Efficacy and tolerance of a combination of tenofovir disoproxil fumarate plus emtricitabine in patients with chronic hepatitis B: a European multicenter study

Synthesis and biological evaluation of novel coumarin derivatives in rhabdoviral clearance

Diseases caused by rhabdoviruses have had a huge impact on the productive lives of the entire human population. The main problem is the lack of drugs for the treatment of this family of viruses. Infectious hematopoietic necrosis virus (IHNV), the causative agent of IHN, is a typical rhabdovirus which has caused huge losses to the salmonid industry. Therefore, in this study, IHNV was studied as a model to evaluate the antiviral activity of 35 novel coumarin derivatives. Coumarin A9 was specifically selected for further validation studies upon comparing the half maximum inhibitory concentration (IC₅₀) of four screened candidate derivatives in epithelioma papulosum cyprinid (EPC) cells, as it exhibited an IC₅₀ value of 2.96 μM against IHNV. The data revealed that A9 treatment significantly suppressed the virus-induced cytopathic effect (CPE) in EPC cells. In addition, A9 showed IC₅₀ values of 1.68 and 2.12 μM for two other rhabdoviruses, spring viremia of carp virus and micropterus salmoides rhabdovirus, respectively. Furthermore, our results suggest that A9 exerts antiviral activity, but not by destroying the virus particles and interfering with the adsorption of IHNV. Moreover, we found that A9 had an inhibitory effect on IHNV-induced apoptosis in EPC cells, as reflected by the protection against cell swelling, formation of apoptotic bodies, and loss of cell morphology and nuclear division. There was a 19.05 % reduction in the number of apoptotic cells in the A9 treatment group compared with that in the IHNV group. In addition, enzyme activity assays proved that A9 suppressed the expression of caspase 3, 8 and 9. These results suggested that A9 inhibit viral replication, to some extent, by blocking IHNV-induced apoptosis. In an in vivo study, A9 exhibited an anti-rhabdovirus effect in virus-infected fish by substantially enhancing the survival rate. Consistent with the above results, A9 repressed IHNV gene expression in virus-sensitive tissues (brain, kidney and spleen) in the early stages of virus infection. Importantly, the data showed that horizontal transmission of IHNV was reduced by A9 in a static cohabitation challenge model, especially in fish that underwent bath treatment, suggesting that A9 might be a suitable therapeutic agent for IHNV in aquaculture. Therefore, coumarin derivatives can be developed as antiviral agents against rhabdoviruses.

Two, three, and four-drug regimens for HIV post-exposure prophylaxis in a North American sexual assault victim population

BACKGROUND/OBJECTIVES

Due to perceived increased tolerability and compliance, and decreased cost, recent trends in practice are moving towards using fewer drugs for HIV post-exposure prophylaxis. However, there is limited literature to assess this is in the North American sexual assault victim population.

METHODS

This retrospective before-and-after cohort study compared patients seen at a sexual assault care facility before and after the introduction of two and three-drug post-exposure prophylaxis regimens. Our primary outcome was completion of the 28-day regimen. Secondary objectives included HIV seroconversion rates and patient reported side effects.

RESULTS

Six-hundred-thirty charts from a 2-year period were reviewed, and 429 met inclusion criteria. There was no difference in completion rates of post-exposure prophylaxis between the two cohorts (50.5% vs. 51.6%). However, there were fewer reported side effects (72.2% vs. 17.6%) in the later cohort. We subsequently compared all patients in either cohort who received four-drug therapy (N=128) versus those who received two or three-drug regimens (N=47). The two or three-drug regimen group had a higher completion rate (66.0% vs. 42.2%; p=0.03), and a lower rate of reported side effects (19.1% vs. 53.9%), specifically for nausea (12.8% vs. 36.7%), constipation (0% vs. 7.9%), diarrhea (2.1% vs. 21.1%), mood changes (0% vs. 10.9%), headache (2.1% vs. 16.4%), and fatigue (6.4% vs. 26.6%). There were no HIV seroconversions in either group.

CONCLUSION

Two and three-drug HIV post-exposure prophylaxis regimens are better tolerated by patients and associated with greater compliance than four-drug therapy, and could be considered in the sexual assault victim population.

