Treatment of chronic hepatitis B

Review

Treatment of chronic hepatitis B

Treatment of chronic hepatitis B Man-Fung Yuen and Ching-Lung Lai

This review updates the treatment of chronic hepatitis B infection. Complete eradication of hepatitis B virus (HBV) is not possible, so the efficacy of treatment has to be assessed by whether it can limit long-term cirrhosis-related complications. We discuss two major groups of treatments—immunomodulators (interferon alfa, thymosin ␣1, therapeutic vaccines) and nucleoside analogues (lamivudine, adefovir, entecavir, emtricitabine, ␤-L-2´-deoxythymidine). To date, interferon alfa and lamivudine are the only two agents approved for chronic hepatitis B. Interferon alfa achieves a short-term outcome of around 20–30% loss of HBeAg. The efficacy is lower in Chinese patients, who are immunotolerant to HBV because of acquisition of the disease during early childhood, than in white patients. This difference is further confirmed on long-term follow-up. Interferon alfa does not affect the development of cirrhosis-related complications in Chinese patients, whereas in white patients, the frequency of long-term complications is reduced if interferon alfa is successful in inducing loss of HBeAg. Lamivudine profoundly suppresses viral replication and achieves an HBeAg seroconversion rate similar to that of interferon alfa. It is equally effective in Chinese and white patients because the main antiviral mechanism is through inhibition of reverse transcription of HBV during viral replication. However, long-term lamivudine therapy is associated with emergence of HBV variants, YMDD variants. Newer nucleoside analogues are being extensively investigated by studies in vivo and in vitro. Combination therapy with two or three nucleoside analogues or immunomodulators plus nucleoside analogues will be the future direction of treatment of chronic hepatitis B. Lancet Infectious Diseases 2001; 1: 232–41

An estimated 400 million people are chronically infected with the hepatitis B virus (HBV; electronmicrograph of the virus shown in figure 1).1 The ultimate long-term aim in the treatment of these patients is to prevent or at least to decrease the risk of the development of cirrhosis and hepatocellular carcinoma.2 However, for clinical trials with follow-up of 1 year or less after therapy, more realistic shortterm objectives are usually used. (1) Viral suppression as shown by loss of HBeAg with or without seroconversion to anti-HBe and a decrease in HBV DNA to amounts undetectable by in-house or commercially available assays (eg, the branched DNA assay, Bayer 232

Figure 1. Electronmicrograph of HBV showing complete double-shelled virions (Dane particles) and excess HBsAg in tubular and small spherical form. Taken from Almeida JD, Rubenstein D, Stott EJ. New antigenantibody system in Australia-antigen-positive hepatitis. Lancet 1971; 2: 1225–27.

Diagnostic Limited, USA; Digene Hybrid Capture assay, Digene Corporation, USA). (2) Reduction in liver damage as shown by the return to normal values of serum aminotransferases (if these are high) and by histological improvement on liver biopsy samples. (3) Complete eradication of the virus as shown by the loss of HBsAg, with seroconversion to anti-HBs, and the inability to detect HBV DNA in serum or liver by PCR assays. (4) With the use of nucleoside analogues as antiviral agents, the eradication of the HBV supercoiled or covalently closed circular (ccc) form from the nuclei of hepatocytes may be used as a marker of therapeutic efficacy in the future. However, with the treatment available at present, complete eradication is not possible. M-FY and C-LL are at the Division of Gastroenterology and Hepatology, Department of Medicine, University of Hong Kong, Queen Mary Hospital, Hong Kong SAR, China Correspondence: Prof Ching-Lung Lai. Tel +852 28554252; fax +852 28162863; email [email protected] THE LANCET Infectious Diseases Vol 1 November 2001

For personal use. Only reproduce with permission from The Lancet Publishing Group.

Review

Treatment of chronic hepatitis B

Panel 1. Agents currently used or under trial for treatment of chronic hepatitis B Immunomodulators Interferon alfa (recombinant, pegylated) Thymosin ␣1 Therapeutic vaccines Antiviral agents: nucleoside/nucleotide analogues Lamivudine Adefovir dipivoxil Entacavir Emtricitabine ␤-L-2´-deoxythymidine Famciclovir Other nucleoside analogues Combination of immunomodulators and antiviral agents Lamivudine plus interferon alfa Lamivudine plus therapeutic vaccines Steroid priming followed by lamivudine or interferon alfa Multiple nucleoside analogues such as lamivudine plus famciclovir and lamivudine plus adefovir dipivoxil

In most clinical trials, the standard therapeutic endpoints are the loss of HBeAg (with or without anti-HBe seroconversion) together with undetectable HBV DNA as measured by commercial assays. Histological improvement, even if analysed, is commonly taken as a secondary endpoint. Total eradication of the virus is rarely achieved and rarely used as a therapeutic endpoint. There is increasing evidence, however, that, at least in Asian patients with chronic hepatitis B, long-term complications of cirrhosis, such as ascites, variceal bleeding, and hepatic encephalopathy, and of hepatocellular carcinoma can develop with the low levels of HBV DNA after HBeAg seroconversion. Whether this is also true for white patients is not known until the natural course of chronic hepatitis B in these patients is better understood. With the availability of more potent antiviral agents, absence of HBV DNA at levels detectable by PCR assays may become one of the primary endpoints.

Agents for the treatment of chronic hepatitis B The agents currently used or under investigation for the treatment of chronic hepatitis B can be broadly divided into two main groups (panel 1, figure 2).3 These agents can also be used in combination. The first group, immunomodulators, act on the immune response of the host to HBV antigens expressed on the surface of the hepatocytes, causing or potentiating the lysis of infected hepatocytes. They also modulate the control by antiviral cytokines of viral replication. In patients with poor hepatic reserve due to cirrhosis, regeneration of healthy hepatocytes after immune destruction of infected cells may be impaired. Immunomodulators should be used cautiously for these patients, because their use may result in hepatic decompensation. Interferon alfa is the best known of the immunodulators. Other newer agents of this class include pegylated interferon, thymosin ␣1, and therapeutic vaccines. THE LANCET Infectious Diseases Vol 1 November 2001

Regeneration

Healthy tissue

Reinfection blockade with antiviral therapy

HBV production

Immune response HBV infected cells Inflammation and cell death

Clinical hepatitis Figure 2. Simplified analysis of the disease process in hepatitis resulting from HBV infection, with points of possible intervention. Adapted from reference 3 with permission of the publisher WB Saunders.

