Clevudine myopathy in patients with chronic hepatitis B

Recent progress in therapeutic applications of fluorinated five-membered heterocycles and their benzo-fused systems

Heterocyclic derivatives grafted with fluorine atom(s) have attracted the attention of scientists due to the unique physicochemical properties of the C-F bond. The inclusion of fluorine atom(s) into organic compounds often increases their lipophilicity and metabolic stability, enhancing their bioavailability and affinity for target proteins. Therefore, it is not surprising to find that more than 20% of the medications on the market contain fluorine, and nearly 300 fluorine-containing drugs have been officially approved for use as medicines. In this review article, we are interested in classifying and describing the reports comprising varied therapeutic activities of the directly fluorinated five-membered heterocycles and their fused systems during the last two decades. These therapeutic activities included antiviral, anti-inflammatory, enzymatic inhibitory, antimalarial, anticoagulant, antipsychotic, antioxidant, antiprotozoal, histamine-H3 receptor, serotonin receptor, chemokine receptor, prostaglandin-D2 receptor, and PBR inhibition activities. In many cases, the activities of fluorinated azoles were almost equal to or exceeded the potency of reference drugs.

A randomized phase 1b trial of the active site polymerase inhibitor nucleotide ATI-2173 in patients with chronic hepatitis B virus infection

ATI-2173 is an active site polymerase inhibitor nucleotide in development as part of a potentially curative regimen for chronic hepatitis B virus (HBV) infection. This study evaluated the safety, tolerability, pharmacokinetics (PK) and antiviral activity of ATI-2173. This was a phase 1b, randomized, double-blind, placebo-controlled trial in treatment-naive adults with chronic HBV infection conducted in the Republic of Moldova and Ukraine (ClinicalTrials.gov: NCT04248426). Patients positive for hepatitis B surface antigen were randomized 6:2 to receive once-daily oral doses of ATI-2173 10, 25, or 50 mg (n = 6 per dose) or placebo (n = 7) for 28 days, with off-treatment monitoring for 24 weeks. Endpoints included PK parameters of ATI-2173 and its metabolite clevudine, maximum reduction from baseline in HBV DNA, and safety and tolerability. Treatment-emergent adverse events occurred in eight patients (47%) receiving ATI-2173 and five (71%) receiving placebo; headache was the most common (n = 4). ATI-2173 PK was generally dose proportional. Systemic clevudine exposure with ATI-2173 dosing was substantially reduced compared with historical values observed with clevudine administration. On Day 28, mean changes from baseline in HBV DNA were -2.72 to -2.78 log₁₀  IU/ml with ATI-2173 and +0.17 log₁₀  IU/ml with placebo. Off-treatment sustained viral suppression and decreases in covalently closed circular DNA biomarkers were observed in most patients; one maintained undetectable HBV DNA at 24 weeks off treatment. In this 28-day monotherapy study, ATI-2173 demonstrated safety and antiviral activity, with sustained off-treatment effects and substantially reduced systemic clevudine exposure. These results support evaluation of ATI-2173 with tenofovir disoproxil fumarate in phase 2 studies.

Active site polymerase inhibitor nucleotides (ASPINs): Potential agents for chronic HBV cure regimens

Chronic hepatitis B virus (HBV) infection affects 240 to 300 million people worldwide. In the nucleus of infected hepatocytes, the HBV genome is converted to covalently closed circular DNA (cccDNA), which persists and serves as a transcriptional template for viral progeny. Therefore, a long-term cure for chronic HBV infection will require elimination of cccDNA. Although currently available nucleos(t)ide analogues (eg, tenofovir disoproxil fumarate, tenofovir alafenamide, entecavir) effectively control HBV replication, they are seldom curative (functional cure rate ∼10%) and require lifelong treatment for most patients. As such, antiviral agents with novel mechanisms of action are needed. Active site polymerase inhibitor nucleotides (ASPINs) noncompetitively distort the HBV polymerase active site to completely inhibit all polymerase functions, unlike traditional chain-terminating nucleos(t)ide analogues, which only target select polymerase functions and are consumed in the process. Clevudine, a first-generation ASPIN, demonstrated potent and prolonged HBV suppression in phase 2 and 3 clinical studies, but long-term treatment was associated with reversible myopathy in a small number of patients. ATI-2173, a novel next-generation ASPIN, is structurally similar to clevudine but targets the liver and demonstrates potent anti-HBV activity on and off treatment, and may ultimately demonstrate an improved pharmacokinetic and safety profile by significantly reducing systemic clevudine exposure. Thus, ATI-2173 is currently in clinical development as an agent for HBV cure. Here, we review the mechanism of action and preclinical and clinical profiles of clevudine and ATI-2173 to support the role of ASPINs as part of curative regimens for chronic HBV infection.

ATI-2173, a Novel Liver-Targeted Non-Chain-Terminating Nucleotide for Hepatitis B Virus Cure Regimens

ATI-2173 is a novel liver-targeted molecule designed to deliver the 5′-monophosphate of clevudine for the treatment of chronic hepatitis B infection. Unlike other nucleos(t)ides, the active clevudine-5′-triphosphate is a noncompetitive, non-chain-terminating inhibitor of hepatitis B virus (HBV) polymerase that delivers prolonged reduction of viremia in both a woodchuck HBV model and in humans for up to 6 months after cessation of treatment. However, long-term clevudine treatment was found to exhibit reversible skeletal myopathy in a small subset of patients and was subsequently discontinued from development.

ATI-2173 is a novel liver-targeted molecule designed to deliver the 5′-monophosphate of clevudine for the treatment of chronic hepatitis B infection. Unlike other nucleos(t)ides, the active clevudine-5′-triphosphate is a noncompetitive, non-chain-terminating inhibitor of hepatitis B virus (HBV) polymerase that delivers prolonged reduction of viremia in both a woodchuck HBV model and in humans for up to 6 months after cessation of treatment. However, long-term clevudine treatment was found to exhibit reversible skeletal myopathy in a small subset of patients and was subsequently discontinued from development. ATI-2173 was designed by modifying clevudine with a 5′-phosphoramidate to deliver the 5′-monophosphate to the liver. Bypassing the first phosphorylation step of clevudine, the 5′-monophosphate is converted to the active 5′-triphosphate in the liver. ATI-2173 is a selective inhibitor of HBV with an anti-HBV 50% effective concentration (EC₅₀) of 1.31 nM in primary human hepatocytes, with minimal to no toxicity in hepatocytes, skeletal muscle, liver, kidney, bone marrow, and cardiomyocytes. ATI-2173 activity was decreased by viral polymerase mutations associated with entecavir, lamivudine, and adefovir resistance, but not capsid inhibitor resistance mutations. A single oral dose of ATI-2173 demonstrated 82% hepatic extraction, no food effect, and greatly reduced peripheral exposure of clevudine compared with equimolar oral dosing of clevudine. Despite reduced plasma clevudine exposure, liver concentrations of the 5′-triphosphate were equivalent following ATI-2173 versus clevudine administration. By selectively delivering the 5′-monophosphate to the liver, while retaining the unique anti-HBV activity of the 5′-triphosphate, ATI-2173 may provide an improved pharmacokinetic profile for clinical use, reducing systemic exposure of clevudine and potentially eliminating skeletal myopathy.