Chronic Hepatitis B Virus Infection: Disease Revisit and Management Recommendations

Chronic hepatitis B virus (HBV) infection evolves from immune-tolerance phase, through immune clearance phase to a quiescent phase or reactivation as hepatitis B e antigen-negative hepatitis. Persistent infection may result in the development of cirrhosis and hepatocellular carcinoma (HCC). Host factors including gender, age, family history, HLA-DP, and viral factors including HBV DNA, genotypes, precore mutations, pre-S deletions, and hepatitis B surface antigen (HBsAg) level are associated with the development of these complications. Risk scores for the development of HCC have been derived. Patients with persistently elevated alanine aminotransferase levels (>30 for males; >19 U/L for females) and HBV DNA levels >2000 IU/mL should be treated. Patients with established cirrhosis with detectable HBV DNA should also be treated. The recommended first-line agents include pegylated interferon and 2 nucleos(t)ide analogs, entecavir and tenofovir. NAs require long-term treatment to maintain suppression of HBV DNA. They have been shown to decrease hepatic fibrosis, or reverse cirrhosis and to reduce the development of HCC. They have very low rates (0% to 1.2%) of resistance. HBsAg seroclearance, although the ideal endpoint, is only achievable in 10% to 12% of patients by multicenter trials usually studying relatively young patients. Patients on long-term treatment should be monitored for viral breakthrough that may be due to noncompliance or the development of resistance. Newer agents are under trials to enhance the rate of HBsAg seroclearance. However, even with the current NAs, long-term treatment of >6 years can markedly reduce the covalently closed circular DNA, the viral component responsible for initiation of viral replication.

Efficacy of Tenofovir-Based Combination Therapy versus Tenofovir Monotherapy in Chronic Hepatitis B Patients Presenting with Suboptimal Responses to Pretreatment: A Meta-Analysis

Background/Aims. It remains unclear whether tenofovir disoproxil fumarate- (TDF-) based combination therapy produces better outcomes than TDF monotherapy in chronic hepatitis B (CHB) patients. The aim of this study was to compare the efficacy of the two regimens by performing a meta-analysis. Methods. A comprehensive literature search was performed on the comparison of TDF-based combination therapy and monotherapy for CHB patients in the PubMed, Embase, Web of Science, and the Cochrane Libraries. Both dichotomous and continuous variables were extracted and pooled outcomes were expressed as risk ratio (RR) or standard mean difference (SMD). Results. Nine eligible studies (1089 subjects in total) were included in our analysis. The proportion of patients with undetectable HBV DNA at 24, 48, and 96 weeks were similar between the two comparable groups (62.5% versus 70.9%, P = 0.086; 78.1% versus 83.7%, P = 0.118; 86.4% versus 87.9%, P = 0.626, resp.). HBV DNA reduction, rates of ALT normalization, hepatitis B e antigen (HBeAg) loss, and HBeAg seroconversion were also similar between the two groups. Conclusions. On the current data, TDF-based combination therapy seemed to be no better than those achieved by monotherapy. Further studies are needed to verify this comparison.

Tenofovir monotherapy for hepatitis B after 1 year does not produce renal dysfunction, but is associated with hyperparathyroidism not related to vitamin D

INTRODUCTION

Viral hepatitis B (VHB) represents a major public health problem. Studies from HIV multidrug patients have associated the use of tenofovir disoproxil fumarate (TDF) with renal dysfunction and phosphate wasting.

OBJECTIVE

The aim of this study was to examine the effect of year-long TDF monotherapy on renal function in VHB patients.

PATIENTS AND METHODS

We evaluated adult patients diagnosed with VHB before treatment initiation (T0), and after 3 and 12 months (T3 and T12) of TDF initiation. Estimated glomerular filtration rate (eGFR) was estimated by serum cystatin C and creatinine. In addition, urinary electrolytes and tubular biomarkers (cystatin C, β2-microglobulin and neutrophil gelatinase-associated lipocalin) were analyzed, as well as parathyroid hormone (PTH) and 25(OH)vitamin D levels.

