Objective Little clinical data are available regarding the optimal treatment of patients who harbour adefovir-resistant HBV.
Design In this multicentre trial, patients who had adefovir-resistant HBV with serum HBV DNA levels >60 IU/mL were randomised to receive tenofovir disoproxil fumarate (TDF, 300 mg/day) monotherapy (n=50) or TDF and entecavir (ETV, 1 mg/day) combination therapy (TDF/ETV, n=52) for 48 weeks. All who completed 48 weeks in either group received TDF monotherapy for 48 additional weeks.
Results Baseline characteristics were comparable between groups, including HBV DNA levels (median, 3.38 log10 IU/mL). All patients had adefovir-resistant HBV mutations; rtA181V/T and/or rtN236T. The proportion of patients with HBV DNA <15 IU/mL was not significantly different between the TDF-TDF and TDF/ETV-TDF groups at weeks 48 (62% vs 63.5%; p=0.88) and 96 (64% vs 63.5%; p=0.96). The mean change in HBV DNA levels from baseline was not significantly different between groups at week 48 (−3.03 log10 IU/mL vs −3.31 log10 IU/mL; p=0.38). Virological breakthrough occurred in one patient on TDF-TDF and two patients on TDF/ETV-TDF over 96 weeks; all were attributed to poor drug adherence. At week 96, five and two patients in the TDF-TDF and TDF/ETV-TDF groups, respectively, retained some of their baseline resistance mutations (p=0.44). None developed additional resistance mutations. Safety profiles were comparable in the two groups.
Conclusions In patients with adefovir-resistant HBV and multiple-drug failure, TDF monotherapy provided a virological response comparable to that of TDF and ETV combination therapy, and was safe up to 96 weeks.
Trial registration number NCT01639066.
- ANTIVIRAL THERAPY
- DRUG RESISTANCE
- HEPATITIS B
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Significance of this study
What is already known on this subject?
Patients with persistent drug-resistant HBV viraemia are more likely to suffer hepatitis flares, disease progression and to die than those without drug-resistant HBV.
Monotherapy with tenofovir disoproxil fumarate (TDF) is efficacious in patients with lamivudine-resistant, entecavir (ETV)-resistant or adefovir dipivoxil (ADV)-refractory HBV.
In vitro studies show that HBV strains expressing the ADV resistance-associated substitutions demonstrate reduced susceptibility to tenofovir.
What are the new findings?
The proportion of patients with virological response and the mean change in HBV DNA levels from baseline was not significantly different between the TDF monotherapy and TDF plus ETV combination therapy groups at week 48 in heavily pretreated patients with HBV mutants resistant to multiple drugs including ADV.
The extension of TDF monotherapy for 96 weeks showed durable viral suppression. The switch from TDF/ETV combination to TDF monotherapy after 48 weeks resulted in an effective viral suppression in most patients.
Few patients in both treatment groups retained their baseline resistance mutations at weeks 48 and 96. None developed additional resistance mutations.
In a subgroup of patients who had double ADV-resistance mutations, that is, both rtA181T/V and rtN236T, the decrease in serum HBV DNA levels tended to be less in the TDF group than in the TDF/ETV-TDF group.
How might it impact on clinical practice in the foreseeable future?
TDF monotherapy may be a treatment option for patients with ADV-resistant HBV.
TDF plus ETV combination therapy might be more beneficial than TDF monotherapy in patients who had double ADV-resistance mutations (both rtA181T/V and rtN236T).
