Long-term therapy for chronic hepatitis B: Hepatitis B virus DNA suppression leading to cirrhosis reversal

Transcription

1 bs_bs_banner doi: /jgh REVIEW Long-term therapy for chronic hepatitis B: Hepatitis B virus DNA suppression leading to cirrhosis reversal Patrick Marcellin and Tarik Asselah Service d Hépatologie, Hôpital Beaujon, University of Paris, Clichy, France Key words chronic hepatitis B, cirrhosis, fibrosis, long term, nucleotide/nucleoside analogs. Accepted for publication 26 March Correspondence Professor Patrick Marcellin, Service d Hépatologie, U773-CRB3, Hôpital Beaujon, University of Paris, Clichy, France. Patrick.marcellin@bjn.aphp.fr Abstract Since the licensing of the first treatment for chronic hepatitis B in the nucleoside/tide analog class almost 15 years ago, considerable progress has been made in improving drug efficacy and safety with highly potent nucleoside/tide analogs exhibiting a high barrier to resistance. Physicians are now able to treat patients safely for many years and to be able to see convincing improvements in histology, including regression of fibrosis and even reversal of cirrhosis. The robust data that have been generated help us build confidence that we can now offer patients with chronic hepatitis B long-term, disease-modifying therapy that can alter the natural course of disease and help prevent the morbidity and mortality associated with it. Conflict of interest: Tarik Asselah is a speaker and investigator for BMS, Boehringer-Ingelheim, Tibotec, Janssen, Gilead, Roche, and Merck. Patrick Marcellin is a speaker and investigator for BMS, Boehringer-Ingelheim, Tibotec, Janssen, Gilead, Roche, and Merck. Funding: Editorial support was provided by Elements Communications Ltd and was funded by Gilead, Foster City, CA, USA. Introduction Chronic hepatitis B (CHB) infection affects over 240 million people worldwide, with long-term morbidity such as cirrhosis and hepatocellular carcinoma (HCC) accounting for around deaths annually. 1 The goal of therapy for CHB is to improve quality of life and survival by preventing progression of the disease. 2 The landmark Risk Evaluation of Viral Load Elevation and Associated Liver Disease/Cancer-Hepatitis B Virus study demonstrated that progression to liver cirrhosis, HCC, and liver-related mortality correlates strongly with the level of circulating hepatitis B virus (HBV) DNA. 3,4 Furthermore, HBV DNA suppression with long-term lamivudine (LAM) has been associated with a reduction in the incidence of hepatic decompensation and HCC. 5 Treatment goals can be achieved by sustained suppression of HBV replication, thereby reducing the histological activity of CHB and lessening the risk of progressive liver disease. 2 Suppression of HBV replication is critical but must be maintained if optimal treatment outcomes are to be achieved. Currently, there are two main treatment strategies for both hepatitis e (HBe) antigen-positive (HBeAg+ve) and antigen-negative (HBeAg-ve) CHB that rely on different modes of action to achieve and maintain viral suppression; a finite treatment (usually 1 year) course of interferon alpha (IFN)/pegylated IFN (PEG-IFN) and long-term therapy with nucleoside/tide analogs (NAs). Finite treatment with PEG-IFN offers the potential for immune-mediated control of HBV infection, with higher rates of HBe seroconversion and the possibility of off-treatment viral suppression, with loss of hepatitis B surface antigen (HBsAg) considered the ultimate goal of therapy in a proportion of patients who maintain undetectable HBV DNA. 2 However, PEG-IFN needs to be administered by subcutaneous injection and is associated with frequent sideeffects; it is also contraindicated in patients with decompensated cirrhosis or relevant autoimmune disease during pregnancy and in patients with uncontrolled severe depression. 2 In contrast, NAs suppress HBV via direct antiviral activity, and if compliance to treatment is good, > 90% of patients treated with the newer, highly potent NAs tenofovir (TDF) and entecavir (ETV) achieve virological remission. 2 NAs are administered orally, and tolerance is generally good, although the safety of these drugs and specifically the newer, more potent NAs over lifelong therapy is unknown. 2 One potentially serious drawback of long-term NA therapy is the 912 Journal of Gastroenterology and Hepatology 28 (2013)

2 P Marcellin and T Asselah Modifying hepatitis B virus disease development of drug resistance; however, although common with earlier less potent NAs such as LAM and adefovir (ADV), resistance has become considerably less of a problem with the highly potent NAs TDF and ETV. 2 Long-term clinical trial data up to 6 years and beyond are emerging for the newer NAs that are providing reassuring data on their safety and resistance profiles. In addition, data show that treatment with potent NAs can lead to improvements in liver histology raising the prospect not only of suppressing and controlling the disease but also of disease modification. Further long-term data are emerging from studies using newer potent NAs in routine clinical practice confirming safety and efficacy of these agents in the real-world setting. In light of these findings, this review focuses on what can be achieved with potent NAs in terms of efficacy and, in particular, histological improvement, and discusses the long-term safety data generated in both clinical trials and real-life studies. Evolution of NA therapy in CHB LAM was the first NA available for the treatment of CHB approved in the United States in Studies showed it was effective in suppressing viral replication in both HBeAg+ve and HBeAg-ve patients, and in preventing progression of cirrhosis and development of HCC with a good safety and tolerability profile However, LAM has a low genetic barrier leading to the development of drug-resistant mutations in around 70% of patients after 5 years of continued therapy (Fig. 1). 