Long-term monitoring shows hepatitis B virus resistance to entecavir in nucleoside-naïve patients is rare through 5 years of therapy

Virological, serological and biochemical outcomes through 3 years of entecavir treatment in nucleoside-naive Chinese chronic hepatitis B patients

Hepatitis B virus (HBV) infection has a high prevalence in China. Entecavir has shown superior efficacy over lamivudine in Chinese nucleoside-naive chronic hepatitis B (CHB) patients over 48 weeks, with continued clinical benefit to 96 weeks. The present study evaluates the long-term efficacy of entecavir in Chinese CHB patients who continued entecavir treatment for 144 weeks. Patients receiving either entecavir 0.5 mg/day (n = 258) or lamivudine 100 mg/day (n = 261) entered the initial 96-week randomized, double-blind, controlled efficacy study. Patients who did not achieve a consolidated response [HBV DNA <0.7 MEq/mL; alanine aminotransferase (ALT) <1.25 x upper limit of normal; and if hepatitis B e antigen (HBeAg) positive at baseline, loss of HBeAg for ≥ 24 weeks] or who experienced viral breakthrough or relapse entered a 48-week entecavir rollover study. A total of 160 patients received continuous entecavir for 144 weeks; of these, 89% had undetectable serum HBV DNA, 86% showed ALT normalization, 20% reported HBeAg loss and 8% experienced HBeAg seroconversion. The cumulative rates of HBeAg loss and seroconversion were 36% and 27% at Week 144, respectively. The development of resistance was low, with three patients up to Week 96 and an additional two patients in Weeks 96-144 showing evidence of associated genotypic mutations. Entecavir was well tolerated. Adverse event rates were similar to those in lamivudine-treated patients, but patients receiving entecavir experienced fewer ALT flares. This study demonstrates that entecavir provides durable, long-term suppression of HBV DNA and ALT normalization in Chinese CHB patients, and is associated with low rates of emerging resistance. The results are consistent with the findings using entecavir globally and in Japan.

Entecavir for the long-term treatment of chronic hepatitis B

Hepatitis B virus is a major cause of chronic liver disease worldwide and is associated with an increased risk of hepatocellular carcinoma, progressive hepatic fibrosis and end-stage liver disease. Suppression of HBV replication is recognized as the primary on-treatment goal of antiviral therapy, as reduction of serum HBV DNA to low or undetectable levels is highly likely to have a positive impact on long-term clinical outcomes in HBV-associated chronic liver disease. Entecavir is an oral nucleoside analogue that effectively inhibits HBV polymerase, resulting in rapid viral suppression. Long-term data on patients receiving entecavir for chronic hepatitis B have demonstrated high potency, a low incidence of antiviral drug resistance and good tolerability, making entecavir an ideal first-line agent for the treatment of chronic hepatitis B.

Monotherapy versus combination therapy for the treatment of chronic hepatitis B

BACKGROUND

Nucleos(t)ide analogues, active against hepatitis B polymerase, suppress viral replication and improve clinical outcome. However, the emergence of drug-resistant mutants can result in treatment failure.

OBJECTIVES

We describe how the choice of first-line therapy is critical to long-term treatment success.

METHODS

A review of current drug therapies is provided.

RESULTS/CONCLUSIONS

Monotherapy with early-generation drugs (lamivudine or adefovir) was associated with a high rate of viral drug resistance and combination therapy with these agents was shown to reduce the incidence of resistance. The latest-generation drugs (entecavir and tenofovir) are potent inhibitors of viral replication and, in treatment-naive subjects, viral resistance to entecavir is uncommon and is not yet reported to tenofovir. Therefore, monotherapy with either entecavir or tenofovir is the current preferred option in treatment-naive patients. Combination therapy is appropriate in those with drug-resistant HBV infection, where drug choice is guided by the viral drug-resistance genotype/phenotype. Although combination therapy has been advocated in other patient groups (e.g., those with decompensated cirrhosis and following liver transplantation), there are, as yet, no data to mandate the use of combination therapy in such patients and any perceived benefit must be weighed against increased cost and risk for toxicity.