High serum HBV DNA levels are an independent risk factor for disease progression to cirrhosis and hepatocellular carcinoma (HCC) in patients with chronic hepatitis B (CHB).1 ,2 By contrast, reducing HBV DNA concentrations to very low or undetectable levels through long-term nucleos(t)ide analogue (NUC) therapy is associated with reduced risk of mortality and/or HCC.3–11
With the availability of potent NUCs, such as tenofovir disoproxil fumarate (TDF) and entecavir (ETV), suppression of serum HBV DNA to levels undetectable by PCR assays is achievable in most NUC treatment-naive patients in the absence of drug-resistant HBV mutants.12 ,13 However, many patients worldwide have developed drug resistance from the widespread use of less potent NUCs, such as lamivudine (LAM) or adefovir dipivoxil (ADV), which have a low genetic barrier to resistance. Patients with persistent drug-resistant HBV viraemia are more likely to suffer hepatitis flares, disease progression and to die than those without drug-resistant HBV.3 ,6
Combination therapy with a nucleoside analogue and a nucleotide analogue is generally recommended for the treatment of patients harbouring drug-resistant HBV.14–17 However, several recent studies including ours have suggested that TDF monotherapy is efficacious in patients with LAM-resistant, ETV-resistant or ADV-refractory HBV.18–22 Nonetheless, the efficacy of TDF monotherapy is still controversial for patients who harbour HBV mutants resistant to multiple NUCs including ADV.
In this multicentre randomised trial, we aimed to compare the efficacy of TDF monotherapy with that of TDF and ETV combination therapy in patients with ADV-resistant HBV. For the combination therapy arm, ETV was selected because it is the most potent nucleoside analogue and has complementary cross-resistance profiles to TDF.23–26
Patients and methods
The study was a multicentre randomised open-label trial (ClinicalTrials.gov ID NCT01639066) conducted in patients who had persistent HBV viraemia with documented genotypic resistance to ADV (rtA181V/T and/or rtN236T). Patients were randomised (in a 1:1 ratio using a centralised procedure and an interactive web response system) to receive either TDF 300 mg once daily (TDF-TDF group) or a combination of TDF 300 mg and ETV 1 mg once daily (TDF/ETV-TDF group). Treatment assignments were generated in a block size of four.
An interim analysis was planned after all subjects have completed week 24 and 50% of the subjects have completed 36 weeks of treatment. If there were no significant differences between the two groups in the virological response at the interim analysis, the patients who were initially randomised to TDF/ETV combination therapy were planned to be rolled over to TDF monotherapy after completing 48 weeks of parallel comparison.
Patients were enrolled between September 2012 and February 2013 from five centres in Korea. Patients with CHB (defined as a positive serum hepatitis B surface antigen (HBsAg) test for at least 6 months) were eligible for enrolment if they had serum HBV DNA levels >60 IU/mL at screening, were currently receiving any NUC other than TDF and were confirmed to have genotypic resistance mutations to ADV (rtA181V/T and/or rtN236T). Patients were required to be between 20 and 75 years old and to have serum creatinine levels <1.5 mg/dL. Prior and/or ongoing LAM, ETV and ADV therapy in any combination was permitted, and prior interferon therapy was allowed if treatment was discontinued at least 12 months before screening. Patients with prior exposure to TDF for >1 week, evidence of decompensated liver disease, any malignant neoplasm or coinfection with hepatitis C, hepatitis D or HIV were excluded.
Efficacy and safety measures
The primary efficacy endpoint was the proportion of patients who achieved a virological response (serum HBV DNA <15 IU/mL) at week 48. Secondary endpoints included the proportion of patients who achieved a virological response at week 96; the proportion of patients with serum HBV DNA levels <60 IU/mL, the change in serum HBV DNA levels from baseline, the proportion of patients with normal alanine aminotransferase (ALT) and the proportion of patients with hepatitis B e antigen (HBeAg) loss/seroconversion (HBeAg-positive patients only) and HBsAg loss/seroconversion, at weeks 48 and 96. The incidence of virological breakthrough (increases in HBV DNA levels ≥1 log10 IU/mL from nadir on two consecutive tests) was evaluated. The probability of developing resistance was evaluated by genotypic analysis for all patients who experienced virological breakthrough or persistent viraemia (ie, HBV DNA >60 IU/mL) by the last time point of treatment and at weeks 48 and 96.
