in 49% of the patients, i.e. HBV DNA levels ≦4700copies/mL and normal ALT. Genotypic analysis was conducted on serum samples with HBV DNA levels >4700copies/mL at week 96. For a majority of these patients, HBV DNA levels were rebounding and were at a level greater than 105 (10,000). At Year 2, 18% of the patients who had received 200mg emtricitabine QD monotherapy for the 2 years were shown to harbor HBV with mutations associated with resistance to emtricitabine.
HBeAg negative patients
Overall, there were 21 HBeAg negative patients enrolled in the study; none of whom discontinued prior to week 48. Although patients tended to be older (median age 45 years) and had lower baseline HBV DNA levels (6.22log10copies/mL), other baseline characteristics were similar to HBeAg positive patients. All doses of emtricitabine demonstrated potent antiviral activity. For this subpopulation, there was no significant difference across dose groups in the primary endpoint, AAUCMB log10 HBV DNA at week 48. This was because a majority of patients were ≦4700copies/mL at both week 48 (76%) and week 96 (71%). All seven HBeAg negative patients treated with 200mg emtricitabine QD during the first 48 weeks had HBV DNA ≦4700copies/mL at week 48. Ninety-five percent and 100% of the patients had normal ALT values at week 48 and 96, respectively.
Treatment-free follow-up period
After patients completed 96 weeks of treatment and emtricitabine was stopped, patients were followed off treatment for 6 months. Treatment-free follow-up data showed continued virologic response for 19 of 69 patients (28% with HBV DNA levels ≦4700copies/mL), serologic response for 20 of 50 patients (40% seroconversion to anti-HBe), and normal ALT for 38 of 66 patients (58%). Similar relapse rates were observed for both HBeAg positive and HBeAg negative patients for both HBV DNA and ALT, i.e. HBV DNA >LOD and/or ALT abnormal at follow-up week 24 for patients with HBV DNA < LOD and/or ALT normal at week 96. Of the patients who had seroconverted to anti-HBe by week 96 (n=22), four patients reverted to HBeAg positive and one patient lost anti-HBe but remained HBeAg negative at the end of the treatment-free follow-up; the other 17 patients (77%) had stable seroconversion. Of the 78 patients with at least 1 day of follow-up, 15 patients (19%) experienced exacerbation of hepatitis. Generally, patients experienced a rebound in HBV DNA prior to the onset of elevated ALT. None of the patients experienced clinical decompensation and all patients recovered with or without antiviral treatment.
The frequency of discontinuation of randomized therapy due to an AE was comparable between the dose groups (one patient per treatment group). Patients with AEs leading to study drug discontinuation included: (1) Henoch-Schonlein purpura (25mg); (2) dizziness (100mg) and (3) asthenia, elevated AST (200mg). One event was considered serious with a possible relationship to study drug (Henoch-Schonlein purpura). There were two additional serious AEs (SAEs) that occurred within the first year of treatment: (1) headache and vomiting (25mg) and (2) nasal polyps requiring surgery, sinusitis (200mg). Headache and vomiting was considered remotely related to study drug and nasal polyps/sinusitis was considered unrelated to study drug. The overall incidence of AEs was similar between dose groups with most AEs mild (Grade 1) or moderate (Grade 2) in severity. Infection, headache, flu syndrome and abdominal pain were the most frequent AEs. The overall incidence of severe (Grade 3) or life-threatening (Grade 4) AEs and laboratory abnormalities was comparable between dose groups.
Patient disposition
Of the 98 patients enrolled in the study, 92 patients completed 48 weeks of randomized double-blind treatment. Four patients discontinued study prior to week 48 (three due to adverse events, and one due to protocol violation), and per protocol, two patients initiated open-label 200mg emtricitabine QD prior to week 48 because of a suboptimal response (both had viral loads >104copies/mL and had not achieved at least a 2log decrease in HBV DNA). Sixteen patients discontinued emtricitabine therapy between weeks 48 and 96; three of these patients completed treatment but discontinued at week 96. A total of 64 patients completed 24 weeks of treatment-free follow-up after 96 weeks of treatment.
Author Discussion
Emtricitabine was well-tolerated and produced a potent antiviral effect at all three doses studied. Virologic results were consistent with the findings from the early 56 day dose ranging study where pharmacodynamic modeling showed that 94% of the maximal activity was reached with the 200mg once-daily dose [18]. A dose response relationship was observed in the present study for virologic and genotypic endpoints, but no difference was observed for serologic (seroconversion to anti-HBe) or biochemical endpoints (normal ALT).