RESULTS

After 1 year, 32 patients completed the study, 22 (68.7%) men and 12 (37.5%) Whites, mean age 44.1±12.0 years. We found that serum electrolytes were similar at baseline and 3 or 12 months after initiation of TDF monotherapy. In addition, urinary fractional excretions of electrolytes as well as proteinuria, albuminuria, urinary β2-microglobulin, and urinary cystatin C showed no significant differences across the treatment timeline. There were also no statistical differences in the eGFR. There was a statistically significant increase in the PTH (Friedman's test, P=0.012), but the 25(OH)vitamin D levels were in the normal range in the beginning and did not change at the follow-up. Moreover, there was no correlation between the initial levels of vitamin D and the corresponding increases in the PTH values.

CONCLUSION

If used as monotherapy in hepatitis B patients for a 12-month period, TDF is not associated with changes in either eGFR or a panel of urinary biomarkers. Serum and urinary electrolytes also remained unchanged. Of note, a significant increase in the PTH was found, although not related to the 25(OH)vitamin D initial status.

Comparative Meta-Analysis of Tenofovir Disoproxil Fumarate versus Emtricitabine and Tenofovir Disoproxil Fumarate as Treatments for Patients with Chronic Hepatitis B

Tenofovir disoproxil fumarate (TDF) monotherapy has proven superior antiviral efficacy in chronic hepatitis B (CHB) patients; however, whether the combination of TDF and emtricitabine (FTC) exerts a significant advantage remains controversial. A meta-analysis was performed to comprehensively compare the therapeutic effects of FTC/TDF combination with TDF alone in CHB patients. Five studies involving 614 patients were identified, and subgroup analysis was performed based on the nucleos(t)ide treatment history. Our results revealed that in patients with nucleos(t)ide-naïve treatment, there were no significant differences between the treatment groups with TDF alone and FTC/TDF combination after 12 and 24 weeks; however, the FTC/TDF combination showed better viral suppression efficacy versus TDF alone after 48 (OR = 2.16, 95% CI = 1.06–4.41, P = 0.03), 96 (OR = 2.76, 95% CI = 1.29–5.92, P = 0.009) and 192 weeks (OR = 2.60, 95% CI = 1.21–5.56, P = 0.01). In patients with nucleos(t)ide treatment history, no differences were noted between the two treatment groups after 12, 24, 48 and 96 weeks. Our results indicated that FTC/TDF combination showed better viral suppression efficacy versus TDF alone in CHB patients with nucleos(t)ide-naïve treatment, while both treatments provided similar viral suppression efficacy in CHB patients with nucleos(t)ide treatment history.

Current and future antiviral drug therapies of hepatitis B chronic infection

Despite significant improvement in the management of chronic hepatitis B virus (HBV) it remains a public health problem, affecting more than 350 million people worldwide. The natural course of the infection is dynamic and involves a complex interplay between the virus and the host’s immune system. Currently the approved therapeutic regimens include pegylated-interferon (IFN)-α and monotherapy with five nucleos(t)ide analogues (NAs). Both antiviral treatments are not capable to eliminate the virus and do not establish long-term control of infection after treatment withdrawal. IFN therapy is of finite duration and associates with low response rates, liver decompensating and numerous side effects. NAs are well-tolerated therapies but have a high risk of drug resistance development that limits their prolonged use. The imperative for the development of new approaches for the treatment of chronic HBV infection is a challenging issue that cannot be over-sided. Research efforts are focusing on the identification and evaluation of various viral replication inhibitors that target viral replication and a number of immunomodulators that aim to restore the HBV specific immune hyporesponsiveness without inducing liver damage. This review brings together our current knowledge on the available treatment and discusses potential therapeutic approaches in the battle against chronic HBV infection.

Differences in nephrotoxicity risk and renal effects among anti-viral therapies against hepatitis B

BACKGROUND

Results are conflicting with respect to the renal effects of anti-viral agents used for hepatitis B virus infection.

AIM

To compare short and long-term renal effects in real-life settings and to determine risk factors for renal impairment during treatment.

METHODS

2221 treatment-naïve patients were enrolled. Among these, 895 (302 lamivudine, 27 telbivudine, 282 entecavir, 273 tenofovir and 11 adefovir initiated patients) had 'repeated measures' of creatinine (baseline, 1st, 6th, 12th and 24th month of treatment). Telbivudine and adefovir groups were excluded from further analysis because of the low number of patients. We calculated the glomerular filtration rate (GFR) using the Modification of Diet in Renal Disease (MDRD) formula at each time point. Hypophosphataemia was also recorded. Risk factors for renal impairment were analysed.

