Telbivudine in the treatment of chronic hepatitis B

Insights into the mechanisms of telbivudine-induced myopathy associated with mitochondrial dysfunction

As a nucleotide analogue (NA), telbivudine was widely used in the treatment for chronic hepatitis B (CHB) by interfering with reverse transcriptase of hepatitis B virus. However, the use of NAs for hepatitis B treatment has been accompanied by numerous reports highlighting the occurrence of neuromyopathy, particularly in the case of telbivudine. This study aimed to investigate the underlying mechanisms responsible for telbivudine-induced myopathy. We established animal and cell models of telbivudine-induced myopathy using C57BL/6 mice and C2C12 cells, respectively. Our findings revealed that telbivudine significantly reduced mitochondrial DNA (mtDNA) copy number and caused increase of oxidative stress. Telbivudine treatment significantly inhibited mitochondrial complex I and IV expression, impairing the oxidative phosphorylation function of the respiratory chain. Modified Gomori trichrome (MGT) staining of the muscle sections displayed an increase in ragged red fibers (RRFs), indicating abnormal mitochondrial accumulation. In conclusion, our study provides compelling evidence suggesting that telbivudine-induced myopathy is associated with mitochondrial toxicity and impaired energy metabolism. The observed muscle pathology, depletion of mtDNA, elevation of oxidative stress and altered mitochondrial function support the hypothesis that telbivudine disrupts mitochondrial homeostasis, ultimately leading to muscle damage. This may be also a common mechanism for NAs to cause neuromyopathy.

Recent Updates on Viral Oncogenesis: Available Preventive and Therapeutic Entities

Human viral oncogenesis is a complex phenomenon and a major contributor to the global cancer burden. Several recent findings revealed cellular and molecular pathways that promote the development and initiation of malignancy when viruses cause an infection. Even, antiviral treatment has become an approach to eliminate the viral infections and prevent the activation of oncogenesis. Therefore, for a better understanding, the molecular pathogenesis of various oncogenic viruses like, hepatitis virus, human immunodeficiency viral (HIV), human papillomavirus (HPV), herpes simplex virus (HSV), and Epstein-Barr virus (EBV), could be explored, especially, to expand many potent antivirals that may escalate the apoptosis of infected malignant cells while sparing normal and healthy ones. Moreover, contemporary therapies, such as engineered antibodies antiviral agents targeting signaling pathways and cell biomarkers, could inhibit viral oncogenesis. This review elaborates the recent advancements in both natural and synthetic antivirals to control viral oncogenesis. The study also highlights the challenges and future perspectives of using antivirals in viral oncogenesis.

Efficacy of 104-week Telbivudine-based optimization strategy in patients with HBeAg-negative chronic hepatitis B virus infections

Background

Evaluate the safety and efficacy of 104-week regimen of Telbivudine(LdT)-based optimization strategy for Chinese patients who have chronic hepatits B(CHB) with HBeAg-negative.

Methods

This multi-center, open-label, prospective study enrolled 108 HBeAg-negative CHB patients who received LdT (600 mg/day) for 24 weeks, Adefovir (ADV) was added if HBV DNA remained detectable at week 24, otherwise LdT was maintained to use until 104 weeks. HBV DNA, alanine amino transferase (ALT), hepatitis B surface antigen(HBsAg), creatinine kinase(CK), and estimated glomerular filtration rate (eGFR) were measured, safety was assessed.

Results

Eighty-eight patients (81%) had HBV-DNA undetectable at 24 weeks and maintained to receive LdT monotherapy until 104 weeks, whereas the other 20 patients had HBV-DNA detectable and ADV was used in combination. For all patients, 72% of patients reached ALT normalization at 24 weeks, which increased to 80% at 52 weeks and 104 weeks, respectively.. 81% of total patients had undetectable HBV-DNA at 24 weeks, 92% at 52 weeks, and 94% at 104 weeks. The HBsAg titre declined steadily from baseline to 104 weeks (3.62 vs. 2.98 log10 IU/mL, p < 0.05), and the eGFR increased steadily from baseline to 104 weeks (92.9 vs. 104.4 mL/min/1.73 m², p < 0.05). Although 79 patients (73%) had at least one time of elevated CK, most of these patients had CK elevated in Grade 1/2.

Conclusions

LdT was well tolerated and effective, and 94% of patients achieved virological suppression after 104 weeks.