Identification and characterization of clevudine-resistant mutants of hepatitis B virus isolated from chronic hepatitis B patients

Clevudine (CLV) is a nucleoside analog with potent antiviral activity against chronic hepatitis B virus (HBV) infection. Viral resistance to CLV in patients receiving CLV therapy has not been reported. The aim of this study was to characterize CLV-resistant HBV in patients with viral breakthrough (BT) during long-term CLV therapy. The gene encoding HBV reverse transcriptase (RT) was analyzed from chronic hepatitis B patients with viral BT during CLV therapy. Sera collected from the patients at baseline and at the time of viral BT were studied. To characterize the mutations of HBV isolated from the patients, we subjected the HBV mutants to in vitro drug susceptibility assays. Several conserved mutations were identified in the RT domain during viral BT, with M204I being the most common. In vitro phenotypic analysis showed that the mutation M204I was predominantly associated with CLV resistance, whereas L229V was a compensatory mutation for the impaired replication of the M204I mutant. A quadruple mutant (L129M, V173L, M204I, and H337N) was identified that conferred greater replicative ability and strong resistance to both CLV and lamivudine. All of the CLV-resistant clones were lamivudine resistant. They were susceptible to adefovir, entecavir, and tenofovir, except for one mutant clone. In conclusion, the mutation M204I in HBV RT plays a major role in CLV resistance and leads to viral BT during long-term CLV treatment. Several conserved mutations may have a compensatory role in replication. Drug susceptibility assays reveal that adefovir and tenofovir are the most effective compounds against CLV-resistant mutants. These data may provide additional therapeutic options for CLV-resistant patients.

Mechanistic characterization and molecular modeling of hepatitis B virus polymerase resistance to entecavir

Background

Entecavir (ETV) is a deoxyguanosine analog competitive inhibitor of hepatitis B virus (HBV) polymerase that exhibits delayed chain termination of HBV DNA. A high barrier to entecavir-resistance (ETVr) is observed clinically, likely due to its potency and a requirement for multiple resistance changes to overcome suppression. Changes in the HBV polymerase reverse-transcriptase (RT) domain involve lamivudine-resistance (LVDr) substitutions in the conserved YMDD motif (M204V/I ± L180M), plus an additional ETV-specific change at residues T184, S202 or M250. These substitutions surround the putative dNTP binding site or primer grip regions of the HBV RT.

Methods/Principal Findings

To determine the mechanistic basis for ETVr, wildtype, lamivudine-resistant (M204V, L180M) and ETVr HBVs were studied using in vitro RT enzyme and cell culture assays, as well as molecular modeling. Resistance substitutions significantly reduced ETV incorporation and chain termination in HBV DNA and increased the ETV-TP inhibition constant (K_i) for HBV RT. Resistant HBVs exhibited impaired replication in culture and reduced enzyme activity (k_cat) in vitro. Molecular modeling of the HBV RT suggested that ETVr residue T184 was adjacent to and stabilized S202 within the LVDr YMDD loop. ETVr arose through steric changes at T184 or S202 or by disruption of hydrogen-bonding between the two, both of which repositioned the loop and reduced the ETV-triphosphate (ETV-TP) binding pocket. In contrast to T184 and S202 changes, ETVr at primer grip residue M250 was observed during RNA-directed DNA synthesis only. Experimentally, M250 changes also impacted the dNTP-binding site. Modeling suggested a novel mechanism for M250 resistance, whereby repositioning of the primer-template component of the dNTP-binding site shifted the ETV-TP binding pocket. No structural data are available to confirm the HBV RT modeling, however, results were consistent with phenotypic analysis of comprehensive substitutions of each ETVr position.

Conclusions

Altogether, ETVr occurred through exclusion of ETV-TP from the dNTP-binding site, through different, novel mechanisms that involved lamivudine-resistance, ETV-specific substitutions, and the primer-template.