Adverse events (clinical and laboratory) were assessed throughout the 96 weeks. Glomerular filtration rate was estimated by using the Modification of Diet in Renal Disease equation as follows27: estimated glomerular filtration rate (eGFR) (mL/min/1.73 m2)=175×serum creatinine−1.154×age−0.203×0.742 (if woman). Bone mineral density (BMD) measurements of the lumbar spine and femur were determined via dual-energy X-ray absorptiometry (DXA) at baseline and at weeks 48 and 96.
Adherence to study drugs was assessed by counting the number of pills and empty blister packets returned at each visit.
Serum HBV DNA levels were measured using a real-time PCR assay (linear dynamic detection range, 15 IU/mL to 1×109 IU/mL; Abbott Laboratories, Chicago, Illinois, USA). HBV genotype was determined by restriction fragment mass polymorphism (RFMP) analysis. Resistance mutations were determined by RFMP analyses28 and direct sequencing of the reverse transcriptase region of the HBV polymerase gene (pol/RT).
The primary dataset for efficacy and safety analyses was defined as all randomised patients (intention-to-treat analysis). Patients who discontinued the study prior to week 96 were considered failures for all endpoints after the time of discontinuation. Efficacy and safety analyses were performed comparing the originally randomised treatment groups, TDF-TDF and TDF/ETV-TDF.
The primary efficacy endpoint was the proportion of patients with a virological response at week 48. Assuming success rates of 60% and 85% for TDF-TDF and TDF/ETV-TDF groups, respectively, and a two-sided 5% significance level, and taking into account a dropout rate of up to 5%, the sample size needed to achieve 80% power was 102 patients in total and 51 patients per arm, based on a test for equality of proportions. This sample size would also provide 99% power to detect a between-group difference in mean HBV DNA levels of 1 log10 IU/mL, assuming a within-group SD of 1 log10 IU/mL and a two-sided significance level of 0.05.
Between-group comparisons of continuous or categorical variables were conducted using the t test, χ2 test or Fisher's exact test, as appropriate. Baseline factors predictive of virological response were evaluated by logistic regression analysis. All statistical analyses were performed using SPSS (V.20, SPSS, Chicago, Illinois, USA) and R (V.3.0, http://cran.r-project.org/). A p value <0.05 was considered statistically significant.
A total of 102 patients were randomised to receive TDF monotherapy (TDF-TDF group, n=50) or TDF and ETV combination therapy (TDF/ETV-TDF group, n=52; see online supplementary figure S1).
Treatment groups were comparable in baseline demographic and laboratory characteristics (table 1). The mean age was 50 years, and the population was predominantly men (86.3%). Also, 19 patients had cirrhosis and 90 patients were HBeAg-positive. The median HBV DNA level was 3.38 log10 IU/mL. All patients were of Korean ethnicity and had HBV genotype C. Almost all patients (98%) had been exposed to LAM and/or ETV in addition to ADV. The median overall duration of prior NUC treatments was 109 months. Most patients (85%) were being treated with various combination therapies at baseline.
All patients had HBV with documented genotypic resistance mutations to ADV; rtA181T/V, rtN236T and rtA181T/V+rtN236T in 63, 5 and 34 patients, respectively (table 2). Most patients also had various combinations of resistance mutations to LAM and ETV (rtM204V/I, rtL180M, rtT184A/C/F/G/I/L/S, rtS202G and rtM250L/V).
No significant difference in the proportion of patients who achieved a virological response at week 48, the primary efficacy endpoint, was observed between the two treatment arms (see table 3, figure 1 and online supplementary figure S2). Of the patients who were randomised to TDF alone, 62% (31/50) had HBV DNA levels <15 IU/mL at week 48 compared with 63.5% (33/52) in those receiving TDF/ETV (p=0.88). At week 96, the proportion of patients with virological response was 64% (32/50) and 63.5% (33/52) in the TDF-TDF and TDF/ETV-TDF groups, respectively, without significant difference (p=0.96).