Trial registration

This study was registered in clinicaltrials.gov on January 31, 2012 and the ID No. was NCT01521975.

Elucidating molecular interactions of L-nucleotides with HIV-1 reverse transcriptase and mechanism of M184V-caused drug resistance

Emtricitabine (FTC) and lamivudine (3TC), containing an oxathiolane ring with unnatural (-)-stereochemistry, are widely used nucleoside reverse transcriptase inhibitors (NRTIs) in anti-HIV therapy. Treatment with FTC or 3TC primarily selects for the HIV-1 RT M184V/I resistance mutations. Here we provide a comprehensive kinetic and structural basis for inhibiting HIV-1 RT by (-)-FTC-TP and (-)-3TC-TP and drug resistance by M184V. (-)-FTC-TP and (-)-3TC-TP have higher binding affinities (1/Kd) for wild-type RT but slower incorporation rates than dCTP. HIV-1 RT ternary crystal structures with (-)-FTC-TP and (-)-3TC-TP corroborate kinetic results demonstrating that their oxathiolane sulfur orients toward the DNA primer 3'-terminus and their triphosphate exists in two different binding conformations. M184V RT displays greater (>200-fold) Kd for the L-nucleotides and moderately higher (>9-fold) Kd for the D-isomers compared to dCTP. The M184V RT structure illustrates how the mutation repositions the oxathiolane of (-)-FTC-TP and shifts its triphosphate into a non-productive conformation.

Synthesis and anti-HIV activity of L-2',3'-Dideoxy-4'-selenonucleosides (L-4'-Se-ddNs)

Based on the potent anti-HIV activity of L-2',3'-dideoxycytidine (L-ddC), L-2',3'-dideoxy-4'-selenonucleosides (L-4'-Se-ddNs) have been synthesized from natural chiral template, L-glutamic acid, using Pummerer-type condensation as a key step. All synthesized compounds were assayed for anti-HIV-1 activity, but none of them did show any significant antiviral activity up to 100 μM, probably due to conformational differences between L-ddC and L-4'-Se-ddC, induced by the bulky selenium atom, which might play an important role in phosphorylation by cellular kinase.

Determination of telbivudine in the plasma of chronic hepatitis B patients in long-term treatment by high-performance liquid chromatographic-tandem mass spectrometry

Creatine kinase elevation is commonly reported in telbivudine-treated patients. However, little is known about the relationship between this adverse drug reaction and plasma concentration. In this study, a sensitive, rapid and safe quantitative bioanalytical method has been established by using LC-MS/MS for the determination of telbivudine in a clinical study of chronic hepatitis B patients. The assay was linear in a dynamic 10-10,000 ng/mL range (r² > 0.999) and total analysis time was 6 min in this method. The validated method was applied to quantitatively determine plasma concentration in chronic hepatitis B patients during long-term telbivudine treatment. The results revealed that telbivudine concentration in the creatine kinase-elevated group (707.92-2788.78 ng/mL) was significantly higher than those with normal creatine kinase (412.63-1108.32 ng/mL). This method was adapted for therapeutic drug monitoring.

Rhabdomyolysis, lactic acidosis, and multiple organ failure during telbivudine treatment for hepatitis B: a case report and review of the literature

Background

Telbivudine can cause severe side effects, including myositis, neuritis, rhabdomyolysis, and lactic acidosis. However, reported cases of telbivudine leading to multiple organ failure are rare. Here, we report a case of telbivudine-induced severe polymyositis, lactic acidosis, and multiple organ failure.

Case presentation

A 30-year-old Chinese man with hepatitis B virus infection received antiviral treatment with 600 mg of telbivudine daily for more than 11 months. He developed progressive weakness and myalgia, and subsequently experienced palpitations, chest tightness, lethargy, hypotension, and hypoxemia. Blood tests showed markedly elevated levels of alanine aminotransferase (955 U/L), aspartate aminotransferase (1375 U/L), blood urea nitrogen (14.9 mmol/L), creatine kinase (peak at 8050 U/L), and blood lactate (>20.0 mmol/L). His symptoms improved after continuous renal replacement therapy and short-term methylprednisolone treatment. Hyperbaric oxygen therapy, physical therapy, and rehabilitation for more than 2 months led to recovery of muscle strength to the normal range.