Efficacy and resistance of entecavir following 3 years of treatment of Japanese patients with lamivudine-refractory chronic hepatitis B

PURPOSE

Lamivudine treatment of chronic hepatitis B (CHB) is associated with frequent resistance and loss of clinical benefit. We present outcomes of lamivudine-refractory Japanese patients treated with entecavir for 3 years.

METHODS

Eighty-two patients refractory to lamivudine therapy received entecavir 0.5 or 1 mg daily for 52 weeks in phase II study ETV-052, directly entered rollover study ETV-060, and received entecavir 1 mg daily. Responses were evaluated among patients with available samples.

RESULTS

After 96 weeks in ETV-060 (148 weeks total entecavir treatment time), 55%(36/65) of patients had hepatitis B virus(HBV) DNA of\400 copies/mL, 85% (52/61) had alanine aminotransferase (ALT) of ≤1 × upper limit of normal (ULN), and 14.6% (7/48) achieved HBe seroconversion.A subset of 42 patients received entecavir 1 mg from phase II baseline through 148 weeks: 54% (19/35) had HBV DNA of <400 copies/mL, 84% (27/32) had ALT of ≤1 × ULN, and 15% (4/27) achieved HBe seroconversion.Sixteen patients in the 1-mg subset had baseline and week 148 evaluable biopsy pairs: 81% (13/16) showed histologic improvement and 38% (6/16) showed improvement in fibrosis. Genotypic resistance to entecavir emerged in 31 patients for a 3-year cumulative resistance probability of 35.9%. Entecavir was generally well tolerated during ETV-060, with no on-treatment ALT flares.

CONCLUSIONS

Long-term entecavir treatment of lamivudine-refractory CHB resulted in virologic suppression, ALT normalization, and improvements in liver histology. Resistance was consistent with that observed in worldwide studies.

Evolution of hepatitis B virus mutation during entecavir rescue therapy in patients with antiviral resistance to lamivudine and adefovir

BACKGROUND

The efficacy of entecavir (ETV) monotherapy in treatment-experienced patients with chronic hepatitis B (CHB) is debatable.

METHODS

A total of 22 hepatitis B e antigen (HBeAg)-positive CHB patients who had shown viral breakthrough or suboptimal response with lamivudine (3TC) and adefovir disoproxil (ADV) therapy were treated with 1.0 mg of ETV. Clinical and virological parameters were monitored every 3 months. Restriction fragment mass polymorphism assays were used to detect antiviral resistance.

RESULTS

During 3TC and ADV therapy, 11 patients had rtM204V/I mutations, 2 had rtA181V/T or rtN236T, 7 had both and 2 had no 3TC- or ADV-related mutations. After switching to ETV monotherapy, the median change in serum hepatitis B virus (HBV) DNA level was -2.1 log(10) copies/ml. Virological response (HBV DNA<300 copies/ml) was achieved in 1 of 18 patients with pre-existing rt204 mutations, whereas it was achieved in all 4 patients without pre-existing rt204 mutations regardless of the presence of rt181 or rt236 mutations. Changes in mutational patterns during ETV therapy showed that rt204 mutations persisted or re-emerged. Relative abundances of rtM204V/I mutations in total viral populations gradually increased under ETV rescue, whereas those with rtA181V/T and rtN236T mutations decreased. ETV resistance mutations (rtL180M+rtT184I/L[rtS202G]+rtM204V) were detected in five patients with pre-existing rt204 mutations.

CONCLUSIONS

ETV monotherapy resulted in a limited virological response in patients who had previously failed 3TC and ADV rescue therapy. The limited efficacy might be associated with residual or reselected rtM204V/I mutations leading to ETV resistance. Combination treatment including potent antiviral agents should be recommended for patients with pre-existing rtM204V/I mutations.