2 The development of resistant mutations is associated with virological breakthrough, hepatic flares, and potentially liver failure. 9,12,13 Resistance also proved to be a potential problem with ADV approved in the United States in 2002, with reported cumulative rates of genotypic resistance of 20% and 29% at 5 years in HBeAg+ve and HBeAg-ve patients, respectively. 14,15 ETV was the third NA approved for the treatment of CHB and was shown in randomized, clinical trials (RCTs) to be Figure 1 Cumulative incidence of hepatitis B virus (HBV) resistance in pivotal trials. Cumulative incidence of HBV resistance to lamivudine (LAM), adefovir (ADV), entecavir (ETV), telbivudine (LdT), and tenofovir (TDF) in pivotal trials in nucleos(t)ide-naïve patients with chronic hepatitis B. Reproduced from European Association for the Study of the Liver 2 with permission from Elsevier. ( ) year 1; ( ) year 2; ( ) year 3; ( ) year 4; ( ) year 5. significantly more effective than LAM in both HBeAg+ve and HBeAg-ve treatment-naïve patients with a similar safety profile ETV has the advantage of a higher genetic barrier, with resistance developing in 1.2% of treatment-naïve patients in longterm clinical trials; however, individuals with mutations conferring LAM resistance have a significantly greater chance of developing ETV resistance. 20 Although more effective than LAM, telbivudine (LdT), approved in the United States in 2006, also has a low barrier to resistance, with around 25% of patients developing resistance mutations after 2 years of treatment. 21,22 Because LdT is not active against LAM-resistant mutations, it is not an option for patients with LAM resistance. TDF, approved for the treatment of CHB in 2008, has potent antiviral activity and has demonstrated efficacy and tolerability in short- and long-term clinical trials in treatmentnaïve and -experienced patients, including those with cirrhosis. 27 Resistance to TDF has not been reported to date, and it has the advantage of being active in patients with LAM resistance Current guidelines recommend the use of TDF and ETV as firstline treatment for CHB because of their potent antiviral activity and high genetic barriers to resistance, with the remaining three drugs only being used if the more potent agents are unavailable. 2 While either agent is recommended for the treatment of ADVresistant patients, TDF, but not ETV, is recommended in LAMresistant patients because of the increased chance of resistance development. 2 Switching to TDF is also recommended in patients with LdT or ETV resistance. 2 Clinical trial results Long-term efficacy of NAs. Given that patients with CHB require long-term and potentially lifelong NA therapy, data from follow-up studies of patients included in the pivotal registration trials are clearly mandatory to establish long-term efficacy and safety. Comparison of long-term clinical trial data up to 5 years indicate that both TDF and ETV show higher rates of long-term virological, biochemical, and serological response compared with LAM, ADV, and LdT (Table 1). The ETV-901 rollover study in HBeAg+ve patients included patients from the 2-year pivotal phase III ETV-022 trial who had received 1 year of ETV (0.5 mg) and had a treatment gap of 35 days. 19 In all, 146 of the original 354 patients included in ETV-022 (126 virological responders, 19 non-responders, and 1 partial responder) were eligible for the long-term study. Of these, only 99 received ETV for 5 years; thus, data are based on a relatively small patient population. It should also be noted that while patients included in the long-term cohort received the currently recommended dose for NA-naïve patients (0.5 mg daily), on enrolment into ETV-901, they initially received a daily combination of ETV 1.0 mg plus LAM for approximately 29 weeks. 19 The possible impact on efficacy of this increased dose of ETV and the combination with LAM is unknown. Assessment of serological data from this study is complicated by the fact that in accordance with the study protocol, most patients who achieved HBeAg seroconversion (31%) or HBsAg loss (5%) during the 2-year treatment period of ETV-022 discontinued study therapy and did not enroll in ETV-901. However, continued treatment in ETV-901 resulted in HBeAg seroconversion in 23% of enrolled patients, with HBsAg loss in two patients. 19 Journal of Gastroenterology and Hepatology 28 (2013)

