Benefits and Risks of Combination Therapy for Hepatitis B

Transcription

1 Benefits and Risks of Combination Therapy for Hepatitis B Norah A. Terrault In successful antiviral therapy of hepatitis B, drug combinations, particularly combinations without cross-resistance, can delay or prevent the emergence of drug-resistant mutants. Because drug-resistant mutants are archived and may limit future therapeutic options, prevention is important for long-term therapeutic efficacy. Additionally, combining drugs may achieve synergistic or additive antiviral effects compared with single drug therapy. Undesirable aspects of combination therapy include higher treatment costs and possibly lower adherence rates (due to pill number or complexity of regimen). Potentially harmful effects of combination therapy include higher rates of side effects, reduced efficacy due to drug competition, and the risk of multidrug-resistant hepatitis B virus (HBV) if combination therapy is insufficient to prevent resistance. Combination therapy has been shown to reduce the rate of drug resistance in chronic hepatitis B, but only when drugs with a low barrier to resistance are used (lamivudine, adefovir). Combination therapies may achieve greater degrees of HBV DNA suppression, but this has not been associated with higher rates of seroconversion (hepatitis B e antigen or hepatitis B surface antigen) compared to single drug therapy. The benefit of combination therapy has yet to be demonstrated with agents that are associated with a high barrier to resistance (tenofovir, entecavir). The use of combination therapy is recommended in specific patient groups: those with decompensated cirrhosis, those coinfected with human immunodeficiency virus and HBV who are on antiretroviral therapy, those who have undergone liver transplantation, and those with drug-resistant HBV infection. There is insufficient evidence to recommend combination therapy as first-line therapy for all patients with chronic hepatitis B. (HEPATOLOGY 2009;49:S122-S128.) Rationale of Combination Therapy of Hepatitis B Abbrevations: HBV, hepatitis B virus; HBsAg, hepatitis B surface antigen; HBeAg, hepatitis B e antigen; HIV, human immunodeficiency virus. From the Departments of Medicine and Surgery, University of California San Francisco, San Francisco, CA. Received January 21, 2009; accepted February 11, Address reprint requests to: Norah Terrault, M.D., S357, 513 Parnassus Avenue, San Francisco, CA Norah.Terrault@ucsf.edu; fax: Copyright 2009 by the American Association for the Study of Liver Diseases. Published online in Wiley InterScience ( DOI /hep Potential conflict of interest: Dr. Terrault has done consulting for Bristol-Meyers- Squibb and Roche Pharmaceuticals, and has received grant support from Roche Pharmaceuticals and Gilead Sciences. Current therapies for chronic hepatitis B virus (HBV) infection are approved for use as monotherapies; however, combination therapy offers several advantages over single drug therapy and has been found to be necessary in many chronic infectious diseases. Combining drugs may achieve synergistic or additive antiviral effects compared with single drug therapy. For example, more rapid achievement of an undetectable HBV DNA level may increase the rates of seroconversion of hepatitis B e antigen (HBeAg) or hepatitis B surface antigen (HBsAg) or improvement in liver tests or liver histology. Additionally, combinations of drugs without cross-resistance can delay or prevent the emergence of drugresistant mutants, a paradigm well established in other chronic viral infections. Because emergence of these drugresistant viral variants can limit future therapeutic options, minimizing this complication is critical for a successful regimen. The ideal combination therapy would target different aspects of HBV replication using agents that have no crossresistance. Interferon (nonpegylated and pegylated forms) has both antiviral and immune-modulating effects. Currently, all of the approved oral drugs for hepatitis B target the HBV polymerase, though there are reported differences in the aspects of polymerase function affected by each drug (Table 1). Combining drugs with the same mechanism of action may lead to drug interference rather than synergy, or to other adverse effects. All of the nucleoside analogs inhibit elongation of the viral minus-strand DNA. Adefovir dipivoxil and entecavir, and to a weaker extent clevudine, inhibit the priming of reverse transcription, and clevudine and entecavir inhibit plus-strand DNA synthesis. 1-5 In general, S122