The proportion of patients who achieved HBV DNA levels <60 IU/mL was not significantly different between the TDF-TDF and TDF/ETV-TDF groups at weeks 48 (74% vs 78.8%; p=0.56) and 96 (76% vs 76.9%; p=0.91; see table 3 and online supplementary figure S3). The mean change from baseline in serum HBV DNA levels was not significantly different between the TDF-TDF and TDF/ETV-TDF groups at weeks 48 (−3.03 log10 IU/mL vs −3.31 log10 IU/mL; p=0.38) and 96 (−3.17 log10 IU/mL vs −3.27 log10 IU/mL; p=0.74; table 3 and figure 2). Among the patients who had HBV DNA detectable at week 24, the decline in HBV DNA levels from week 24 to week 96 was slow but significant (mean, −0.69 log10 IU/mL; p<0.001) without significant difference between the two groups (p=0.73).
Virological response in patient subgroups
A subgroup analysis of patients who harboured single-resistance mutations to ADV, that is, either rtA181T/V or rtN236T, showed no significantly different proportion of patients with virological response between the TDF-TDF and TDF/ETV-TDF groups at weeks 48 (74.3% (26/35) vs 63.6% (21/33); p=0.34) and 96 (77.1% (27/35) vs 69.7% (23/33); p=0.49; see figure 3A and online supplementary figure S4). The mean change in serum HBV DNA levels from baseline was not significantly different between the two groups in these patients at weeks 48 (p=0.91) and 96 (p=0.77; see online supplementary figure S5A). In patients who harboured double ADV-resistance mutations, that is, both rtA181T/V and rtN236T, the proportion of patients with virological response was not significantly different between the TDF-TDF and TDF/ETV-TDF groups at weeks 48 (33.3% (5/15) vs 63.2% (12/19); p=0.08) and 96 (33.3% (5/15) vs 52.6% (10/19); p=0.26; see figure 3B and online supplementary figure S6). The decrease in serum HBV DNA levels tended to be less in the TDF-TDF group than in the TDF/ETV-TDF group, although the difference was not statistically significant at week 48 (p=0.09; see online supplementary figure S5B).
Among patients who had a high viral load (HBV DNA levels >5 log10 IU/mL) at baseline, the mean changes in serum HBV DNA levels from baseline were not significantly different between the TDF-TDF (n=11) and TDF/ETV-TDF (n=10) groups at weeks 48 (p=0.37) and 96 (p=0.87; see online supplementary figure S7). The proportion of patients who achieved a virological response was also comparable between the two groups at weeks 48 (3/11 (27.3%) vs 6/10 (60%); p=0.20) and 96 (3/11 (27.3%) vs 5/10 (50%); p=0.39).
In a subgroup of patients without prior exposure to ETV, the mean change in serum HBV DNA levels from baseline was not significantly different between the TDF-TDF (n=9) and TDF/ETV-TDF (n=13) groups at weeks 48 (p=0.13) and 96 (p=0.28; see online supplementary figure S8). In patients with prior exposure to ETV, the mean change in serum HBV DNA levels from baseline was not significantly different between the TDF-TDF (n=41) and TDF/ETV-TDF (n=39) groups at weeks 48 (p=0.14) and 96 (p=0.52).
Multivariable analysis showed that higher HBV DNA level (log10 IU/mL) at baseline (OR 0.62; 95% CI 0.46 to 0.84; p=0.002) and harbouring double ADV-resistance mutations (OR 0.21; 95% CI 0.07 to 0.61; p=0.004) were significantly associated with lower rate of virological response at 48 weeks (table 4). Treatment with TDF/ETV combination therapy was not associated with higher rate of virological response (OR 0.89; 95% CI 0.34 to 2.38; p=0.82). The number of HBV-resistance mutations at baseline (p=0.15), the number of NUCs that the patients had been previously exposed to (p=0.13) or the overall duration of previous NUC treatment (p=0.80) was not associated with the probability of achieving a virological response.