3 Modifying hepatitis B virus disease P Marcellin and T Asselah Table 1 Long-term efficacy of NAs in CHB in terms of laboratory parameters: phase III randomized, controlled trials and extension studies HBeAg status Duration of therapy (years) Patients (n) Virological response Biochemical response Serological response Resistance HBeAg HBsAg Loss sc Loss sc Adefovir Median change from baseline in serum HBV DNA 4.05 log10 copies/ml (n = 41) Median change from baseline in ALT -50 U/L (n = 41) 58% 48% 2% 2% 13/65 (20%) developed mutations; 12 had virological resistance %, 69% N/A N/A 5% 4% 29/125 (23%) developed mutations; 20/29 had virological resistance Entecavir % 80% NR 23% 1.4% NR 1/146 (0.7%) developed resistance with virological breakthrough Telbivudine + or HBeAg+ve 213 HBeAg-ve 186 Tenofovir + or HBeAg+ve 238 HBeAg-ve 347 HBeAg+ve: 77% HBeAg+ve: 81% HBeAg ve: 85% HBeAg ve: 83% HBeAg+ve: 97% HBeAg+ve: 73% HBeAg-ve: 99% HBeAg-ve: 85% 52% 37% 1.6% 0.5% HBeAg+ve: 11.3% HBeAg ve: 6.5% 49% 40% 11% 9% 0/495 Normalization of ALT unless otherwise stated. HBV DNA < 1000 copies/ml. ITT analysis (missing = failure for resistance or HCC). HBV DNA < 300 copies/ml. HBV DNA < 400 copies/ml. ALT, alanine aminotransferase; CHB, chronic hepatitis B; HBeAg, hepatitis B e antigen; HBeAg ve, HBeAg-negative; HBeAg+ve, HBeAg-positive; HBsAg, hepatitis B surface antigen; HBV, hepatitis B virus; HCC, hepatocellular carcinoma; ITT, intent-to-treat; NA, nucleoside/tide analog; N/A, not applicable; NR, not reported; sc, seroconversion. 914 Journal of Gastroenterology and Hepatology 28 (2013)

4 P Marcellin and T Asselah Modifying hepatitis B virus disease Long-term treatment with TDF is being evaluated in an 8-year study of patients included in the pivotal phase III 102 (HBeAg-ve) and 103 (HBeAg+ve) studies. All patients were eligible for the long-term study and were treated with open-label TDF from the end of the initial trials. Patients with confirmed HBV DNA 400 copies/ml on or after week 72 could be given additional emtricitabine (FTC) at the discretion of the investigator; this option was taken up in 4 (1%) of the HBeAg-ve and 34 (13%) of HBeAg+ve patients. In all, 585 of the 641 patients (91%) who were randomized and treated in studies 102 and 103 entered the open-label follow-up study. 26 Retention in the study was high; of the initial long-term cohort, 489 (84%) completed 240 weeks of treatment. In a retrospective analysis, results were found to be comparable after 5 years of treatment in patients with and without cirrhosis at baseline. 27 Overall, TDF and ETV show long-term efficacy with high rates of virological and biochemical response (Table 1). This efficacy is related in part to a lack of emergence of drug-resistant mutations in treatment-naïve patients, with long-term studies confirming the high barrier to resistance of TDF and ETV compared with other NAs (Table 1) (Fig. 1). During the ETV-901 rollover study, one patient was found to have developed ETV resistance. 19 The patient who had been treated with ETV plus LAM for 16 weeks on enrollment into the rollover study developed simultaneous L180M/M204V (LAM-resistant) and S202G (ETV-resistant) mutations at week 139, with virological breakthrough at week However, NA-naïve patients who only achieve a partial virological response (PVR) to ETV may be at increased risk of developing ETV resistance during continued ETV therapy. For example, Korean patients who achieved only PVR (defined as > 1 log 10 decline in viremia but detectable HBV DNA by polymerase chain reaction) after 48 weeks of ETV had cumulative rates of virological breakthrough and of genotypic ETV resistance of 5.9% for each at week 144 compared with 0% in those patients who achieved undetectable HBV DNA at week While ETV has a low rate of resistance development in NA-naïve patients, 19,20,33 patients with LAM-resistant HBV are at high risk of developing subsequent ETV resistance. ETV resistance arises when additional changes at positions T184, S202, or M250 occur in the presence of the M204V and L180M substitutions associated with LAM resistance, 34 resulting in a 5-year cumulative probability of genotypic ETV resistance of 51% in LAM-resistant patients. 20 The incidence of ETV-resistant mutations is also high in patients with ADVresistant mutations treated with ETV monotherapy. In a study of 53 patients with ADV-resistant mutations (44 with previous LAMresistance), the cumulative rate of ETV-resistant mutations and virological breakthrough was 46.8% after 36 months. 35 To date, there is no evidence for virological resistance to TDF up to 5 years in treatment-naïve and treatment-experienced patients, or in LAM-resistant patients to 96 weeks. 26,29,36 In the long-term follow up of patients treated in the pivotal phase III clinical trials, 20 patients experienced a virological breakthrough up to year 5; however, phenotypic analysis showed no evidence of reduced susceptibility to TDF in vitro. 26 In 265 patients with confirmed LAM-resistant mutations (M204V L180M) treated with TDF or TDF + FTC, there were five reported cases of virological breakthrough up to 2 years of treatment (1.9%), although none of these cases was confirmed and none had ETV resistance. 36 In addition, no resistance to TDF was reported in a phase IIIb study including 280 LAM-resistant patients treated with either TDF or TDF + FTC over 96 weeks of treatment. 