At Year 1, among patients given emtricitabine 200mg QD, 55% had HBV DNA ≦4700copies/mL, 19% seroconverted to anti-HBe, 84% had normal ALT and 9% developed resistance mutations. The observed numerical decrease in the incidence of resistance mutations as the dose of emtricitabine increased (16, 12, and 9% in the 25, 100, and 200mg groups, respectively) suggests an inverse relationship between antiviral potency and the risk of emergence of viral resistance with this drug. The composite endpoint, HBV DNA ≦4700copies/mL and normal ALT, was achieved in a numerically greater proportion of patients in the 200mg group at week 48 relative to other dose groups. Most patients had clinically significant virologic suppression after 1 year of treatment as defined by a viral load below 105copies/mL (HBeAg positive patients) or below 104copies/mL (HBeAg negative patients) [4,28]. During the second year, patients essentially maintained their response.
Emtricitabine was well-tolerated and no dose-dependent toxicities were identified. Most adverse events were mild to moderate and there were few Grade 3 and 4 AEs or laboratory abnormalities observed over the 2-year period. Within 6 months after stopping emtricitabine, the frequency of post-treatment exacerbation was comparable with what has been reported for adefovir and lamivudine [20,21].
Though historical comparisons are limited by the variability in patient populations, the serologic, biochemical and genotypic response was comparable to currently approved therapies. At Year 1, the overall rate of seroconversion to anti-HBeAg and ALT normalization for emtricitabine compared to published rates for interferon, adefovir dipivoxil, and lamivudine [6,8,10,12,22]. Additionally, the Year 2 results were comparable with HBV DNA, ALT and serology data published for both lamivudine and adefovir [26,27]. The rate of resistance mutations appeared linear for patients treated with 200mg emtricitabine for 1 and 2 years, i.e. 9 and 18%, respectively. And although the rate of resistance mutations was greater for the emtricitabine treated patients compared to published data for adefovir dipivoxil at 1, 2 or 3 years, the resistance rate with 200mg emtricitabine appeared to be lower than resistance rate published for lamivudine [6,8,10,12,22-25].
In conclusion, emtricitabine had potent antiviral activity in both HBeAg positive and HBeAg negative patients at a dose of 200mg per day for up to 2 years. Two hundred milligram of emtricitabine was well-tolerated for up to 2 years and emtricitabine resistant mutations developed in 18% of the patients. Based on these results, 200mg emtricitabine QD was selected as the optimal dose for use in Phase 3 clinical trials.
Infection with hepatitis B virus (HBV) is a major health problem with about 400 million people chronically infected in the world. It is estimated that 1-2 million persons will die every year from HBV-related liver diseases (e.g. primary from hepatocellular carcinoma or cirrhosis of the liver) making chronic HBV one of the top 10 causes of death worldwide [1-5]. With the use of antiviral therapy, delay in disease progression is achieved by suppression of viral replication. Currently available treatments for chronic HBV infection are responsible for significant improvement in patient outcomes; however they can be frequently associated with side-effects, suboptimal response and selection of antiviral resistant strains leading to clinical failure [6-13].
(5-Fluoro-1-[(2R,5S)-2-(hydroxymethyl)-[1,3]oxathiolan-5-yl]cytosine, FTC) is a pyrimidine analogue, which has been shown to be a potent and selective inhibitor of Human Immunodeficiency Virus (HIV-1) and HBV. Specifically, emtricitabine inhibits HBV DNA polymerase and HIV-1 reverse transcriptase (RT) both in vivo and in vitro [14-17].
Emtricitabine is anabolized to its triphosphate form which is the active moiety that inhibits the polymerase. The anti-HBV activity of emtricitabine has been demonstrated in the woodchuck hepatitis model as well as in a short term (56 days) dose ranging study in man [18,19]. In the initial human trial, emtricitabine was well-tolerated and showed significant antiviral activity at all doses tested.
To confirm the dose of emtricitabine for HBV infection, three doses of emtricitabine (25mg QD, 100mg QD and 200mg QD) were compared in this prospective randomized double-blind clinical trial for 1 year. Patients were then treated with open-label 200mg emtricitabine for an additional year at the end of the randomized phase.