Biochemical and serological responses
The proportion of patients with normal ALT levels was not significantly different between the TDF-TDF and TDF/ETV-TDF groups at weeks 48 (80% vs 67.3%; p=0.15) and 96 (78% vs 78.8%; p=0.92; table 3).
The proportion of HBeAg-positive patients who achieved HBeAg seroconversion was low without significant difference between the two groups at weeks 48 (2.3% vs 0%; p=0.49) and 96 (9.1% vs 2.2%; p=0.20; table 3). None achieved HBsAg loss or seroconversion.
Virological breakthrough and resistance surveillance
Over the initial 48-week treatment period, one patient in the TDF-TDF group and one patient in the TDF/ETV-TDF group experienced virological breakthrough. Both were associated with decreased adherence to study medication (<80%). No additional substitutions were detected in the pol/RT during virological breakthrough in these patients compared with baseline. The patient in the TDF-TDF group had multiple resistance mutations (rtA181T/V+rtM204V/I+rtL180M) prior to starting the study, but only rtA181T/V was detected during the virological breakthrough at week 36. In the other patient in the TDF/ETV-TDF group who had rtA181T/V+rtN236T+rtM204V/I+rtL180M+rtT184L mutations at baseline, only rtM204V+rtL180M+rtT184L was detected during virological breakthrough at week 36.
During TDF monotherapy between weeks 48 and 96, a patient in the TDF/ETV-TDF group experienced virological breakthrough. Serum HBV DNA level in the patient rose from <15 IU/mL at week 48 to 390 IU/mL at week 96, which was associated with decreased adherence to study medication. No resistance mutation was detected in the pol/RT during virological breakthrough in this patient.
At week 48, 13 and 9 patients in the TDF-TDF and TDF/ETV-TDF groups, respectively, had HBV DNA levels >60 IU/mL (p=0.56), and qualified for genotypic resistance analysis. The baseline HBV DNA levels were significantly higher in the patients who qualified for resistance analyses compared with those who did not at 48 weeks (mean, 5.22 log10 IU/mL vs 3.55 log10 IU/mL; p=0.001). The mean change in HBV DNA levels from baseline was not significantly different between patients who did or did not qualify for resistance analysis at week 48 (−2.78 log10 IU/mL vs −3.28 log10 IU/mL; p=0.30). The number of patients who had at least one detectable HBV-resistance mutation in the TDF-TDF and TDF/ETV-TDF groups was 10 and 6, respectively, at week 48 (p=0.28), and 5 and 2, respectively, at week 96 (p=0.44; table 2), all of which were present prior to the initiation of TDF treatment. Pre-existing ADV-resistance mutations (rtA181T/V and/or rtN236T) were detectable in the TDF-TDF and TDF/ETV-TDF groups in nine and one patient(s), respectively, at week 48 (p=0.01), and in four and two patients, respectively, at week 96 (p=0.36; table 2). No patient developed additional substitutions in the pol/RT compared with baseline.
Safety profiles were similar between treatment groups through the 96-week treatment period, with comparable frequencies of adverse events and serious adverse events (table 5). Adverse events leading to study drug discontinuation were infrequent, occurring only in the TDF/ETV-TDF group. Two patients in the TDF/ETV-TDF group discontinued the study because of epigastric pain and headache at weeks 4 and 12, respectively. The TDF dose was reduced for 2 weeks in one patient in the TDF-TDF group because of a mild increase in creatinine level (0.4 mg/dL), which was ascribed to the use of non-steroidal anti-inflammatory drugs for trauma. A transient on-treatment ALT flare was observed in one patient in the TDF-TDF group at week 4 and was not associated with an increase in HBV DNA levels.