Mechanism of entecavir resistance of hepatitis B virus with viral breakthrough as determined by long-term clinical assessment and molecular docking simulation

The mechanism by which entecavir resistance (ETVr) substitutions of hepatitis B virus (HBV) can induce breakthrough (BT) during ETV therapy is largely unknown. We conducted a cross-sectional study of 49 lamivudine (LVD)-refractory patients and 59 naïve patients with chronic hepatitis B. BT was observed in 26.8% of the LVD-refractory group during weeks 60 to 144 of ETV therapy. A line probe assay revealed ETVr substitutions only in the LVD-refractory group, i.e., in 4.9% of patients at baseline, increasing to 14.6%, 24.4%, and 44.8% at weeks 48, 96, and 144, respectively. Multivariate logistic regression analysis adjusted for age, gender, HBV DNA levels, and LVD resistance (LVDr) (L180M and M204V, but not M204I) indicated that T184 substitutions and S202G (not S202C) were a significant factor for BT (adjusted odds ratio [OR], 141.12, and 95% confidence interval [CI], 6.94 to 2,870.20; OR, 201.25, and 95% CI, 11.22 to 3608.65, respectively). Modeling of HBV reverse transcriptase (RT) by docking simulation indicated that a combination of LVDr and ETVr (T184L or S202G) was characterized by a change in the direction of the D205 residue and steric conflict in the binding pocket of ETV triphosphate (ETV-TP), by significantly longer minimal distances (2.2 A and 2.1 A), and by higher potential energy (-117 and -99.8 Kcal/mol) for ETV-TP compared with the wild type (1.3 A; -178 Kcal/mol) and LVDr substitutions (1.5 A; -141 Kcal/mol). Our data suggest that the low binding affinity of ETV-TP for the HBV RT, involving conformational change of the binding pocket of HBV RT by L180M, M204V plus T184L, and S202G, could induce BT.

Screening and early treatment of migrants for chronic hepatitis B virus infection is cost-effective

BACKGROUND & AIMS

Persons with chronic hepatitis B virus (HBV) infection are at risk of developing cirrhosis and hepatocellular carcinoma. Early detection of chronic HBV infection through screening and treatment of eligible patients has the potential to prevent these sequelae. We assessed the cost-effectiveness in The Netherlands of systematically screening migrants from countries that have high and intermediate HBV infection levels.

METHODS

Epidemiologic data of the expected numbers of patients with active chronic HBV infection in the target population and information about the costs of a screening program were used in a Markov model and used to determine costs and quality-adjusted life years (QALY) for patients who were and were not treated.

RESULTS

Compared with the status quo, a 1-time screen for HBV infection can reduce mortality of liver-related diseases by 10%. Using base case estimates, the incremental cost-effectiveness ratio (ICER) of screening, compared with not screening, is euros (euro) 8966 per QALY gained. The ICER ranged from euro7936 to euro11,705 based on univariate sensitivity analysis, varying parameter values of HBV prevalence, participation rate, success in referral, and treatment compliance. Using multivariate sensitivity analysis for treatment effectiveness, the ICER ranged from euro7222 to euro15,694; for disease progression, it ranged from euro5568 to euro60,418.

CONCLUSIONS

Early detection and treatment of people with HBV infection can have a large impact on liver-related health outcomes. Systematic screening for chronic HBV infection among migrants is likely to be cost-effective, even using low estimates for HBV prevalence, participation, referral, and treatment compliance.

Entecavir treatment for up to 5 years in patients with hepatitis B e antigen-positive chronic hepatitis B