Conclusions

We conclude that continuous renal replacement and steroid therapies play key roles in stabilizing telbivudine-induced severe rhabdomyolysis, lactic acidosis, and multiple organ failure. Hyperbaric oxygen, physical therapy, and rehabilitation may aid in functional recovery after the acute phase of lactic acidosis and organ failure.

Efficacy of telbivudine with conditional tenofovir intensification in patients with chronic hepatitis B: results from the 2-year roadmap strategy

Background:

A 2-year roadmap study was conducted to evaluate the efficacy and safety of tenofovir intensification at Week 24 in patients with chronic hepatitis B (CHB) receiving telbivudine.

Scope:

A prospective multicenter study was conducted in treatment-naive patients with hepatitis B e antigen (HBeAg)-positive CHB. All patients received telbivudine (600 mg/day) until Week 24. Thereafter, patients with detectable hepatitis B virus (HBV) DNA (≥300 copies/mL) were administered tenofovir (300 mg/day) plus telbivudine, and patients with undetectable HBV DNA continued telbivudine monotherapy until Week 104. The primary endpoint was the proportion of patients with undetectable HBV DNA (<300 copies/mL) at Weeks 52 and 104.

Findings:

A total of 105 patients were enrolled in the trial, of which 100 were eligible for efficacy analysis. Undetectable HBV DNA levels were observed at Week 24 in 55 patients who continued on with telbivudine monotherapy. The remaining 45 patients with detectable HBV DNA received tenofovir add-on therapy. With monotherapy, 100% (55/55) and 94.5% (52/55) of patients achieved HBV DNA <300 copies/mL at Weeks 52 and 104, respectively; the corresponding values for patients with add-on therapy were 84.4% (38/45) and 93.3% (42/45). Overall, undetectable HBV DNA (<300 copies/mL) was found in 93% (93/100) and 94% (94/100) of patients at Weeks 52 and 104, respectively. HBeAg seroconversion rate was 44.4% (44/99) at Week 104 for the overall patient population. One patient in the monotherapy group and six in the intensification group demonstrated HBsAg clearance at Week 104. HBsAg seroconversion was observed in four patients at Week 104, all belonged to the tenofovir intensification group. Eight patients sustained HBsAg loss during a posttreatment follow-up period of 16 weeks. Alanine aminotransferase (ALT) normalization was constant in the telbivudine monotherapy group, whereas a progressive improvement was observed in the tenofovir intensification group. Two patients in the monotherapy and none in the intensification group experienced viral breakthrough by Week 104. There were no reports of myopathy in either group. The mean changes in estimated glomerular filtration rate (eGFR), estimated using the Modification of Diet in Renal Disease (MDRD) formula, from baseline to Week 104 were +6.145 mL/min/1.73 m² (p=0.0230) and +7.954 mL/min/1.73 m² (p=0.0154) in the telbivudine monotherapy and tenofovir intensification groups, respectively. The incidence of serious AEs was four in the telbivudine monotherapy and two in the tenofovir intensification group. The main limitation of this study was limited sample size, which made the power of the observation low, and the absence of a comparative subgroup to assess the progression of patients with detectable HBV DNA without treatment intensification.

Conclusions:

Data from this 2-year roadmap study confirmed that telbivudine with add-on tenofovir was effective and well tolerated in patients with CHB. Telbivudine was associated with an improvement in eGFR from baseline in both the groups.

Immunotherapy for Chronic Hepatitis B using HBsAg-based Vaccine Formulations: From Preventive Commercial Vaccines to Therapeutic Approach Julio Cesar Aguilar

Despite the existence of effective prophylactic vaccines, hepatitis B virus (HBV) infections remain a major public health problem. It has been estimated that about 370 million people are chronically infected with this virus worldwide. These individuals act as a reservoir for viral spread and chronic infection also increases the risk of liver diseases, such as cirrhosis and hepatocellular carcinoma. Current antiviral therapies fail to control viral replication in the long term in most patients. Viral persistence has been associated with a defect in the development of HBV-specific cellular immunity. The limitations of the current available therapies underline the need for alternative therapies. Specific immunotherapeutic strategies target not only the induction or stimulation of CD4(+) and CD8(+) T-cell responses but also the induction of proinflammatory cytokines capable of controlling viral replication. Therapeutic vaccination has been extensively studied in chronic hepatitis B (CHB) based in the properties of hepatitis B surface antigen (HBsAg) and taking advantage of its previous use in preventive vaccination. In this sense, pioneer studies were carried out employing HBsAg-based vaccines, including prophylactic commercial vaccines and HBsAg-based formulations with novel adjuvants. The results and general knowledge coming from these studies are discussed in the present review. The decision on developing new generations of vaccines including new antigens or formulations should take into account the experience with HBsAg-based vaccine formulations in order to decide about changing the vaccine antigen or adding new antigens to improve the composition. How to cite this article: Aguilar JC, Lobaina Y. Immunotherapy for Chronic Hepatitis B using HBsAg-based Vaccine Formulations: From Preventive Commercial Vaccines to Therapeutic Approach. Euroasian J Hepato-Gastroenterol 2014;4(2):92-97.