The mean change in eGFR was minimal and comparable between the TDF-TDF and TDF/ETV-TDF groups at weeks 48 (3.58 mL/min/1.73 m2 vs 3.46 mL/min/1.73 m2; p=0.97) and 96 (−2.45 mL/min/1.73 m2 vs 2.25 mL/min/1.73 m2; p=0.05; see online supplementary figure S9). The mean change in serum phosphate level was minimal and comparable between the TDF-TDF and TDF/ETV-TDF groups at weeks 48 (0.12 mg/dL vs 0.13 mg/dL; p=0.93) and 96 (0.13 mg/dL vs 0.05 mg/dL; p=0.48; see online supplementary figure S10). At week 48, mean eGFR and serum phosphate levels were significantly higher compared with those at baseline (p=0.01 and 0.04, respectively).
Baseline DXA spine assessments revealed 7.8% (8/102) of patients with evidence of osteoporosis (T-scores <−2.5) and 33.3% (34/102) with evidence of osteopenia (T-score range, −1 to >−2.5) at baseline. The proportion of patients with osteoporosis and osteopenia was 8.2% (8/98) and 31.6% (31/98), respectively, at week 96, which was not significantly different between the TDF-TDF and TDF/ETV-TDF groups (p=0.61). An analysis of the mean per cent change in BMD (g/cm2) of the spine and femur over the 96 weeks of treatment (see online supplementary figure S11) showed small decreases that were not significantly different between the TDF-TDF and TDF/ETV-TDF groups (−0.1% vs −0.2%; p=0.91 for spine and −1.0% vs −0.8%; p=0.76 for femur). No bone fractures were reported.
This trial demonstrates that TDF monotherapy for 96 weeks resulted in a virological response in a significant proportion of patients with HBV mutants resistant to multiple drugs including ADV. After parallel comparison for 48 weeks, combined treatment with TDF plus ETV did not result in a significantly higher proportion of patients with virological response, ALT normalisation or HBeAg seroclearance than TDF monotherapy. The reduction in mean serum HBV DNA levels during the 48 weeks of treatment was also similar between the two groups. The extension of TDF monotherapy for 96 weeks showed durable viral suppression. The switch from TDF/ETV combination to TDF monotherapy after 48 weeks showed that both virologically controlled and uncontrolled patients on TDF/ETV maintained an effective viral suppression. Very few patients in either group experienced virological breakthrough during treatment, which were associated with low adherence to the drug. Both treatments were associated with no additional emergence, but a marked reduction, in detectable resistance mutations. Although not comparative post-week 48, this long-term data can provide some information (albeit limited) about the safety and efficacy of prolonged TDF monotherapy in patients with HBV mutants resistant to multiple drugs including ADV.
Our patients had persistent viraemia during median 108 months of overall treatments with various NUCs except TDF before entering this study. These heavily pretreated patients had developed multidrug-resistant HBV through sequential accumulation of resistance mutations to LAM, ETV and later to ADV.29–31 Single-point mutation at rtA181 may also exhibit a multidrug-resistant phenotype.26 ,32
Treatment options for patients with multidrug-resistant HBV are severely limited. In vitro clonal analyses showed that multidrug-resistance mutations usually reside in the same viral genome,30 ,31 and antiviral sensitivities revealed that replicating clones with LAM-associated and ADV-associated mutations had >50-fold reduced susceptibility to combination of LAM and ADV.33 ,34 In fact, our previous cohort study demonstrated that, in patients with HBV resistant to LAM and ADV, combination therapy with these two drugs was not effective and was even inferior to ETV monotherapy in suppressing HBV DNA.35 However, the response to ETV monotherapy was not optimal. We demonstrated that ETV was far less effective in patients refractory to both LAM and ADV than in those with LAM mono-resistance.36
Although TDF has superior antiviral efficacy relative to that of ADV,18 ,19 ,37 in vitro studies show that HBV strains expressing the ADV-resistance-associated substitutions, rtA181T/V and/or rtN236T, demonstrate reduced susceptibility to tenofovir, ranging from 2.9-fold to 10-fold of that of the wild-type virus.25 ,26 ,29 ,31 Several cohort studies also show reduced TDF efficacy in patients with ADV-resistant HBV.21 ,38 An European cohort study showed that the probability of achieving HBV DNA levels <400 copies/mL was significantly lower with TDF monotherapy in patients with ADV-resistant HBV and high viral load (>107 copies/mL) at baseline compared with those without ADV-resistant HBV.38 Another cohort study also showed that the efficacy of TDF was lower in patients with ADV-resistant HBV than in treatment-naive patients, especially when they had previously failed to respond to both LAM and ADV.21 On the other hand, a combination of TDF and ETV, which is currently regarded as the strongest combination therapy against HBV, induced a virological response in up to 90% of patients after a median 6 months of treatment regardless of pre-existing ADV resistance or ETV resistance.39 However, whether a combination of TDF and ETV exerts better antiviral efficacy than TDF monotherapy in patients with multidrug-resistant HBV could not be identified by these single-arm studies.