RESULTS

Tenofovir caused a decline in GFR at each time point when compared to baseline levels. However, lamivudine and entecavir did not change GFR. GFR-shifting from ≥90 to 60-89 mL/min/1.73 m(2) was comparable among groups. The proportion of patients whose baseline creatinine increased more than 25% was comparable among all anti-virals. GFR showed a decline in patients who switched from entecavir to tenofovir. One patient with compensated cirrhosis needed to change from tenofovir because of renal safety. Seven and three patients developed transient hypophosphataemia in the tenofovir and lamivudine groups, respectively.

CONCLUSIONS

Although tenofovir caused a decline in GFR, differences between the anti-viral agents do not appear to be so impressive. In patients with and without renal risk factors at baseline, there is no impact of anti-virals, including tenofovir.

Current developments in nucleoside/nucleotide analogues for hepatitis B

There had been remarkable development in nucleos(t)ide analogues (NAs) and evolution in treatment strategies in last 15 years. Currently, there are five NAs available for chronic hepatitis B treatment, namely lamivudine, telbivudine and entecavir (nucleoside analogues), adefovir dipivoxil and tenofovir disoproxil fumarate (nucleotide analogues). The advantages of relatively infrequent side effects and easy administration per oral make NAs popular treatment options. The major drawback of earlier generation NAs is the risk of emergence of drug resistance. Current international guidelines recommend the use of more potent agents with high genetic barriers to resistance including entecavir and tenofovir as first line chronic hepatitis B treatment. However, there is no consensus regarding the subsequent treatment regimens in patients with suboptimal responses to NAs. De novo combination therapy of two NAs, response-guided therapy and roadmap concept in NAs with subsequent switch or add-on therapy can also potentially improve treatment efficacy and avoid resistance.

Long-term efficacy and safety of emtricitabine plus tenofovir DF vs. tenofovir DF monotherapy in adefovir-experienced chronic hepatitis B patients

BACKGROUND & AIMS

Suboptimal virologic response to nucleos(t)ide analogs may represent a significant risk factor for resistance development in patients with chronic hepatitis B virus infection; treatment options have not been well studied. We evaluated long-term efficacy and safety of tenofovir alone and in combination with emtricitabine in a prospective, placebo-controlled trial in patients who remained viremic on adefovir therapy.

METHODS

Hepatitis B e antigen-positive and -negative patients with hepatitis B virus DNA ⩾ 1000 copies/ml despite up to 96 weeks of adefovir were randomized to double-blind tenofovir or emtricitabine/tenofovir for 168 weeks. Patients with hepatitis B virus DNA ⩾ 400 copies/ml (⩾ 69IU/ml) at or after week 24 could switch to open-label emtricitabine/tenofovir.

RESULTS

Overall, 90/105 (86%) patients (46/53 tenofovir and 44/52 emtricitabine/tenofovir) completed the 168-week study period, including 74/105 (70%) patients (35/53 tenofovir and 39/52 emtricitabine/tenofovir) who completed the study on their initial randomized treatment. Long-term viral suppression (hepatitis B virus DNA <400 copies/ml) was maintained at week 168 in 84% and 82% of patients receiving either emtricitabine/tenofovir combination or tenofovir monotherapy, respectively (non-completer equal to failure analysis). Baseline viral load as well as the presence of lamivudine and/or adefovir resistance-associated mutations at baseline had no impact on long-term treatment response. No resistance to tenofovir was observed through 168 weeks. Both treatments had a favorable safety profile.

CONCLUSIONS

Tenofovir monotherapy is as effective as emtricitabine/tenofovir combination therapy in maintaining long-term viral suppression in patients with a suboptimal response to adefovir, and is well tolerated in this population.

Similar evolution of hepatitis B virus quasispecies in patients with incomplete adefovir response receiving tenofovir/emtricitabine combination or tenofovir monotherapy

BACKGROUND & AIMS

Adefovir (ADV) resistance mutations induce low-level cross-resistance to tenofovir in vitro. Our aim was to compare viral kinetics, nucleos(t)ide analog resistance mutations, and quasispecies (QS) evolution during therapy with tenofovir disoproxil fumarate (TDF) or emtricitabine + TDF (FTC/TDF) in selected patients with incomplete ADV responses.