Clevudine Induced Mitochondrial Myopathy

Clevudine was approved as an antiviral agent for hepatitis B virus, which showed marked, rapid inhibition of virus replication without significant toxicity. However, several studies have reported myopathy associated with clevudine therapy. Also, we experienced seven patients who suffered from myopathy during clevudine therapy. To characterize clevudine-induced myopathy, we collected previously reported cases of clevudine myopathy and analyzed all the cases including our cases. We searched electronic databases that were published in English or Korean using PubMed and KoreaMed. Ninety-five cases with clevudine myopathy, including our seven cases, were selected and analyzed for the demographic data, clinical features, and pathologic findings. The 95 patients with clevudine-induced myopathy comprised 52 women and 43 men aged 48.9 years (27-76 years). The patients received clevudine therapy for about 14.2 months (5-24 months) before the development of symptoms. Weakness mainly involved proximal extremities, especially in the lower extremities, and bulbar and neck weakness were observed in some cases (13.7%). Creatine kinase was elevated in the majority of patients (97.9%). Myopathic patterns on electromyography were observed in most patients examined (98.1%). Muscle biopsy presented patterns compatible with mitochondrial myopathy in the majority (90.2%). The weakness usually improved within about 3 months after the discontinuation of clevudine. Though clevudine has been known to be safe in a 6-month clinical trial, longer clevudine therapy for about 14 months may cause reversible mitochondrial myopathy. Careful clinical attention should be paid to patients with long-term clevudine therapy.

Lactate serum concentrations during treatment with nucleos(t)ide analogues in hepatitis B with or without cirrhosis

OBJECTIVE

The aim of this study is to evaluate the clinical implications of lactate concentrations in patients with hepatitis B with or without cirrhosis during treatment with nucleos(t)ide analogues.

PATIENTS AND METHODS

One hundred and seven consecutive patients with chronic hepatitis B and median age 57 (24-85) years were prospectively included. Lactate concentrations were measured at baseline and at 12, 24, 36, 48, and 60 months following the baseline measurements. Eight (n=8, 7.5%) patients received lamivudine, 38 (n=38, 35.5%) patients received tenofovir, 34 (n=34, 31.8%) patients received entecavir, and 27 (n=27, 25.2%) patients received combined therapy.

RESULTS

None of the patients developed lactic acidosis during follow-up [median: 58 (6-155) months]. Overall, no trends of the lactic acid evolution were observed over time; however, there was a nonsignificant increasing trend in patients with cirrhosis up to 24 months of treatment. This increasing trend was significant in female patients with cirrhosis (P=0.016). The age of the patients, the presence of cirrhosis, and hepatocellular carcinoma were strongly associated with the survival of all patients. In the group of cirrhotic patients, the only independent prognostic factor that was associated with patients' survival was the Child-Pugh class.

CONCLUSION

None of the patients developed lactic acidosis. There is an indication of an increasing trend of lactic acid levels up to 24 months of therapy in female cirrhotic patients.

Adverse effects of oral antiviral therapy in chronic hepatitis B

Oral nucleoside/nucleotide analogues (NAs) are currently the backbone of chronic hepatitis B (CHB) infection treatment. They are generally well-tolerated by patients and safe to use. To date, a significant number of patients have been treated with NAs. Safety data has accumulated over the years. The aim of this article is to review and update the adverse effects of oral NAs. NAs can cause class adverse effects (i.e., myopathy, neuropathy, lactic acidosis) and dissimilar adverse effects. All NAs carry a "Black Box" warning because of the potential risk for mitochondrial dysfunction. However, these adverse effects are rarely reported. The majority of cases are associated with lamivudine and telbivudine. Adefovir can lead to dose- and time-dependent nephrotoxicity, even at low doses. Tenofovir has significant renal and bone toxicity in patients with human immunodeficiency virus (HIV) infection. However, bone and renal toxicity in patients with CHB are not as prominent as in HIV infection. Entecavir and lamivudine are not generally associated with renal adverse events. Entecavir has been claimed to increase the risk of lactic acidosis in decompensated liver disease and high Model for End-Stage Liver Disease scores. However, current studies reported that entecavir could be safely used in decompensated cirrhosis. An increase in fetal adverse events has not been reported with lamivudine, telbivudine and tenofovir use in pregnant women, while there is no adequate data regarding entecavir and adefovir. Further long-term experience is required to highlight the adverse effects of NAs, especially in special patient populations, including pregnant women, elderly and patients with renal impairment.

Management of Clevudine-Resistant Chronic Hepatitis B: A Multicenter Cohort Study

BACKGROUND/AIMS

Data are lacking regarding the management of chronic hepatitis B (CHB) with resistance to clevudine (CLV). This study evaluated the efficacy of different rescue therapies for CLV-resistant CHB.

METHODS

Patients with CLV-resistant CHB were enrolled in the cohort, and all patients developed virologic breakthrough during CLV therapy and had confirmed-genotypic resistance to CLV (rtM204I mutation) before enrollment.

RESULTS

Of the 107 patients, 12 received adefovir (ADV), 21 received a CLV plus ADV combination (CLV+ADV), 34 received a lamivudine plus ADV combination (LAM+ADV), and 40 received entecavir (ETV) therapy for 48 weeks. The CLV+ADV group had the lowest hepatitis B virus (HBV) DNA level (p<0.0001) and showed the greatest reduction of HBV DNA levels from baseline compared to all other groups (p=0.004) at week 48. HBV DNA was undetectable (<70 IU/mL) in 0%, 57.1%, 21.2%, and 27.5% (p=0.003) of the patients in each group, respectively, at week 48. At the end of the study, the mean alanine transaminase (ALT) level, rate of ALT normalization, and rate of hepatitis B envelope antigen loss or seroconversion did not differ between groups.

CONCLUSIONS

CLV+ADV combination therapy in patients with CLV-resistant CHB more effectively suppresses HBV replication than ETV, ADV, or LAM+ADV therapy.