2 HEPATOLOGY, Vol. 49, No. 5, Suppl., 2009 TERRAULT S123 Table 1. Nucleoside Analogs: Structural Groups and Polymerase Inhibitory Activities Drug Structural Group Priming Polymerase Functions Elongation Negative Strand however, these nucleoside analogs have very similar mechanisms of action, and drugs with different targets and mechanisms of action are desirable for combination therapy. Combined drugs should have complementary resistance profiles. There is no clinically-evident resistance to peginterferon, whereas selection of drug-resistant mutants occurs with all the nucleoside analogs to greater or lesser extent. The nucleoside analogs approved for use in hepatitis B fall into three groups in terms of structure and resistance patterns. The L-nucleosides include lamivudine, emtricitabine, telbivudine, and clevudine; the acyclic nucleoside phosphonates include tenofovir and adefovir; and the deoxyguanosine analogs include entecavir. 6 Resistance to one drug confers at least some resistance to others within the group and may reduce sensitivity to nucleoside analogs from other groups. Studies using combination L-nucleosides have not shown success in terms of antiviral efficacy or prevention of resistance. 7,8 Current Indications for Combination Antiviral Therapy of Hepatitis B Plus Strand Synthesis Lamivudine L-Nucleosides Telbivudine Clevudine Emtricitabine Entecavir Adefovir Tenofovir Deoxyguanosine analogs Acyclic nucleotide phosphonates The American Association for the Study of Liver Diseases and other societal treatment guidelines recommend the use of combination therapy in a limited number of patient subgroups, including those with decompensated cirrhosis, those with human immunodeficiency virus (HIV)/HBV coinfection on antiretroviral therapy, and patients after liver transplantation These recommendations are not based on results of randomized controlled, prospective trials but rather upon anecdotal data, small case series, and the recognized risk of rapid disease progression and life-threatening complications in the absence of controlled HBV replication in these patient populations. 12,13 Combination therapy is also recommended for patients with evidence of drug resistance to minimize the risk of multidrug-resistant HBV with sequential monotherapy. 14,15 This latter use of combination therapy is particularly important given the limited number of treatment options available for patients with drug-resistant HBV infection. Combination therapy in this setting does not represent de novo combination therapy because these patients already have archived resistance mutations from prior drug exposures. The combination therapy recommended for these select groups of patients is two or more nucleoside analogs without cross-resistance. Combination Therapy for Drug-Resistant HBV Infection In patients with lamivudine-resistant HBV infection, the combination of adefovir with lamivudine is superior to adefovir alone. Two randomized controlled studies have addressed this issue (Table 2). While no differences in rates of response or virological breakthrough were evident with treatment for 12 months, 16 longer duration treatment showed superiority of combination therapy over adefovir monotherapy in preventing adefovir resistance. 17 The largest study was based on a retrospectiveprospective cohort of 585 patients with lamivudineresistant chronic hepatitis B (86% HBeAg-negative) treated with adefovir in addition to lamivudine (N 264) or adefovir alone (N 273) for a median of 33 months. 18 The 3-year cumulative risk of adefovir resistance was 16% in the adefovir monotherapy group versus 0% in the combination group (P 0.001). Other cohortstudies have reported superior efficacy with the strategy of adding adefovir to lamivudine rather than switching to Table 2. Randomized Controlled Studies of Combination Therapy for Lamivudine-Resistant HBV Infection Study Population (Reference Number) N Groups Duration of % HBV DNA Levels Undetectable (copies/ml) HBeAg Seroconverson % with Drug- Resistance LMV-resistant HBeAg-positive LMV 12 months 0 ( 1000) ADV 26 ( 1000) ADV & LMV 35 ( 1000) 6 0 LMV-resistant HBeAg-negative ADV 30 months 79 ( 1000) NA ADV & LMV 40 months (median) 68 ( 1000) NA 0 LMV, lamivudine; ADV, adefovir; NA, not applicable.