The second group of agents used in the treatment of chronic hepatitis B is the nucleoside analogues. These act by suppressing the replication of HBV and hence blocking reinfection of healthy hepatocytes. In addition, there is evidence that they may enhance immune clearance of infected hepatocytes indirectly. For these agents to eradicate HBV infection, the pool of ccc HBV DNA in the nuclei of infected hepatocytes has to be eradicated. This replication intermediate is little affected by current nucleoside analogues. However, there is now theoretical evidence that, provided viral replication is adequately suppressed and reinfection of healthy hepatocytes is prevented, the pool of ccc HBV DNA may be depleted through natural cell division and cell death with long-term therapy. This review mainly concentrates on interferon alfa and lamivudine, because these two agents are the most extensively studied and have been registered in a large number of countries.

Immunomodulating agents Interferon alfa

Interferon alfa was the first agent to be approved for use in the treatment of patients with chronic hepatitis B. It is generally given parenterally (subcutaneously) in a 16-week course of either 5 MU daily or 10 MU three times per week. Meta-analyses of randomised placebo-controlled studies have shown that interferon alfa is beneficial (table 1).4,5 However, the difference between treated and control groups in the proportions of patients with loss of HBeAg and HBV DNA is only 20%, and that for loss of HBsAg is only 6%. Interferon alfa has significant effects on normalisation of serum alanine aminotransferase concentrations. Most studies have shown that in patients whose treatment is successful (ie, with loss of HBeAg), there is improvement in Table 1. Summary of results of a meta-analysis of 15 randomised placebo-controlled trials of interferon alfa in chronic hepatitis B infection4 Proportion of patients Interferon alfa group Control group

p

Loss of HBV DNA 37%

17%

0·0001

Loss of HBeAg

33%

12%

0·0001

Loss of HBsAg

7·8%

1·8%

0·001

233

For personal use. Only reproduce with permission from The Lancet Publishing Group.

Review liver histology. From the meta-analysis, though interferon alfa to some extent hastened loss of HBeAg in Chinese patients, the treatment was generally less effective than in white patients. The difference in response between Chinese and white patients was probably due to the fact that white people mostly acquire HBV infection during adolescence or adulthood. These patients would progress directly from the acute infection to immune clearance of HBV.6 By contrast, the majority of Chinese people acquire the infection at birth or during the early postnatal period.7,8 These patients would have a long period of immune tolerance to the virus for several decades of life.9,10 A short (16-week) course of interferon alfa is unlikely to alter the natural course of HBV infection in these patients. Steroid therapy in chronic hepatitis B causes increased viral replication, possibly acting through the glucocorticoidresponsive element of the HBV genome. When steroids are discontinued, there is an immunological rebound associated with an increase in T-lymphocyte function, resulting in a decline in HBV DNA. The increase in T-lymphocyte function may potentiate the effect of interferon. However, in a large multicentre trial by Perrillo and colleagues,11 the rate of HBeAg seroconversion was nearly identical in white patients treated with interferon alfa alone and in others treated with steroid priming followed by interferon alfa, though patients with low concentrations of alanine aminotransferase before treatment were more likely to respond to the combined treatment than to interferon alfa alone. In a trial of 120 Chinese patients,12 Liaw and colleagues found that among those with baseline alanine aminotransferase concentrations of 200 IU/L or lower, steroid priming followed by interferon was better than interferon alone (p=0·056). However, steroid withdrawal is known to precipitate hepatic decompensation in patients with marginal liver function due to severe hepatic necrosis. Occasionally, such decompensation may be fatal. Withdrawal of steroids is not recommended as routine before treatment with interferon alfa. The factors associated with poor response to interferon alfa treatment are listed in panel 2. The two major considerations are serum alanine aminotransferase and HBV-DNA concentrations; high activity of the former and low levels of the latter indicate that the patient is already in the immune clearance phase. Infection with HBV strains carrying precore mutations, which result in HBeAg-negative chronic hepatitis B, are rare in western Europe and North America but common in

Panel 2. Factors associated with poor response to interferon alfa Male sex Long duration of infection Asian origin Low alanine aminotransferase concentrations High HBV DNA concentrations Liver histology showing low to mild activity Precore mutations Homosexual Impaired immunity (eg, coinfection with HIV) 234

Treatment of chronic hepatitis B

Panel 3. Adverse effects of interferon alfa Influenza-like syndrome (rapid tachyphylaxis) Myalgia Marrow suppression (moderate in most cases) Alopecia Depression (severe in some cases) Induction of autoantibodies Induction of interferon neutralising antibodies In patients with advanced hepatitis/cirrhosis: susceptibility to bacterial infections worsening of liver function

Mediterranean and Asian countries. The response to interferon alfa is significantly weaker in patients infected with virus with precore or basal core promoter mutations than in those infected with other strains. In an Italian trial of 115 patients,13 the response rate (as defined by undetectable HBV DNA by an in-house dot-blot hybridisation assay) was 19·4% in patients with precore mutations compared with 47·3% in patients with wild-type HBV. Relapses were also more frequent in patients with precore mutations (85·7%) than in those with wild-type HBV (19·4%). The major adverse effects are listed in panel 3. These can be severe and debilitating and are typically dose-related. Though most adverse effects can be decreased by lowering the dose of interferon alfa, some can necessitate premature cessation of therapy. Fever can be alleviated by the use of paracetamol. The initial influenza-like syndrome can be kept to a minimum by gradual escalation of the dose during initiation of therapy. Induction of autoantibodies, generally clinically silent, can lead to hypothyroidism, hyperthyroidism, and idiopathic thrombocytopenic purpura. Interferon use may also induce the development of autoimmune hepatitis in individuals who are genetically predisposed to develop autoimmune liver disease. The presence of interferon neutralising antibodies is of no clinical importance in most cases, but when present in high titre, these antibodies can counteract the effects of interferon alfa. In patients with mild or moderate hepatic decompensation, interferon alfa should be used only under close monitoring and in low doses with very cautious dose escalation. For white patients with chronic hepatitis B, there are good long-term follow-up data. Up to 20–70% of patients who have loss of HBeAg and seroconversion to anti-HBe will eventually also lose HBsAg.14–16 (Most clinical trials of interferon alfa, unlike the trials with lamivudine, have used loss of HBeAg rather than seroconversion to anti-HBe as endpoint. In most patients, loss of HBeAg will be followed by seroconversion to anti-HBe within a few months; the subsequent discussion mentions only HBeAg seroconversion for simplicity.) In most patients, HBV DNA is still detectable by PCR assay after HBeAg seroconversion if they remain positive for HBsAg, but it will become undetectable in 60–100% of those who lose HBsAg. However, whether or not they are HBsAg positive, patients who have HBeAg seroconversion, compared with those who remain positive for HBeAg, have a lower risk of developing cirrhosis-related complications, and longer THE LANCET Infectious Diseases Vol 1 November 2001

For personal use. Only reproduce with permission from The Lancet Publishing Group.