Comparison of the Effects of Telbivudine and Entecavir Treatment on Estimated Glomerular Filtration Rate in Patients with Chronic Hepatitis B

BACKGROUND/AIMS

The aim of this study was to evaluate the estimated glomerular filtration rate (eGFR) during telbivudine (LdT) versus entecavir (ETV) treatment in chronic hepatitis B (CHB) patients with underlying comorbidities such as diabetes mellitus (DM), hypertension, and cirrhosis.

METHODS

From 2010 to 2012, 116 CHB patients treated with LdT and 578 treated with ETV were compared in this real-practice cohort. The mean changes in eGFR (Modification of Diet in Renal Disease [MDRD] formula) from baseline to months 6, 12, and 18 were analyzed using a linear mixed model.

RESULTS

In LdT-treated patients, the mean eGFR increased by 7.6% at month 18 compared with the eGFR at baseline (MDRD formula in mL/min/1.73 m(2)). However, in ETV-treated patients, the mean eGFR decreased by 4.1% at month 18 compared with the eGFR at baseline. In the LdT-treated patients with DM, hypertension, cirrhosis or low eGFR <90 mL/min/1.73 m(2), the mean eGFR showed a steady improvement, whereas the mean eGFR was reduced in the same subgroups of ETV-treated patients.

CONCLUSIONS

The eGFR gradually increased over time during LdT treatment, especially in patients with mild abnormal eGFR at baseline, and in those with DM, hypertension, and cirrhosis, whereas a reduction in eGFR was seen with ETV treatment.

Cumulative incidence and risk factors of creatine kinase elevation associated with telbivudine

PURPOSE

An increasing number of studies are reporting a high frequency of creatine kinase (CK) elevation during telbivudine therapy; however, few reports have focused on the cumulative incidence and risk factors of CK elevation. This study was performed to investigate the cumulative incidence and risk factors of CK elevation in Chinese patients treated with telbivudine.

METHODS

In this observational study, patients with chronic hepatitis B receiving telbivudine therapy between July 2008 and December 2013 were enrolled. The cumulative incidence of CK elevation was analyzed using the Kaplan-Meier method combined with the log rank test. Risk factors were determined using Cox proportional hazards regression models.

RESULTS

A total of 207 eligible patients were analyzed. The cumulative incidence of CK elevation at 12, 24, 36, 48, 60, and 72 months was 51.2 %, 68.9 %, 75.1 %, 78.1 %, 78.1 %, and 78.1 %, respectively. Multivariate analysis revealed that male and lower baseline estimated glomerular filtration rate (eGFR) were significant risk factors for CK elevation.

CONCLUSIONS

The cumulative incidence of CK elevation after long-term telbivudine use is quite high, and gender and baseline eGFR may be useful predictors. However, when combined with regular monitoring of CK levels, especially for patients with lower eGFR, telbivudine is a relatively safe nucleoside analog treatment for chronic hepatitis B.

Therapy of Delta Hepatitis

Delta hepatitis is the less frequently encountered but most severe form of viral hepatitis. Acute delta hepatitis, as a result of coinfection with hepatitis B and hepatitis delta, is rare, but may lead to fulminant hepatitis, and no therapy exists for this form. Chronic delta hepatitis (CDH) mostly develops as a result of superinfection of a hepatitis B surface antigen (HBsAg) carrier with hepatitis delta virus (HDV). In general, HDV is the dominant virus. However, a dynamic shift of the dominant virus may occur with time in rare instances, and hepatitis B virus (HBV) may become the dominant virus, at which time nucleos(t)ide analog therapy may be indicated. Otherwise, the only established management of CDH consists of conventional or pegylated interferon therapy, which has to be administered at doses used for hepatitis B for a duration of at least 1 year. Posttreatment week-24 virologic response is the most widely used surrogate marker of treatment efficacy, but it does not represent a sustained virologic response, and late relapse can occur. As an easy-to-use simple serological test, anti-HDV-immunoglobulin M (IgM) correlates with histological inflammatory activity and clinical long-term outcome; however, it is not as sensitive as HDV RNA in assessing treatment response. No evidence-based rules for treating CDH exist, and treatment duration needs to be individualized based on virologic response at end of treatment or end of follow-up. Effective treatment may decrease liver-related complications, such as decompensation or liver-related mortality. In patients with decompensated cirrhosis, interferons are contraindicated and liver transplantation has to be considered. Alternative treatment options are an urgent need in CDH. New treatment strategies targeting different steps of the HDV life cycle, such as hepatocyte entry inhibitors or prenylation inhibitors, are emerging and provide hope for the future.

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.

Emerging antivirals for the treatment of hepatitis B

Chronic infection with hepatitis B virus (HBV) constitutes a major global public health threat, causing substantial disease burdens such as liver cirrhosis and hepatocellular carcinoma, thus representing high unmet medical needs. Currently available therapies are safe, well tolerated, and highly effective in decreasing viremia and improving measured clinical outcomes with low rates of antiviral resistance. However, long-term management remains a clinical challenge, mainly due to the slow kinetics of HBV surface antigen clearance. In this article, we review emerging antivirals directed at novel targets derived from mechanisms of viral cellular entry, viral replication, viral assembly, and the host immune response, leading to preclinical and clinical trials for possible future therapeutic intervention. The recent therapeutic advances in the development of all categories of HBV inhibitors may pave the way for regimens of finite duration that result in long-lasting control of chronic hepatitis B infection.

Extrahepatic effects of nucleoside and nucleotide analogues in chronic hepatitis B treatment

Oral nucleoside/nucleotide analogues (NAs) are the mainstay of therapy for patients with chronic hepatitis B and are generally well tolerated. Despite this, the safety profile of NAs is of paramount importance since the majority of patients will require long-term treatment. All NAs can potentially affect human DNA polymerase with decrease in mitochondrial DNA, leading to manifestations of mitochondrial toxicity. As a class effect, therefore, NAs can potentially cause extrahepatic conditions, such as myopathy, nephropathy, neuropathy, and lactic acidosis. Indeed, effects on muscles, including myopathy and creatine kinase elevations, have been described with clevudine and telbivudine use. Both adefovir and tenofovir are associated with dose-dependent nephropathy, predominantly affecting the proximal renal tubules. Neuropathy appears to be rare, and most commonly reported in patients receiving combination therapy with telbivudine and interferon. Increased risk of lactic acidosis has also been described for those with impaired liver and renal function taking entecavir. Loss of bone mineral density and hypophosphatemia have been described with the use of NAs, although the overwhelming studies have been with human immunodeficiency virus-infected patients. However, not all extrahepatic effects are detrimental. Recent evidence has suggested a potential renal beneficial effect with the use of telbivudine. The effect of NAs on pregnancy appears to be minimal for all NAs, with telbivudine and tenofovir having a more favorable category B rating. Ongoing pharmacovigilance is essential to identify new and monitor existing extrahepatic effects associated with NA use.