29 Histological improvement. While the goal of therapy for CHB is to improve quality of life and survival by preventing progression of the disease, 2 there is increasing interest in the potential for potent long-term NA therapy, particularly with the more potent agents, to do more than just prevent progression but to actually lead to regression of liver disease. There is an increasing body of evidence that fibrosis caused by a variety of factors, including viral hepatitis, is reversible if the underlying cause of the liver disease is removed. In the case of chronic hepatitis C (CHC) infection for example, a large pooled analysis of 3010 patients with paired liver biopsies included in four RCTs showed that treatment with PEG-IFN plus ribavirin for a relatively short mean of 20 months resulted in improvements in fibrosis in 20% of patients, with those who achieved a sustained virological response showing significantly lower rates of progression of fibrosis. 37 Given that the development of fibrosis is a long-term process, it would seem likely that regression of fibrosis (i.e. a decrease in fibrosis-based Ishak score regardless of the initial stage) or reversal of cirrhosis (i.e. loss of histological cirrhosis as defined by a decrease in Ishak score to below 5 in those patients with initial Ishak scores of 5 6) might also be expected to be long term. Long-term follow-up studies in CHC appear to confirm this. Data up to 18 years post-treatment show significant improvements in fibrosis in the majority of sustained responders to IFN-based therapy, including those with advanced fibrosis/cirrhosis, with a substantial proportion of patients showing regression of cirrhosis While complete eradication of the underlying cause of liver damage (i.e. the hepatitis C virus) is achievable with therapy in CHC, the situation in CHB is somewhat more complex. Permanent elimination of HBV is rare or may even be unachievable because of the virus s ability to establish a persistent reservoir in the form of covalently closed circular DNA in hepatocytes, which can lead to reactivation of infection if viral suppression fails. While guidelines acknowledge that sustained suppression of HBV replication can prevent progression of liver disease, 2 long-term data with NAs suggest that successful treatment may in fact go further than preventing progression and can result in improvements in liver histology. Treatment with LAM for 3 years was shown to result in improvements in histological response in more than half of HBeAg+ve and HBeAg-ve patients, with improvements in baseline bridging fibrosis and cirrhosis 42,43 (Table 2). Long-term benefits are of course reduced or negated in patients in whom resistance emerges. In HBeAg+ve patients for example, patients who developed LAM resistance are significantly less likely to show improved histology and more likely to show disease progression compared with those patients who did not develop resistant mutations. 42 Long-term histological data for ADV are only available for a small group of patients but show improvements in histological response and in fibrosis 14,15 (Table 2). The effects of the emergence of ADV-resistant mutations are unclear. 15 In the rollover ETV-901 study, 96% of 57 patients treated with ETV for up to 7 years showed histological improvement ( 2- point decrease in Knodell necroinflammatory score and no worsening of Knodell fibrosis score), with improvements in fibrosis Journal of Gastroenterology and Hepatology 28 (2013)

5 Modifying hepatitis B virus disease P Marcellin and T Asselah Table 2 Long-term histological response to NAs HBeAg status Duration of therapy Patients with matched paired biopsies/with cirrhosis (n) Histological response (%) Additional comments Lamivudine + 3 years 42 63/11 35/63 (56%) Patients with YMDD variants for > 2 years were least likely to improve (8/22 [36%]). Bridging fibrosis improved by 1 level in 12/19 (63%), and cirrhosis improved (score of 4 to 3) in 8/11 (73%). 1/52 patients showed progression to cirrhosis, and 3/34 showed progression to bridging fibrosis (all with YMDD variants). - 3 years 43 48/6 Overall: 18/48 (37.5%) YMDD mutations: 4/26 (15%) No mutation: 14/22 (64%) 24/48 patients (50%) had no bridging fibrosis pretreatment; 4/24 (17%) progressed to bridging fibrosis (all YMDD for 2 years). 42 patients had no cirrhosis at baseline; none progressed to cirrhosis, including 22 with YMDD mutations. Adefovir + 5 years 15 15/NR 9/15 (60%) 9/15 (60%) showed improvement in fibrosis. Five patients developed adefovir resistance: four had a decrease in HAI; one had an increase in HAI. - 5 years 14 45/12 83% 71% had improvement in fibrosis. Entecavir +72% -28% Telbivudine +69% -31% Tenofovir +36% -64% 6 years 44 57/4 55/57 (96%) 1-point improvement in the Ishak fibrosis score in 88% of patients, including all six patients with advanced fibrosis and four patients with cirrhosis. 5 years 45 60/6 59/60 (98%) no/minimal necroinflammation 51/60 (85%) no/minimal fibrosis 5 years /96 HBeAg+ve: 110/124 (89%) HBeAg-ve: 194/224 (87%) Ishak fibrosis score reduced by a median of 3 points in six patients with bridging fibrosis/cirrhosis at baseline. In patients with cirrhosis at baseline, 71/96 (74%) had an Ishak fibrosis score < 5 at year 5; 95/96 (99%) had a decrease of 2 units, and the majority (58%, 56 patients) experienced a 3 unit decrease. Overall, 95% had no change or improvement in fibrosis score. Histological response defined as decrease by 2 points in HAI without worsening in fibrosis unless otherwise stated. Bridging fibrosis/cirrhosis. HAI, Histology Activity Index; NA, nucleoside/tide analog; NR, not reported; YMDD, tyrosine-methionine-aspartate-aspartate. 