Review

Treatment of chronic hepatitis B

overall survival as well as survival without these complications.14 This finding applies both for patients who have HBeAg seroconversion induced by interferon alfa and those who have spontaneous HBeAg seroconversion, but the clearance rate for HBeAg (and HBsAg) remains significantly higher in interferon-alfa-treated patients during long-term follow-up. To date there have been only two studies on the longterm follow-up of interferon alfa therapy in Asian patients. In a Taiwan study of 120 patients with median alanine aminotransferase on entry to the study of over 200 U/L, median follow-up was 6·5–7·4 years.17 There was a marginally significant increase in cumulative HBeAg seroconversion in the group assigned interferon alfa, especially in those who had steroid priming before receiving interferon alfa (p=0·049). There was no difference in the development of new cirrhosis or of cirrhosis with complications between the treated and control patients. In view of this, the finding that hepatocellular carcinoma occurred in a significantly higher proportion of the control patients is rather surprising. The second series consisted of 411 patients from Hong Kong, and had median follow-up of 9 years.18 The cumulative HBeAg seroconversion rate was similar in both the interferon-alfa-treated and the control patients, irrespective of alanine aminotransferase concentrations. HBV DNA was detectable by PCR assay in 88·6% of treated patients and 91·1% of control patients who had HBeAg seroconversion. Complications of cirrhosis and hepatocellular carcinoma occurred with equal frequency in both groups (nine of 208 treated patients and two of 203 controls). According to this study, interferon alfa confers no long-term benefit with respect to HBeAg seroconversion and cirrhotic complications. The discrepancies between the two series are more apparent than actual, because the higher HBeAg seroconversion rate of interferon-alfa-treated patients in the Taiwan series was of borderline significance, and neither series found a difference in the development of cirrhotic complications. Some of the discrepancies between the series are probably related to selection; in the Taiwan study, patients were selected to have very active disease with fairly high alanine aminotransferase concentrations and therefore represented a special subgroup of Chinese patients with chronic hepatitis B. From the data to date, interferon alfa appears to be of little long-term benefit in the majority of Asian patients. Thymosin ␣1

Thymosin ␣1 is a synthetic polypeptide of 28 aminoacids originally isolated from thymosin fraction 5. It has several modes of action. It primarily promotes T-cell maturation, but it also acts after maturation, inducing increased production of cytokines (eg, interferon gamma, interleukin 2). It can upregulate the expression of cytokine receptors. In patients with chronic hepatitis B, there is a deficiency of thymosin ␣1 compared with the normal population. In a study of woodchucks infected with the woodchuck hepatitis virus, all six animals treated with thymosin ␣1 showed a large decrease in viral titres, of 1000 fold or greater in four of them.19 THE LANCET Infectious Diseases Vol 1 November 2001

Though thymosin ␣1 may have some delayed effects in inducing loss of HBeAg and decrease in HBV DNA, the results of the randomised trials so far are conflicting. Two trials, one in 33 patients with precore mutants20 and one in 98 Chinese HBeAg-positive patients,21 showed that the effect of 6–12 months’ treatment is negligible at the end of the course but increases 6 months after therapy. However, a third multicentre study of 99 HBeAg-positive patients showed that thymosin ␣1 had little effect at the end of therapy and 6 months later.22 It is difficult to explain the delayed response observed in the first two trials because the response can be further delayed by a longer course of treatment. Therapeutic vaccines

Therapeutic vaccines are being developed and tested alone or in combination with interferon alfa and nucleoside analogues. The aim of giving the vaccines is to improve the inefficient response of T helper cells and/or cytotoxic T lymphocytes (CTLs) in patients with chronic hepatitis B as well as to correct the Th1/Th2 imbalance in the patients. The challenges with developing therapeutic vaccines are the selection of the most antigenic sites of the HBV genome and the search for a potent and effective adjuvant. The available data on therapeutic vaccines are preliminary or disappointing. CY-1899 is a lipopeptide consisting of three components: a CTL epitope of aminoacids 18–27 of HBcAg; a T-helper cell epitope of residues 830–843 of tetanus toxoid; and two palmitic acid molecules. In a pilot study of 90 patients and various doses of CY-1899,23 CTL activity remained well below that seen with the resolution of acute hepatitis B. No viral clearance was achieved. Other potential therapeutic vaccines are undergoing phase II/III trials. Some are examining the effect of combining the vaccines with lamivudine or interferon alfa. One of these is the vaccine HBV/MF59 of the Chiron Corporation, USA. It consists of recombinant pre S2 and S antigen combined with the adjuvant MF59, an oil-in-water emulsion of squalene, a metabolisable oil, and surfactants. Preliminary results24 in healthy volunteers showed immunogenicity 100 times higher than licensed recombinant vaccines. Another potential use of therapeutic vaccine is being investigated by the Institut Pasteur, France. Six injections of the currently available vaccines, either GenHevac B from Chinese hamster ovary cells (Institut Pasteur) or Recombivax vaccine from yeast cells (Saccharomyces cerevisiae; Merck and Co, USA) were given over a year, before a 6-month course of interferon gamma, 5 MU three times a week. This course was followed by a seventh booster dose of either vaccine. Vaccination elicited peripheral-blood mononuclear-cell proliferative responses specific for envelope antigen mediated by CD4 T lymphocytes in seven of 27 patients.25 There was some reduction in serum HBV DNA in these individuals. The trial is still continuing, and the results of the subsequent interferon therapy are not yet known. 235

For personal use. Only reproduce with permission from The Lancet Publishing Group.