Telbivudine decreases proportion of peripheral blood CD4+CD25+CD127low T cells in parallel with inhibiting hepatitis B virus DNA

Regulatory T cells (Treg) have significant roles in the immunopathology of patients with chronic hepatitis B (CHB) and exhibit an evident correlation with antiviral immunity when antiviral therapy is applied. In order to investigate how circulating Tregs are affected by telbivudine treatment and its significance in patients with CHB, peripheral blood mononuclear cells (PBMCs) were isolated and the proportions of circulating cluster of differentiation (CD)4+CD25+CD127low and CD8+CD25+ T cells of CHB patients prior to and during the three or six months of treatment were assessed and detected by flow cytometric analysis. The levels of forkhead/winged helix transcription factor (Foxp3) mRNA were also quantified using quantitative polymerase chain reaction. A significantly higher percentage of CD4+CD25+CD127low and CD8+CD25+ T cells in the PBMCs of patients with CHB were identified compared with that of healthy individuals. Patients with CHB also demonstrated significantly higher levels of Foxp3 mRNA compared with that of healthy individuals. Following six months of telbivudine treatment, the proportion of circulating CD4+CD25+CD127low and CD8+CD25+ T cells and the relative levels of Foxp3 mRNA in patients with CHB was comparable to the proportion in healthy individuals. The proportions of circulating peripheral blood CD4+CD25+CD127low T cells were paralleled with its HBV DNA inhibition. The results of the present study indicate that telbivudine treatment reduces HBV DNA levels rapidly and indirectly affects the immune system by downregulating the proportion of circulating Treg markedly, which may be beneficial to restore the antiviral immune response.

Correlation of hepatitis B surface antigen level with response to telbivudine in naive patients with chronic hepatitis B

AIM

Hepatitis B surface antigen (HBsAg) has become a marker to judge immunological response to hepatitis B therapy. Quantified serum HBsAg levels can predict the response to pegylated interferon and entecavir. In this study, we aimed to explore the correlation of serum HBsAg levels with response to telbivudine (LdT) treatment in patients with chronic hepatitis B (CHB).

METHODS

Seventy-three treatment-naive CHB patients were recruited and received LdT monotherapy for 52 weeks and serial HBsAg levels were measured at five protocol time points. According to therapeutic efficacy at week 52, three subgroups of patients were identified, including complete responders (CR), partial responders (PR) and non-responders (NR).

RESULTS

After 52 weeks of treatment, CR, PR and NR represented 19 (26%), 33 (45%) and 21 (29%) patients in the sample of 73, respectively. The median values of baseline HBsAg (log10 IU/mL) were 4.05, 4.50 and 5.03 for CR, PR and NR, respectively. There was a distinct decline of HBsAg at week 52; median log10 HBsAg levels (IU/mL) were 3.61 (CR), 3.86 (PR) and 4.31 (NR). Positive correlation between HBsAg levels and HBV DNA loads was observed in the group of NR and early antiviral treatment of PR, but not in CR.

CONCLUSION

Initial HBsAg level was closely correlated with the efficacy of LdT. Patients with low HBsAg levels presented satisfactory responses. Therefore, initial level and correlation with HBV DNA of the serum HBsAg levels could predict responsiveness in CHB patients receiving LdT.