Sustained virologic suppression is a primary goal of therapy for chronic hepatitis B (CHB). In study entecavir (ETV)-022, 48 weeks of entecavir 0.5 mg was superior to lamivudine for virologic suppression for hepatitis B e antigen (HBeAg)-positive CHB. A total of 183 entecavir-treated patients from ETV-022 subsequently enrolled in study ETV-901. We present the results after up to 5 years (240 weeks) of continuous entecavir therapy. The entecavir long-term cohort consists of patients who received >or=1 year of entecavir 0.5 mg in ETV-022 and then entered ETV-901 with a treatment gap <or=35 days. In ETV-901 the entecavir dose was 1.0 mg daily. For patients with samples available at Year 5, proportions with hepatitis B virus (HBV) DNA <300 copies/mL, normal alanine aminotransferase (ALT) levels, HBeAg loss, and HBeAg seroconversion were determined. In all, 146 patients met criteria for inclusion in the entecavir long-term cohort. At Year 5, 94% (88/94) had HBV DNA <300 copies/mL and 80% (78/98) had normal ALT levels. In addition to patients who achieved serologic responses during study ETV-022, 23% (33/141) achieved HBeAg seroconversion and 1.4% (2/145) lost hepatitis B surface antigen (HBsAg) during study ETV-901. Through 5 years, entecavir resistance emerged in one patient. The safety profile of entecavir was consistent with previous reports.

CONCLUSION

Extended therapy with entecavir through 5 years maintained or increased rates of HBV DNA suppression and ALT normalization. Additional patients also achieved HBeAg loss and seroconversion. Entecavir provides sustained viral suppression with minimal resistance during long-term treatment of HBeAg-positive CHB.

Efficacy of entecavir in treatment-naïve patients with hepatitis B virus-related decompensated cirrhosis

BACKGROUND & AIMS

The effect of entecavir (ETV) therapy on viral suppression and hepatic function in hepatitis B virus (HBV) patients with decompensated cirrhosis has not been established. We evaluated ETV as first-line monotherapy in these patients.

METHODS

We consecutively enrolled 70 HBV-infected patients with decompensated cirrhosis primarily treated with 0.5mg/day ETV, and evaluated the clinical outcomes by intention-to-treat analyses. We also compared the virological responses of 55 patients treated for 12 months (decompensated group) with those of 144 chronic hepatitis or compensated cirrhosis patients (compensated group).

RESULTS

The cumulative transplantation-free survival was 87.1% at 1year. ETV treatment for 12 months resulted in improved Child-Turcotte-Pugh (CTP) and model for end-stage liver disease (MELD) scores. Sixty-six percent (36/55) of patients achieved CTP class A and 49% (27/55) showed improvement in the CTP score of 2 points after 12 months of ETV. The 1-year cumulative rates of HBV DNA negativity and HBeAg loss were 92.3% and 54.0%, respectively, by intention-to-treat analysis. The rates of HBV DNA negativity, HBeAg seroconversion/loss and ALT normalization at month 12 were similar for the decompensated and compensated groups. Cox regression analysis showed that pretreatment HBeAg seropositivity was a negative predictor of HBV DNA clearance during ETV therapy (hazard ratio, 0.514; 95% confidence interval 0.367-0.719; p<0.001).

CONCLUSIONS

One-year initial ETV therapy was similarly effective in both compensated and decompensated liver disease HBV patients. In addition, it improved underlying liver function in decompensated patients.

HBV and HCV therapy

One year of interferon therapy inhibits HBV replication in one third of the patients whereas long-term administration of oral nucleos(t)ide analogues is efficient in most of them, as long as early treatment adaptation in patients with partial virological response and resistance is provided. Following the demonstration of a more potent antiviral effect in terms of sustained virological response (SVR) rates, Pegylated-IFN coupled with Ribavirin has become the standard treatment for chronic hepatitis C, with nearly 65% of all treated patients achieving a SVR. Long-term suppression of HBV and eradication of HCV would halt the progression of chronic hepatitis to cirrhosis, hepatocellular carcinoma and liver decompensation.