3 S124 TERRAULT HEPATOLOGY, May 2009 Table 3. Randomized Studies of Combination Therapy: Peginterferon and Lamivudine: 24 Weeks Posttreatment Results Outcomes Janssen et al. 23 HBeAg-Positive Lau et al. 27 HBeAg-Positive Chan et al. 24 HBeAg-Positive Marcellin et al. 25 HBeAg-Negative Arms Peg-IFN 100 g/week for 32 weeks, 350 g/ week for 12 weeks Peg-IFN 100 g/week and LMV 100 mg/day for 52 weeks Peg-IFN & LMV 100 mg/day for 48 weeks Peg-IFN 180 g/week for 48 weeks for 48 weeks for 52 weeks Peg-IFN 1.5 g/kg for 32 weeks & for 52 weeks* for 52 weeks Peg-IFN 180 g/week for 48 weeks N HBV DNA copies/ml (%) HBeAg seroconversion (%) NA NA NA HBsAg loss (%) LMV Resistance (%) LMV, lamivudine; Peg-IFN, peginterferon; NA, not available. *LMV added 8 weeks after peg-ifn and continued 8 weeks beyond stop of peg-ifn. Maximum dose peg-ifn given 100 g/week. Peg-IFN 180 g/week & LMV 100 mg/day for 48 weeks adefovir. 19,20 The combination of lamivudine and adefovir significantly reduced but did not completely prevent virological breakthrough due to resistance. Although data are sparse, the factors that were associated with a higher likelihood of virological breakthrough due to resistance were higher baseline HBV DNA levels, persistence of detectable HBV DNA during therapy, 20 and presence of pre-existing drug-resistant variants. 19 There have been no comparison studies of therapy of chronic hepatitis B with adefovir-resistant, tenofovir-resistant, or entecavir-resistant HBV mutations, as rates of resistance to these agents is less than with lamivudine, and these drugs have been available for shorter periods of time. Nonetheless, the lessons learned from the lamivudineresistance studies support use of combination therapy in patients with drug-resistant HBV and lead to the recommendation that the drugs used should have high antiviral potency and a high barrier to resistance. To optimize the choices of drugs used in treating drug-resistant HBV infection, pretreatment resistance testing may be useful to fully characterize the viral variants present. Combination Therapy in -Naïve Patients Combination therapy has been evaluated as first-line therapy for patients with chronic HBV infection. Randomized studies of combination therapy versus monotherapy have included peginterferon with lamivudine (Table 3) and combinations of nucleoside analogs (Table 4). 7,21-27 These data are limited in several ways. First, there are no or very limited data on combination therapy with recently approved therapies such as entecavir, telbivudine and tenofovir. Additionally, the studies of combination nucleoside analogs were of small sample size, were of relatively short duration, and were underpowered to detect small-tomoderate treatment differences. 7,21,22,26 Peginterferon and Nucleoside Analog Combination Therapy There have been four randomized controlled trials evaluating combined peginterferon and lamivudine (Table 3) and one evaluating peginterferon and adefovir 28 Table 4. Randomized Studies of Combination Nucleoside Analog Therapy: On Responses Study Population (Reference Number) N Groups Duration of % HBV DNA Levels (copies/ml) % HBeAg Seroconversion % Drug-Resistance HBeAg-positive LMV 2 years 14 ( 200) LMV & ADV 26 ( 200) 13 17** HBeAg-positive ADV 96 wks 38 ( 300) ADV & EMT 79 ( 300) 14 0 HBeAg-positive, HIV/HBV 13 LMV 1 year 46 ( 170) coinfection TDF 75 ( 170) TDF & LMV 64 ( 170) 43 0 HBeAg-positive 7 19 LMV 1 year 32 ( 170) TBV61 ( 170) TBV & LMV 49 ( 170) 15 12* *Three M204I and one L180M M204V mutations, 1 wild-type. **One N236 and six M204V/I mutations. LMV, lamivudine; ADV, adefovir; EMT, emtricitabine; TDF, tenofovir; TBV, telbivudine

4 HEPATOLOGY, Vol. 49, No. 5, Suppl., 2009 TERRAULT S125 compared to one or the other agent alone. Four of the five studies started and stopped both peginterferon and the nucleoside analog at the same time; the fifth study used a staggered approach. 24 In all studies, patients were treated for one year and evaluated at the end-of-treatment and 24 weeks after treatment for clinical, biochemical, and virological responses. Long-term follow-up data are available in one study of HBeAg-negative patients 29 and one study of HBeAg-positive patients. 