Review

Treatment of chronic hepatitis B

lamivudine therapy the responses to both antigens showed a rapid and significant increase that persisted throughout the Lamivudine is the (⫺)enantiomer of the deoxycytidine treatment period. A temporal association was noted between analogue 2'-deoxy-3'-thiacytidine. It is metabolised in recovery of T-cell reactivity to viral antigens and a decrease hepatocytes, where stepwise addition of phosphate groups in viral load in blood. Because lamivudine mainly acts by chain termination of yields the active 5'-triphosphate form.26 Unlike some nucleoside analogues, lamivudine has little activity against viral DNA and by competitive inhibition of DNA mammalian DNA polymerase-␥, the enzyme that brings polymerase/reverse transcriptase, it is equally effective in about synthesis of mitochondrial DNA. Nor is it Asian and white patients with chronic hepatitis B, and incorporated into mitochondrial DNA. As a result, it has achieves almost identical viral suppression for wild-type little or no effect on bone marrow, hepatocytes, kidney, HBV and precore HBeAg-negative mutants. nerves, or muscle tissue. Large-scale placebo-controlled trials have been carried Lamivudine acts mainly by suppressing the out in Asian and white patients, and also in those with replication of HBV.27 However, it also has some precore HBV mutants.29–31 The results of the three trials indirect immunomodulatory effect. Lamivudine shows were similar (table 2). The rate of HBeAg seroconversion two modes of viral suppression. First, the active to anti-HBe with undetectable HBV DNA at the end of triphosphate metabolite mimics deoxycytidine 1 year of lamivudine therapy (16–32%)29,30 is similar to triphosphate and is incorporated into newly synthesised that of interferon alfa (21–37%).11,32 In the Asian study, a HBV DNA, leading to chain termination. Second, the raised alanine aminotransferase concentration before active form shows competitive inhibition of both viral therapy was the strongest determinant for HBeAg DNA-dependent and RNA-dependent DNA polymerase seroconversion; the rate of HBeAg seroconversion was 5% for patients with pretreatment values less than twice activity (ie, reverse transcriptase activity). There are different possible sites of action for lamivudine the upper limit of normal, 26% for those with values two on the HBV-replication cycle (figure 3). The first site of to five times the upper limit of normal, and 64% for inhibition is the step of reverse transcription of the those with values more than five times above the upper pregenomic mRNA into the nascent minus-strand DNA limit of normal.33 Lamivudine is as effective for viral suppression for HBV (pathway 1). The second site of action blocks the formation of plus-strand DNA from the nascent minus-strand DNA, with precore mutations as for wild-type HBV. It is also safe which is dependent on viral DNA polymerase activity and effective when used in patients with decompensated (pathway 2). DNA-chain-terminating drugs such as cirrhosis, even in those awaiting liver transplantation. In a lamivudine can also exert their antiviral effect by inhibiting study of 35 patients by Villeneuve and colleagues (ten with the completion of double-stranded DNA, thus reducing disease of Child-Pugh class B and 25 with Child-Pugh class cccDNA formation (pathway 3). This action would impair C cirrhosis),34 the 23 patients who had more than 6 months the amplification and replenishment of the cccDNA pool in of lamivudine showed slow but significant improvement in the nucleus. Finally, the formation of cccDNA during the liver function, which was most pronounced after 9 months initial entry of the virus into the hepatocyte nucleus may be of treatment. Three patients developed lamivudine-resistant HBV mutants, but their liver function did not deteriorate. also affected (pathway 4). At the immunological level, Boni and colleagues studied However, the effect of drug-resistant HBV mutants in the 12 patients with HBeAg-positive chronic active hepatitis longer term must be monitored very carefully, because any who received lamivudine for 12 months and were then hepatic flare in this group can have disastrous consequences. The drug is remarkably free of side effects.26 Mild followed up for 6 months.28 The T-cell response to HBcAg and HBeAg before treatment initiation was low, but with constitutional symptoms such as fatigue, headache, and nausea occur as frequently in placebotreated patients as in those treated Infectious Infectious Lamivudine with lamivudine. Pancreatitis has been HBV virion HBV virion reported in children receiving 4 3 2 1 lamivudine for HIV infection but has not been seen in adults or children treated for hepatitis B alone. Non-specific rises HBsAg in amylase have also been reported. DNA pol envelopes Rises in serum alanine and aspartate RT Partly aminotransferase concentrations during double-stranded (–)–DNA therapy occur in up to 30–40% of DNA patients, but they are commonly Encapsidated without symptoms, mostly moderate in pregenomic A(n) severity, and similar in frequency to mRNA cccDNA mRNA placebo patients. Occasionally, the occurrence of such increases is related to the emergence and selection of Figure 3. Four possible sites of action of lamivudine in HBV replicative cycle. See text for details. Adapted from reference 27 with permission of the publisher Wiley-Liss Inc. lamivudine-resistant mutants of HBV.

Nucleoside/nucleotide analogues Lamivudine

236

THE LANCET Infectious Diseases Vol 1 November 2001

For personal use. Only reproduce with permission from The Lancet Publishing Group.

Treatment of chronic hepatitis B

Table 2. Summary of effect of 1 year of lamivudine 100 mg daily in three placebo-controlled trials

Number of patients

Lai et al29 143

Dienstag et al30 Tassopoulos et al31 66 60

Special characteristic Chinese 59% white Histological 56% 52% improvement* (placebo 25%, (placebo 23%, p<0·001) p<0·001)

Precore mutant HBV 60% (placebo data not available)

Worsening of fibrosis 0% 5% 2% (placebo 15%, (placebo 20%, (placebo data not p=0·01) p=0·01) available) HBeAg seroconversion

16% 17% (placebo 4%, (placebo 4%, p=0·02) p=0·04)

Not applicable

Decrease in HBV DNA 98% 95–99% ·· (placebo 23%, (placebo 40%) p<0·001) Sustained suppression of HBV DNA

··

44% 65% (placebo 16%, (placebo data not p<0·001) available)

Normalisation of alanine aminotransferase

72% 41% (placebo 24%, (placebo 7%, p<0·001) p<0·001)

··

Complete biochemical ·· and HBV-DNA response

··

63%† (placebo 32%, p<0·01)

YMDD variant

32%

27%

15%

*2 or more points reduction in Knodell necroinflammatory score. †Assessed at 24 weeks.

An increase in the activities of these enzymes also occurs in over 20% of patients after cessation of lamivudine therapy, probably reflecting the immune response to resurgence of viral replication on discontinuation of the drug. These events are usually mild to moderate in severity, are seldom associated with jaundice or hepatic decompensation, and may be followed by spontaneous HBeAg seroconversion. They are rare in patients who have already had HBeAg seroconversion during therapy.35 Resumption of lamivudine for patients with increased aminotransferase concentrations results in HBV DNA and alanine aminotransferase responses similar to those in drug-naïve patients first treated with lamivudine. However, this practice may increase the rate of emergence of drug resistance. Mathematical modelling of viral dynamics has been used to calculate the required duration of treatment with nucleoside analogues.36 The estimated half-life of the free virus is about 24 h, with a lifespan of 35 days and a daily turnover rate of 50%. The estimated half-life of infected hepatocytes is 10–100 days and the daily turnover 1–7%, depending on the activity of the immune response. The time taken for a nucleoside analogue to clear the patient of infected cells will depend on several factors: the efficacy with which it inhibits infection of uninfected cells; the efficacy of inhibition of new virus production; the rate of decline of infected cells; and the rate of decline of intranuclear cccDNA. With assumed efficacy of 100% for the drug, 1 year of antiviral treatment can reduce the number of infected cells to 10⫺11 of its initial value if the half-life of the infected cells is 10 days, whereas it will be decreased to 8% of its initial value if the half-life of the THE LANCET Infectious Diseases Vol 1 November 2001