1 point in Ishak fibrosis score in 88% (Fig. 2). 44 Ten patients in this study had advanced fibrosis at baseline (Ishak fibrosis score 4), including four with cirrhosis. After approximately 6 years of cumulative ETV therapy, all 10 patients showed improvement in liver histology and Ishak fibrosis score. A reduction in Ishak fibrosis score to 4 was seen for the four patients who had cirrhosis at baseline. 46 To date, the largest long-term prospective study of histological improvement has been seen with TDF, which included 348 patients with pretreatment and prespecified follow-up biopsies at 5 years of therapy, including 96 with cirrhosis at baseline. 26 Five years of treatment with TDF resulted in significant improvements in liver histology, with a progressive increase in the proportion of patients with mild disease and decreases in the proportion with severe disease (Fig. 3). Overall, 96% of patients showed no change or improvement in fibrosis score. 26 The proportion of patients with cirrhosis (Ishak score 5) progressively decreased from 28% at baseline to 8% at year 5; of the 96 patients with cirrhosis at baseline, 74% had an Ishak score < 5 by year 5 with 73% showing a decrease of 2 points (Fig. 4). 26 The data from these studies demonstrate that regression of fibrosis is possible with maintained on-treatment HBV inhibition during long-term therapy. In addition, data from the large, longterm TDF dataset provide strong evidence that cirrhosis can also be reversed. What remains to be determined is whether the regression of fibrosis or cirrhosis reduced the incidence of HCC. There are reports of HCC occurring in NA-treated patients even in patients in whom HBV DNA has been adequately suppressed, and there may be more than one underlying mechanism leading to HCC development. 47 It is therefore important that surveillance for HCC is continued in patients with cirrhosis even if complete suppression of HBV DNA has been achieved. Safety and tolerability. In general, NAs are well tolerated in CHB, although there are specific issues associated with some agents. LAM has a well-established safety profile, and no treatmentassociated major adverse events (AEs) or complications arose in long-term studies up to 6 years in patients with CHB; however, the 916 Journal of Gastroenterology and Hepatology 28 (2013)

6 P Marcellin and T Asselah Modifying hepatitis B virus disease Figure 2 Distribution of Ishak fibrosis score at baseline, year 1, and year 5 of treatment with entecavir (ETV). Distribution of Ishak fibrosis scores at the phase III baseline, after 48 weeks of ETV treatment, and at the time of long-term biopsy (median 6 years of ETV treatment [range 3 7 years]) among histologically evaluable patients in the long-term histology cohort (n = 57). Copyright 2010 American Association for the Study of Liver Diseases. Reproduced from Chang et al. 44 with permission from John Wiley and Sons. Ishak fibrosis score: ( ) 6;( )5; ( )4;( )3;( )2;( )1;( )0;( ) missing. Figure 3 Distribution of Ishak fibrosis score at baseline, year 1, and year 5 of treatment with TDF. Distribution of Ishak fibrosis scores at baseline, year 1, and year 5 in 348 patients with baseline and year 5 biopsies, and 344 patients with biopsy results at all three time points. An Ishak score of 0 indicates the absence of fibrosis, whereas a score 5 is indicative of cirrhosis. Over time, an increasing proportion of patients had regression of fibrosis as reflected in 63% (219/348) of patients having Ishak scores 2atyear5(P < 0.001, sign test). Reproduced from Marcellin et al. 26 *For baseline = year 5-matched biopsies; n = 344 for biopsies at three time points. Ishak fibrosis score: ( ) 6; ( )5;( )4;( )3;( )2;( )1;( )0. Figure 4 Change in Ishak fibrosis score at year 5 of treatment with TDF for patients with cirrhosis at baseline. Change from baseline at year 5 in Ishak fibrosis scores for the subset of 96 patients with cirrhosis (Ishak score 5) at baseline with each cell representing an individual patient response. At year 5, reversal of cirrhosis was observed in 74% (n = 71) of patients, with the majority (73%, n = 70) showing a 2-point or greater response to treatment. Reproduced from Marcellin et al. 26 development of resistance may be associated with hepatitis flares and worsening of liver disease. 12,48 The major side-effect associated with ADV treatment is nephrotoxicity, which is doserelated. 49 At the recommended dose of 10 mg daily, ADV was well tolerated in clinical trials with renal side-effects being reported in 3% of patients with compensated liver disease after 5 years of treatment. 14 Creatinine clearance should be calculated in all patients prior to initiating ADV therapy, with dose adjustment as required; ADV is not recommended in patients with creatinine clearance of 30 ml/min or who are receiving dialysis. 50 Renal Journal of Gastroenterology and Hepatology 28 (2013)