30 The studies were consistent in their findings. Peginterferon (with or without lamivudine) was superior to lamivudine monotherapy, but there was no advantage of combination therapy over use of peginterferon alone. Interestingly, the decline in HBV DNA levels during treatment was greater with combination therapy compared to peginterferon alone or lamivudine alone, with a mean 2.7 log 10 copies/ml greater fall in HBV DNA with combination therapy than with peginterferon monotherapy in HBeAg-positive patients and mean 0.9 log 10 copies/ml greater decline in HBsAg-negative patients. 25,27 However, these differences did not translate into higher rates of HBeAg seroconversion or HBsAg loss. 23,25,27 Furthermore, sustained suppression of HBV DNA at 4 years after treatment was not significantly different in HBeAg-negative patients receiving peginterferon than in those receiving both peginterferon and lamivudine. 25 Similar preliminary results were obtained in a smaller randomized controlled trial of peginterferon and adefovir versus peginterferon alone for 48 weeks in HBeAg-negative chronic hepatitis B. 28 Although greater HBV DNA decline was seen during combination therapy, rates of sustained responses (virological and biochemical) 24 weeks after treatment were not significantly different. In terms of preventing lamivudine resistance, the combination of peginterferon and lamivudine was associated with significantly lower rates of genotypic resistance at the end of 48 weeks of treatment compared to lamivudine alone 24,25,27 ; nevertheless, lamivudine resistance was not completely prevented (Table 3). Whether specific subgroups may benefit from the combination of a nucleoside analog and peginterferon therapy has yet to be determined. One post-hoc analysis of factors associated with sustained responses in HBeAg-negative chronic hepatitis B suggested that patients infected with HBV genotype D had higher rates of responses with combination peginterferon and lamivudine than with peginterferon monotherapy. 31 Uncontrolled studies of the combination of peginterferon with a nucleoside analog suggest that declines in intrahepatic HBV DNA and covalently closed circular DNA levels are greater than those historically achieved with monotherapy using a nucleoside analog, but whether intrahepatic HBV DNA and covalently closed circular DNA levels are reduced more with the combination of peginterferon and a nucleoside analog compared to peginterferon alone is unknown. There is a lack of controlled trials evaluating current first-line therapies (entecavir, tenofovir, peginterferon) alone and in combination. Additionally one treatment strategy has predominated, namely combination therapy starting and ending at the same time. Few studies have examined alternative combination approaches. Of note, the one study that started peginterferon 8 weeks before adding lamivudine reported the highest rate of HBeAg seroconversion among the combination studies of a nucleoside analog and peginterferon. 24 Combination Nucleotide Analog Therapy Published controlled trials comparing combinations of nucleoside analogs versus nucleoside analog monotherapy with one or the other for treatment-naïve patients are few in number and predominantly studied drugs that are no longer considered first-line treatment for chronic hepatitis B. 21,22,26 Nonetheless, these studies revealed little additive or synergistic antiviral effects of combination nucleoside analog therapy over monotherapy. The decline in HBV DNA levels and rate of HBeAg and HBsAg seroconversion were comparable between groups (Table 4). However, a greater proportion of patients on combination therapy achieved long-term HBV suppression seemingly related to a lower rate of virological breakthrough compared to single drug therapy. For example, in a study of patients with HBeAg-positive chronic hepatitis B, only 17% of patients treated with the combination of adefovir and lamivudine developed genotypic resistance after 2 years compared to 43% of those on lamivudine monotherapy. 21 In a small study of patients coinfected with HIV/HBV who were randomized to receive lamivudine, tenofovir, or the combination of the two, genotypic resistance was not seen after 1 year in the tenofovir or combination group but was found in 15% of patients treated with lamivudine monotherapy. 22 In contrast, the combination of lamivudine and telbivudine was not effective in reducing the risk of genotypic resistance, 7 highlighting the importance of combining drugs with different drug resistance patterns. In general, antiviral efficacy appears to be driven primarily by the most potent of the nucleoside analogs in the combination, and synergistic or additive effects are not apparent. For example, in a small study of 40 HBV/HIV coinfected patients who had not previously received antiretroviral therapy, treatment with the combination of tenofovir and lamivudine (n 11) or tenofovir alone (n 12) was superior to lamivudine alone (n 13) for reduc-