Entecavir-associated myopathy: a case report and literature review

INTRODUCTION

Entecavir, a nucleoside analog (NA), is effective for treatment of chronic hepatitis B virus (HBV) infection.

METHODS

We report the case of a patient we encountered with entecavir-associated myopathy. We also performed a literature review of myopathies associated with nucleoside analogs.

RESULTS

A 44-year-old man presented with a 3-month history of myalgia and progressive weakness. He had HBV infection and had received entecavir antiviral treatment for 5 years. Laboratory tests showed that serum creatine kinase levels were significantly elevated. Muscle histopathology showed abundant T-lymphocyte infiltration of muscle fibers, and HBV surface antigen and HBV core antigen were not present in muscle fibers. Entecavir-associated myopathy was subsequently diagnosed. The patient's symptoms eventually resolved, and serum CK levels decreased rapidly after he stopped receiving entecavir treatments.

CONCLUSIONS

Patients who receive NA therapy should be closely monitored for myopathic side effects. Muscle Nerve 49:610-614, 2014.

Antiviral Agents☆

Antiviral agents are drugs approved in the USA by the Food and Drug Administration (FDA) for the treatment or control of viral infections. Available antiviral agents mainly target stages in the viral life cycle. The target stages in the viral life cycle are; viral attachment to host cell, uncoating, synthesis of viral mRNA, translation of mRNA, replication of viral RNA and DNA, maturation of new viral proteins, budding, release of newly synthesized virus, and free virus in body fluids.

Two important factors that can limit the utility of antiviral drugs are toxicity and the development of resistance to the antiviral agent by the virus. In addition, host phenotypic behaviors toward antiviral drugs because of either genomic or epigenetic factors could limit the efficacy of an antiviral agent in an individual. This article summarizes the most relevant pharmacologic and clinical properties of current antiviral agents, and targets for novel antiviral agents.

[Efficacy of entecavir switching therapy in chronic hepatitis B patients with clevudine-induced myopathy]

BACKGROUND/AIMS

Clevudine is a potent antiviral agent against HBV. However, long-term clevudine therapy may cause myopathy. This study was carried out to identify the efficacy of entecavir switching therapy in chronic hepatitis B patients experiencing clevudine-induced myopathy.

METHODS

One hundred forty six patients with chronic hepatitis B treated with 30 mg of clevudine per day for 73 weeks (range, 36-132 weeks) were enrolled. Among them, clevudine-induced myopathy occurred in 21 patients (14.4%) which was diagnosed if the patients had symptoms related to myopathy with concurrent CK and AST elevation. All the patients who were diagnosed as clevudine-induced myopathy stopped the therapy, and 17 patients (81%) were switched to entecavir 0.5 mg.

RESULTS

The patients with clevudine-induced myopathy were switched to entecavir 0.5 mg for median 68 weeks, and all of them showed disappearance of clinical myopathic symptoms and normalization of CK and AST level within median 2.2 months. Eight patients (47%) were HBeAg positive before entecavir treatment, and HBeAg seroconversion was achieved in 2 patients (25%). HBV DNA level was elevated in 3 patients (17.6%) at the time when the patients were diagnosed as myopathy, all of them achieved virological response with entecavir switching therapy. ALT level was elevated in 3 patients (17.6%) before entecavir treatment, all of them showed normalization of ALT level. During entecavir therapy, genotypic resistance to entecavir or virological breakthrough was not noted.

CONCLUSIONS

In chronic hepatitis B patients experiencing clevudine-induced myopathy, switching to entecavir 0.5 mg per day showed a resolution of myopathy and adequate viral suppression.

Virological Response and Muscular Adverse Events during Long-Term Clevudine Therapy in Chronic Hepatitis B Patients

BACKGROUND

Recently, several reports issued clevudine induced myopathy in the long term use.

OBJECTIVES

The aim of this study was to investigate antiviral effects and adverse events of clevudine monotherapy in patients with chronic hepatitis B (CHB).

PATIENTS AND METHODS

The subjects were 110 treatment-naïve CHB patients. They were treated with 30 mg clevudine/day for more than six months. Virological and biochemical tests, including that for serum creatine kinase (CK), were monitored at baseline and at 3-month intervals during treatment period.

RESULTS

In HBeAg-positive patients, the cumulative rates of virological response were 74.0 %, 68.5 %, and 67.3 % after one, two, and three years of clevudine treatment, respectively. Cumulative rates of HBeAg loss or seroconversion were 17.8 %, 30 %, and 31.5 % after one, two and, three years of clevudine treatment, respectively. In HBeAg-negative patients, the cumulative rates of virological response were 97.3 %, 100 %, and 94.6 %, respectively. Virological breakthrough occurred in 27 patients. The rtM204I mutation in HBV polymerase was predominantly detected. Muscular adverse events were observed in 15 patients. All patients with myopathy recovered after the cessation of clevudine monotherapy. Fluctuations in CK level during the clevudine treatment period were frequently observed irrespective of development of myopathy. Multiple episodes of CK elevation were significantly related to the development of myopathy.

CONCLUSIONS

Long-term clevudine monotherapy is effective for suppression of serum HBV DNA level and normalization of serum alanine amino transaminase levels, but associated with occurrence of rtM204I mutation. Clevudine-induced muscular adverse events are not uncommon, although they are totally reversible after cessation of the treatment. Muscular adverse events and serum CK level should be carefully monitored during long-term treatment with clevudine.

Long-term treatment outcomes of clevudine in antiviral-naive patients with chronic hepatitis B

AIM: To evaluate the treatment outcomes of clevudine compared with entecavir in antiviral-naive patients with chronic hepatitis B (CHB).

METHODS: We retrospectively analyzed the clinical data of CHB patients treated with clevudine 30 mg/d and compared their clinical outcomes with patients treated with entecavir 0.5 mg/d. The biochemical response, as assessed by serum alanine aminotransferase (ALT) activity, virologic response, as assessed by serum hepatitis B virus DNA (HBV DNA) titer, serologic response, as assessed by hepatitis B e antigen (HBeAg) status, and virologic breakthrough with genotypic mutations were assessed.