Review infected cells is 100 days. If the efficacy is 99·3% (the drug chosen for this model was adefovir dipivoxil), 517 days of treatment can reduce the viral load to one copy of HBV DNA.37 In practice, possibly because of the amplification and transmission of cccDNA to daughter hepatocytes, treatment for years may be required. The obvious disadvantages of longer durations of treatment are the rising cost and the increasing development of resistance to lamivudine used as a single agent. The current practice is to stop lamivudine at around 6 months after the patient has undergone HBeAg seroconversion. After HBeAg seroconversion, follow-up of more than a year after cessation of lamivudine shows that this response is durable in 81% of both Asian and white patients. This response is similar to the durability of HBeAg seroconversion after interferon alfa and the natural HBeAg seroconversion in Asian patients with chronic hepatitis B. As yet only scanty data are available on long-term follow-up of lamivudine therapy. After 4 years of continuous lamivudine in the trial with Asian patients, the overall rate of HBeAg seroconversion in 58 patients was 47%.38 The HBeAg seroconversion rate for patients with pretherapy alanine aminotransferase concentrations more than twice the upper limit of normal was 73%. Most patients continue to have normal alanine aminotransferase concentrations and undetectable HBV DNA. In the patients with biopsy samples taken at end of the third year of lamivudine therapy, 56% showed improvement in total histological activity index by 2 points or more. The major drawback to the use of lamivudine as a single agent is the emergence of resistance due to the development of mutant strains of HBV.39 The major site of mutation is the methionine residue in the tyrosine-methionine-asparateaspartate (YMDD) aminoacid motif. YMDD is a highly conserved motif in the catalytic domain of the reverse transcriptase DNA polymerase and is shared by all hepadnaviruses and retroviruses. The mutants are characterised by a change of methionine to valine or isoleucine (YMDD to YVDD or YIDD). There is often a compensatory mutation in B domain of the reverse transcriptase where the leucine in codon 528 is mutated to methionine. In wild-type HBV, the YMDD motif is in a region with high affinity for nucleotides, hence facilitating the formation of the nascent minus strand of the HBV DNA. Lamivudine has an affinity for the reverse-transcriptase domain of the virus probably because it binds at a pocket formed partly by the methionine of the YMDD motif. The presence of lamivudine will suppress the formation of the minus strand HBV DNA by chain termination and competitive inhibition of the reverse-transcriptase activity. With the mutation of methionine in the YMDD motif to isoleucine or valine, the aminoacid side chain gets shorter. Allen and co-workers postulated that this change increases the size of the binding pocket, thereby attenuating the affinity of lamivudine for the reverse-transcriptase domain.39 Lamivudine therefore has little or no inhibitory effect on the replication of the lamivudine-resistant HBV mutant. However, the change in the size of the binding pocket also affects the affinity of the virus for nucleotides. 237

For personal use. Only reproduce with permission from The Lancet Publishing Group.

Review

Treatment of chronic hepatitis B

Lamivudine and interferon alfa

Lamivudine alone

Interferon alfa alone

Placebo

Schalm et al50 (n=230) HBeAg seroconversion

29%

18%

19%

··

Histological improvement

28%

38%

36%

··

By regression analysis in 100 patients who developed lamivudine-resistant HBV mutants after a year of lamivudine treatment, the following baseline variables were positively correlated with the occurrence of lamivudine-resistant HBV mutants: weight, body-mass index, male sex, baseline HBV DNA, height, and age.42

Schiff et al51 (n=238) HBeAg seroconversion

21%

33%

··

13%

Adefovir dipivoxil

Histological improvement

32%

52%*

··

25%

Table 3. Effect of lamivudine and interferon alfa combination therapy compared with lamivudine or interferon monotherapy or with placebo

Adefovir is an acyclic analogue of dAMP which has broad-spectrum antiviral *p=0·01 for comparison with lamivudine and interferon, p=0·002 for comparison with placebo. activity. It is a potent inhibitor of HBV replication. Laboratory-based studies have shown that isolates of HBV Treatment with adefovir results in a rapid decrease in bearing the YI/VDD mutations have lower rates of serum HBV DNA, within 1–2 weeks in phase I/II studies. The replication.40 However, several compensatory mutations have drug is active against lamivudine-resistant HBV isolates. In now been identified which restore replication competence. addition, resistance to adefovir dipivoxil has not been When lamivudine treatment is withdrawn from patients with detected after more than 52 weeks of continuous treatment in lamivudine-resistant HBV, the wild-type virus takes over and immunosuppressed transplant recipients.43 At doses of 60–120 mg daily, previously used for the replaces the mutant in 3–4 months, but the mutant is rapidly treatment of HIV infection, adefovir has mild to severe re-established when lamivudine treatment is reinstated. The frequency of lamivudine-resistant HBV mutants nephrotoxic effects. It may also cause a lowering of serum varies. At the end of 1 year, they are detectable in 15–32% of carnitine concentrations because pivalic acid, one of the patients. In the Asian study, in which the patients were breakdown products of the drug, is metabolised by maintained on lamivudine as monotherapy long term, the conjugation with carnitine before renal excretion. Currently, rates at the end of the second, third, and fourth years were a 10 mg daily dose is used in the trials for treatment of HBV 38%, 56%, and 67%, respectively, by a sensitive PCR assay infection.44 With this dose, nephrotoxicity has not been that can detect 500 copies of the variants per mL.41 The reported, and carnitine depletion is less likely. Analysis of emergence of the lamivudine-resistant HBV mutant even long-term phase III treatment data will provide more definite after HBV DNA has been suppressed to below the detection conclusions on the toxicity issues. limits (7⫻105 genomes/mL) of the branched DNA (bDNA) assay emphasises the point that lamivudine does not Entecavir completely suppress viral replication. In a study examining Entecavir is a carbocyclic deoxyguanosine analogue with the factors associated with HBV-DNA breakthrough in potent activity against herpesviruses and hepadnaviruses.45 patients with YMDD variants, those with HBV-DNA loads at Phase I/II trials have shown potent activity against HBV,46 6 months of lamivudine therapy of more than 103 with doses of 0·1–0·5 mg daily inducing significantly more genomes/mL, measured by a sensitive PCR assay (Cobas HBV-DNA suppression than lamivudine at 6 months. Amplicor Monitor Test, Roche Diagnostics Limited, lower Entecavir-resistant HBV has not been detected to date.46 detection limit 200 genomes/mL) had a 63% chance of development of YMDD variants within 29 months of follow- Emtricitabine up.35 Furthermore, none of the patients with HBV-DNA Emtricitabine is the 5-fluorinated derivative of lamivudine. breakthroughs had the YMDD variants detectable 9 Antiviral cross-resistance between lamivudine and months before the breakthroughs. emtricitabine has been reported for HBV. Emtricitabine has Clinically, the median HBV-DNA concentration in excellent oral bioavailability (60–90%) and is excreted patients with mutants remains significantly lower than the unchanged in urine, and the drug has entered phase II pretreatment value when the patients have wild-type HBV, clinical studies. probably because the replication competence of the mutants is lower. The median serum alanine aminotransferase ␤-L-2'-deoxythymidine concentration rises with the development of the mutants but ␤-L-2'-deoxythymidine belongs to a series of “unnatural” also remains below the pretreatment value. Patients with the beta-L-enantiomer nucleosides, the other members being ␤mutant seem to have less aggressive disease than those with L-2'-deoxycytidine and ␤-L-2'-deoxyadenosine.47 The 3' hydroxyl group of the ␤-L-2'-deoxyribose of this series has the wild-type virus, at least initially. In the short term, patients in whom the lamivudine- potent, specific, and selective activity against HBV replication. resistant HBV mutants emerge after lamivudine therapy are ␤-L-2'-deoxythymidine is metabolised into its 5'-triphosphate not more likely to develop more severe liver damage than derivative, and this form brings about the inhibitory action. those who do not have these drug-resistant mutants. In the woodchuck model, the drug decreases concentrations However, the long-term effects of the mutants, especially with of viral DNA by as much as eight logs within 4 weeks of respect to the development of hepatocellular carcinoma and treatment. (␤-L-2'-deoxycytidine lowers concentrations by six logs and ␤-L-2'-deoxyadenosine by 1·5 logs.) Like other complications of cirrhosis, remain unknown. 238