On-treatment monitoring of HBV DNA levels: predicting response and resistance to oral antiviral therapy at week 24 versus week 48

The suppression of hepatitis B viral (HBV) load correlates with favorable histologic, biochemical, and serologic responses in clinical trials of patients with chronic hepatitis B (CHB). The ability to identify patients who will not experience durable viral suppression in response to a specific antiviral regimen affords the opportunity for early treatment modification to optimize outcomes and avoid the development of antiviral resistance. Substantial evidence demonstrates that on-treatment serum HBV DNA levels are predictive of virologic response and risk of resistance. Regional clinical practice guidelines for the management of CHB universally recommend monitoring serum HBV DNA levels at treatment week 24. However, the value of this time point as a predictor of long-term success may not be applicable to all types of antiviral therapy. Indeed, each oral nucleos(t)ide analog (NA) antiviral therapy has a unique profile of potency, genetic barriers to resistance, and viral kinetics that may affect the optimal time point for on-treatment monitoring. This review discusses available data for appropriate predictors for long-term response and antiviral resistance for patients receiving specific oral NA antiviral therapy. Guidelines for on-treatment monitoring are also discussed.

Entecavir: a review of its use in chronic hepatitis B

Entecavir (Baraclude), a nucleoside analogue, is rapidly phosphorylated to the active intracellular 5'-triphosphate form that inhibits replication of hepatitis B virus (HBV). Oral entecavir is approved in the US, EU and several countries worldwide for the treatment of chronic HBV infection in adults (> or =16 years of age) with evidence of active viral replication and persistently elevated serum ALT and/or AST levels, and/or histological evidence of active disease. In several randomized, double-blind, multicentre trials, oral entecavir was an effective and generally well tolerated treatment in nucleoside-naive and lamivudine-refractory adult patients with chronic HBV infection, irrespective of whether patients were hepatitis B e antigen (HBeAg)-positive or -negative. Furthermore, it was more efficacious, associated with a lower risk of resistance, and more cost effective than lamivudine in these patient populations, with both drugs having a similar tolerability profile. In the EARLY trial, entecavir was significantly more effective than and as well tolerated as adefovir dipivoxil therapy in nucleoside-naive patients. In addition, in a double-blind, multicentre trial, entecavir plus lamivudine-based highly active antiretroviral therapy (HAART) was more effective than placebo plus lamivudine-based HAART in patients co-infected with HBV and HIV. Although the exact position of entecavir relative to other agents, such as tenofovir disoproxil fumarate and adefovir dipivoxil, for the treatment of chronic HBV infection remains to be fully determined, an important aspect in this positioning is the emergence of drug resistance. Hence, entecavir therapy provides a valuable first-line option in nucleoside-naive patients with chronic HBV infection and is a useful alternative in lamivudine-refractory patients.

Differential impact of immune escape mutations G145R and P120T on the replication of lamivudine-resistant hepatitis B virus e antigen-positive and -negative strains

Immune escape variants of the hepatitis B virus (HBV) represent an emerging clinical challenge, because they can be associated with vaccine escape, HBV reactivation, and failure of diagnostic tests. Recent data suggest a preferential selection of immune escape mutants in distinct peripheral blood leukocyte compartments of infected individuals. We therefore systematically analyzed the functional impact of the most prevalent immune escape variants, the sG145R and sP120T mutants, on the viral replication efficacy and antiviral drug susceptibility of common treatment-associated mutants with resistance to lamivudine (LAM) and/or HBeAg negativity. Replication-competent HBV strains with sG145R or sP120T and LAM resistance (rtM204I or rtL180M/rtM204V) were generated on an HBeAg-positive and an HBeAg-negative background with precore (PC) and basal core promoter (BCP) mutants. The sG145R mutation strongly reduced HBsAg levels and was able to fully restore the impaired replication of LAM-resistant HBV mutants to the levels of wild-type HBV, and PC or BCP mutations further enhanced viral replication. Although the sP120T substitution also impaired HBsAg secretion, it did not enhance the replication of LAM-resistant clones. However, the concomitant occurrence of HBeAg negativity (PC/BCP), sP120T, and LAM resistance resulted in the restoration of replication to levels of wild-type HBV. In all clones with combined immune escape and LAM resistance mutations, the nucleotide analogues adefovir and tenofovir remained effective in suppressing viral replication in vitro. These findings reveal the differential impact of immune escape variants on the replication and drug susceptibility of complex HBV mutants, supporting the need of close surveillance and treatment adjustment in response to the selection of distinct mutational patterns.