7 Modifying hepatitis B virus disease P Marcellin and T Asselah function should be monitored during treatment. The development of resistance to ADV can be associated with viral load rebound and exacerbation of liver disease that may lead to liver decompensation. Safety concerns for LdT include creatine kinase (CK) elevations, myopathy and rhabdomyolysis, and peripheral neuropathy. In the GLOBE trial, 13% of patients treated with LdT experienced grade 3/4 increases in CK levels versus 4% in patients treated with LAM (P < 0.001). 22 Longer term, the 3-year cumulative incidence of CK elevations and myopathy was 84.3% and 5%, respectively. 51 A combination therapy study of LdT with PEG-IFN was prematurely terminated due to cases of peripheral myopathy. 52 In clinical trials of ETV, the most commonly reported treatmentassociated AEs over a median of 184 weeks were myalgia- and neuropathy-related. 53 Three cases of de novo non-liver cancers arose (two gastric and one pancreatic adenocarcinoma). 53 The development of tumors in rodents during preclinical studies of ETV had previously raised concerns, and the post-approval observational REALM (Randomized, Observational Study of Entecavir to Assess Long-term Outcomes Associated with Nucleoside/ Nucleotide Monotherapy for Patients with Chronic HBV Infection) study includes evaluation of the risk of cancer development over 5 8 years of ETV therapy (ClinicalTrials.gov identifier NCT ). Lactic acidosis has been reported in CHB patients with impaired liver function and Model for End-Stage Liver Disease scores > 20 treated with ETV and proved fatal in 1 of 16 affected patients. 54 However, only one case of lactic acidosis was reported in a clinical trial of ETV in CHB with decompensated liver disease, 55 and no cases were reported in the ETV-901 rollover study. 19 Adherence to long-term TDF therapy was good in clinical trials with 76% of patients remaining on treatment at year 5 and only 1% of patients discontinuing treatment as a result of serious AEs (predominantly increases in liver enzymes). 26 A recent study by Gara and colleagues concluded that renal tubular dysfunction developed in 7 (15%) of 51 patients treated with ADV (5 patients) or TDF (2 patients) for 2 9 years. 56 However, given that only one of the affected patients in this study had received TDF alone (the other TDF patient switched to TDF following initial therapy with ADV), together with the low overall patient number and high proportion of patients with comorbidities, the conclusions of this study, at least with respect to TDF, are questionable. 57 No renal toxic effects were reported in TDF-treated CHB patients with preserved renal function at baseline during the pivotal 48-week trial. 23 The long-term extension of the pivotal studies of TDF also showed no concerns regarding renal function, with only one patient withdrawing from treatment because of a mild serum creatinine elevation (1.3 mg/dl), and one patient experienced a confirmed decrease in creatinine clearance < 50 ml/min that resolved with dose adjustment through 5 years of treatment. 26 In nucleoside-naïve patients treated for up to 96 weeks, the incidence of creatinine level elevations of 0.3 mg/dl was similar in patients treated with ETV or with ETV + TDF (3.3% vs 2%, respectively), while elevations of creatinine by 0.5 mg/dl were more frequent in patients receiving ETV monotherapy (1.6% vs 0%, respectively). 58 There have been reports of bone mineral density (BMD) loss in patients treated with TDF for HIV infection, 59,60 which has been reported to be non-progressive after the initial year of therapy. 61 However, there is no evidence of clinically relevant BMD loss in HBV-monoinfected patients. BMD scores for the hip and lumbar spine were stable over 2 years of evaluation during the ongoing long-term study, with no consistent trends in T and Z score category shifts. 62 No clinically relevant bone loss was seen by assessment of spine and hip BMD T and Z scores in a 96-week study of TDF in LAM-resistant patients. 29 Given the need for long-term therapy, pregnancy may be an issue for some patients. There is a lack of adequate data in pregnancy for ADV, LdT, and ETV, and the use of contraception is recommended. 50,63,64 Both ADV and LdT might be used during pregnancy only where the risk to the mother outweighs the potential risk to the fetus, and ETV should not be used during pregnancy unless clearly necessary. 50,63,64 Based on more extensive data, TDF and LAM can be used in pregnancy. 65,66 The safety of TDF and LAM in pregnancy has been confirmed by recent data from the Antiretroviral Pregnancy Registry, which found no increased risk of major birth defects including non-live births for pregnant women exposed to TDF or LAM compared with population-based controls. 67 In this analysis, second and third trimester birth defects had a prevalence of 2.7% in 3864 pregnancies exposed to LAM and 2.0% in 1092 pregnancies exposed to TDF compared with a prevalence of birth defects in the general population of 2.7%. 