THE LANCET Infectious Diseases Vol 1 November 2001

For personal use. Only reproduce with permission from The Lancet Publishing Group.

Review

Treatment of chronic hepatitis B

HBeAg +ve

ALT normal

HBV DNA -ve

ALT

HBV DNA +ve

Observe

HBV DNA -ve

HBV DNA +ve

Observe

No treatment

Observe

HBV DNA persistently -ve

HBeAg seroconversion

ALT persistently normal

Interferon (for whites)

HBeAg seroconversion

Lamivudine (for whites or Asians)

YMDD emergence

Interferon failure

No treatment

HBV DNA -ve

HBeAg seroconversion

HBV DNA +ve

No treatment

No treatment

Observe

Add other nuceloside analogues eg, adefovir

Anti-HBe+ve Anti-HBe +ve

ALT ALT↑

ALT ALTnormal normal

HBV DNA -ve-ve HBV DNA

HBV DNA +ve+ve HBV DNA

HBV DNA -ve-ve HBV DNA

Observe Observe

HBV DNA +ve+ve HBV DNA

Observe Observe No treatment No treatment

Observe Observe

ALT ALT persistently normal persistently normal

Lamivudine LAM

HBV DNA HBV DNA persistently -ve persistently -ve

YMDD YMDDemergence emergence

No No treatment treatment

No No treatment treatment

HBV DNA -ve-ve HBV DNA

Observe Observe

HBV DNA persistently -ve -ve HBV DNA persistently

HBV DNA +ve+ve HBV DNA

Add Addother other nuceloside nuceloside analogues analogues eg, adefovir e.g., adefovir

Figure 4. Flow charts illustrating the guidelines for the treatment of chronic hepatitis B infection. The upper panel shows the flow chart for patients positive for HBeAg; the lower panel shows the flow chart for patients positive for anti-HBe. HBV DNA “negativity” is defined as HBV DNA undetectable by commercially available assays such as the branched DNA assay or the Digene hybrid capture assay.

THE LANCET Infectious Diseases Vol 1 November 2001

239

For personal use. Only reproduce with permission from The Lancet Publishing Group.

Review lamivudine, which is also the (⫺)enantiomer of a nucleoside analogue, it has almost no effect on mitochrondrial function. Another advantage of ␤-L-2'-deoxythymidine is its selectivity against HBV and other hepadnaviruses. Phase I studies48 in human beings confirm its potent activity against HBV and its lack of side-effects. Phase II studies are being initiated.

Combination chemotherapy Combination chemotherapy for the treatment of HBV offers three advantages over monotherapy.49 First, agents acting through different antiviral mechanisms may be additive or complementary to each other. Therefore, combination therapy may reduce the duration of treatment needed to achieve desired endpoints. Second, with the theoretical advantage of using a lower dose of individual agent to achieve the same efficacy, side-effects will be lessened. Third, the more effective viral suppression should decrease the risk of viral mutations. A nucleoside analogue can be combined with an immunomodulator or with one or more other nucleoside analogues. In the former approach, a nucleoside analogue may enhance the effect of an immunomodulator by lowering the viral load and preventing the infection of healthy hepatocytes. With the combination of two or more nucleoside analogues, the suppression of viral replication will be more profound, thus decreasing the chance that resistant mutants will develop. It is also possible that one nucleoside analogue can be active against the resistant mutants of another nucleoside analogue. Combination of interferon alfa and lamivudine

Two multicentre trials combining interferon alfa and lamivudine have been completed, one on treatment-naive patients and one on patients who had previously not responded to interferon therapy (table 3).50,51 In both trials, the patients were given 8 weeks of lamivudine followed by 16 weeks of lamivudine and interferon alfa (10 MU three times a week). The results of the combination treatment were not significantly better than monotherapy with either agent alone. There are several criticisms of these trials: the timing of the interferon alfa administration when the viral load had been greatly reduced by 8 weeks of lamivudine; and the timing of the repeat liver biopsy at 1 year of follow-up when the patients on the combination therapy had been off treatment for more than 6 months whereas the patients on lamivudine monotherapy were still receiving the assigned treatment. Further trials of nucleoside analogues in combination with immunomodulators such as therapeutic vaccines are being actively pursued.

Treatment of chronic hepatitis B

Search strategy and selection criteria Data presented in this review were identified by searches of Medline and references from relevant articles. Search terms were “treatment”, “chronic hepatitis B infection”, “interferon”, “lamivudine”, “randomized controlled trial”, “meta-analysis”, and “review”. Only papers published in English were reviewed. In addition, important studies that have been published only in abstract form were reviewed.

concentrations of less than five times the upper limit of normal, receiving 3 weeks of prednisolone followed by 9 months of lamivudine.52 The 20 patients who had an alanine aminotransferase rebound of over five times the upper limit of normal had a significantly higher HBeAg seroconversion rate than those without significant alanine aminotransferase rebound (60% vs 10%, p<0·002). However, we emphasise that steroid withdrawal can result in severe, even fatal, reactivation not only in patients with cirrhosis but even in precirrhotic patients. Steroid priming for either interferon or lamivudine therapy is not advocated for routine use. Combination of nucleoside analogues

Combination of nucleoside analogues has several attractive features.49 The goal of nucleoside analogue therapy is to lower the viral load as much and for as long as possible. Combination of nucleoside analogues has been found, in vitro, in animal models, and in preliminary clinical studies, to stimulate the initial phase of decline in HBV DNA; this phase probably represents the clearance of virions before blockage of viral replication.