The inhibitors of nucleotide biosynthesis leflunomide, FK778, and mycophenolic acid activate hepatitis B virus replication in vitro

The inhibitors of pyrimidine synthesis, leflunomide and FK778, have been reported to exert broad antiviral effects, in addition to their immunosuppressive activities. Their possible therapeutic benefit for transplantation medicine is currently discussed, because they also block the replication of human cytomegalovirus and human polyomavirus BK, which both cause important complications in transplant recipients. Here, we show that leflunomide and FK778 strongly enhance hepatitis B virus (HBV) replication in vitro. This activity is shared by mycophenolic acid (MPA), an inhibitor of purine biosynthesis. Stimulation of HBV replication by these agents was linked to their inhibitory effects on de novo nucleotide biosynthesis because it could be efficiently counteracted by external nucleoside supply. Mechanistically, we found that mitogen-activated protein kinase p38 played a key role for the enhancement of HBV replication by leflunomide, FK778, and MPA. All three HBV-activating compounds increased p38 phosphorylation, in contrast to the HBV inhibitors, telbivudine and cyclosporine A. Moreover, silencing of p38 expression through RNA interference efficiently counteracted the stimulatory effect of leflunomide, FK778, and MPA on HBV replication.

CONCLUSION

Our data indicate that, in contrast to their reported inhibitory effects on other viruses, both leflunomide and FK778 can augment HBV replication. Treatment with leflunomide, FK778, or MPA may bear the risk to enhance HBV replication in infected patients.

Effect of telbivudine therapy on the cellular immune response in chronic hepatitis B

Weak T-cell reactivity to the hepatitis B virus (HBV) is believed to be the dominant cause of chronic HBV infection. Several lines of experimental evidence suggest that treatment with telbivudine increases the rate of HBV e antigen (HBeAg) loss, undetectable HBV DNA, and normalization of serum alanine aminotransferase (ALT) in chronic hepatitis B patients (CHB). However, it is still unclear how early antiviral therapy affects cellular immune responses during sustained telbivudine treatment. In order to investigate this issue, we measured detailed prospective clinical, virological, and biochemical parameters, and we examined the frequency of T cell subgroups as well as the ability of peripheral blood mononuclear cells (PBMC) to respond to stimuli at five protocol time points for 51 CHB patients who received telbivudine therapy for one year. The preliminary data from this study revealed that effective-treated patients showed an increased frequency of peripheral blood CD4(+)T lymphocytes, an augmented proliferative response of HBV-specific T-cells to the hepatitis B core antigen (HBcAg), and the induction of cytokines, such as interferon gamma (IFN-γ), tumour necrosis factor alpha (TNF-α) release at the site of infection compared to non-responsive patients. Enhanced HBV-specific T-cell reactivity to telbivudine therapy, which peaked at treatment week 12, was confined to a subgroup of effective-treated patients who achieved greater viral suppression.

Comparison of the efficacy of tenofovir and adefovir in the treatment of chronic hepatitis B: a systematic review

Chronic viral hepatitis B remains a global public health concern. Currently, several drugs, such as tenofovir and adefovir, are recommended for treatment of patients with chronic hepatitis B. tenofovir is a nucleoside analog with selective activity against hepatitis b virus and has been shown to be more potent in vitro than adefovir. But the results of trials comparing tenofovir and adefovir in the treatment of chronic hepatitis B were inconsistent. However, there was no systematic review on the comparison of the efficacy of tenofovir and adefovir in the treatment of chronic hepatitis B. To evaluate the comparison of the efficacy of tenofovir and adefovir in the treatment of chronic hepatitis B we conducted a systematic review and meta-analysis of clinical trials. We searched PUBMED, Web of Science, EMBASE, CNKI, VIP database, WANFANG database, the Cochrane Central Register of Controlled Trials and the Cochrane Database of Systematic Review. Finally six studies were left for analysis which involved 910 patients in total, of whom 576 were included in tenofovir groups and 334 were included in adefovir groups. At the end of 48-week treatment, tenofovir was superior to adefovir at the HBV-DNA suppression in patients[RR = 2.59; 95%CI(1.01-6.67), P = 0.05]. While there was no significant difference in the ALT normalization[RR = 1.15; 95%CI(0.96-1.37), P = 0.14], HBeAg seroconversion[RR = 1.32; 95%CI(1.00-1.75), P = 0.05] and HBsAg loss rate[RR = 1.19; 95%CI(0.74-1.91), P = 0.48]. More high-quality, well-designed, randomized controlled, multi-center trails are clearly needed to guide evolving standards of care for chronic hepatitis B.