METHODS

Patients with chronic hepatitis B and incomplete response to ADV were randomized in a double-blind trial of TDF vs. FTC/TDF. Extensive analysis of QS evolution was performed in 17 patients through 48 weeks of treatment.

RESULTS

At week 24, 48% of patients (9/17) achieved HBV DNA undetectability (<69 IU/ml) with no difference between treatment groups. ADV and/or LAM resistance mutations were detected in all 17 patients at baseline and in 5/6 analyzable patients at week 48. A total of 1224 reverse transcriptase clones were analyzed. Clonal analysis revealed no significant difference at baseline in QS complexity or diversity between treatment groups. There was a trend in both treatment groups for an increase in QS complexity at week 12, followed by a decrease in complexity and diversity by week 48. Analysis of individual patients showed no consistent selection/accumulation of specific viral resistance patterns during treatment, but at week 48, mutations at rtA181 persisted in 4 patients.

CONCLUSIONS

TDF or FTC/TDF demonstrated strong viral suppression in patients with an incomplete response to ADV and no significant selective pressure on pre-existing ADV or LAM resistant strains. TDF monotherapy and FTC/TDF combination therapy had a comparable impact on QS evolution.

Treatment of children with chronic viral hepatitis: what is available and what is in store

BACKGROUND

At present, therapy of children with chronic hepatitis B and C is still based on few drugs, all burdened by a series of side-effects, unsatisfactory serum conversion rates, and/or drug-resistance. Moreover, selection of subjects to treat with conventional therapies is not univocal, especially during the pediatric age when the disease course is often mild with significant spontaneous seroconversion rate. Our review deals with pros and cons points when a physician decides to design a drug therapy for a child with chronic viral hepatitis, and different possible therapeutic opportunities.

METHODS

A literature search was performed through PubMed. The newest articles, reviews, systematic reviews, and guidelines were included in this review.

RESULTS

The management of children with viral hepatitis is still controversial over whom and when to treat and the use of drug(s). Novel therapeutic strategies have been evaluated only in clinical and preclinical trials involving, for instance, "therapeutic" vaccines. The data on safety and effectiveness of new drugs are also reviewed.

CONCLUSION

The results of reported studies confirmed that at least some of the new drugs, with greater efficacy and/or minor side-effects, will be used clinically.

Suppression of HBV by tenofovir in HBV/HIV coinfected patients: a systematic review and meta-analysis

BACKGROUND

Hepatitis B coinfection is common in HIV-positive individuals and as antiretroviral therapy has made death due to AIDS less common, hepatitis has become increasingly important. Several drugs are available to treat hepatitis B. The most potent and the one with the lowest risk of resistance appears to be tenofovir (TDF). However there are several questions that remain unanswered regarding the use of TDF, including the proportion of patients that achieves suppression of HBV viral load and over what time, whether suppression is durable and whether prior treatment with other HBV-active drugs such as lamivudine, compromises the efficacy of TDF due to possible selection of resistant HBV strains.

METHODS

A systematic review and meta-analysis following PRISMA guidelines and using multilevel mixed effects logistic regression, stratified by prior and/or concomitant use of lamivudine and/or emtricitabine.

RESULTS

Data was available from 23 studies including 550 HBV/HIV coinfected patients treated with TDF. Follow up was for up to seven years but to ensure sufficient power the data analyses were limited to three years. The overall proportion achieving suppression of HBV replication was 57.4%, 79.0% and 85.6% at one, two and three years, respectively. No effect of prior or concomitant 3TC/FTC was shown. Virological rebound on TDF treatment was rare.

INTERPRETATION

TDF suppresses HBV to undetectable levels in the majority of HBV/HIV coinfected patients with the proportion fully suppressed continuing to increase during continuous treatment. Prior treatment with 3TC/FTC does not compromise efficacy of TDF treatment. The use of combination treatment with 3TC/FTC offers no significant benefit over TDF alone.