Hepatitis B virus resistance to nucleos(t)ide analogues

Patients with chronic hepatitis B (CHB) can be successfully treated using nucleos(t)ide analogs (NA), but drug-resistant hepatitis B virus (HBV) mutants frequently arise, leading to treatment failure and progression to liver disease. There has been much research into the mechanisms of resistance to NA and selection of these mutants. Five NA have been approved by the US Food and Drug Administration for treatment of CHB; it is unlikely that any more NA will be developed in the near future, so it is important to better understand mechanisms of cross-resistance (when a mutation that mediates resistance to one NA also confers resistance to another) and design more effective therapeutic strategies for these 5 agents. The genes that encode the polymerase and envelope proteins of HBV overlap, so resistance mutations in polymerase usually affect the hepatitis B surface antigen; these alterations affect infectivity, vaccine efficacy, pathogenesis of liver disease, and transmission throughout the population. Associations between HBV genotype and resistance phenotype have allowed cross-resistance profiles to be determined for many commonly detected mutants, so genotyping assays can be used to adapt therapy. Patients that experience virologic breakthrough or partial response to their primary therapy can often be successfully treated with a second NA, if this drug is given at early stages of these events. However, best strategies for preventing NA resistance include first-line use of the most potent antivirals with a high barrier to resistance. It is important to continue basic research into HBV replication and pathogenic mechanisms to identify new therapeutic targets, develop novel antiviral agents, design combination therapies that prevent drug resistance, and decrease the incidence of complications of CHB.

Current challenges in viral hepatitis, antimicrobial resistance and the influenza pandemic

The 3rd Ditan International Conference on Infectious Diseases was held from 29 July to 2 August 2009 at the Beijing International Conference Center, Beijing, China. Over 1000 participants from 27 countries attended the 4-day conference, titled 'World Dialogue on Infectious Diseases'. A broad range of topics were covered this year, including TB, methicillin-resistant Staphylococcus aureus, HIV, influenza and gastrointestinal infections. In addition, there was a particularly strong focus on two contrasting topics of viral hepatitis and antibiotic resistance, which is the focus of this meeting report.

Efficacy of entecavir in nucleoside-naïve patients with hepatitis B e antigen-positive chronic hepatitis B

AIM: To investigate the efficacy and safety of entecavir in nucleoside-naïve patients with hepatitis B e antigen (HBeAg)-positive chronic hepatitis B.

METHODS: One hundred and one nucleoside-naïve patients with chronic hepatitis B were randomly divided into two groups. The entecavir (ENT) treatment group was given 0.5 mg of ENT once daily, while the adefovir dipivoxil (AD) treatment group was given 10 mg of AD once daily. The primary outcome measures assessed included serum hepatitis B virus (HBV) DNA level, HBeAg seroconversion or normalization of alanine aminotransferase (ALT) level.

RESULTS: At week 48 after the treatment, serum HBV DNA levels decreased in both the ENT and AD treatment groups. The percentage of patients showing a reduction greater than 103 copies/mL in HBV DNA titer was significantly higher in the ENT treatment group than in the AD treatment group (95.83% vs 60.38%, P < 0.001). The percentage of patients achieving normalization of ALT level was also significantly higher in the ENT treatment group than in the AD treatment group (52.08% vs 28.30%, P = 0.015). No significant difference was observed in the incidence rate of adverse events (77.08% vs 71.69%, P = 0.536) between the two groups. No HBeAg seroconversion was noted in both groups.

CONCLUSION: In nucleoside-naïve patients with HBeAg-positive chronic hepatitis B, entecavir is superior to adefovir dipivoxil in the suppression of serum HBV DNA level. Both two drugs have poor effects on HBeAg seroconversion.