RESULTS: Two-hundred and fifty-four patients [clevudine (n = 118) vs entecavir (n = 136)] were enrolled. In clevudine-treated patients, the cumulative rates of serum ALT normalization were 83.9% at week 48 and 91.5% at week 96 (80.9% and 91.2% in the entecavir group, respectively), the mean titer changes in serum HBV DNA were -6.03 and -6.55 log₁₀ copies/mL (-6.35 and -6.86 log₁₀ copies/mL, respectively, in the entecavir group), and the cumulative non-detection rates of serum HBV DNA were 72.6% and 83.1% (74.4% and 83.8%, respectively, in the entecavir group). These results were similar to those of entecavir-treated patients. The cumulative rates of HBeAg seroconversion were 21.8% at week 48 and 25.0% at week 96 in patients treated with clevudine, which was similar to patients treated with entecavir (22.8% and 27.7%, respectively). The virologic breakthrough in the clevudine group occurred in 9 (7.6%) patients at weeks 48 and 15 (12.7%) patients at week 96, which primarily corresponded to genotypic mutations of rtM204I and/or rtL180M. There was no virologic breakthrough in the entecavir group.

CONCLUSION: In antiviral-naive CHB patients, long-term treatment outcomes of clevudine were not inferior to those of entecavir, except for virologic breakthrough.

Long-term treatment efficacy and safety of clevudine therapy in naïve patients with chronic hepatitis B

BACKGROUND/AIMS

Clevudine (CLV) has potent antiviral activity against chronic hepatitis B (CHB) virus infection. The long-term efficacy and safety of CLV therapy in naïve patients with CHB were investigated.

METHODS

In this retrospective study, 152 naïve Korean patients with CHB who received 30 mg of CLV once daily for at least 12 months were investigated.

RESULTS

The cumulative rates at months 12, 24, and 36, respectively, were 65.8%, 74.7%, and 74.7% for undetectable serum hepatitis B virus (HBV) DNA (<12 IU/mL); 77.6%, 86.2%, and 86.2% for normalization of serum alanine aminotransferase (<40 IU/L); 17.6%, 23.5%, and 23.5% for hepatitis B e antigen (HBeAg) loss or seroconversion; and 6.6%, 22.5%, and 30.0% for viral breakthrough. HBeAg positivity (p=0.010), baseline serum HBV DNA level ≥6 log(10) IU/mL (p=0.032) and detectable serum HBV DNA (≥12 IU/mL) at week 24 (p=0.023) were independently associated with the development of viral breakthrough. During follow-up, CLV-induced myopathy developed in 5.9% of patients.

CONCLUSIONS

The results of long-term CLV therapy for the treatment of naïve patients with CHB showed a high frequency of antiviral resistance and substantial associated myopathy. Therefore, we advise that CLV should not be used as a first-line treatment for naïve patients given the availability of other more potent, safer antiviral agents.

Telbivudine myopathy in a patient with chronic hepatitis B

CASE

A 25-year-old man with hepatitis B virus (HBV) infection received antiviral treatment with telbivudine 600 mg daily. Six months after starting treatment, the patient developed progressive weakness and myalgia. Physical examination showed symmetrical proximal weakness. Blood tests at admission revealed positive hepatitis b surface antigen (HBs Ag), and, elevated creatine kinase (CK) level (1,614 U/L, normal range: 38-174 U/L). Aspartate aminotransferase was 64.7 U/L (normal range: 8-40 U/L), and LDH was 293 U/L (normal range: 80-285 U/L). Electrodiagnostic studies indicated myopathic changes. A muscle biopsy revealed myositis and no mitochondrial changes were found. Drug-induced myopathy was suspected and telbivudine was changed to entecavir. The muscle weakness and laboratory findings improved.

CONCLUSION

A patient developed drug-induced myopathy during long-term treatment with telbivudine for chronic HBV. To promptly detect this reversible adverse event, monitoring of serum CK level and recognition of myopathic signs and symptoms are necessary. Further investigations are needed to clarify the possible mechanism of telbivudine-induced myopathy.

Comparison of clevudine and entecavir for treatment-naive patients with chronic hepatitis B virus infection: two-year follow-up data

BACKGROUND/AIM

Clevudine and entecavir are highly potent antiviral agents being used in treatment of chronic hepatitis B. However, no data comparing clinical efficacy and safety of these 2 drugs over a long-term period is available. The aims of this study are to compare virologic, biochemical, and serologic response rates of clevudine and entecavir, as well as treatment failure rates up to 2 years.

METHODS

Data of patients who started clevudine (n = 86) or entecavir (n = 159) as a primary treatment for chronic hepatitis B at Korea University Ansan or Guro Hospital between January 2007 and June 2008 were analyzed.

RESULTS

Treatment responses were compared at 3-month intervals up to 24 months. Per protocol analysis showed no difference in virologic responses between the 2 groups at all time points, except at 18 months. When analyzed on intention-to-treat basis for virologic response at 24 months, the response rates were 45.3% in the clevudine group and 72.3% in the entecavir group, which are significantly different (P < 0.001). Rates of biochemical response and HBeAg seroconversion were not significantly different between the groups at all time points. Up to 24 months, antiviral resistance developed in 18 patients (24.4%) in the clevudine group. Clevudine was discontinued owing to muscle-related problems in 10 patients (11.6%).

CONCLUSIONS

Although both drugs showed potent antiviral activity, entecavir showed better virologic response at 24 months, primarily owing to treatment failures in the clevudine group that were associated with development of drug resistance and muscle-related problems.

Nucleoside/nucleotide analogues in the treatment of chronic hepatitis B

The current available agents for the treatment of chronic hepatitis B (CHB) include immunomodulatory agents, such as interferon-α and pegylated interferon-α, and oral nucleoside/nucleotide analogues (NAs), including lamivudine, adefovir, telbivudine, entecavir and tenofovir. The NAs work mainly by inhibiting hepatitis B virus (HBV) DNA polymerase activity and thus suppress HBV replication. Oral NAs have become the mainstay of CHB treatment, mainly due to their profound viral suppressive effects and also due in part to the ease of single daily dosing and lack of significant side effects. One major drawback of NA therapy is the development of drug resistance mutations with long-term treatment. Lamivudine, the first oral NA approved for CHB patients, is associated with high rates of drug resistance, with resultant virological relapse and biochemical flare. Fortunately, newer and more potent NAs, such as entecavir and tenofovir, have very low resistance rates, with potent and durable viral suppression. This review is aimed at the current developments in NAs for CHB treatment, detailing the mechanisms of antiviral activity of the different agents, the efficacy of viral suppression, the achievement of treatment endpoints, the development of drug resistance and the optimal strategies for using these drugs.