Update on tenofovir toxicity in the kidney

Tenofovir (TFV) is a widely used and effective treatment for HIV infection. Numerous studies have shown that TFV exposure is associated with small but significant declines in estimated glomerular filtration rate (eGFR). However, TFV toxicity is targeted mainly at the proximal tubule (PT), and in severe cases can cause the renal Fanconi syndrome or acute kidney injury. Severe toxicity occurs in a minority of patients, but milder PT dysfunction is more common; the long-term significance of this on kidney and bone health is uncertain. Recent work suggests that changes in eGFR on TFV therapy might be explained by inhibition of PT creatinine secretion rather than actual alterations in glomerular function. Risk factors for nephrotoxicity include pre-existing kidney disease, increased age, and low body mass. Mitochondria in the PT are the targets of TFV toxicity, but the exact mechanisms remain unclear. Substantial improvement of renal function occurs in many patients with TFV toxicity upon stopping therapy, but function does not always return to baseline. In recent years, TFV usage has been extended to new clinical spheres, including pediatrics, resource-poor settings and treatment of hepatitis B infection; theoretical reasons exist as to why some of these patients might be at higher or lower risk of TFV toxicity. Finally, strategies have been proposed to prevent TFV toxicity or enhance recovery.

Randomized trial of emtricitabine/tenofovir disoproxil fumarate after hepatitis B immunoglobulin withdrawal after liver transplantation

Long-term prophylaxis with hepatitis B immunoglobulin (HBIG) for the prevention of hepatitis B virus (HBV) recurrence after orthotopic liver transplantation (OLT) in patients with chronic HBV infection is inconvenient and costly. This randomized, prospective phase 2 study compared emtricitabine (FTC)/tenofovir disoproxil fumarate (TDF) after HBIG withdrawal to FTC/TDF plus HBIG for the prevention of HBV recurrence after OLT. Forty patients with a median time since liver transplantation of 3.4 years (interquartile range = 1.9-5.6 years) received 24 weeks of open-label FTC/TDF plus HBIG before randomization. Patients who maintained confirmed viral suppression were randomized to continue FTC/TDF plus HBIG (n = 19) or receive FTC/TDF alone (n = 18) for an additional 72 weeks. No patient experienced HBV recurrence through 72 weeks of the study while he or she was receiving the randomized treatment. Both treatment arms were safe and well tolerated; no serious or severe drug-related adverse events were observed. Renal function was consistent with that observed in a posttransplant population. The withdrawal of HBIG after 6 months' treatment with FTC/TDF should be considered in liver transplant recipients to prevent chronic HBV recurrence.

Are novel combination therapies needed for chronic hepatitis B?

The treatment of chronic hepatitis B remains limited to monotherapy with pegInterferon-alpha or one of 5 different nucleoside analogues (NUC). While viral suppression can be achieved in approximately 95% of patients with new-generation NUCs, the rate of HBeAg seroconversion ranges from only 20% with NUCs to 30% with pegInterferon-alpha. HBsAg loss is achieved in only 10% of patients with both classes of drugs after a follow-up of 5years. Attempts to improve the response by administering two different NUCs or a combination of NUC and pegInterferon-alpha have been unsuccessful. This situation has led researchers to investigate a number of steps in the HBV replication cycle as potential targets for new antiviral drugs. Novel targets and compounds could readily be evaluated in in vitro and in vivo models of HBV infection. The addition of one or more new drugs to the current regimen should offer the prospect of markedly improving the response to therapy, reducing the future burden of drug resistance, cirrhosis and hepatocellular carcinoma.

Evaluation of single and combination therapies with tenofovir disoproxil fumarate and emtricitabine in vitro and in a robust mouse model supporting high levels of hepatitis B virus replication