Our results are in agreement with a previous trial comparing TDF and emtricitabine (FTC) plus TDF in patients with ADV-refractory CHB, which demonstrated that the rate of decrease in HBV DNA levels did not differ between TDF and FTC/TDF therapies.18 ,19 In this study, a subgroup analysis of patients with detectable ADV-resistance mutations at baseline also showed no difference in antiviral efficacy between the two treatment groups. However, this subgroup analysis included only 18 patients with ADV-resistant HBV, and thus, was underpowered to adequately evaluate the efficacy of TDF monotherapy in ADV-resistant patients. Furthermore, most of the patients had HBV harbouring a single ADV-resistance mutation without LAM resistance.
The proportion of patients with virological response of TDF monotherapy was 62% and 64% after 48 and 96 weeks, respectively, in the current study. These rates of virological response with TDF monotherapy are superior to those of combination therapies based on ADV, such as LAM plus ADV or ETV plus ADV, in multidrug-refractory patients.40–42 In a previous randomised trial at our institution,40 ,41 the proportion of patients with serum HBV DNA levels <60 IU/mL at 52 weeks was only 29% in the ETV plus ADV group. These findings suggest that TDF monotherapy would be a better treatment option than combination therapies based on ADV in multidrug-resistant patients.
However, the rates of virological response in our patients were lower compared with those reported in previous clinical trials of TDF in treatment-naive, LAM-resistant or ADV-refractory patients,18 ,20 ,37 despite the fact that baseline viraemia was low (3.38 log10 IU/mL). Our results also seem to be inferior to those of a recent 96-week single-arm trial with TDF/ETV combination in patients with CHB with previous NUC treatment failure, which showed that 85% (78/92) of patients had HBV DNA <50 IU/mL by week 96.43 However, only 7% of the patients had resistance to ADV at baseline in the study. Taken together, these differences might have originated from the extensive multidrug-resistance profiles of our patients.
The potential superiority of TDF/ETV combination therapy was observed in patients with double ADV-resistant mutations (both rtA181T/V and rtN236T). These results are in accordance with previous in vitro susceptibility data showing that the double mutation (rtA181T/V and rtN236T) results in a 7-fold to 10-fold reduction in sensitivity to tenofovir compared with that of the single rtA181T mutant.25 ,26 Because there were only 34 patients with double ADV-resistant mutations in the current study, further larger-scale studies are warranted in this regard.
The majority (88%) of our patients were HBeAg-positive at baseline. The overall HBeAg seroclearance rate at 48 weeks was relatively low (7.8%) compared with those of previous reports in treatment-naive patients treated with TDF (21%) or ETV (21%).37 ,44 The likely explanation is that these patients represent a poorly responding group who failed to achieve serological endpoints with previous therapies. Whatever the mechanism of low HBeAg seroclearance is, it suggests that far longer NUC treatment may be required for these patients than treatment-naive patients. Thus, considering higher cost and higher potential risk of adverse events with long-term combination therapy, TDF monotherapy may have a role in the treatment of patients with multidrug-resistant CHB.