Virologic and biochemical responses to clevudine in patients with chronic HBV infection-associated cirrhosis: data at week 48

Clevudine shows high rates of virologic and biochemical responses in patients with chronic hepatitis B. However, the efficacy and safety of clevudine in patients with cirrhosis are unknown. The aims of this study were to evaluate the safety and to assess the virologic and the biochemical responses to clevudine in patients with cirrhosis with chronic hepatitis B virus (HBV) infection. We reviewed data from treatment-naïve patients with chronic hepatitis B with and without cirrhosis who started clevudine between April 2007 and March 2008 (n = 52, hepatitis B without cirrhosis n = 21 and chronic hepatitis B with cirrhosis n = 31) at Korea University Ansan/Guro Hospital. All of the patients were treated for more than 48 weeks. The mean age was older in the patients with cirrhosis. Baseline HBV DNA levels were 6.9 and 7.78 log copies/mL (P = 0.042), and alanine aminotransferase (ALT) levels were 104.9 and 147.4 IU/L (P = 0.204), for those with and without cirrhosis, respectively. Virologic response (HBV DNA <1000 copies/mL) (87.1%vs 71.4%, P = 0.24) and biochemical response (83.9%vs 80.9%, P = 0.99) at week 48 were not significantly different between the two groups. Early virologic response at week 12 was even higher in the patients with cirrhosis (61.3%vs 28.6%, P = 0.026). Neither ALT flare nor newly onset hepatic decompensation was found in the patients with cirrhosis, whereas ALT flare was transiently observed in 14.3% of the chronic hepatitis group. In conclusion, although clevudine may produce a transient elevation of ALT during the early treatment period, such findings were not observed in patients with cirrhosis and the virologic and biochemical responses of the groups were comparable.

[Treatment of chronic hepatitis B: adherence and safety]

Second generation nucleos (t) idic analogues result in a complete viral suppression after 48 to 96 weeks of therapy in most patients, regardless of the virus (HBV genotype, wild type or pre-C mutant), the underlying liver disease (cirrhosis or not) or the immune status (mono- or HIV/HBV co-infection). This antiviral efficacy may result in HBe or HBs seroconversion. Its clinical impact is important since inactivation of necroinflammation allows, in the absence of liver comorbidities, a stabilisation then a reversal of fibrosis and cirrhosis, and consequently a decrease in the occurrence of carcinomatous or non-carcinomatous complications. The future issues for long-term anti-HBV therapy will be adherence on the one hand and safety on the other hand. Therapeutic failures are mainly related to poor adherence more than to viral resistance. Adherence of patients has to be optimized by therapeutic education and education of physicians. Long-term safety has to be systematically evaluated. More than the neuromuscular or metabolic side effects (lactic acidosis), the renal and bone-related adverse events have to be monitored, followed-up and anticipated by good clinical practices.

Clinical and virological responses to clevudine therapy of hepatocelluar carcinoma patients with chronic hepatitis B

BACKGROUND/AIMS

The clinical effects of clevudine have been reported in patients with chronic hepatitis B virus infections (CHIs). In this investigation, we assessed whether clevudine induced biochemical and virological improvements in hepatocellular carcinoma (HCC) patients with CHI.

METHODS

Fifty-four patients who received 30 mg clevudine for more than 24 weeks between 2007 and 2009 at the National Cancer Center Hospital, Korea, were enrolled. Among these cases, 39 had HCC (CHI/HCC group) and 15 did not (CHI group).

RESULTS

In relation to the CHI group, the CHI/HCC group was older (55.5 years.) and had a higher liver cirrhosis rate (79.5%) (p<0.05). Median changes in serum hepatitis B virus (HBV) DNA levels from baseline at weeks 12, 24, and 36 of treatment in the CHI/HCC group were not significantly different from those of the CHI group (-2.3, -2.7, -2.6 vs -1.7, -1.8, -2.4, respectively). HBV DNA <2,000 copies/mL was achieved in 76.5% of the CHI/HCC group at 24 weeks. Rates of ALT normalization in the CHI/HCC and CHI groups were 62.5% and 66.7%, respectively (p>0.05). Liver function was preserved with clevudine treatment in patients displaying response or stable disease under anti-cancer therapy. Four patients (7.4%) developed viral resistance during clevudine therapy. Among these, one was naïve, and three had previously received antiviral therapy. One CHI/HCC patient (1.9%) discontinued clevudine treatment due to symptomatic myopathy.

CONCLUSIONS

Our findings clearly indicate that clevudine has comparable antiviral and biochemical effects in patients with CHI and with CHI/HCC and preserves the underlying liver function in HBV-related HCC patients.

HBV life cycle and novel drug targets

With up to 400 million affected people worldwide, chronic hepatitis B virus (HBV) infection is still a major health care problem. During the last decade, several novel therapeutic approaches have been developed and evaluated. In most regions of the world, interferon-α, and nucleos(t)ide analogues (NUCs) are currently approved. Despite major improvements, none of the existing therapies is optimal since viral clearance is rarely achieved. Recently, a better understanding of the HBV life cycle and the development of novel model systems of HBV infection have led to the development of novel antiviral strategies and drug targets. This review will focus on current and potential future drug targets in the HBV life cycle and strategies to modulate the virus-host interaction.

Clevudine-induced viral response, associated with continued reduction of HBsAg titer, was durable after the withdrawal of therapy

BACKGROUND

This study was conducted to evaluate the durability of clevudine-induced viral response after the withdrawal of treatment.

METHODS

Patients who showed a complete response [alanine aminotransferase (ALT) normalization and hepatitis B virus (HBV) DNA <4,700 copies/mL for hepatitis B envelope antigen (HBeAg)-negative patients; ALT normalization, HBV DNA <4,700 copies/mL, and HBeAg seroconversion for HBeAg-positive patients] in the previous clevudine phase III trials were followed for an additional 96 weeks without any treatment for hepatitis B.

RESULTS

Of the 63 patients in the study cohort, 73% and 35% of the patients had HBV DNA <141,500 and <4,700 copies/mL, respectively, and 75% of the patients had normal ALT at the end of follow-up. HBeAg seroconversion was maintained in 81% of the patients and hepatitis B surface antigen (HBsAg) loss occurred in 3 patients. Continued HBsAg titer decrease (-0.5 log IU/mL) was observed in the sustained viral responders, suggesting the reduction of covalently closed circular DNA in hepatocytes.