67 There were insufficient data to assess ADV, ETV, or LdT. Real-world studies RCTs provide the information required for the evaluation and eventual registration of drugs and are, by necessity, highly controlled and conducted under standardized conditions with strict enrollment criteria. Most RCTs therefore exclude patients routinely encountered in clinical practice, for example, those with advanced liver diseases or comorbidities where concomitant medications are required, which could impact on pharmacokinetics, and efficacy and safety because of drug drug interactions or altered liver metabolism. Real-world studies conducted in routine practice tend to be made up of a wide range of patients and therefore provide a better representation of the patients routinely reporting to the clinic. Such studies are important to confirm data from RCTs and may also help identify rare or late-emerging AEs. A number of medium-to-large-scale real-life trials have reported data for up to 52 months of treatment with ETV predominantly in NA-naïve patients (Table 3) In general, these studies confirm the efficacy of ETV as demonstrated in RCTs in routine practice, with ETV monotherapy resulting in a rapid and significant reduction in viral load and a progressive increase in overall rates of undetectable HBV DNA over time. In the longest of these studies to date, rates of undetectable HBV were 99% by year 4, with alanine aminotransferase (ALT) normalization in 74% of patients, HBeAg seroconversion in 15% of patients, and HBsAg loss reported in 12 patients. 70 Similar findings were reported in other long-term European studies, 68,69 although somewhat lower efficacy was reported recently in a long-term study of Chinese patients where treatment of NA-naïve patients for up to 4 years resulted in 45% of patients achieving undetectable HBV DNA, with normalization of ALT in 58% and HBeAg seroconversion in 24%. 71 The study included a markedly higher proportion of HBeAg+ve patients (70%) relative to the European long-term studies. Overall, reported rates of HBV DNA negativity in these long-term studies was lower in HBeAg+ve patients compared with HBeAg-ve patients; in the ORIENTE study for example, the rate of HBV 918 Journal of Gastroenterology and Hepatology 28 (2013)

8 P Marcellin and T Asselah Modifying hepatitis B virus disease Table 3 Real-world data Treatment naïve or experienced HBeAg status Duration of therapy Patients Virological response (%) Serological response Resistance HBeAg HBsAg Loss sc Loss sc Entecavir ORIENTE 68 Naïve Overall 48 weeks NR 1% NR 0% + 30% 61 21% - 70% 92 VIRGIL 69 Naïve Overall 144 weeks 243 NR 0% + 36% 90 34% 24% 0.7% - 64% 99 1% Experienced Overall , 0 8% NR 4/90 treatment-experienced + 63% 0 33% 0 25% patients - 37% Italian cohort 70 Naïve Overall 42 months NR 56% 2.1% NR 1 patient at year % - 83% Chinese cohort 69 Naïve Overall 4 years NR 24% NR NR NR + 70% - 30% Tenofovir VIREAL 73 Both Overall 48 weeks (interim data) NR NR n = 4 NR NR + 26% 80-74% 94 Naïve Overall Experienced Overall GEMINIS 74 Naïve or experienced Overall 1 year (interim data) % n = 9 NR + 31% 71 18% 17% 5.5% - 69% 82 1% Italian cohort 72 Naïve Overall 33 months NR 13% NR NR + 21% 86 36% - 79% 98 European cohort 75 Experienced Overall 44 months NR NR NR + 54% 20% 2% - 46% Figure is for initial cohort enrollment. Patient numbers varied at different time points and were not always specified; % = proportion of HBeAg-positive and HBeAg-negative patients. HBV DNA < 50 IU/mL. HBV DNA < 80 IU/mL. Depending on previous treatment. Undetectable; cut-off not specified. HBV DNA < 69 IU/mL. HBeAg, hepatitis B e antigen; HBsAg, hepatitis B surface antigen; HBV, hepatitis B virus; NR, not reported; sc, seroconversion. Journal of Gastroenterology and Hepatology 28 (2013)

9 Modifying hepatitis B virus disease P Marcellin and T Asselah DNA negativity at 12 months was 61% in HBeAg+ve patients versus 92% for HBeAg-ve patients. 66 As TDF was approved in the United States for the treatment of CHB 3 years later than ETV, long-term studies in routine clinical practice are at an earlier stage (Table 3). In a European cohort study of NA-naïve patients, rates of undetectable HBV DNA increased over time to 91% at 30 months, with HBeAg seroconversion in 33% at 30 months and HBsAg loss in 11%. 72 Similarly, interim 48-week data from the VIREAL study reported 90% of NA-naïve and -experienced (but TDF-naïve) patients had undetectable HBV DNA, 47% had normalized ALT, and HBsAg loss occurred in four patients, two of whom seroconverted. 73 Interim 12-month data from the German multicenter GEMINIS study, which includes NA-experienced and -naïve patients, also reported results similar to those seen in RCTs, although HBsAg loss (2.3%) was somewhat higher compared with registration studies. 74 In a European multicentre cohort study, 98% of TDF-naïve, NA-experienced, or NA-naïve patients had undetectable HBV DNA after 24 months, with HBeAg and HBsAg loss in 20% and 2%, respectively, after a mean of 15 (range 1 36) months of treatment. 75 These studies have also confirmed the safety and tolerability of TDF and ETV in routine clinical practice. The safety of ETV in NA-naïve patients treated in routine practice is in line with that seen in clinical trials. No serious AEs were reported in NA-naïve patients followed for 4 years in the European ETV cohort; serum creatinine was unchanged overall, and < 1% of patients showed > 0.5 mg increase in serum creatinine and/or blood phosphorus levels below 2 mg/dl or significant proteinuria. 