The present and the future Interferon alfa and lamivudine are two important milestones for the treatment of HBV infection. However, despite the favourable outcomes in measures such as alanine aminotransferase, viral load, HBeAg seroconversion, and even histology, neither agent can completely eradicate the virus. The flow chart shown in figure 4 summarises the current guidelines adopted for the treatment of patients with chronic hepatitis B. This approach will almost certainly be superseded in the near future with further drug development. Combination therapy will be the direction of treatment in the future. After confirmation of the promise of some of the newer agents mentioned above in phase I and II studies, further trials should aim at establishing the ideal combination of and the optimum timing for treatment.

Prednisolone priming and lamivudine

References

Since patients with high pretreatment alanine aminotransferase concentrations have higher rates of HBeAg seroconversion with lamivudine therapy, the alanine aminotransferase rebound after costicosteroid priming should theoretically increase the effect of lamivudine therapy for patients with low alanine aminotransferase concentrations. This idea has been supported by a pilot study of 30 Chinese patients with alanine aminotransferase

1 Lee WM. Hepatitis B virus infection. N Engl J Med 1997; 337: 1733–45. 2 Yuen MF, Lai CL. Debates in hepatitis: how to assess HBV DNA reductions in association with therapy? Viral Hepat Rev 1999; 5: 159–75. 3 Averett DR, Mason WS. Evaluation of drugs for antiviral activity against hepatitis B virus. Viral Hepat Rev 1995; 1: 129–42. 4 Wong DKH, Cheung AM, Q’Rourke K, Naylor CD, Detsky AS, Heathcote J. Effect of alpha-inteferon treatment in patients with hepatitis B e antigen-positive chronic hepatitis B: a meta-analysis. Ann Intern Med 1993; 119: 312–23.

240

THE LANCET Infectious Diseases Vol 1 November 2001

For personal use. Only reproduce with permission from The Lancet Publishing Group.

Treatment of chronic hepatitis B

5 Wong JB, Koff RS, Tine F, Pauker SG. Cost-effectiveness of interferon-␣2b treatment for hepatitis B e antigen-positive chronic hepatitis B. Ann Intern Med 1995; 122: 664–75. 6 Perrillo RP. Treatment of chronic hepatitis B with interferon: experience in western countries. Semin Liver Dis 1989; 9: 240–48. 7 Lai CL, Lok ASF, Lin HJ, Wu PC, Yeoh EK, Yeung CY. Placebocontrolled trial of recombinant 2-interferon in Chinese HBsAgcarrier children. Lancet 1987; 2: 877–80. 8 Lai CL, Lin HJ, Lau JYN, et al. Effect of recombinant alpha-2 interferon with or without prednisone in Chinese HBsAg carrier children. QJM 1991; 78: 155–63. 9 Lok ASF, Lai CL, Wu PC, Lau JYN, Leung EKY, Wong LSK. Treatment of chronic hepatitis B with interferon: experience in Asian patients. Semin Liver Dis 1989; 9: 249–53. 10 Derso A, Boxall EH, Tarlow MJ, Flewett TH. Transmission of HBsAg from mother to infant in four ethnic groups. BMJ 1978; 1: 949–52. 11 Perrillo RP, Schiff ER, Davis GL, et al. A randomized, controlled trial of interferon alfa-2b alone and after prednisone withdrawal in the treatment of chronic hepatitis B. N Engl J Med 1990; 323: 295–301. 12 Liaw YF, Liu SM, Chan TJ, Chien RN, Sheen IS, Chu CM. Beneficial effect of prednisolone withdrawal followed by human lymphoblastoid interferon on the treatment of chronic type B hepatitis in Asians: a randomized controlled trial. Hepatology 1994; 20: 175–80. 13 Brunetto MR, Giarin M, Saracco G, et al. Hepatitis B virus unable to secret e antigen and response to interferon in chronic hepatitis B. Gastroenterology 1993; 105: 845–50. 14 Niederau C, Heintges T, Lange S, et al. Long-term follow-up of HBeAg-positive patients treated with interferon alfa for chronic hepatitis B. N Engl J Med 1996; 334: 1422–27. 15 Lau DT, Everhart J, Kleiner DE, et al. Long-term follow-up of patients with chronic hepatitis B treated with interferon alfa. Gastroenterology 1997; 113: 1660–67. 16 Korenman J, Baker B, Waggoner J, Everhart JE, Di Bisceglie AM, Hoofnagle JH. Long-term remission of chronic hepatitis B after alfainterferon therapy. Ann Intern Med 1991; 114: 629–34. 17 Lin SM, Sheen IS, Chien RN, Chu CM, Liaw YF. Long-term beneficial effect of interferon therapy in patients with chronic hepatitis B virus infection. Hepatology 1999; 29: 979–75. 18 Yuen MF, Hui CK, Cheng CC, Wu CH, Lai YP, Lai CL. Long-term follow-up of interferon-alfa treatment in Chinese patients with chronic hepatitis B infection: the effect on HBeAg seroconversion and the development of cirrhosis-related complications. Hepatology 2001; 34: 139–45. 19 Gerin JL, Korba BE, Cote PJ, Tennant BC. A preliminary report of a controlled study of thymosin alfa-1 in the woodchuck model of hepadnavirus infection. Adv Exp Med Biol 1992; 312: 121–23. 20 Andreone P, Cursaro C, Gramenzi A, et al. A randomized controlled trial of thymosin-␣1 versus interferon alfa treatment in patients with hepatitis B e antigen antibody- and hepatitis B virus DNA-positive chronic hepatitis B. Hepatology 1996; 24: 774–77. 21 Chien RN, Liaw YF, Chen TC, Yeh CT, Sheen IS. Efficacy of thymosin ␣1 in patients with chronic hepatitis B: a randomized, controlled trial. Hepatology 1998; 27: 1383–87. 22 Mutchnick MG, Lindsay KL, Schiff ER, Cummings GD, Appelman HD. Thymosin ␣1 treatment of chronic hepatitis B: a multicenter, randomized, placebo-controlled double blind study. Gastroenterology 1995; 108: A1127 (abstract). 23 Heathcote J, McHutchinson J, Lee S, et al. A pilot study of the CY1899 T-cell vaccine in subjects chronically infected with hepatitis B virus. The CY1899 T Cell Vaccine Study Group. Hepatology 1999; 30: 531–36. 24 Heineman TC, Clements-Mann ML, Poland GA, et al. A randomized, controlled study in adults of the immunogenicity of a novel hepatitis B vaccine containing MF59 adjuvant. Vaccine 1999; 17: 2769–78. 25 Couillin I, Pol S, Mancini M, et al. Specific vaccine therapy in chronic hepatitis B: induction of T cell proliferative responses specific for envelope antigens. J Infect Dis 1999; 180: 15–26. 26 Johnson MA, Moore KHP, Yuen GJ, Bye A, Pakes GE. Clinical pharmacokinetics of lamivudine. Clin Pharmacokinet 1999; 26: 41–66. 27 Lai CL, Yuen MF. Profound suppression of hepatitis B virus replication with lamivudine. J Med Virol 2000; 61: 367–73. 28 Boni C, Bertoletti A, Penna A, et al. Lamivudine treatment can restore T cell responsiveness in chronic hepatitis B. J Clin Invest 1998; 102: 968–75. THE LANCET Infectious Diseases Vol 1 November 2001