CONCLUSIONS

The clevudine-induced viral response was durable in the majority of patients for 2 years after the withdrawal of treatment.

Clevudine for chronic hepatitis B: antiviral response, predictors of response, and development of myopathy

Clevudine has been approved for the treatment of chronic hepatitis B (CHB) in South Korea. However, its long-term antiviral effect and safety awaits more study. The aim of this study was to evaluate antiviral efficacy, predictors of virologic response, and development of myopathy after clevudine therapy for CHB. The study included 102 nucleoside naïve CHB patients who had received clevudine for more than 6 months with good compliance. The median duration of clevudine treatment was 53 weeks (range, 25-90 weeks). A retrospective analysis of data retrieved from medical records was performed. The cumulative rate of virologic response [hepatitis B virus (HBV) DNA level <2000 copies/mL] at 48 weeks of clevudine therapy was 81%, and cumulative rate of clevudine resistance was 11% at 60 weeks of treatment. Independent predictors of virologic response to clevudine therapy were hepatitis B e antigen (HBeAg) negativity and rapid decrease of viral load during the early phase of treatment. The clevudine-related myopathy developed in 3.9% of patients, and was reversible after discontinuation of clevudine. Clevudine showed a potent antiviral response, and its effect was higher in HBeAg-negative patients, with rapid viral load reduction after therapy. However, long-term therapy for more than 1 year resulted in the development of considerable resistance and myopathy. Therefore, we should consider alternative antiviral agents if clevudine resistance or clevudine-induced myopathy is developed in patients on clevudine for the treatment of CHB.

A comparison of 48-week treatment efficacy between clevudine and entecavir in treatment-naïve patients with chronic hepatitis B

PURPOSE

Clevudine and entecavir are currently available in Korea as antiviral drugs against chronic hepatitis B (CHB). We aimed to compare the efficacy of clevudine and entecavir therapy.

METHODS

Treatment-naïve CHB patients who received 30 mg of clevudine or 0.5 mg of entecavir a day were analyzed. Mean reduction of hepatitis B virus (HBV) DNA levels, complete virological response (cVR, undetectable HBV DNA by real-time PCR), biochemical response (recovery to normal ALT level), and hepatitis B e antigen (HBeAg) seroconversion rate at the 48th week of treatment were assessed.

RESULTS

A number of 59 patients in clevudine group and 61 patients in entecavir group were included. Mean HBV DNA reductions from baseline were similar in the clevudine and entecavir groups, -6.4 versus -6.8 log(10) copies/mL in HBeAg-positive (p = 0.417) and -6.9 versus -7.0 log(10) copies/mL in HBeAg-negative patients (p = 0.640). The proportion of patients who achieved cVR was not different between the two groups, 53 versus 55% in HBeAg-positive (p = 1.000) and 100 versus 95% in HBeAg-negative patients (p = 0.452). Biochemical response rates and HBeAg seroconversion rates were also similar in both the groups. Two (3.4%) patients in clevudine group showed virologic breakthrough with rtM204I mutation using direct sequencing analysis. Clinical myopathy occurred in two (3.4%) patients in clevudine group.

CONCLUSION

Mean reduction of viral loads was similar between clevudine and entecavir groups during 48 weeks. However, virologic breakthrough and significant myopathy were noted only in clevudine-treated patients. Therefore, more attention should be paid to patients receiving clevudine.

Natural history and treatment of chronic delta hepatitis

Chronic delta hepatitis (CDH) represents a severe form of chronic viral hepatitis, induced by the hepatitis delta virus (HDV) in conjunction with the hepatitis B virus (HBV). Delta hepatitis may lead to disease in humans through co-infection. The former leads to acute hepatitis which clinically can range from mild hepatitis to fulminant hepatitis and death. Severe or fulminant hepatitis is more often observed with HBV-HDV co-infection compared to HBV mono-infection. Chronic infection after acute hepatitis B + D co-infection is infrequent and similar to the rate in mono-infected patients. CDH develops in 70-90% of patients with superinfection. CDH runs a more progressive course than chronic hepatitis B and may lead to cirrhosis within 2 years in 10-15% of patients. However, as with any immune-mediated disease, different patterns of progression, ranging from mild to severe progressive disease, are observed. Active replication of both HBV and HDV may be associated with a more progressive disease pattern. Further, different HDV and HBV genotypes may contribute to various disease outcomes. CDH may be frequently associated with hepatocellular carcinoma development although recent studies provided conflicting results. The only established therapy for CDH is treatment with interferons for a duration of at least 1 year. On treatment, 6 month HDV RNA assessment may give clues as to whether to stop treatment at 1 year or continue beyond 1 year. New approaches to treatment of CDH are an urgent need of which the use of prenylation inhibitors appears the most promising.

Clinical, biochemical, and pathological characteristics of clevudine-associated myopathy

BACKGROUND & AIMS

The aim of this study was to define the clinical, biochemical, and pathological characteristics of myopathy developed during clevudine therapy.

METHODS

We prospectively enrolled 36 consecutive myopathy patients who were receiving clevudine therapy for the treatment of chronic hepatitis B (CHB). We evaluated patients with a complete medical history, neurologic examination with a questionnaire on neuromuscular diseases, laboratory tests, electrophysiology studies, and muscle biopsies.

RESULTS

The median duration of clevudine therapy was 18.0 months (ranging from 9 to 24 months). The chief complaint was weakness of the lower extremities in 30 patients (83.3%) and asthenia in five patients (13.9%). One patient (2.8%) had only persistently elevated serum muscle enzyme without any symptoms. Weakness of the lower extremity mainly involved proximal muscle group of the lower extremity, characterized by difficulty in climbing stairs (83.3%), a decrease in exercise capacity (75.0%) and difficulty in walking (55.6%). All patients showed an elevation of more than two of serum creatine kinase, lactate dehydrogenase, and lactate levels. Muscle biopsies performed in 23 patients revealed myopathic features with abnormal mitochondria in 21 patients, and nonspecific myositis in two patients. Motor weakness gradually improved after discontinuation of clevudine.

CONCLUSIONS

Myopathy associated with clevudine is characterized by a weakness in proximal muscles of the lower extremities with elevated muscle enzymes and presumably caused by mitochondrial toxicities. Careful medical and serologic examinations are essential for the early detection and management of this potential adverse reaction in CHB patients under clevudine therapy.