5 S126 TERRAULT HEPATOLOGY, May 2009 tion in HBV DNA levels and proportion of patients with HBV DNA levels below 1000 copies/ml. There were no significant differences in the viral outcomes between the tenofovir monotherapy and the combination tenofovirlamivudine arms. 22 This study, like others that have evaluated combination nucleoside analogs in treatment-naïve patients, was of small sample size. Thus, the overall benefit of combination nucleoside analogs therapy compared to single agents with potent activity against HBV (such as entecavir or tenofovir) has yet to be shown. While the available data indicate that combination therapy reduces the risk of genotype resistance, this benefit is evident only in studies that used drugs with a high rate of resistance. In studies using drugs with a low rate of resistance, such as entecavir and tenofovir, the benefits of combination therapy versus monotherapy have not been established. Indeed, given the low reported rates of resistance with these drugs, large-scale studies of prolonged duration will be necessary to establish such a benefit. Adding Versus Switching Nucleoside Analogs in Therapy for Patients with a Suboptimal Antiviral Response A related, but separate issue relates to the role of add on combination therapy in current treatment algorithms. For patients treated with nucleoside analogs, it is recommended that antiviral response to treatment be evaluated at specific intervals and changes in therapy made in those with a suboptimal virological response. 9,35 The guidelines indicate this change in drug therapy can either be add on (i.e., adding the second agent resulting in combination therapy) or a switch (i.e., switching to alternative single drug). There are no randomized studies that directly assess which strategy is better. Preliminary results from observational studies provide some insights into the factors of potential importance in making this decision. In a small study of 79 patients ( 60% LMV-experienced) with suboptimal responses to adefovir therapy after a median treatment period of 415 days, patients were randomized to receive tenofovir (switch, N 39) or tenofovir plus emtricitabine (add, n 40). After 24 weeks, those with HBV DNA 400 copies/ml were eligible to receive open-label combination therapy. At the end of 48 weeks treatment, the proportion of patients with undetectable HBV DNA levels was the same in patients receiving combination versus tenofovir monotherapy (81% in both groups). 36 In another small study of 69 HBeAg-positive patients with suboptimal response to adefovir, defined as less than 3-log decline in HBV DNA, after 24 weeks therapy, those who switched to telbivudine had a 2.1 log decline in the subsequent 28 weeks compared to only a 0.8 log decline in those continuing adefovir. None of the patients switching therapy developed virologic breakthrough during the study period. 37 Finally, in the registration trials for tenofovir, patients initially randomized to adefovir were switched to tenofovir at week Of the 125 patients who were initially treated with adefovir but continued to have HBV DNA levels above 400 copies/ml, suppression of HBV DNA to undetectable levels was achieved in 75% of 90 HBeAg-positive and 94% of 35 HBeAg-negative patients 24 weeks after the change to tenofovir monotherapy. Thus, based on current understanding of factors influencing treatment failure, the add-on strategy may be preferred if the initial drug has a low genetic barrier to resistance and/or if the time from initiation of therapy to change is prolonged, such that resistance mutations are likely to have been selected. However, switching to an agent with a higher genetic barrier to resistance may be more effective than adding a second agent with a low genetic barrier to resistance. Regardless of whether an add-on or switch of therapy is undertaken, the