Next-generation therapies for chronic hepatitis B virus (HBV) infection will involve combinations of established and/or experimental drugs. The current study investigated the in vitro and in vivo efficacy of tenofovir disoproxil fumarate (TDF) and/or emtricitabine [(-)-FTC] alone and in combination therapy for HBV infection utilizing the HepAD38 system (human hepatoblastoma cells transfected with HBV). Cellular pharmacology studies demonstrated increased levels of (-)-FTC triphosphate with coincubation of increasing concentrations of TDF, while (-)-FTC had no effect on intracellular tenofovir (TFV) diphosphate levels. Quantification of extracellular HBV by real-time PCR from hepatocytes demonstrated the anti-HBV activity with TDF, (-)-FTC, and their combination. Combination of (-)-FTC with TDF or TFV (ratio, 1:1) had a weighted average combination index of 0.7 for both combination sets, indicating synergistic antiviral effects. No cytotoxic effects were observed with any regimens. Using an in vivo murine model which develops robust HBV viremia in nude mice subcutaneously injected with HepAD38 cells, TDF (33 to 300 mg/kg of body weight/day) suppressed virus replication for up to 10 days posttreatment. At 300 mg/kg/day, (-)-FTC strongly suppressed virus titers to up to 14 days posttreatment. Combination therapy (33 mg/kg/day each drug) sustained suppression of virus titer/ml serum (<1 log(10) unit from pretreatment levels) at 14 days posttreatment, while single-drug treatments yielded virus titers 1.5 to 2 log units above the initial virus titers. There was no difference in mean alanine aminotransferase values or mean wet tumor weights for any of the groups, suggesting a lack of drug toxicity. TDF-(-)-FTC combination therapy provides more effective HBV suppression than therapy with each drug alone.

Management of treatment failure in chronic hepatitis B

Antiviral therapy of chronic hepatitis B remains a clinical challenge. The primary goal of therapy is to prevent liver disease progression. Because of the mechanism of viral persistence in infected hepatocytes, long-term antiviral therapy is needed in the majority of patients. Incomplete viral suppression and emergence of drug resistance is a major concern. The correct choice of a first-line potent therapy to achieve sustained long-term suppression of viral replication provides the best chance of preventing treatment failure and drug resistance. Clinical studies have demonstrated that drugs with a high barrier to resistance, such as entecavir and tenofovir, have significantly lower rates of resistance when compared with those with a low barrier to resistance such as lamivudine, adefovir, or telbivudine. Management of treatment failure requires a precise clinical and accurate virologic monitoring as well as an early treatment intervention with appropriate complementary drugs with respect to their cross-resistance profile. Long-term surveillance for treatment efficacy and possible emergence of drug resistance is necessary for those patients who have been sequentially treated with multiple antivirals. Finally, the identification of novel treatment targets remains a major research challenge to improve the efficacy of current antiviral therapy.

Asian-Pacific consensus statement on the management of chronic hepatitis B: a 2012 update

Large volume of new data on the natural history and treatment of chronic hepatitis B virus (HBV) infection have become available since 2008. These include further studies in asymptomatic subjects with chronic HBV infection and community-based cohorts, the role of HBV genotype/naturally occurring HBV mutations, the application of non-invasive assessment of hepatic fibrosis and quantitation of HBV surface antigen and new drug or new strategies towards more effective therapy. To update HBV management guidelines, relevant new data were reviewed and assessed by experts from the region, and the significance of the reported findings was discussed and debated. The earlier "Asian-Pacific consensus statement on the management of chronic hepatitis B" was revised accordingly. The key terms used in the statement were also defined. The new guidelines include general management, indications for fibrosis assessment, time to start or stop drug therapy, choice of drug to initiate therapy, when and how to monitor the patients during and after stopping drug therapy. Recommendations on the therapy of patients in special circumstances, including women in childbearing age, patients with antiviral drug resistance, concurrent viral infection, hepatic decompensation, patients receiving immune suppression or chemotherapy and patients in the setting of liver transplantation and hepatocellular carcinoma, are also included.

Selection of chronic hepatitis B therapy with high barrier to resistance

Antiviral drug resistance is a crucial factor that frequently determines the success of long-term therapy for chronic hepatitis B. The development of resistance to nucleos(t)ide analogues has been associated with exacerbations in liver disease and increased risk of emergence of multidrug resistance. The selection of a potent nucleos(t)ide analogue with a high barrier to resistance as a first-line therapy, such as entecavir or tenofovir, provides the best chance of achieving long-term treatment goals and should be used wherever possible. The barrier to resistance of a given nucleos(t)ide analogue is influenced by genetic barrier, drug potency, patient adherence, pharmacological barrier, viral fitness, mechanism of action, and cross-resistance. In countries with limited health-care resources, the selection of a therapy with a high barrier to resistance is not always possible and alternative strategies for preventing resistance might be needed, although limited data are available to support these strategies.