Antiviral therapy for chronic hepatitis B

The goal of antiviral therapy for chronic hepatitis B is to prevent the development of cirrhosis and hepatocellular carcinoma. End points, including viral suppression, alanine aminotransferase normalization, hepatitis B e antigen loss, hepatitis B surface antigen loss, and improvement in liver histology, are used to determine treatment success. Treatment is based on hepatitis B virus (HBV) replication status and stage of liver disease, modulated by the age of the patient, hepatitis B e antigen (HBeAg) status and patient preference. Seven therapies are approved, including two formulations of interferon and five orally administered nucleos(t)ide analogs. These therapies are effective in suppressing HBV replication and have also been shown to prevent disease progression.

A transient kinetic approach to investigate nucleoside inhibitors of mitochondrial DNA polymerase gamma

Nucleoside analogs play an essential role in treating human immunodeficiency virus (HIV) infection since the beginning of the AIDS epidemic and work by inhibition of HIV-1 reverse transcriptase (RT), a viral polymerase essential for DNA replication. Today, over 90% of all regimens for HIV treatment contain at least one nucleoside. Long-term use of nucleoside analogs has been associated with adverse effects including mitochondrial toxicity due to inhibition of the mitochondrial polymerase, DNA polymerase gamma (mtDNA pol gamma). In this review, we describe our efforts to delineate the molecular mechanism of nucleoside inhibition of HIV-1 RT and mtDNA pol gamma based upon a transient kinetic approach using rapid chemical quench methodology. Using transient kinetic methods, the maximum rate of polymerization (k(pol)), the dissociation constant for the ground state binding (K(d)), and the incorporation efficiency (k(pol)/K(d)) can be determined for the nucleoside analogs and their natural substrates. This analysis allowed us to develop an understanding of the structure activity relationships that allow correlation between the structural and stereochemical features of the nucleoside analog drugs with their mechanistic behavior toward the viral polymerase, RT, and the host cell polymerase, mtDNA pol gamma. An in-depth understanding of the mechanisms of inhibition of these enzymes is imperative in overcoming problems associated with toxicity.

Comparison between clevudine and entecavir treatment for antiviral-naïve patients with chronic hepatitis B

BACKGROUND AND AIMS

There has been no study comparing the clinical efficacy of clevudine and entecavir in antiviral-naïve patients with chronic hepatitis B (CHB).

METHODS

A total of 128 antiviral-naïve CHB patients were included to receive clevudine 30 mg (n=55) or entecavir 0.5 mg (n=73) once daily for a mean follow-up period of 18.4 months.

RESULTS

Thirty-three (60.0%) in the clevudine group and 40 (54.8%) in the entecavir group were HBeAg positive (P>0.05). At 6 months from the baseline, the mean decreases in HBV-DNA were 4.86 and 4.72 log(10) copies/ml in the clevudine and entecavir groups respectively (P>0.05). The proportion of patients with undetectable serum HBV-DNA (<300 copies/ml) at 6 months was 65.5 and 74.0% in the clevudine and entecavir groups respectively (P>0.05). The proportion of patients with normal alanine aminotransferase levels at 6 months was 74.5 and 84.9% in the clevudine and entecavir groups respectively. During the mean follow-up of 18.4 months, genotypic resistance was noted in three patients (5.5%) in the clevudine group and no cases in the entecavir group. Eight patients (14.6%) in the clevudine group experienced symptoms, signs and laboratory abnormalities relevant to clevudine-induced myopathy.

CONCLUSIONS

Clevudine and entecavir treatment effectively suppresses HBV replication in most antiviral-naïve patients with CHB. During a mean follow-up of 18.9 months, a small proportion (5.5%) of patients in the clevudine group developed genotypic resistance. However, a substantial proportion (14.6%) of patients in the clevudine group had an adverse effect of clevudine-induced myopathy.

A Review of Oral Antiretroviral Therapy for the Treatment of Chronic Hepatitis B

Objective:

To describe the current evidence for the use of oral antiretroviral (ARV) agents in the treatment of chronic hepatitis B (CHB).

Data Sources:

A search from 1950 to April 2010 was conducted using the databases PubMed and MEDLINE with the search terms chronic hepatitis B, lamivudine, entecavir, adefovir, telbivudine, tenofovir, emtricitabine, clevudine, and pradefovir. The search was limited to trials conducted in humans that were published in the English language.

Study Selection and Data Extraction:

Studies were included if they evaluated the use of oral ARVs in patients with CHB infection who were not coinfected with hepatitis C, hepatitis D, or HIV.

Data Synthesis:

Oral ARVs have revolutionized the treatment of CHB. Studies conducted comparing ARVs have favored entecavir and tenofovir with respect to their ability to decrease hepatitis B virus DNA viral load while minimizing the development of resistance. However, low seroconversion rates, recurrent viremia when ARV therapy is discontinued, and increased resistance rates with longer treatment durations limit the benefit of oral ARVs in the treatment of CHB. Combination therapy has been a suggested solution; however, studies have yet to prove additional benefit over currently recommended monotherapy.

Conclusions:

Oral ARVs should continue to be used in the treatment of CHB; however, research is needed to define the optimal duration of therapy, evaluate the utility of combination therapy, and explore novel targets within the hepatitis B life cycle.

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.

A mechanistic view of human mitochondrial DNA polymerase gamma: providing insight into drug toxicity and mitochondrial disease

Mitochondrial DNA polymerase gamma (Pol gamma) is the sole polymerase responsible for replication of the mitochondrial genome. The study of human Pol gamma is of key importance to clinically relevant issues such as nucleoside analog toxicity and mitochondrial disorders such as progressive external ophthalmoplegia. The development of a recombinant form of the human Pol gamma holoenzyme provided an essential tool in understanding the mechanism of these clinically relevant phenomena using kinetic methodologies. This review will provide a brief history on the discovery and characterization of human mitochondrial DNA polymerase gamma, focusing on kinetic analyses of the polymerase and mechanistic data illustrating structure-function relationships to explain drug toxicity and mitochondrial disease.

Myopathy and neuropathy associated with nucleos(t)ide analog therapy for hepatitis B

The development of clevudine as a treatment for hepatitis B was terminated recently because of case reports of myopathy. In each case, the onset of symptoms occurred between 8 and 13 months after the initiation of treatment. Electromyography and muscle biopsy confirmed the presence of myonecrosis. One report also found evidence of mitochondrial toxicity. The delayed onset and the finding of mitochondrial damage are reminiscent of fialuridine toxicity. Telbivudine has also been reported to be associated with myopathy and neuropathy, particularly when used in combination with pegylated interferon. These findings serve as a sober reminder of the lack of data on long-term safety of nucleos(t)ide analogs for hepatitis B, the importance of balancing benefits versus risks before initiating treatment, and the need for more stringent post-marketing surveillance for drug toxicities.