70 In NA-naïve patients treated for up to 144 weeks in the VIRGIL study, reported AEs were rare; there were no reports of clinically relevant lactic acidosis, although lactate was not measured routinely. 69 In a subset of patients with available data, there was a non-significant mean decline of ml/min in estimated glomerular filtration rate (GFR) during follow up, with no patient experiencing an increase in serum creatinine > 0.5 mg/dl. 69 TDF has a well-established safety profile, with an estimated cumulative worldwide exposure to TDF-containing products (excluding generic forms) of almost 5.5 million patient years across all therapy indications, over 2 million patient years of use worldwide, and over across Europe in CHB and HIV indications (data on file). In the VIREAL study that included TDF-naïve, but potentially NA-experienced, patients there were no clinically significant AEs related to TDF and no significant change in renal function. 73 In addition, no safety issues arose in patients with prior renal dysfunction. 76 In the European cohort, the proportion of patients with GFR < 50 ml/min was 3% at baseline and remained unchanged during the study (30 months); TmPO4/ GFR ratio (an experimental marker of urinary phosphate reabsorption, not yet been fully validated) was < 0.70 in ~20% at baseline and throughout the TDF study. 72 Similar TmPO4/GFR ratios at baseline and on therapy were also reported for ETV. 70 In the GEMINIS study, consistently fewer adverse drug reactions were seen compared with registration trials, mean GFR was stable throughout 1 year of therapy, and mean estimated GFR and phosphorous showed no change over time. 74 In all, three cases of renal impairment were reported, all in NA-experienced patients; of these, only one event was considered serious and resulted from overdosing with once-daily TDF in a patient with known renal insufficiency. 74 Recently, a retrospective, community-based cohort analysis demonstrated a similar risk of renal events in age- and sex-matched patients treated with TDF compared with ETV. 77 In this study, a history of transplant and pre-existing renal insufficiency were the only factors independently associated with increases in serum creatinine. Conclusions Long-term CHB treatment. Data from both RCTs and real-life studies have demonstrated that the potent NAs TDF and ETV have excellent efficacy, safety, and tolerability for long-term suppression of viral replication in CHB. Resistance development is extremely low in NA-naïve patients treated with TDF or ETV; however, the high rate of development of ETV resistance in LAMand LAM/ADV-resistant patients limits the use of ETV in the NA-experienced population. In addition, treatment with these agents raises the prospect of not only suppressing viral activity to prevent disease progression but of modifying the disease process itself. The clinical relevance of histological improvement on the incidence of serious complications such as decompensated cirrhosis and HCC needs to be established. There is evidence that sustained response and reversal of histological cirrhosis following antiviral therapy in patients with CHC is associated with reductions in hepatic venous pressure gradient. 78 This is encouraging given that portal hypertension is a key driver in the complications of advanced liver diseases; however, clinical trial data are currently lacking for such parameters in CHB. Very long-term studies, potentially using non-invasive methods to assess fibrosis and response to treatment (e.g. liver stiffness measurement, serological biomarkers [reviewed in Poynard et al. 79 ]) may provide such data. It may also be possible to establish genomic factors associated with progression of fibrosis or treatment response in CHB as has been investigated in CHC. 80 It will also be of value to conduct further studies of patients in whom histological improvement is not observed despite effective long-term suppression of HBV DNA replication. The mechanisms of HCC development also warrant further elucidation. Until such data are available, continuing HCC surveillance in NA-treated patients even in patients who achieve and maintain complete HBV DNA suppression remains important. Future strategies. There is considerable interest in the potential for finite therapy in patients following successful HBsAg seroconversion. Studies are underway to determine if it is possible to successfully combine the potent effects of NAs with an immunomodulatory therapy to allow more patients to stop therapy. Studies investigating this strategy are currently underway. For example, a phase IV study is currently investigating off-treatment sustained response at 120 weeks following 48 weeks of different TDF plus PEG-IFN combination therapy regimens compared with 48 weeks of PEG-IFN alone or continuous TDF monotherapy (ClinicalTrials.gov identifier: NCT ). Data from such studies may eventually lead us from long-term therapy with NAs into an era of more effective finite therapy strategies that can alter the natural course of disease and stop disease progression. 920 Journal of Gastroenterology and Hepatology 28 (2013)

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