Review 29 Lai CL, Chien RN, Leung NWY, et al. A one-year trial of lamivudine for chronic hepatitis B. N Engl J Med 1998; 339: 61–68. 30 Dienstag JL, Schiff ER, Wright TL, et al. Lamivudine as initial treatment for chronic hepatitis B in the United States. N Engl J Med 1999; 341: 1256–63. 31 Tassopoulos NC, Volpes R, Pastore G, et al. Efficacy of lamivudine in patients with hepatitis B e antigen-negative/hepatitis B virus DNA-positive (precore mutant) chronic hepatitis B. Hepatology 1999; 29: 889–96. 32 Lok AS, Wu PC, Lai CL, et al. A controlled trial of interferon with or without prednisone priming for chronic hepatitis B. Gastroenterology 1992; 102: 2091–97. 33 Chien RN, Liaw Y-F, Atkins M, The Asian Hepatitis Lamivudine Trial Group. Pretherapy alanine transaminase level as a determinant for hepatitis B e antigen seroconversion during lamivudine therapy in patients with chronic hepatitis B. Hepatology 1999; 30: 770–74. 34 Villeneuve JP, Condreay LD, Willems B, et al. Lamivudine treatment for decompensated cirrhosis resulting from chronic hepatitis B. Hepatology 2000; 31: 207–10. 35 Yuen MF, Sablon E, Hui CK, Yuan HJ, Decraemer H, Lai CL. Factors associated with hepatitis B virus DNA breakthrough in patients receiving prolonged lamivudine therapy. Hepatology 2001; 34: 785–91. 36 Nowak MA, Bonhoeffer S, Hill AM, Boehme R, Thomas HC, McDade H. Viral dynamics in hepatitis B virus infection. Proc Natl Acad Sci USA 1996; 93: 4398–402. 37 Tsiang M, Rooney JF, Toole JJ, Gibbs CS. Biphasic clearance kinetics of hepatitis B virus from patients during adefovir dipivoxil therapy. Hepatology 1999; 29: 1863–69. 38 Leung NWY, Lai CL, Chang TT, et al. Extended lamivudine treatment in patients with chronic hepatitis B enhances hepatitis B e antigen seroconversion rates: results after 3 years of therapy. Hepatology 2001; 33: 1527–32. 39 Allen MI, Deslauriers M, Andrew CW, et al. Identification and characterization of mutations in hepatitis B virus resistant to lamivudine. Hepatology 1998; 27: 1670–77. 40 Melegari M, Scaglioni PP, Wands JR. Hepatitis B virus mutants associated with 3TC and famciclovir administration are replication defective. Hepatology 1998; 27: 628–33. 41 Lok AS, Heathcote EJ, Hoofnagle JH. Management of hepatitis B: 2000—summary of a workshop. Gastroenterology 2001; 120: 1828–53. 42 Lai CL, Liaw YF, Leung NWY, et al. Genotypic resistance to lamivudine in a placebo-controlled multicentre study in Asia of lamivudine therapy for chronic hepatitis infection: incidence, kinetics of emergence and correlation with disease parameters. Hepatology 1997; 26 (suppl 4 pt 2): 522A (abstract). 43 Perrillo R, Schiff E, Yoshida E, et al. Adefovir dipivoxil for the treatment of lamivudine-resistant hepatitis B mutants. Hepatology 2000; 32: 129–34. 44 Benhamou Y, Bochet M, Thibault V, et al. Safety and efficacy of adefovir dipivoxil for lamivudine resistant HBV in HIV infected patients. J Hepatol 2001; 34 (suppl 1): 1253A (abstract). 45 Yamanaka G, Wilson T, Innaimo S, et al. Metabolic studies on BMS-200475, a new antiviral compound active against hepatitis B virus. Antimicrob Agents Chemother 1999; 43: 190–93. 46 De Man R, Wolters L, Nevens F, et al. Safety and efficacy of oral entecavir given for 28 days in patients with chronic hepatitis B infection. Hepatology 2001; 34: 578–82. 47 Bryant ML, Bridges EG, Placidi L, et al. Antiviral L-nucleosides specific for hepatitis B virus infection. Antimicrob Agents Chemother 2001; 45: 229–35. 48 Lim SG, Lai CL, Lee YM, Pow DM, Maureen WM. L-dt: an ongoing phase I/IIa dose-escalation trial in patients with chronic HBV infection (NV-02-001). Gastroenterology 2001; 120 (suppl 1): 572A (abstract). 49 Shaw T, Locarnini, S. Combination chemotherapy for hepatitis B virus: the final solution? Hepatology 2000; 32: 430–32 50 Schalm SW, Heathcote J, Cianciara J, et al. Lamivudine and alpha interferon combination treatment of patients with chronic hepatitis B infection: a randomised trial. Gut 2000; 46: 562–68. 51 Schiff E, Karayalcin S, Grimm I, et al. A placebo controlled study of lamivudine and interferon alpha-2b in patients with chronic hepatitis B who previously failed interferon therapy. Hepatology 1998; 28S: 388A (abstr). 52 Liaw Y-F, Tsai S-L, Chien R-N, Yeh C-T, Chu C-M. Prednisolone priming enhances Th 1 response and efficacy of subsequent lamivudine therapy in patients with chronic hepatitis B. Hepatology 2000; 32: 604–09.

241

For personal use. Only reproduce with permission from The Lancet Publishing Group.