Patients and methods

The study was conducted at six sites in North America and one site in Hong Kong. All sites obtained protocol approval from their institutional review board or ethics committees, and an informed consent was obtained for each patient prior to enrollment into the study. Eligible patients included HBeAg negative or positive men and women 18-70 years of age, chronically infected with HBV (HBsAg positive for more than 6 months), with detectable serum HBV DNA levels (>3.0MEq/mL by Chiron HBV Quantiplex™ assay). In addition, patients could be either nucleoside naïve or have limited exposure to emtricitabine (less than 2 months of exposure). Patients were not eligible if they: had decompensated liver disease; were co-infected with HIV, hepatitis C or D virus; used interferon within 3 months, or nucleoside analogues within 60 days of screening or for more than 2 months; were pregnant or lactating. Additionally, patients with the following laboratory abnormalities at screening were excluded: ALT or AST>10ULN, total bilirubin >2ULN, prothrombin time (PT) less than 60% of control or >1.5ULN, neutrophil count <1000cells/mm3, platelet count <75,000cells/mm3 and hemoglobin <9.2g/deciliter (dL) for men and <8.8g/dL for women.
Study design
This was a Phase 2, randomized, double-blind, multi-center, dose-ranging study. Patients were randomized to one of three different once daily doses of emtricitabine (25, 100 and 200mg) and treated for 48 weeks. Randomization was stratified based on HBV DNA levels at screening (<500 or ≥500MEq/mL) and prior exposure to emtricitabine. Patients returned to the clinic for routine laboratory safety assessments (hematology, biochemistry and urinalysis), physical examinations and vital signs. Serum was assayed for HBV DNA and hepatitis HBe and HBs antigens. Patients initiated open-label 200mg emtricitabine at week 48 and continued on emtricitabine through week 96. After patients discontinued therapy, they were followed off treatment for up to an additional 6 months. Patients were monitored for both efficacy and safety. Exacerbation of hepatitis was defined in the protocol a priori as an elevation in liver transaminases either to a level 20ULN or to a level greater than 10 above the lowest on-study value.
Serum samples were collected at study visits and used for serum HBV DNA analysis and resistance surveillance. Serum HBV DNA was analyzed both during and after treatment using the Digene HBV DNA Test Hybrid Capture II assay with a lower limit of detection of 4700copies/mL. This assay is a signal amplification hybridization microplate assay that uses chemiluminescence for the detection and quantification of HBV DNA in human serum. Resistance surveillance was performed using dideoxy-sequencing technology and the primers used for amplification allowed for sequence analysis for domains A through E (amino acids rt75-rt255) of the HBV Polymerase (Pol). Resistance surveillance was performed on all patients with detectable viremia at week 56 (or week 48) and week 96 and included all genotypic changes from baseline. The overall incidence of mutations associated with resistance to emtricitabine (rtM204I/V with or without the rtL180M and rtV173L) was determined by dose group. Additionally, sequence from amino acid 67 through 226 of the small surface antigen was used to determine baseline genotype.
Statistical analysis
The primary population for the efficacy and safety analyses was the Intent-to-Treat population, defined as all randomized patients who were dispensed at least one dose of study medication. The primary safety parameter was permanent discontinuation of emtricitabine as the result of an adverse event (tolerability failure). For efficacy, the primary parameter was serum HBV DNA; log10 HBV DNA level was evaluated and compared across dose groups using the AAUCMB through week 48 as the primary endpoint. The AAUCMB, derived from the area under the curve (AUC), was defined as the area of the trapezoid under the response-time curve divided by time to the last available evaluation of the patient minus the baseline value. Patients with at least one post-baseline evaluation were included in these analyses.
Secondary parameters included the comparison across dose groups through week 48 and the overall response at week 96 of the proportion of patients with: HBeAg or HBsAg loss, seroconversion to anti-HBe or anti-HBs, ALT normalization, normal ALT, undetectable HBV DNA, emtricitabine resistant mutations, adverse events (AEs) and laboratory abnormalities. Additional secondary parameters included log10 serum HBV DNA change from baseline and ALT change from baseline. For continuous data, the van Elteren test, stratifying by screening HBV DNA (<500 or ≥500MEq/mL) and previous experience to emtricitabine was used to compare dose groups. This test was used as an overall test, as well as for all pair-wise comparisons between dose groups for the first 48 weeks of the study. For categorical data, a Cochran-Mantel-Haenszel test, stratified as above, was used as an overall test as well as for all pair-wise comparisons for the first 48 weeks of the study. In Year 1, HBV DNA and serology data were analyzed using missing=failure methodology, whereas in Year 2 which was an extension to the original protocol, all analyses were conducted using only observed data.
Sample size
A sample size of 33 patients per treatment arm provided 97% power to detect a 0.5log10 difference between dose groups in AAUCMB (serum HBV DNA) assuming a common standard deviation of 0.5log10copies/mL and an alpha risk of 0.05 using a two-sided test.
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