Chronic hepatitis B and C: update on therapy

Chronic infections with HBV and HCV are a major cause of liver-associated morbidity and mortality worldwide. An increased knowledge of HBV and HCV virology, natural history and predictors of virological response has led to the development of new strategies to improve treatment outcomes. The use of new antiviral agents with greater potency and a high genetic barrier to resistance, as well as on-treatment monitoring of virological response, may result in improved outcomes in HBV therapy. A greater understanding of predictors of virological response has led to the ability to individualize therapy in chronic HCV infection. Several new antiviral agents specifically targeting HCV are in development and should have a major impact on treatment response rates over the next few years.

Ultrasensitive genotypic detection of antiviral resistance in hepatitis B virus clinical isolates

Amino acid substitutions that confer reduced susceptibility to antivirals arise spontaneously through error-prone viral polymerases and are selected as a result of antiviral therapy. Resistance substitutions first emerge in a fraction of the circulating virus population, below the limit of detection by nucleotide sequencing of either the population or limited sets of cloned isolates. These variants can expand under drug pressure to dominate the circulating virus population. To enhance detection of these viruses in clinical samples, we established a highly sensitive quantitative, real-time allele-specific PCR assay for hepatitis B virus (HBV) DNA. Sensitivity was accomplished using a high-fidelity DNA polymerase and oligonucleotide primers containing locked nucleic acid bases. Quantitative measurement of resistant and wild-type variants was accomplished using sequence-matched standards. Detection methodology that was not reliant on hybridization probes, and assay modifications, minimized the effect of patient-specific sequence polymorphisms. The method was validated using samples from patients chronically infected with HBV through parallel sequencing of large numbers of cloned isolates. Viruses with resistance to lamivudine and other l-nucleoside analogs and entecavir, involving 17 different nucleotide substitutions, were reliably detected at levels at or below 0.1% of the total population. The method worked across HBV genotypes. Longitudinal analysis of patient samples showed earlier emergence of resistance on therapy than was seen with sequencing methodologies, including some cases of resistance that existed prior to treatment. In summary, we established and validated an ultrasensitive method for measuring resistant HBV variants in clinical specimens, which enabled earlier, quantitative measurement of resistance to therapy.

[Development of clevudine resistance after switching from lamivudine in a patient with chronic hepatitis B]

Background/Aims

Newly developed and potent antiviral agents suffer from the problem of drug resistance. Multidrug resistance is a major impediment in the treatment of patients with chronic hepatitis B (CHB). In line with American Association for the Study of Liver Diseases guidelines, adefovir dipivoxil (ADV) add-on therapy is recommended in the case of lamivudine resistance, while tenofovir disoproxil fumarate (TDF) is recommended for ADV or entecavir (ETV) resistance. TDF is currently not available in Korea. ADV+ETV combination therapy may be a viable alternative to TDF in patients with either ADV or ETV resistance. However, the efficacy of ADV+ETV combination therapy in patients with CHB and multidrug resistance is unclear. This study investigated the efficacy of ADV+ETV combination therapy in patients with multidrug resistance.

Methods

Twenty-five patients were enrolled and were administered ADV+ETV combination therapy for at least 6 months. Blood was drawn at baseline and at 3, 6, 9, and 12 months after commencing treatment, and the following blood parameters were analyzed: alanine transaminase, hepatitis B e-antigen (HBeAg), anti-hepatitis B e-antigen, and hepatitis B virus (HBV) DNA levels. The initial virological response (IVR) was defined as an HBV DNA level of <4 log₁₀ copies/mL after 6 months of combination therapy.

Results

The IVR rate was 76%. The proportion of patients with a high viral load (≥5.0 log) dropped from 76% at baseline to only 5% after 6 months of treatment. The biochemical response rate during the first 6 months was 71%. HBeAg was lost in 2 patients (10%).

Conclusions

ADV+ETV combination therapy induced a good IVR in CHB patients who were refractory to more than 2 antiviral agents. This regimen may be a good alternative to TDF in Korea, where that drug is not available.