subsequent drug used should be one without cross-resistance to the first drug. Risks of Combination Therapy Combination therapy may have undesirable or harmful effects. Undesirable aspects of combination therapy include higher treatment costs and possibly lower adherence rates (because of pill number or complexity of regimen). Cost considerations are complex because a cheaper drug with a higher rate of resistance has additional costs in terms of managing drug-resistant disease. Cost-effectiveness models will be useful in assessing this issue in future, but none are available at present. Indeed, the lack of clinical data on long-term outcomes of combination therapy makes it challenging to develop cost-effectiveness models. Adherence is influenced by the duration and complexity of a regimen. Although the development of combination pills may be important for improving adherence with combination regimens, enhanced monitoring tools and greater emphasis on education of patient and provider are also important. Potentially harmful effects of combination therapy include higher rates of side effects, reduced efficacy due to drug competition, and the risk of multidrug-resistant HBV if combination therapy is insufficient to prevent resistance. In prospective control trials, the combination of peginterferon and lamivudine had similar tolerability to peginterferon alone, but was associated with more symptoms than in patients who received lamivudinemonotherapy. 24,25,27 Combinations of nucleoside analogs

6 HEPATOLOGY, Vol. 49, No. 5, Suppl., 2009 TERRAULT S127 Table 5. Summary of Efficacy Outcomes with Combination Therapy in -Naïve Patients with Chronic Hepatitis B Outcomes HBV DNA suppression Rapidity of achieving HBV DNA suppression HBeAg serconversion HBsAg seroconversion Rate of virologic resistance Histological improvement Combination Versus Monotherapy Combinations of nucleoside analogs do not yield increases in HBV DNA suppression; Combination of peginterferon and lamivudine appears to have additive effects No advantage of combination therapy No difference between combination therapy and monotherapy No difference between combination therapy and monotherapy Rates are lower with combination therapy, but resistance is not completely prevented No difference between combination therapy and monotherapy appear to be well-tolerated in the short term, in studies to date. 21,22 Adherence has not been adequately evaluated outside of clinical trial settings. Conclusions 1. At present, combination therapy can be recommended only for patients who are at high risk of complications in the event of virological breakthrough (e.g., patients with advanced cirrhosis, liver transplant recipients, patients with HBV/HIV coinfection) and patients who already have drug-resistant HBV. 2. For patients with drug-resistant HBV, combination therapy of drugs without cross-resistance and preferably with high genetic barrier to resistance is recommended to prevent the subsequent development of multidrug-resistant HBV. 3. There is insufficient evidence to recommend combination therapy as first-line therapy for the typical patient with chronic hepatitis B requiring treatment (Table 5). This lack of evidence is particularly true with current first-line agents that have no (peginterferon) or low (entecavir or tenofovir) rates of antiviral resistance. 4. There have been no studies addressing the issue of whether add-on (combination) therapy versus switching to an alternative monotherapy is preferable in patients with a suboptimal initial virological response to a single nucleoside analog. Add-on therapy may be advisable if the initial drug used has a low genetic barrier to resistance or if the duration of therapy has been prolonged because these factors increase the likelihood of drug-resistant HBV being present. Needs for Future Research 1. Defining efficacy of add-on versus switching nucleoside analog therapy for patients with a suboptimal initial virologic response. 2. Evaluation of monotherapy with a nucleoside analog with a high resistance barrier to combination nucleoside analog therapy. 3. Evaluation of the relative efficacy and safety of starting treatment with a combination of nucleoside analogs versus adding a second agent only once antiviral resistance has arisen. 4. 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