Molecular methods in the diagnosis and management of chronic hepatitis B

Chronic hepatitis B (CHB) infection remains a major global problem but the recent advances in molecular methods have revolutionized the diagnosis and management of CHB. Hepatitis B virus (HBV) DNA quantitation is the most useful molecular marker for the diagnosis and management of CHB. There is increasing evidence that the clinical outcome and efficacy of antiviral therapy for CHB could vary with the infecting HBV genotype, core promoter and precore mutations. Early identification of drug resistance is imperative in the management of CHB. The molecular methods for HBV DNA quantitation, HBV genotyping, the identification of mutants, genotypic and phenotypic methods for monitoring drug resistance and their utility and limitations for use in the diagnosis and monitoring of CHB are discussed in this article.

Myotoxicity of telbivudine in pre-existing muscle damage

Objectives

It is unknown if telbivudine causes muscle damage only in patients with pre-existing muscle pathology.

Case report

A 27 yo male of African origin received telbivudine for hepatitis B during 3 months. Three weeks after initiation of the drug he developed myalgia, and tiredness. Creatine-kinase increased from 278 U/l (n, <170 U/l) at baseline to 3243 U/l. Shortly after discontinuation of telbivudine muscle symptoms and hyper-CK-emia disappeared. The findings suggest that pre-existing muscle damage favored the myotoxic effect of telbivudine.

Conclusions

Telbivudine appears to cause accelerated muscle toxicity if given to patients who already have muscle damage. Patients under telbivudine should be closely monitored for muscular side effects and those with pre-existing muscle damage should not receive the drug.

Comparison of the efficacy of lamivudine and telbivudine in the treatment of chronic hepatitis B: a systematic review

Background

Chronic viral hepatitis B remains a global public health concern. Currently, several drugs, such as lamivudine and telbivudine, are recommended for treatment of patients with chronic hepatitis B. However, there are no conclusive results on the comparison of the efficacy of lamivudine (LAM) and telbivudine (LdT) in the treatment of chronic hepatitis B.

Results

To evaluate the comparison of the efficacy of LAM and LdT in the treatment of chronic hepatitis B by a systematic review and meta-analysis of clinical trials, we searched PUBMED (from 1990 to April 2010), Web of Science (from 1990 to April 2010), EMBASE (from 1990 to April 2010), CNKI (National Knowledge Infrastructure) (from 1990 to April 2010), VIP database (from 1990 to April 2010), WANFANG database (from 1990 to April 2010), the Cochrane Central Register of Controlled Trials and the Cochrane Database of Systematic Review. At the end of one-year treatment, LdT was better than LAM at the biochemical response, virological response, HBeAg loss, therapeutic response, while less than at the viral breakthrough and viral resistance, but there was no significant difference in the HBeAg seroconversion and HBsAg response. LdT was better than LAM at the HBeAg seroconversion with prolonged treatment to two years.

Conclusions

In summary, LdT was superior in inhibiting HBV replication and preventing drug resistance as compared to LAM for CHB patients. But LdT may cause more nonspecific adverse events and can lead to more CK elevation than LAM. It is thus recommended that the LdT could be used as an option for patients but adverse events, for example CK elevation, must be monitored.

Discovery and development of anti-HBV agents and their resistance

Hepatitis B virus (HBV) infection is a prime cause of liver diseases such as hepatitis, cirrhosis and hepatocellular carcinoma. The current drugs clinically available are nucleot(s)ide analogues that inhibit viral reverse transcriptase activity. Most drugs of this class are reported to have viral resistance with breakthrough. Recent advances in methods for in silico virtual screening of chemical libraries, together with a better understanding of the resistance mechanisms of existing drugs have expedited the discovery and development of novel anti-viral drugs. This review summarizes the current status of knowledge about and viral resistance of HBV drugs, approaches for the development of novel drugs as well as new viral and host targets for future drugs.

Antiviral treatment of chronic hepatitis B virus (HBV) infections

While 25 compounds have been formally licensed for the treatment of HIV infection (AIDS), only seven licensed products are currently available for the treatment of chronic hepatitis B virus (HBV) infection: interferon-α, pegylated interferon-α, lamivudine, adefovir (dipivoxil), entecavir, telbivudine and tenofovir (disoproxil fumarate). In contrast to the treatment of HIV infections where the individual drugs are routinely used in combination, for the treatment of chronic HBV infection the individual drugs are generally used in monotherapy. In principle, combination drug therapy should allow reducing the likelihood of drug-resistant development.