Treatment with TDF and TDF/ETV was well tolerated throughout the 96 weeks, consistent with other prospective clinical trials of TDF in treatment-naive and LAM-resistant patients.13 ,20 ,45 Interestingly, the mean eGFR and serum phosphate level increased significantly from baseline at week 48. These observations may be associated with the fact that almost all the patients were taking ADV prior to enrolment. Because ADV is associated with decrease in eGFR more than TDF or ETV,46–48 the switch of treatment from ADV to TDF or TDF/ETV might have caused our observations.
This study has a number of limitations. First, this was an open-label study and blinding was not performed. Although objective endpoints (virological and biochemical) were used and drug adherence was ascertained, the lack of blinding might have affected the attention of the study patients or biased the investigators in reporting the adherence and adverse events. Second, the predominant population had relatively low HBV DNA levels at baseline. This may be associated with the decreased replicative fitness of multiple drug-resistant HBV49 and the long-term partially effective previous combination therapies, that is, ETV plus ADV.40–42
In conclusion, TDF monotherapy for 48 weeks provided a comparable rate of virological response compared with TDF/ETV combination therapy in heavily pretreated patients with HBV mutants resistant to multiple drugs including ADV. Both maintaining TDF monotherapy for 96 weeks and switch from TDF/ETV to TDF after 48 weeks were reassuring, maintaining effective viral suppression in most patients. Very few patients experienced virological breakthrough, no additional resistance mutations emerged and HBV DNA levels continued to decline during 96 weeks of TDF monotherapy. Given the necessity of long-term, almost indefinite NUC treatment to maintain viral suppression, our data suggest that TDF monotherapy may be a reasonable option for the treatment of patients resistant to multiple drugs including ADV. However, the flat pattern of virological response beyond week 24 is worrisome, and a prolongation of TDF therapy did not significantly raise the rate of virological response. Because the combination of TDF/ETV does not seem to further increase the rate of virological response, our findings indicate that a more potent antiviral agent may be required for patients with HBV mutants resistant to multiple drugs including ADV.
We indebted to Dr Seungbong Han for his excellent help with statistical analyses. We thank Dr Ji Hoon Kim, Dr Geum-Youn Gwak, Sinae Kim, Hyang Ki Lee and Bomi Park for their help with data collection. We also thank the Academic Research Office and the Clinical Trial Center affiliated to Asan Medical Center for their operational oversight of the trial.
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Correction notice This article has been corrected since it published Online First. The affiliation and corresponding address for Byung Chul Yoo has been updated.
Contributors YSL was responsible for the conception and design of the study, the acquisition, analysis and interpretation of the data, and the drafting of the manuscript. BCY, KSB, SYK, YJK, JA, HCL and YSL helped with the design of the study, acquisition of the data and critical revision of the manuscript for important intellectual content. BCY supervised the study.
Funding This work was supported by Gilead Sciences, which also provided the study drug (tenofovir disoproxil fumarate). Gilead Sciences was permitted to review the manuscript and suggest changes, but had no role in the study design, data collection, analysis, decision to publish or preparation of the manuscript. The final decision on content was exclusively retained by the authors. This study was also supported by a grant from the Korean Health Technology R& D Project, Ministry of Health & Welfare, Republic of Korea (HI14C1731).
Competing interests YSL is an advisory board member of Bayer Healthcare, Bristol-Myers Squibb and Gilead Sciences, and receives research funding from Bayer Healthcare, Bristol-Myers Squibb, Gilead Sciences and Novartis. The remaining authors have nothing to disclose that would be relevant for the publication of this manuscript.
Patient consent Obtained.
Ethics approval Asan Medical Center IRB.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement A part of this study was presented at the International Liver Congress, London, UK, on 12 April 2014.
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